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Sample records for cdms ii fermi

  1. The CDMS II data acquisition system

    SciTech Connect

    Bauer, D.A.; Burke, S.; Cooley, J.; Crisler, M.; Cushman, P.; DeJongh, F.; Duong, L.; Ferril, R.; Golwala, S.R.; Hall, J.; Holmgren, D.; /Fermilab /Texas A-M

    2011-01-01

    The Data Acquisition System for the CDMS II dark matter experiment was designed and built when the experiment moved to its new underground installation at the Soudan Lab. The combination of remote operation and increased data load necessitated a completely new design. Elements of the original LabView system remained as stand-alone diagnostic programs, but the main data processing moved to a VME-based system with custom electronics for signal conditioning, trigger formation and buffering. The data rate was increased 100-fold and the automated cryogenic system was linked to the data acquisition. A modular server framework with associated user interfaces was implemented in Java to allow control and monitoring of the entire experiment remotely.

  2. Beyond the CDMS-II dark matter search: SuperCDMS

    SciTech Connect

    Brink, Paul L.; et al.

    2005-03-01

    Presently the CDMS-II collaboration's Weakly Interacting Massive Particle (WIMP) search at the Soudan Underground Laboratory sets the most stringent exclusion limits of any WIMP cold dark matter direct-detection experiment. To extend our reach further, to WIMP-nucleon cross sections in the range 10{sup -46}-10{sup -44} cm{sup 2}, we propose SuperCDMS, which would take advantage of a very deep site. One promising site is the recently approved SNOLab facility in Canada. In this paper we will present our overall plan, identify primary issues, and set the goals that need to be met prior to embarking upon each phase of SuperCDMS.

  3. Dark matter searches with the CDMS II experiment

    SciTech Connect

    Saab, T.; Collaboration: CDMS Collaboration

    2014-06-24

    The CDMS II experiment ran between 2003 and 2009. A total of 30 germanium and silicon ZIP detectors were operated, producing a high quality set of data that has been analyzed for evidence of and placed leading constraints on standard, low-mass, electron-recoil, and annually modulating WIMP interactions. This article will describe the general operation principles behind the CDMS detectors, report on the results of major Ge and Si detector analyses, and describe the current and future activities of the SuperCDMS program.

  4. Advancing the Search for Dark Matter: from CDMS II to SuperCDMS

    SciTech Connect

    Hertel, Scott A.

    2012-09-01

    An overwhelming proportion of the universe (83% by mass) is composed of particles we know next to nothing about. Detecting these dark matter particles directly, through hypothesized weak-force-mediated recoils with nuclear targets here on earth, could shed light on what these particles are, how they relate to the standard model, and how the standard model ts within a more fundamental understanding. This thesis describes two such experimental eorts: CDMS II (2007-2009) and SuperCDMS Soudan (ongoing). The general abilities and sensitivities of both experiments are laid out, placing a special emphasis on the detector technology, and how this technology has evolved from the rst to the second experiment. Some topics on which I spent signicant eorts are described here only in overview (in particular the details of the CDMS II analysis, which has been laid out many times before), and some topics which are not described elsewhere are given a somewhat deeper treatment. In particular, this thesis is hopefully a good reference for those interested in the annual modulation limits placed on the low-energy portion of the CDMS II exposure, the design of the detectors for SuperCDMS Soudan, and an overview of the extremely informative data these detectors produce. It is an exciting time. The technology I've had the honor to work on the past few years provides a wealth of information about each event, more so than any other direct detection experiment, and we are still learning how to optimally use all this information. Initial tests from the surface and now underground suggest this technology has the background rejection abilities necessary for a planned 200kg experiment or even ton-scale experiment, putting us on the threshold of probing parameter space orders of magnitude from where the eld currently stands.

  5. WIMP search with the final year of CDMS II data

    SciTech Connect

    Hsu, L.; /Fermilab

    2010-07-01

    The Cryogenic Dark Matter Search (CDMS) has pioneered the use of ionization and athermal phonon signals to discriminate between candidate (nuclear recoil) and background (electron recoil) events in Ge crystals cooled to {approx}50 mK. The yield and timing information allows for the maximization of discovery potential by adjusting the expected background in the signal region to less than one event. A blind analysis on 612 kg-days of raw exposure from the CDMS II experiment was performed. Two events with an expected background of {approx}0.9 events were observed. No statistically significant evidence for WIMP interactions is reported. Combining this data with previously analyzed CDMS II data sets an upper limit on the WIMP-nucleon spin-independent cross-section of 3.8 x 10{sup -44} cm{sup 2} for a WIMP of mass 70 GeV/c{sup 2}.

  6. Dark matter search results from the CDMS II experiment.

    PubMed

    Ahmed, Z; Akerib, D S; Arrenberg, S; Bailey, C N; Balakishiyeva, D; Baudis, L; Bauer, D A; Brink, P L; Bruch, T; Bunker, R; Cabrera, B; Caldwell, D O; Cooley, J; Cushman, P; Daal, M; DeJongh, F; Dragowsky, M R; Duong, L; Fallows, S; Figueroa-Feliciano, E; Filippini, J; Fritts, M; Golwala, S R; Grant, D R; Hall, J; Hennings-Yeomans, R; Hertel, S A; Holmgren, D; Hsu, L; Huber, M E; Kamaev, O; Kiveni, M; Kos, M; Leman, S W; Mahapatra, R; Mandic, V; McCarthy, K A; Mirabolfathi, N; Moore, D; Nelson, H; Ogburn, R W; Phipps, A; Pyle, M; Qiu, X; Ramberg, E; Rau, W; Reisetter, A; Saab, T; Sadoulet, B; Sander, J; Schnee, R W; Seitz, D N; Serfass, B; Sundqvist, K M; Tarka, M; Wikus, P; Yellin, S; Yoo, J; Young, B A; Zhang, J

    2010-03-26

    Astrophysical observations indicate that dark matter constitutes most of the mass in our universe, but its nature remains unknown. Over the past decade, the Cryogenic Dark Matter Search (CDMS II) experiment has provided world-leading sensitivity for the direct detection of weakly interacting massive particle (WIMP) dark matter. The final exposure of our low-temperature germanium particle detectors at the Soudan Underground Laboratory yielded two candidate events, with an expected background of 0.9 +/- 0.2 events. This is not statistically significant evidence for a WIMP signal. The combined CDMS II data place the strongest constraints on the WIMP-nucleon spin-independent scattering cross section for a wide range of WIMP masses and exclude new parameter space in inelastic dark matter models.

  7. Results from the Final Exposure of the CDMS II Experiment

    SciTech Connect

    Ahmed, Z.; Akerib, D.S.; Arrenberg, S.; Bailey, C.N.; Balakishiyeva, D.; Baudis, L.; Bauer, D.A.; Brink, P.L.; Bruch, T.; Bunker, R.; Cabrera, B.; /Stanford U., Phys. Dept. /UC, Santa Barbara

    2009-12-01

    We report results from a blind analysis of the final data taken with the Cryogenic Dark Matter Search experiment (CDMS II) at the Soudan Underground Laboratory, Minnesota, USA. A total raw exposure of 612 kg-days was analyzed for this work. We observed two events in the signal region; based on our background estimate, the probability of observing two or more background events is 23%. These data set an upper limit on the Weakly Interacting Massive Particle (WIMP)-nucleon elastic-scattering spin-independent cross-section of 7.0 x 10{sup -44} cm{sup 2} for a WIMP of mass 70 GeV/c{sup 2} at the 90% confidence level. Combining this result with all previous CDMS II data gives an upper limit on the WIMP-nucleon spin-independent cross-section of 3.8 x 10{sup -44} cm{sup 2} for a WIMP of mass 70 GeV/c{sup 2}. We also exclude new parameter space in recently proposed inelastic dark matter models.

  8. Search for lightly ionizing particles using CDMS-II data and fabrication of CDMS detectors with improved homogeneity in properties

    SciTech Connect

    Prasad, Kunj Bihari

    2013-12-01

    Fundamental particles are always observed to carry charges which are integral multiples of one-third charge of electron, e/3. While this is a well established experimental fact, the theoretical understanding for the charge quantization phenomenon is lacking. On the other hand, there exist numerous theoretical models that naturally allow for existence of particles with fractional electromagnetic charge. These particles, if existing, hint towards existence of physics beyond the standard model. Multiple high energy, optical, cosmological and astrophysical considerations restrict the allowable mass-charge parameter space for these fractional charges. Still, a huge unexplored region remains. The Cryogenic Dark Matter Search (CDMS-II), located at Soudan mines in northern Minnesota, employs germanium and silicon crystals to perform direct searches for a leading candidate to dark matter called Weakly Interacting Massive Particles (WIMPs). Alternately, the low detection threshold allows search for fractional electromagnetic-charged particles, or Lightly Ionizing Particles (LIPs), moving at relativistic speed. Background rejection is obtained by requiring that the magnitude and location of energy deposited in each detector be consistent with corresponding \\signatures" resulting from the passage of a fractionally charged particle. In this dissertation, the CDMS-II data is analyzed to search for LIPs, with an expected background of 0.078 0.078 events. No candidate events are observed, allowing exclusion of new parameter space for charges between e/6 and e/200.

  9. Development of CDMS-II Surface Event Rejection Techniques and Their Extensions to Lower Energy Thresholds

    NASA Astrophysics Data System (ADS)

    Hofer, Thomas James

    2014-10-01

    The CDMS-II phase of the Cryogenic Dark Matter Search, a dark matter direct-detection experiment, was operated at the Soudan Underground Laboratory from 2003 to 2008. The full payload consisted of 30 ZIP detectors, totaling approximately 1.1 kg of Si and 4.8 kg of Ge, operated at temperatures of 50 mK. The ZIP detectors read out both ionization and phonon pulses from scatters within the crystals; channel segmentation and analysis of pulse timing parameters allowed effective fiducialization of the crystal volumes and background rejection sufficient to set world-leading limits at the times of their publications. A full re-analysis of the CDMS-II data was motivated by an improvement in the event reconstruction algorithms which improved the resolution of ionization energy and timing information. The Ge data were re-analyzed using three distinct background-rejection techniques; the Si data from runs 125--128 were analyzed for the first time using the most successful of the techniques from the Ge re-analysis. The results of these analyses prompted a novel "mid-threshold" analysis, wherein energy thresholds were lowered but background rejection using phonon timing information was still maintained. This technique proved to have significant discrimination power, maintaining adequate signal acceptance and minimizing background leakage. The primary background for CDMS-II analyses comes from surface events, whose poor ionization collection make them difficult to distinguish from true nuclear recoil events. The novel detector technology of SuperCDMS, the successor to CDMS-II, uses interleaved electrodes to achieve full ionization collection for events occurring at the top and bottom detector surfaces. This, along with dual-sided ionization and phonon instrumentation, allows for excellent fiducialization and relegates the surface-event rejection techniques of CDMS-II to a secondary level of background discrimination. Current and future SuperCDMS results hold great promise for

  10. Development of CDMS-II Surface Event Rejection Techniques and Their Extensions to Lower Energy Thresholds

    SciTech Connect

    Hofer, Thomas James

    2014-12-01

    The CDMS-II phase of the Cryogenic Dark Matter Search, a dark matter direct-detection experiment, was operated at the Soudan Underground Laboratory from 2003 to 2008. The full payload consisted of 30 ZIP detectors, totaling approximately 1.1 kg of Si and 4.8 kg of Ge, operated at temperatures of 50 mK. The ZIP detectors read out both ionization and phonon pulses from scatters within the crystals; channel segmentation and analysis of pulse timing parameters allowed e ective ducialization of the crystal volumes and background rejection su cient to set world-leading limits at the times of their publications. A full re-analysis of the CDMS-II data was motivated by an improvement in the event reconstruction algorithms which improved the resolution of ionization energy and timing information. The Ge data were re-analyzed using three distinct background-rejection techniques; the Si data from runs 125 - 128 were analyzed for the rst time using the most successful of the techniques from the Ge re-analysis. The results of these analyses prompted a novel \\mid-threshold" analysis, wherein energy thresholds were lowered but background rejection using phonon timing information was still maintained. This technique proved to have signi cant discrimination power, maintaining adequate signal acceptance and minimizing background leakage. The primary background for CDMS-II analyses comes from surface events, whose poor ionization collection make them di cult to distinguish from true nuclear recoil events. The novel detector technology of SuperCDMS, the successor to CDMS-II, uses interleaved electrodes to achieve full ionization collection for events occurring at the top and bottom detector surfaces. This, along with dual-sided ionization and phonon instrumentation, allows for excellent ducialization and relegates the surface-event rejection techniques of CDMS-II to a secondary level of background discrimination. Current and future SuperCDMS results hold great promise for mid- to low

  11. Results from a Low-Energy Analysis of the CDMS II Germanium Data

    SciTech Connect

    Ahmed, Z.; Akerib, D.S.; Arrenberg, S.; Bailey, C.N.; Balakishiyeva, D.; Baudis, L.; Bauer, D.A.; Brink, P.L.; Bruch, T.; Bunker, R.; Cabrera, B.; /Stanford U., Phys. Dept. /UC, Santa Barbara

    2010-11-01

    We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below {approx}10 GeV/c{sup 2}. This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c{sup 2} and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.

  12. Results from a low-energy analysis of the CDMS II germanium data.

    PubMed

    Ahmed, Z; Akerib, D S; Arrenberg, S; Bailey, C N; Balakishiyeva, D; Baudis, L; Bauer, D A; Brink, P L; Bruch, T; Bunker, R; Cabrera, B; Caldwell, D O; Cooley, J; do Couto e Silva, E; Cushman, P; Daal, M; DeJongh, F; Di Stefano, P; Dragowsky, M R; Duong, L; Fallows, S; Figueroa-Feliciano, E; Filippini, J; Fox, J; Fritts, M; Golwala, S R; Hall, J; Hennings-Yeomans, R; Hertel, S A; Holmgren, D; Hsu, L; Huber, M E; Kamaev, O; Kiveni, M; Kos, M; Leman, S W; Liu, S; Mahapatra, R; Mandic, V; McCarthy, K A; Mirabolfathi, N; Moore, D; Nelson, H; Ogburn, R W; Phipps, A; Pyle, M; Qiu, X; Ramberg, E; Rau, W; Reisetter, A; Resch, R; Saab, T; Sadoulet, B; Sander, J; Schnee, R W; Seitz, D N; Serfass, B; Sundqvist, K M; Tarka, M; Wikus, P; Yellin, S; Yoo, J; Young, B A; Zhang, J

    2011-04-01

    We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from weakly interacting massive particles (WIMPs) with masses below ∼10  GeV/c(2). This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9  GeV/c(2) and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.

  13. Measurement of Nuclear Recoils in the CDMS II Dark Matter Search

    SciTech Connect

    Fallows, Scott Mathew

    2014-12-01

    The Cryogenic Dark Matter Search (CDMS) experiment is designed to directly detect elastic scatters of weakly-interacting massive dark matter particles (WIMPs), on target nuclei in semiconductor crystals composed of Si and Ge. These scatters would occur very rarely, in an overwhelming background composed primarily of electron recoils from photons and electrons, as well as a smaller but non-negligible background of WIMP-like nuclear recoils from neutrons. The CDMS II generation of detectors simultaneously measure ionization and athermal phonon signals from each scatter, allowing discrimination against virtually all electron recoils in the detector bulk. Pulse-shape timing analysis allows discrimination against nearly all remaining electron recoils taking place near detector surfaces. Along with carefully limited neutron backgrounds, this experimental program allowed for \\background- free" operation of CDMS II at Soudan, with less than one background event expected in each WIMP-search analysis. As a result, exclusionary upper-limits on WIMP-nucleon interaction cross section were placed over a wide range of candidate WIMP masses, ruling out large new regions of parameter space.

  14. Background Characterization and Discrimination in the Final Analysis of the CDMS II Phase of the Cryogenic Dark Matter Search

    SciTech Connect

    Fritts, Matthew C.

    2011-02-01

    The Cryogenic Dark Matter Search (CDMS) is designed to detectWeakly-Interacting Massive Particles (WIMPs) in the Milky Way halo. The phase known as CDMS II was performed in the Soudan Underground Laboratory. The final set of CDMS II data, collected in 2007-8 and referred to as Runs 125-8, represents the largest exposure to date for the experiment. We seek collisions between WIMPs and atomic nuclei in disk-shaped germanium and silicon detectors. A key design feature is to keep the rate of collisions from known particles producing WIMP-like signals very small. The largest category of such background is interactions with electrons in the detectors that occur very close to one of the faces of the detector. The next largest category is collisions between energetic neutrons that bypass the experimental shielding and nuclei in the detectors. Analytical efforts to discriminate these backgrounds and to estimate the rate at which such discrimination fails have been refined and improved throughout each phase of CDMS. Next-generation detectors for future phases of CDMS require testing at cryogenic test facilities. One such facility was developed at the University of Minnesota in 2007 and has been used continuously since then to test detectors for the next phase of the experiment, known as SuperCDMS.

  15. The Cryogenic Dark Matter Search (CDMS-II) Experiment: First Results from the Soudan Mine

    SciTech Connect

    Chang, Clarence Leeder

    2004-09-01

    There is an abundance of evidence that the majority of the mass of the universe is in the form of non-baryonic non-luminous matter that was non-relativistic at the time when matter began to dominate the energy density. Weakly Interacting Massive Particles, or WIMPs, are attractive cold dark matter candidates because they would have a relic abundance today of ~0.1 which is consistent with precision cosmological measurements. WIMPs are also well motivated theoretically. Many minimal supersymmetric extensions of the Standard Model have WIMPs in the form of the lightest supersymmetric partner, typically taken to be the neutralino. The CDMS II experiment searches for WIMPs via their elastic scattering off of nuclei. The experiment uses Ge and Si ZIP detectors, operated at <50 mK, which simultaneously measure the ionization and athermal phonons produced by the scattering of an external particle. The dominant background for the experiment comes from electromagnetic interactions taking place very close to the detector surface. Analysis of the phonon signal from these interactions makes it possible to discriminate them from interactions caused by WIMPs. This thesis presents the details of an important aspect of the phonon pulse shape analysis known as the ''Lookup Table Correction''. The Lookup Table Correction is a position dependent calibration of the ZIP phonon response which improves the rejection of events scattering near the detector surface. The CDMS collaboration has recently commissioned its experimental installation at the Soudan Mine. This thesis presents an analysis of the data from the first WIMP search at the Soudan Mine. The results of this analysis set the world's lowest exclusion limit making the CDMS II experiment at Soudan the most sensitive WIMP search to this date.

  16. Task I: Dark Matter Search Experiments with Cryogenic Detectors: CDMS-I and CDMS-II Task II: Experimental Study of Neutrino Properties: EXO and KamLAND

    SciTech Connect

    Cabrera, Blas; Gratta, Giorgio

    2013-08-30

    Dark Matter Search - During the period of performance, our group continued the search for dark matter in the form of weakly interacting massive particles or WIMPs. As a key member of the CDMS (Cryogenic Dark Matter Search) collaboration, we completed the CDMS II experiment which led the field in sensitivity for more than five years. We fabricated all detectors, and participated in detector testing and verification. In addition, we participated in the construction and operation of the facility at the Soudan Underground Laboratory and played key roles in the data acquisition and analysis. Towards the end of the performance period, we began operating the SuperCDMS Soudan experiment, which consists of 15 advanced Ge (9 kg) detectors. The advanced detector design called iZIP grew out of our earlier DOE Particle Detector R&D program which demonstrated the rejection of surface electrons to levels where they are no longer the dominant source of background. Our group invented this advanced design and these larger detectors were fabricated on the Stanford campus in collaboration with the SLAC CDMS group and the Santa Clara University group. The sensitivity reach is expected to be up to 5 times better than CDMS II after two years of operation. We will check the new limits on WIMPs set by XENON100, and we expect improved sensitivity for light mass WIMPs beyond that of any other existing experiment. Our group includes the Spokesperson for SuperCDMS and continues to make important contributions to improvements in the detector technology which are enabling the very low trigger thresholds used to explore the low mass WIMP region. We are making detailed measurements of the charge transport and trapping within Ge crystals, measuring the diffusive trapping distance of the quasiparticle excitations within the Al phonon collector fins on the detector surface, and we are contributing to the development of much improved detector Monte Carlos which are essential to guide the detector

  17. Measurement of Nuclear Recoils in the CDMS II Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Fallows, Scott M.

    The Cryogenic Dark Matter Search (CDMS) experiment is designed to directly detect elastic scatters of weakly-interacting massive dark matter particles (WIMPs), on target nuclei in semiconductor crystals composed of Si and Ge. These scatters would occur very rarely, in an overwhelming background composed primarily of electron recoils from photons and electrons, as well as a smaller but non-negligible background of WIMP-like nuclear recoils from neutrons. The CDMS~II generation of detectors simultaneously measure ionization and athermal phonon signals from each scatter, allowing discrimination against virtually all electron recoils in the detector bulk. Pulse-shape timing analysis allows discrimination against nearly all remaining electron recoils taking place near detector surfaces. Along with carefully limited neutron backgrounds, this experimental program allowed for "background-free'' operation of CDMS~II at Soudan, with less than one background event expected in each WIMP-search analysis. As a result, exclusionary upper-limits on WIMP-nucleon interaction cross section were placed over a wide range of candidate WIMP masses, ruling out large new regions of parameter space. These results, like any others, are subject to a variety of systematic effects that may alter their final interpretations. A primary focus of this dissertation will be difficulties in precisely calibrating the energy scale for nuclear recoil events like those from WIMPs. Nuclear recoils have suppressed ionization signals relative to electron recoils of the same recoil energy, so the response of the detectors is calibrated differently for each recoil type. The overall normalization and linearity of the energy scale for electron recoils in CDMS~II detectors is clearly established by peaks of known gamma energy in the ionization spectrum of calibration data from a 133Ba source. This electron-equivalent keVee) energy scale enables calibration of the total phonon signal (keVt) by enforcing unity

  18. Improved WIMP-search reach of the CDMS II germanium data

    DOE PAGES

    Agnese, R.

    2015-10-12

    CDMS II data from the five-tower runs at the Soudan Underground Laboratory were reprocessed with an improved charge-pulse fitting algorithm. Two new analysis techniques to reject surface-event backgrounds were applied to the 612 kg days germanium-detector weakly interacting massive particle (WIMP)-search exposure. An extended analysis was also completed by decreasing the 10 keV analysis threshold to ~5 keV, to increase sensitivity near a WIMP mass of 8 GeV/c2. After unblinding, there were zero candidate events above a deposited energy of 10 keV and six events in the lower-threshold analysis. This yielded minimum WIMP-nucleon spin-independent scattering cross-section limits of 1.8×10–44 andmore » 1.18×10–41 at 90% confidence for 60 and 8.6 GeV/c2 WIMPs, respectively. This improves the previous CDMS II result by a factor of 2.4 (2.7) for 60 (8.6) GeV/c2 WIMPs.« less

  19. Improved WIMP-search reach of the CDMS II germanium data

    SciTech Connect

    Agnese, R.

    2015-10-12

    CDMS II data from the five-tower runs at the Soudan Underground Laboratory were reprocessed with an improved charge-pulse fitting algorithm. Two new analysis techniques to reject surface-event backgrounds were applied to the 612 kg days germanium-detector weakly interacting massive particle (WIMP)-search exposure. An extended analysis was also completed by decreasing the 10 keV analysis threshold to ~5 keV, to increase sensitivity near a WIMP mass of 8 GeV/c2. After unblinding, there were zero candidate events above a deposited energy of 10 keV and six events in the lower-threshold analysis. This yielded minimum WIMP-nucleon spin-independent scattering cross-section limits of 1.8×10–44 and 1.18×10–41 at 90% confidence for 60 and 8.6 GeV/c2 WIMPs, respectively. This improves the previous CDMS II result by a factor of 2.4 (2.7) for 60 (8.6) GeV/c2 WIMPs.

  20. A dark-matter search using the final CDMS II dataset and a novel detector of surface radiocontamination

    SciTech Connect

    Ahmed, Zeeshan

    2012-01-01

    Substantial evidence from galaxies, galaxy clusters, and cosmological scales suggests that ~85% of the matter of our universe is invisible. The missing matter, or "dark matter" is likely composed of non-relativistic, non-baryonic particles, which have very rare interactions with baryonic matter and with one another. Among dark matter candidates, Weakly Interacting Massive Particles (WIMPs) are particularly well motivated. In the early universe, thermally produced particles with weak-scale mass and interactions would `freeze out’ at the correct density to be dark matter today. Extensions to the Standard Model of particle physics, such as Supersymmetry, which solve gauge hierarchy and coupling unification problems, naturally provide such particles. Interactions of WIMPs with baryons are expected to be rare, but might be detectable in low-noise detectors. The Cryogenic Dark Matter Search (CDMS) experiment uses ionization- and phonon- sensitive germanium particle detectors to search for such interactions. CDMS detectors are operated at the Soudan Underground Laboratory in Minnesota, within a shielded environment to lower cosmogenic and radioactive background. The combination of phonon and ionization signatures from the detectors provides excellent residual-background rejection. This dissertation presents improved techniques for phonon calibration of CDMS II detectors and the analysis of the final CDMS II dataset with 612 kg-days of exposure. We set a limit of 3.8x10$^{-}$44 cm$^{2}$ on WIMP-nucleon spin-independent scattering cross section for a WIMP mass of 70 GeV/c$^{2}$. At the time this analysis was published, these data presented the most stringent limits on WIMP scattering for WIMP masses over 42 GeV/c$^{2}$, ruling out previously unexplored parameter space. Next-generation rare-event searches such as SuperCDMS, COUPP, and CLEAN will be limited in sensitivity, unless they achieve stringent control of the surface radioactive contamination on their detectors. Low

  1. A Search for WIMP Dark Matter Using an Optimized Chi-square Technique on the Final Data from the Cryogenic Dark Matter Search Experiment (CDMS II)

    SciTech Connect

    Manungu Kiveni, Joseph

    2012-12-01

    This dissertation describes the results of a WIMP search using CDMS II data sets accumulated at the Soudan Underground Laboratory in Minnesota. Results from the original analysis of these data were published in 2009; two events were observed in the signal region with an expected leakage of 0.9 events. Further investigation revealed an issue with the ionization-pulse reconstruction algorithm leading to a software upgrade and a subsequent reanalysis of the data. As part of the reanalysis, I performed an advanced discrimination technique to better distinguish (potential) signal events from backgrounds using a 5-dimensional chi-square method. This dataanalysis technique combines the event information recorded for each WIMP-search event to derive a backgrounddiscrimination parameter capable of reducing the expected background to less than one event, while maintaining high efficiency for signal events. Furthermore, optimizing the cut positions of this 5-dimensional chi-square parameter for the 14 viable germanium detectors yields an improved expected sensitivity to WIMP interactions relative to previous CDMS results. This dissertation describes my improved (and optimized) discrimination technique and the results obtained from a blind application to the reanalyzed CDMS II WIMP-search data.

  2. Probing the light Higgs pole resonance annihilation of dark matter in the light of XENON100 and CDMS-II observations

    SciTech Connect

    Chattopadhyay, Utpal; Ghosh, Dilip Kumar; Das, Debottam; Maity, Manas

    2010-10-01

    We consider the prospect of lightest neutralino ({chi}-tilde{sub 1}{sup 0}) as a dark matter candidate in light of recent interesting observations from the XENON100 and CDMS-II experiments in minimal supergravity framework with large tan{beta} and nonvanishing A{sub 0}. Within the WMAP satisfied zone, there is a large direct detection reach of lighter {chi}-tilde{sub 1}{sup 0} in the lighter Higgs boson mediated resonance annihilation domain of the above scenario. It is seen that the heavier Higgs boson plays a dominating role in the {chi}-tilde{sub 1}{sup 0}-p cross section in the associated zone of parameter space in spite of having a larger mass. Possible LHC signatures are discussed.

  3. A Search for WIMP Dark Matter using an Optimized Chi-square Technique on the Final Data from the Cryogenic Dark Matter Search Experiment (CDMS II)

    NASA Astrophysics Data System (ADS)

    Manungu Kiveni, Joseph

    2012-06-01

    During the last two decades, cosmology has become a precision observational science thanks (in part) to the incredible number of experiments performed to better understand the composition of the universe. The large amount of data accumulated strongly indicates that the bulk of the universe's matter is in the form of non-baryonic matter that does not interact electromagnetically. Combined evidence from the dynamics of galaxies and galaxy clusters confirms that most of the mass in the universe is not composed of any known form of matter. Measurements of the cosmic microwave background, big bang nucleosynthesis and many other experiments indicate that ˜80% of the matter in the universe is dark, non-relativistic and cold. The dark matter resides in the halos surrounding galaxies, galaxy clusters and other large-scale structures. Weakly Interacting Massive Particles (WIMPs) are well motivated class of dark matter candidates that arise naturally in supersymmetric extensions to the Standard Model of particles physics, and can be produced as non-relativistic thermal relics in the early universe with about the right density to account for the missing mass. The Cryogenic Dark Matter Search (CDMS) experiment seeks to directly detect the keV-scale energy deposited by WIMPs in the galactic halo when they scatter from nuclei in the crystalline detectors made of germanium and silicon. These detectors, called Z-sensitive Ionization and Phonon detectors (ZIPs) are operated at ˜ 45 mK and simultaneously measure the ionization and the (athermal) phonons produced by particle interactions. The ratio of ionization and phonon energies allows discrimination of a low rate of nuclear recoils (expected for WIMPs) from an overwhelming rate of electron recoils (expected for most backgrounds). Phonon-pulse shape and timing enables further suppression of lower-rate interactions at the detector surfaces. This dissertation describes the results of a WIMP search using CDMS II data sets

  4. Magnetic description of the Fermi arc in type-I and type-II Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Tchoumakov, Serguei; Civelli, Marcello; Goerbig, Mark O.

    2017-03-01

    We consider finite-sized interfaces of a Weyl semimetal and show that the corresponding confinement potential is similar to the application of a magnetic field. Among the numerous states, which can be labeled by indices n like in Landau levels, the n =0 surface state describes the Weyl semimetal Fermi arc at a given chemical potential. Moreover, the analogy with a magnetic field shows that an external in-plane magnetic field can be used to distort the Fermi arc and would explain some features of magnetotransport in Weyl semimetals. We derive the Fermi arc for type-I and type-II Weyl semimetals where we deal with the tilt anisotropy by the use of Lorentz boosts. In the case of type-II Weyl semimetals, this leads to many additional topologically trivial surface states at low energy. Finally, we extend the Aharonov-Casher argument and demonstrate the stability of the Fermi arc over fluctuations of the surface potential.

  5. Cryogenic Dark Matter Search (CDMS): The Hunt for Dark Matter

    SciTech Connect

    Sadoulet, Bernard

    2006-03-06

    Deciphering the nature of dark matter has great scientific importance. A leading hypothesis is that dark matter is made of Weakly Interactive Massive Particles (WIMPs), which may result from supersymmetry or additional spatial dimensions. The underground search for elastic scattering of WIMPs on suitable targets (the so-called 'direct detection') is currently led by the Cryogenic Dark Matter Search II (CDMS II) experiment. Its sensitivity is ten times better than any other experiment and we hope to obtain another factor ten in the coming two years. After a brief recall of our recent results, I will describe the complementarity between direct detection experiments, the LHC and the ILC and I will outline the role that SLAC could play in this SuperCDMS program.

  6. Surface Fermi arc connectivity in the type-II Weyl semimetal candidate WTe2

    NASA Astrophysics Data System (ADS)

    Sánchez-Barriga, J.; Vergniory, M. G.; Evtushinsky, D.; Aguilera, I.; Varykhalov, A.; Blügel, S.; Rader, O.

    2016-10-01

    We perform ultrahigh-resolution angle-resolved photoemission experiments at a temperature T =0.8 K on the type-II Weyl semimetal candidate WTe2. We find a surface Fermi arc connecting the bulk electron and hole pockets on the (001) surface. Our results show that the surface Fermi arc connectivity to the bulk bands is strongly mediated by distinct surface resonances dispersing near the border of the surface-projected bulk band gap. By comparing the experimental results to first-principles calculations, we argue that the coupling to these surface resonances, which are topologically trivial, is compatible with the classification of WTe2 as a type-II Weyl semimetal hosting topological Fermi arcs. We further support our conclusion by a systematic characterization of the bulk and surface character of the different bands and discuss the similarity of our findings to the case of topological insulators.

  7. Nuclear Recoil Identification in CDMS Experiment

    NASA Astrophysics Data System (ADS)

    Wang, Gensheng; Akerib, Dan

    2004-05-01

    The Cryogenic Dark Matter Search (CDMS) experiment achieves high sensitivity for WIMP dark matter particles recoiling from nuclei because of the rejection of predominant electromagnetic backgrounds. The measured charge energy and phonon energy ratio, or ionization yield, is a powerful tool for discrimination between nuclear recoil and electron recoil in CDMS experiment. However, since events occurring within a thin surface layer, notably low-energy background beta particles, suffer a loss in ionization charge collection, other method of surface--event rejection becomes important. I will describe the CDMS detector ionization measurement and ballistic phonon readout, with an emphasis on detector phenomenology. In particular, I will describe the primary CDMS detector quantities--ionization yield, phonon risetime, event location information and phonon energy partition distribution. The application of these parameters in nuclear recoil identification and in surface event rejection in CDMS experiment will be summarized.

  8. A search for particle dark matter using cryogenic germanium and silicon detectors in the one- and two- tower runs of CDMS-II at Soudan

    SciTech Connect

    Reuben Walter Ogburn, IV

    2008-06-01

    Images of the Bullet Cluster of galaxies in visible light, X-rays, and through gravitational lensing confirm that most of the matter in the universe is not composed of any known form of matter. The combined evidence from the dynamics of galaxies and clusters of galaxies, the cosmic microwave background, big bang nucleosynthesis, and other observations indicates that 80% of the universe's matter is dark, nearly collisionless, and cold. The identify of the dar, matter remains unknown, but weakly interacting massive particles (WIMPs) are a very good candidate. They are a natural part of many supersymmetric extensions to the standard model, and could be produced as a nonrelativistic, thermal relic in the early universe with about the right density to account for the missing mass. The dark matter of a galaxy should exist as a spherical or ellipsoidal cloud, called a 'halo' because it extends well past the edge of the visible galaxy. The Cryogenic Dark Matter Search (CDMS) seeks to directly detect interactions between WIMPs in the Milky Way's galactic dark matter halo using crystals of germanium and silicon. Our Z-sensitive ionization and phonon ('ZIP') detectors simultaneously measure both phonons and ionization produced by particle interactions. In order to find very rare, low-energy WIMP interactions, they must identify and reject background events caused by environmental radioactivity, radioactive contaminants on the detector,s and cosmic rays. In particular, sophisticated analysis of the timing of phonon signals is needed to eliminate signals caused by beta decays at the detector surfaces. This thesis presents the firs two dark matter data sets from the deep underground experimental site at the Soudan Underground Laboratory in Minnesota. These are known as 'Run 118', with six detectors (1 kg Ge, 65.2 live days before cuts) and 'Run 119', with twelve detectors (1.5 kg Ge, 74.5 live days before cuts). They have analyzed all data from the two runs together in a single

  9. The SuperCDMS Experiment

    SciTech Connect

    Schnee, Richard W.; Akerib, D.S.; Attisha, M.J.; Bailey, C.N.; Baudis, L.; Bauer, Daniel A.; Brink, P.L.; Brusov, P.P.; Bunker, R.; Cabrera, B.; Caldwell, D.O.; Chang, C.L.; Cooley, J.; Crisler, M.B.; Cushman, P.; Denes, P.; Dragowsky, M.R.; Duong, L.; Filippini, J.; Gaitskell, R.J.; Golwala, S.R.; /Case Western Reserve U. /Brown U. /Florida U. /Fermilab /Stanford U., Phys. Dept. /UC, Santa Barbara /Minnesota U. /LBL, Berkeley /UC, Berkeley /Caltech /Colorado U., Denver /NIST, Boulder /Santa Clara U.

    2005-02-01

    Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrounds negligible during the three phases of SuperCDMS. By developing production designs that require only modest testing, detector production rates may be improved sufficiently to allow an exposure of 500 ton d within a reasonable time and budget. Overall, the improvement estimates described above are conservative. Previous development efforts have shown that some areas prove easier and provide larger factors while others prove more difficult. The conservative estimates together with the broad approach reduce the risk and give us confidence that we will succeed, providing the surest way to probe to WIMP-nucleon cross sections of 10{sup -46} cm{sup 2}.

  10. Experimental observation of topological Fermi arcs in type-II Weyl semimetal MoTe2

    NASA Astrophysics Data System (ADS)

    Deng, Ke; Wan, Guoliang; Deng, Peng; Zhang, Kenan; Ding, Shijie; Wang, Eryin; Yan, Mingzhe; Huang, Huaqing; Zhang, Hongyun; Xu, Zhilin; Denlinger, Jonathan; Fedorov, Alexei; Yang, Haitao; Duan, Wenhui; Yao, Hong; Wu, Yang; Fan, Shoushan; Zhang, Haijun; Chen, Xi; Zhou, Shuyun

    2016-12-01

    Weyl semimetal is a new quantum state of matter hosting the condensed matter physics counterpart of the relativistic Weyl fermions originally introduced in high-energy physics. The Weyl semimetal phase realized in the TaAs class of materials features multiple Fermi arcs arising from topological surface states and exhibits novel quantum phenomena, such as a chiral anomaly-induced negative magnetoresistance and possibly emergent supersymmetry. Recently it was proposed theoretically that a new type (type-II) of Weyl fermion that arises due to the breaking of Lorentz invariance, which does not have a counterpart in high-energy physics, can emerge as topologically protected touching between electron and hole pockets. Here, we report direct experimental evidence of topological Fermi arcs in the predicted type-II Weyl semimetal MoTe2 (refs ,,). The topological surface states are confirmed by directly observing the surface states using bulk- and surface-sensitive angle-resolved photoemission spectroscopy, and the quasi-particle interference pattern between the putative topological Fermi arcs in scanning tunnelling microscopy. By establishing MoTe2 as an experimental realization of a type-II Weyl semimetal, our work opens up opportunities for probing the physical properties of this exciting new state.

  11. The SuperCDMS SNOLAB Detector Tower

    NASA Astrophysics Data System (ADS)

    Aramaki, Tsuguo

    2016-08-01

    The SuperCDMS collaboration is moving forward with the design and construction of SuperCDMS SNOLAB, where the initial deployment will include ˜ 30 kg of Ge and ˜ 5 kg of Si detectors. Here, we will discuss the associated cryogenic cold hardware required for the detector readout. The phonon signals will be read out with superconducting quantum interference device arrays and the ionization signals will use high electron mobility transistor amplifiers operating at 4 K. A number of design challenges exist regarding the required wiring complex impedance, noise pickup, vibration, and thermal isolation. Our progress to date will be presented.

  12. Observation of Fermi arcs in the type-II Weyl semimetal candidate WTe2

    DOE PAGES

    Wu, Yun; Mou, Daixiang; Jo, Na Hyun; ...

    2016-09-14

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe2, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 were proposed to emerge at the crossing points of electron and hole pockets, and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe2. Here, we also find that trivial andmore » topological domains coexist on the same surface of the sample due to the presence of inhomogeneous strain detected by scanning electron microscopy data. This is in agreement with the theoretical prediction that strain can drive this system from topological Weyl to trivial semimetal. WTe2 therefore provides a tunable playground for studying exotic topological quantum effects.« less

  13. Fermi Arcs and Their Topological Character in the Candidate Type-II Weyl Semimetal MoTe2

    NASA Astrophysics Data System (ADS)

    Tamai, A.; Wu, Q. S.; Cucchi, I.; Bruno, F. Y.; Riccò, S.; Kim, T. K.; Hoesch, M.; Barreteau, C.; Giannini, E.; Besnard, C.; Soluyanov, A. A.; Baumberger, F.

    2016-07-01

    We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal MoTe2 . Using laser-based angle-resolved photoemission, we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface states observed experimentally are reproduced by an electronic structure calculation for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2 .

  14. Determining the Appropriate Package and Transportation Methodology for the Detroit Edison, Fermi II Msrs and Associated Components

    SciTech Connect

    Weber, B.

    2007-07-01

    During the spring of 2005, Detroit Edison, Enrico Fermi II Nuclear Power Station (Fermi) decided to disposition two MSRs and associated components scheduled for replacement in the spring of 2006 during the MSR Replacement Outage. Of concern to Fermi was the proper packaging and transportation methodology when dis-positioning a component measuring approximately 110' in length and 13' in diameter and weighing over 300 tons. Upon removal from the Turbine Deck the retired MSRs and associated components were turned over to the Rad Waste Group for packaging and final disposition. Fermi requested quotations from vendors to package, transport, and disposition the MSRs and associated components. However, multiple Vendors informed Fermi that the size and weight of the MSRs were questionable in passing permitting requirements and would require segmentation and volume reduction on site or at a waste processor. Fermi contracted with MHF Logistical Solutions (MHF-LS) based on their ability to receive clearances for shipping the MSRs in one piece via two heavy haul rail conveyances acting as a bolstered load with professionally engineered blocking and bracing configured to support the retired MSRs. (authors)

  15. Results and Prospects for the Cryogenic Dark Matter Search (CDMS) Experiment

    NASA Astrophysics Data System (ADS)

    Serfass, B.

    2012-06-01

    The Cryogenic Dark Matter Search (CDMS) experiment, located at the Soudan underground mine, operated 30 low-temperature Ge and Si detectors for several years to search for Weakly Interacting Massive dark matter Particles (WIMPs). Due to their excellent background discrimination power and low energy threshold, our detectors have provided world-leading sensitivity for WIMP-nucleon interactions for most of the past decade over a large WIMP mass range. The final exposure of our CDMS II detectors yielded two candidate events, with an expected background of 0.9 ± 0.2 events, and this result was published in March 2010 in Science. A reanalysis of 8 Ge detectors with a lowered, 2 keV recoil energy threshold, provided increased sensitivity to interactions from WIMPs with masses below 10 GeV/c2 and excluded possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments. The CDMS collaboration is moving forward with the SuperCDMS experiments at Soudan and SNOLAB with the goal of probing the zeptobarn scale and beyond over the next decade. To achieve this goal, a new generation of larger mass detectors with interleaved geometry for the phonon and ionization readout has been developed.

  16. Characterization of the CDMS Ionization Readout

    NASA Astrophysics Data System (ADS)

    Phipps, Arran

    2007-10-01

    Current cosmological models predict that a large portion of the total mass of the universe, about eighty percent, consists of putative dark matter. Theory predicts this dark matter may be in the form of particles constantly passing through the Earth. A class of these particles may interact with ordinary matter, earning the name weakly-interacting massive particles (WIMPs). The Cryogenic Dark Matter Search (CDMS) aims to directly detect the existence of WIMPs. CDMS has designed ZIP (Z-dependent Ionization & Phonon) detectors which measure phonon production and ionization of an interaction, making it possible to determine the interacting particle. The low-energy threshold of the ZIP detectors is determined by the signal-to-noise ratio of the ionization readout. A characterization of the signal-to-noise ratio of the ionization readout, along with possible modifications for improved sensitivity will be presented.

  17. Looking for Dark Matter with the CDMS Detectors

    NASA Astrophysics Data System (ADS)

    Kos, Mark

    2009-10-01

    The Cryogenic Dark Matter Search (CDMS) has the world's best sensitivity to Weakly Interacting Massive Particle (WIMP) interactions. By independently measuring phonon and ionization energy, CDMS distinguishes electromagnetic backgrounds from possible WIMP nuclear recoil events. CDMS consists of five towers of Ge and Si detectors. Recently a SuperTower has been installed with larger Ge detectors and improved phonon readout. I will present the experiment's most recent results and discuss operation of the new detectors.

  18. From PAMELA to CDMS and back.

    SciTech Connect

    Cao, Q.-H.; Low, I.; Shaughnessy, G.; High Energy Physics; Univ. Chicago; Northwestern Univ.

    2010-01-01

    We study implications of the recent results from the CDMS Collaboration on astrophysical probes of dark matter. By crossing symmetry an elastic scattering cross section with the nucleon implies annihilation of dark matter into hadrons inside the halo, resulting in an anti-proton flux that could be constrained by data from the PAMELA Collaboration if one includes a large boost factor necessary to explain the PAMELA excess in the positron fraction. As an illustration, we present a model-independent analysis for a fermionic dark matter and study the upper bound on the boost factor using the PAMELA anti-proton flux.

  19. Search for axions with the CDMS experiment.

    PubMed

    Ahmed, Z; Akerib, D S; Arrenberg, S; Bailey, C N; Balakishiyeva, D; Baudis, L; Bauer, D A; Beaty, J; Brink, P L; Bruch, T; Bunker, R; Cabrera, B; Caldwell, D O; Cooley, J; Cushman, P; Dejongh, F; Dragowsky, M R; Duong, L; Figueroa-Feliciano, E; Filippini, J; Fritts, M; Golwala, S R; Grant, D R; Hall, J; Hennings-Yeomans, R; Hertel, S; Holmgren, D; Hsu, L; Huber, M E; Kamaev, O; Kiveni, M; Kos, M; Leman, S W; Mahapatra, R; Mandic, V; Moore, D; McCarthy, K A; Mirabolfathi, N; Nelson, H; Ogburn, R W; Pyle, M; Qiu, X; Ramberg, E; Rau, W; Reisetter, A; Saab, T; Sadoulet, B; Sander, J; Schnee, R W; Seitz, D N; Serfass, B; Sundqvist, K M; Tarka, M; Wang, G; Yellin, S; Yoo, J; Young, B A

    2009-10-02

    We report on the first axion search results from the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. An energy threshold of 2 keV for electron-recoil events allows a search for possible solar axion conversion into photons or local galactic axion conversion into electrons in the germanium crystal detectors. The solar axion search sets an upper limit on the Primakov coupling g(agammagamma) of 2.4x10(-9) GeV-1 at the 95% confidence level for an axion mass less than 0.1 keV/c2. This limit benefits from the first precise measurement of the absolute crystal plane orientations in this type of experiment. The galactic axion search analysis sets a world-leading experimental upper limit on the axioelectric coupling g(aee) of 1.4x10(-12) at the 90% confidence level for an axion mass of 2.5 keV/c2.

  20. Fermi Bubbles under Dark Matter Scrutiny Part II: Particle Physics Analysis

    SciTech Connect

    Huang, Wei-Chih; Urbano, Alfredo; Xue, Wei E-mail: alfredo.urbano@sissa.it

    2014-04-01

    The analysis of the gamma-ray photons collected by the Fermi Large Area Telescope reveals, after removal of astrophysical background, the existence of an excess towards the Galactic center. This excess peaks around few GeV, and its origin is compatible with the gamma-ray flux originating from Dark Matter annihilation. In this work we take a closer look on this interpretation; we investigate which kind of Dark Matter, and which type of interactions with the Standard Model fields are able to reproduce the observed signal. The structure of the paper is twofold. In the first part, we follow an effective field theory approach considering both fermionic and scalar Dark Matter. The computation of the relic density, the constraint imposed from the null result of direct searches, and the reliability of the effective field theory description allow us to single out only two viable dim-6 operators in the case of fermionic Dark Matter. In the second part, we analyze some concrete models. In particular, we find that the scalar Higgs portal can provide a simple, concrete and realistic scenario able to explain the GeV excess under scrutiny.

  1. THE ACCRETION WIND MODEL OF FERMI BUBBLES. II. RADIATION

    SciTech Connect

    Mou, Guobin; Yuan, Feng; Gan, Zhaoming; Sun, Mouyuan

    2015-09-20

    In a previous work, we have shown that the formation of Fermi bubbles can be due to the interaction between winds launched from the hot accretion flow in Sgr A* and the interstellar medium (ISM). In that work, we focus only on the morphology. In this paper we continue our study by calculating the gamma-ray radiation. Some cosmic-ray protons (CRp) and electrons (CRe) must be contained in the winds, which are likely formed by physical processes such as magnetic reconnection. We have performed MHD simulations to study the spatial distribution of CRp, considering the advection and diffusion of CRp in the presence of magnetic field. We find that a permeated zone is formed just outside of the contact discontinuity between winds and the ISM, where the collisions between CRp and thermal nuclei mainly occur. The decay of neutral pions generated in the collisions, combined with the inverse Compton scattering of background soft photons by the secondary leptons generated in the collisions and primary CRe, can well explain the observed gamma-ray spectral energy distribution. Other features such as the uniform surface brightness along the latitude and the boundary width of the bubbles are also explained. The advantage of this “accretion wind” model is that the adopted wind properties come from the detailed small-scale MHD numerical simulation of accretion flows and the value of mass accretion rate has independent observational evidences. The success of the model suggests that we may seriously consider the possibility that cavities and bubbles observed in other contexts such as galaxy clusters may be formed by winds rather than jets.

  2. Prototyping an active neutron veto for SuperCDMS

    NASA Astrophysics Data System (ADS)

    Calkins, Robert; Loer, Ben

    2015-08-01

    Neutrons, originating cosmogenically or from radioactive decays, can produce signals in dark matter detectors that are indistinguishable from Weakly Interacting Massive Particles (WIMPs). To combat this background for the SuperCDMS SNOLAB experiment, we are investigating designs for an active neutron veto within the constrained space of the compact SuperCDMS passive shielding. The current design employs an organic liquid scintillator mixed with an agent to enhance thermal neutron captures, with the scintillation light collected using wavelength-shifting fibers and read out by silicon photo-multipliers. We will describe the proposed veto and its predicted efficiency in detail and give some recent results from our R&D and prototyping efforts.

  3. Prototyping an Active Neutron Veto for SuperCDMS

    SciTech Connect

    Calkins, Robert; Loer, Ben

    2015-08-17

    Neutrons, originating cosmogenically or from radioactive decays, can produce signals in dark matter detectors that are indistinguishable from Weakly Interacting Massive Particles (WIMPs). To combat this background for the SuperCDMS SNOLAB experiment, we are investigating designs for an active neutron veto within the constrained space of the compact SuperCDMS passive shielding. The current design employs an organic liquid scintillator mixed with an agent to enhance thermal neutron captures, with the scintillation light collected using wavelength-shifting fibers and read out by silicon photo-multipliers. We will describe the proposed veto and its predicted efficiency in detail and give some recent results from our R&D and prototyping efforts.

  4. Command and data management system (CDMS) of the Philae lander

    NASA Astrophysics Data System (ADS)

    Balázs, A.; Baksa, A.; Bitterlich, H.; Hernyes, I.; Küchemann, O.; Pálos, Z.; Rustenbach, J.; Schmidt, W.; Spányi, P.; Sulyán, J.; Szalai, S.; Várhalmi, L.

    2016-08-01

    The paper covers the principal requirements, design concepts and implementation of the hardware and software for the central on-board computer (CDMS) of the Philae lander in the context of the ESA Rosetta space mission, including some technical details. The focus is on the implementation of fault tolerance, autonomous operation and operational flexibility by means of specific linked data structures and code execution mechanisms that can be interpreted as a kind of object oriented model for mission sequencing.

  5. The SuperCDMS Soudan High Mass Analysis

    NASA Astrophysics Data System (ADS)

    Cornell, Brett; SuperCDMS Collaboration

    2017-01-01

    The SuperCDMS Soudan experiment searches for direct interactions of WIMP dark matter particles with germanium nuclei. The experiment uses detectors (iZIPs) with sophisticated ionization and phonon sensors to distinguish nuclear recoils from electron-recoil backgrounds or surface contaminants. We report the status of an analysis, based on a 1700 kg-day exposure, that seeks to maximize our experimental sensitivity to spin-independent WIMP-nucleon interaction in the high mass regime (M > 10 Gev /c2).

  6. Testing and Characterization of SuperCDMS Dark Matter Detectors

    SciTech Connect

    Shank, Benjamin

    2014-05-01

    The Cryogenic Dark Matter Search (SuperCDMS) relies on collection of phonons and charge carriers in semiconductors held at tens of milliKelvin as handles for detection of Weakly Interacting Massive Particles (WIMPs). This thesis begins with a brief overview of the direct dark matter search (Chapter 1) and SuperCDMS detectors (Chapter 2). In Chapter 3, a 3He evaporative refrigerator facility is described. Results from experiments performed in-house at Stanford to measure carrier transport in high-purity germanium (HPGe) crystals operated at sub-Kelvin temperatures are presented in Chapter 4. Finally, in Chapter 5 a new numerical model and a time-domain optimal filtering technique are presented, both developed for use with superconducting Transition Edge Sensors (TESs), that provide excellent event reconstruction for single particle interactions in detectors read out with superconducting W-TESs coupled to energy-collecting films of Al. This thesis is not intended to be read straight through. For those new to CDMS or dark matter searches, the first two chapters are meant to be a gentle introduction for experimentalists. They are by no means exhaustive. The remaining chapters each stand alone, with different audiences.

  7. Maximum Likelihood Analysis of Low Energy CDMS II Germanium Data

    DOE PAGES

    Agnese, R.

    2015-03-30

    We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in low-energy data of the Cryogenic Dark Matter Search experiment using a maximum likelihood analysis. A background model is constructed using GEANT4 to simulate the surface-event background from Pb210decay-chain events, while using independent calibration data to model the gamma background. Fitting this background model to the data results in no statistically significant WIMP component. In addition, we also perform fits using an analytic ad hoc background model proposed by Collar and Fields, who claimed to find a large excess of signal-like events in ourmore » data. Finally, we confirm the strong preference for a signal hypothesis in their analysis under these assumptions, but excesses are observed in both single- and multiple-scatter events, which implies the signal is not caused by WIMPs, but rather reflects the inadequacy of their background model.« less

  8. Maximum Likelihood Analysis of Low Energy CDMS II Germanium Data

    SciTech Connect

    Agnese, R.

    2015-03-30

    We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in low-energy data of the Cryogenic Dark Matter Search experiment using a maximum likelihood analysis. A background model is constructed using GEANT4 to simulate the surface-event background from Pb210decay-chain events, while using independent calibration data to model the gamma background. Fitting this background model to the data results in no statistically significant WIMP component. In addition, we also perform fits using an analytic ad hoc background model proposed by Collar and Fields, who claimed to find a large excess of signal-like events in our data. Finally, we confirm the strong preference for a signal hypothesis in their analysis under these assumptions, but excesses are observed in both single- and multiple-scatter events, which implies the signal is not caused by WIMPs, but rather reflects the inadequacy of their background model.

  9. Remembering Fermi

    SciTech Connect

    Cronin, James

    2005-03-30

    A combination of the discovery of nuclear fission and the circumstances of the 2nd World War brought Enrico Fermi to Chicago, where he led the team that produced the first controlled, self-sustained nuclear chain reaction. Following the war in 1945 Chancellor Hutchins, William Zachariasen, and Walter Bartky convinced Fermi to accept a professorship at the University of Chicago, where the Institute for Nuclear Studies was established. Fermi served as the leading figure in surely the greatest collection of scientists the world has ever seen. Fermi's tenure at Chicago was cut short by his death in 1954. My talk will concentrate on the years 1945-54. Examples of his research notebooks, his speeches, his teaching, and his correspondence will be discussed.

  10. Anisotropic Fermi couplings due to large unquenched orbital angular momentum: Q-band (1)H, (14)N, and (11)B ENDOR of bis(trispyrazolylborate) cobalt(II).

    PubMed

    Myers, William K; Scholes, Charles P; Tierney, David L

    2009-08-05

    We report Q-band ENDOR of (1)H, (14)N, and (11)B at the g( parallel) extreme of the EPR spectrum of bis(trispyrazolylborate) cobalt(II) [Co(Tp)(2)] and two structural analogs. This trigonally symmetric, high-spin (hs) S = 3/2 Co(II) complex shows large unquenched ground-state orbital angular momentum, which leads to highly anisotropic electronic g-values (g( parallel) = 8.48, g( perpendicular) = 1.02). The large g-anisotropy is shown to result in large dipolar couplings near g( parallel) and uniquely anisotropic (14)N Fermi couplings, which arise from spin transferred to the nitrogen 2s orbital (2.2%) via antibonding interactions with singly occupied metal d(x(2)-y(2)) and d(z(2)) orbitals. Large, well-resolved (1)H and (11)B dipolar couplings were also observed. Taken in concert with our previous X-band ENDOR measurements at g( perpendicular) ( Myers, W. K.; et al. Inorg. Chem. 2008, 47, 6701-6710 ), the present data allow a detailed analysis of the dipolar hyperfine tensors of two of the four symmetry distinct protons in the parent molecule. In the substituted analogs, changes in hyperfine coupling due to altered metal-proton distances give further evidence of an anisotropic Fermi contact interaction. For the pyrazolyl 3H proton, the data indicate a 0.2 MHz anisotropic contact interaction and approximately 4% transfer of spin away from Co(II). Dipolar coupling also dominates for the axial boron atoms, consistent with their distance from the Co(II) ion, and resolved (11)B quadrupolar coupling showed approximately 30% electronic inequivalence between the B-H and B-C sp(3) bonds. This is the first comprehensive ENDOR study of any hs Co(II) species and lays the foundation for future development.

  11. Observation of Fermi arcs in the type-II Weyl semimetal candidate WTe2

    SciTech Connect

    Wu, Yun; Mou, Daixiang; Jo, Na Hyun; Sun, Kewei; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2016-09-14

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe2, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 were proposed to emerge at the crossing points of electron and hole pockets, and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe2. Here, we also find that trivial and topological domains coexist on the same surface of the sample due to the presence of inhomogeneous strain detected by scanning electron microscopy data. This is in agreement with the theoretical prediction that strain can drive this system from topological Weyl to trivial semimetal. WTe2 therefore provides a tunable playground for studying exotic topological quantum effects.

  12. A possible explanation of low energy γ-ray excess from galactic centre and Fermi bubble by a Dark Matter model with two real scalars

    SciTech Connect

    Modak, Kamakshya Prasad; Majumdar, Debasish

    2015-03-09

    We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of Ω{sub DM}, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles.

  13. A possible explanation of low energy γ-ray excess from galactic centre and Fermi bubble by a Dark Matter model with two real scalars

    SciTech Connect

    Modak, Kamakshya Prasad; Majumdar, Debasish

    2015-03-01

    We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of Ω{sub DM}, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles.

  14. The CDMS view on molecular data needs of Herschel, SOFIA, and ALMA

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Endres, C. P.; Stutzki, J.; Schlemmer, S.

    2013-07-01

    The catalog section of the Cologne Database for Molecular Spectroscopy, CDMS, contains mostly rotational transition frequencies, with auxiliary information, of molecules observable in space. The frequency lists are generated mostly from critically evaluated laboratory data employing established Hamiltonian models. The CDMS has been online publicly for more than 12 years, e.g., via the short-cut http://www.cdms.de. Initially constructed as ascii tables, its inclusion into a database environment within the Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) has begun in June 2008. A test version of the new CDMS is about to be released. The CDMS activities have been part of the extensive laboratory spectroscopic investigations in Cologne. Moreover, these activities have also benefit from collaborations with other laboratory spectroscopy groups as well as with astronomers. We will provide some basic information on the CDMS and its participation in the VAMDC project. In addition, some recent detections of molecules as well as spectroscopic studies will be discussed to evaluate the spectroscopic data needs of Herschel, SOFIA, and ALMA in particular in terms of light hydrides, complex molecules, and metal containing species.

  15. Supersymmetric model for dark matter and baryogenesis motivated by the recent CDMS result.

    PubMed

    Allahverdi, Rouzbeh; Dutta, Bhaskar; Mohapatra, Rabindra N; Sinha, Kuver

    2013-08-02

    We discuss a supersymmetric model for cogenesis of dark and baryonic matter where the dark matter (DM) has mass in the 8-10 GeV range as indicated by several direct detection searches, including most recently the CDMS experiment with the desired cross section. The DM candidate is a real scalar field. Two key distinguishing features of the model are the following: (i) in contrast with the conventional weakly interacting massive particle dark matter scenarios where thermal freeze-out is responsible for the observed relic density, our model uses nonthermal production of dark matter after reheating of the Universe caused by moduli decay at temperatures below the QCD phase transition, a feature which alleviates the relic overabundance problem caused by small annihilation cross section of light DM particles and (ii) baryogenesis occurs also at similar low temperatures from the decay of TeV scale mediator particles arising from moduli decay. A possible test of this model is the existence of colored particles with TeV masses accessible at the LHC.

  16. A low-threshold analysis of CDMS shallow-site data

    SciTech Connect

    Akerib, D.S.; Attisha, M.J.; Baudis, L.; Bauer, D.A.; Bolozdynya, A.I.; Brink, P.L.; Bunker, R.; Cabrera, B.; Caldwell, D.O.; Chang, C.L.; Clarke, R.M.; /Stanford U., Phys. Dept. /Southern Methodist U.

    2010-10-01

    Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four {approx}224 g germanium and two {approx}105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of {approx}1 keV and {approx}2 keV, respectively. Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c{sup 2}. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments data as WIMP signals, and exclude new parameter space for WIMP masses between 3 GeV/c{sup 2} and 4 GeV/c{sup 2}.

  17. A Low-threshold Analysis of CDMS Shallow-site Data

    SciTech Connect

    Akerib, D.S.; Attisha, M.J.; Baudis, L.; Bauer, D.A.; Bolozdynya, A.I.; Brink, P.L.; Bunker, R.; Cabrera, B.; Caldwell, D.O.; Chang, C.L.; Clarke, R.M.; Cooley, J.; Crisler, M.B.; Cushman, P.; DeJongh, F.; Dixon, R.; Driscoll, D.D.; Filippini, J.; Funkhouser, S.; Gaitskell, R.J.; Golwala, S.R.; /Caltech /Fermilab /Fermilab /Colorado U., Denver /Case Western Reserve U. /Texas A-M /Minnesota U. /UC, Berkeley /UC, Berkeley /Caltech /Stanford U., Phys. Dept. /UC, Santa Barbara /Stanford U., Phys. Dept. /Minnesota U. /Queen's U., Kingston /Minnesota U. /St. Olaf Coll. /Florida U. /LBL, Berkeley /UC, Berkeley /Texas A-M /UC, Santa Barbara /Syracuse U. /UC, Berkeley /Princeton U. /Case Western Reserve U. /Stanford U., Phys. Dept. /UC, Santa Barbara /Fermilab /Santa Clara U.

    2012-06-04

    Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four {approx}224 g germanium and two {approx}105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of {approx}1 and {approx}2 keV, respectively. Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c{sup 2}. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments data as WIMP signals, and exclude new parameter space for WIMP masses between 3 and 4 GeV/c{sup 2}.

  18. Comparison of CDMS [100] and [111] Oriented Germanium Detectors

    SciTech Connect

    Leman, S.W.; Hertel, S.A.; Kim, P.; Cabrera, B.; Do Couto E.Silva, E.; Figueroa-Feliciano, E.; McCarthy, K.A.; Resch, R.; Sadoulet, B.; Sundqvist, K.M.; /UC, Berkeley

    2012-09-14

    The Cryogenic Dark Matter Search (CDMS) utilizes large mass, 3-inch diameter x 1-inch thick target masses as particle detectors. The target is instrumented with both phonon and ionization sensors and comparison of energy in each channel provides event-by-event classification of electron and nuclear recoils. Fiducial volume is determined by the ability to obtain good phonon and ionization signal at a particular location. Due to electronic band structure in germanium, electron mass is described by an anisotropic tensor with heavy mass aligned along the symmetry axis defined by the [111] Miller index (L valley), resulting in large lateral component to the transport. The spatial distribution of electrons varies significantly for detectors which have their longitudinal axis orientations described by either the [100] or [111] Miller indices. Electric fields with large fringing component at high detector radius also affect the spatial distribution of electrons and holes. Both effects are studied in a 3 dimensional Monte Carlo and the impact on fiducial volume is discussed.

  19. SuperCDMS status from Soudan and plans for SNOLab

    SciTech Connect

    Sander, J.; Jastram, A.; Koch, K.; Mahapatra, R.; Prasad, K.; Ahmed, Z.; Cornell, B.; Golwala, S. R.; Moore, D. C.; Nelson, R.; Anderson, A. J.; Figueroa-Feliciano, E.; Hertel, S. A.; Leman, S. W.; Mccarthy, K. A.; Arrenberg, S.; Balakishiyeva, D.; Saab, T.; Welliver, B.; Thakur, R. B.; and others

    2013-05-23

    Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of Dark Matter. The nature of Dark Matter is yet to be discovered and is one of the biggest questions in Physics. Particle Physics combined with astrophysical measurements of the abundance gives rise to a Dark Matter candidate called Weakly Interacting Massive Particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper describes the status of the SuperCDMS experiment.

  20. SuperCDMS status from Soudan and plans for SNOLab

    NASA Astrophysics Data System (ADS)

    Sander, J.; Ahmed, Z.; Anderson, A. J.; Arrenberg, S.; Balakishiyeva, D.; Thakur, R. B.; Bauer, D. A.; Brandt, D.; Brink, P. L.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Cerdeno, D. G.; Chagani, H.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Silva, E. Do Couto E.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Fox, J.; Fritts, M.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Hasi, J.; Hertel, S. A.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kim, P.; Kiveni, M.; Koch, K.; Kos, M.; Leman, S. W.; Liu, S.; Loer, B.; Mahapatra, R.; Mandic, V.; Martinez, C.; Mccarthy, K. A.; Mirabolfathi, N.; Moffat, R.; Moore, D. C.; Nadeau, P.; Nelson, R.; Page, K.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Qiu, X.; Radpour, R.; Rau, W.; Reisetter, A.; Resch, R. W.; Ricci, Y.; Saab, T.; Sadoulet, B.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Shneck, K.; Speller, D.; Sundqvist, K. M.; Villano, A. N.; Welliver, B.; Yellin, S.; Yen, J.; Yoo, J.; Young, B. A.; Zhang, J.

    2013-05-01

    Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of Dark Matter. The nature of Dark Matter is yet to be discovered and is one of the biggest questions in Physics. Particle Physics combined with astrophysical measurements of the abundance gives rise to a Dark Matter candidate called Weakly Interacting Massive Particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper describes the status of the SuperCDMS experiment.

  1. Towards a Low Threshold SuperCDMS Experiment

    NASA Astrophysics Data System (ADS)

    Welliver, Bradford

    2013-04-01

    Astrophysical evidence points to the existence of particle dark matter that comprises the majority of the mass of the universe. A natural candidate for these particles are Weakly Interacting Massive Particles, or WIMPs. Lately there has been much interest in dark matter search experiments for low mass WIMPs. Detection of WIMP dark matter with mass below 20 GeV/c^2 requires a low-energy trigger threshold. However, lowering the trigger threshold also makes us sensitive to triggering on random noise which can hamper livetime. In order to minimize triggering on this random noise the original trigger filters for SuperCDMS were replaced with improved filters that reduce the amplitude of random noise substantially compared to an event-generated signal, thus allowing us to lower the trigger thresholds without the livetime penalty we would otherwise accrue. An overview of how this was accomplished as well as post-triggering methods of noise discrimination will be discussed. Predictions for the improved low thresholds will be compared to data, and the impact on a low mass WIMP search will be described.

  2. Enrico Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Enrico Fermi was, of all the great physicists of the 20th century, among the most respected and admired. He was respected and admired because of his contributions to both theoretical and experimental physics, because of his leadership in discovering for mankind a powerful new source of energy, and above all, because of his personal character. He was always reliable and trustworthy. He had both of his feet on the ground all the time. He had great strength, but never threw his weight around. He did not play to the gallery. He did not practise one-up-manship. He exemplified, I always believe, the perfect Confucian gentleman...

  3. Observation of Fermi arc and its connection with bulk states in the candidate type-II Weyl semimetal WTe2

    NASA Astrophysics Data System (ADS)

    Wang, Chenlu; Zhang, Yan; Huang, Jianwei; Nie, Simin; Liu, Guodong; Liang, Aiji; Zhang, Yuxiao; Shen, Bing; Liu, Jing; Hu, Cheng; Ding, Ying; Liu, Defa; Hu, Yong; He, Shaolong; Zhao, Lin; Yu, Li; Hu, Jin; Wei, Jiang; Mao, Zhiqiang; Shi, Youguo; Jia, Xiaowen; Zhang, Fengfeng; Zhang, Shenjin; Yang, Feng; Wang, Zhimin; Peng, Qinjun; Weng, Hongming; Dai, Xi; Fang, Zhong; Xu, Zuyan; Chen, Chuangtian; Zhou, X. J.

    2016-12-01

    A kind of topological material, the type-II Weyl semimetal, was proposed recently where the Weyl points emerge at the contact points of the electron and hole pockets, resulting in a highly tilted Weyl cone. In type-II Weyl semimetals, the Lorentz invariance is violated and a different type of Weyl fermion is generated that leads to intriguing physical properties. WTe2 is interesting because it is predicted to be a good candidate for realizing type-II Weyl semimetals. By utilizing laser-based angle-resolved photoemission spectroscopy with high energy and momentum resolutions, we have revealed a full picture of the electronic structure of WTe2. A clear surface state has been identified and its connection with the bulk electronic states in the momentum and energy space shows good agreement with band structure calculations. Our results provide electronic signatures that are consistent with type-II Weyl states in WTe2. They lay a foundation for further investigations on the topological nature of WTe2 and the exploration of unique phenomena and physical properties in type-II Weyl semimetals.

  4. Parallelizing Climate Data Management System, version 3 (CDMS3)

    NASA Astrophysics Data System (ADS)

    Nadeau, D.; Williams, D. N.; Painter, J.; Doutriaux, C.

    2015-12-01

    The Climate Data Management System is an object-oriented data management system, specialized for organizing multidimensional, gridded data used in climate analyses for data observation and simulation. The basic unit of computation in CDMS3 is the variable, which consist of a multidimensional array that represents climate information in four dimensions corresponding to: time, pressure levels, latitudes, and longitudes. As model become more precise in their computation, the volume of data generated becomes bigger and difficult to handle due to the limit of computational resources. Model today can produce data a time frequency of one hourly, three hourly, or six hourly for spatial footprint close to satellite data used run models. The amount of time for scientists to analyze the data and retrieve useful information is more and more unmanageable. Parallelizing libraries such as CMDS3 would ease the burden of working with such big datasets. Multiple approaches of parallelizing are possible. The most obvious one is embarrassingly parallel or pleasingly parallel programming where each computer node processes one file at a time. A more challenging approach is to send a piece of the data to each node for computation and each node will save the results at its right place in a file as a slab of data. This is possible with Hierarchical Data Format 5 (HDF5) using the Message Passing Interface (MPI). A final approach would be the use of Open Multi-Processing API (OpenMP) where a master thread is split in multiple threads for different sections of the main code. Each method has its advantages and disadvantages. This poster bring to light each benefit of these methods and seek to find an optimal solution to compute climate data analyses in a efficient fashion using one or a mixtures of these parallelized methods.

  5. Global analysis of the pMSSM in light of the Fermi GeV excess: prospects for the LHC Run-II and astroparticle experiments

    SciTech Connect

    Bertone, Gianfranco; Calore, Francesca; Caron, Sascha; Ruiz, Roberto; Weniger, Christoph

    2016-04-18

    We present a new global fit of the 19-dimensional phenomenological Minimal Supersymmetric Standard Model (pMSSM-19) that complies with all the latest experimental results from dark matter indirect, direct and accelerator dark matter searches. We show that the model provides a satisfactory explanation of the excess of gamma rays from the Galactic centre observed by the Fermi Large Area Telescope, assuming that it is produced by the annihilation of neutralinos in the Milky Way halo. We identify two regions that pass all the constraints: the first corresponds to neutralinos with a mass ∼80−100 GeV annihilating into WW with a branching ratio of 95%; the second to heavier neutralinos, with mass ∼180−200 GeV annihilating into t-bart with a branching ratio of 87%. We show that neutralinos compatible with the Galactic centre GeV excess will soon be within the reach of LHC run-II — notably through searches for charginos and neutralinos, squarks and light smuons — and of Xenon1T, thanks to its unprecedented sensitivity to spin-dependent cross-section off neutrons.

  6. Cdms 2012: a Database Within the Framework of the Virtual Atomic and Molecular Data Centre - Recent Developments

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Endres, C. P.; Stutzki, J.; Schlemmer, S.

    2012-06-01

    The catalog section of the Cologne Database for Molecular Spectroscopy, CDMS, contains experimental and calculated transition frequencies of molecules and atoms observable by radioastronomical means with information on uncertainties, intensities and quantum numbers. Initially constructed as ascii tables, its inclusion into a database environment within the framework of the European Framework Programme 7 project Virtual Atomic and Molecular Data Centre (VAMDC) has begun in June 2008. The conversion required time because of the extensive content of the CDMS, the desire to maintain the existing functionality, the additional requisites as part of the VAMDC framework, and the sustained development of the VAMDC infrastructure. The new CDMS is scheduled to be available publicly prior to this conference; the old CDMS will be accessible for a transitional period. We will present some of the new CDMS features, provide some overview on new or updated entries from our last account three years ago as well as activities in other sections of the CDMS. Internet address: http://www.astro.uni-koeln.de/cdms/ H. S. P. Müller, F. Schlöder, J. Stutzki, and G. Winnewisser, J. Mol. Struct. 742, 215-227 (2005) H. S. P. Müller, S. Thorwirth, D. A. Roth, and G. Winnewisser, Astron. Astrophys. 370, L49-L52 (2001) Internet address: http://www.vamdc.org/ H. S. P. Müller, J. Stutzki, S. Schlemmer, contribution WH07, presented at the 64th International Symposium on Molecular Spectroscopy, Columbus, OH, USA, 2009

  7. Low-mass right-handed sneutrino dark matter: SuperCDMS and LUX constraints and the Galactic Centre gamma-ray excess

    SciTech Connect

    Cerdeño, D.G.; Peiró, M.; Robles, S. E-mail: miguel.peiro@uam.es

    2014-08-01

    Recent results from direct and indirect searches for dark matter (DM) have motivated the study of particle physics models that can provide weakly interacting massive particles (WIMPs) in the mass range 1–50 GeV. Viable candidates for light WIMP DM must fulfil stringent constraints. On the one hand, the observation at the LHC of a Higgs boson with Standard Model properties set an upper bound on the coupling of light DM particles to the Higgs, thereby making it difficult to reproduce the correct relic abundance. On the other hand, the recent results from direct searches in the CDMSlite, SuperCDMS and LUX experiments have set upper constraints on the DM scattering cross section. In this paper, we investigate the viability of light right-handed sneutrino DM in the Next-to-Minimal Supersymmetric Model (NMSSM) in the light of these constraints. To this aim, we have carried out a scan in the NMSSM parameter space, imposing experimental bounds on the Higgs sector and low-energy observables, such as the muon anomalous magnetic moment and branching ratios of rare decays. We demonstrate that the enlarged Higgs sector of the NMSSM, together with the flexibility provided by the RH sneutrino parameters, make it possible to obtain viable RH sneutrino DM with a mass as light as 2 GeV. We have also considered the upper bounds on the annihilation cross section from Fermi LAT data on dwarf spheroidal galaxies, and extracted specific examples with mass in the range 8–50 GeV that could account for the apparent low-energy excess in the gamma-ray emission at the Galactic Centre. Then, we have computed the theoretical predictions for the elastic scattering cross-section of RH sneutrinos. Finally, after imposing the recent bounds from SuperCDMS and LUX, we have found a wide area of the parameter space that could be probed by future low-threshold direct detection experiments.

  8. Cdms and JPL Molecular Spectroscopy Catalogues in a Common Infrastructure: Vamdc

    NASA Astrophysics Data System (ADS)

    Schlemmer, S.; Endres, C. P.; Drouin, B. J.; Yu, S.; Pearson, J. C.; Müller, H. S. P.; Schilke, P.; Stutzki, J.

    2012-06-01

    The virtual atomic and molecular data centre (VAMDC, http://www.vamdc.org/) is a collection of databases with a common data model. It combines molecular spectroscopy databases; like the Cologne Database for Molecular Spectroscopy (CDMS), the Jet Propulsion Laboratory microwave, millimeter and submillimeter spectral line catalogue (JPL) and the HITRAN databases, with other databases, e.g., on molecular collisions (BASECOL, KIDA). VAMDC is open to include other databases adopting the same data structure and access protocols to the data. Due to the common data model all data can be accessed through one portal. The individual databases are located on a system of distributed servers which all can handle a common query language which enables the combined access to the very different data. In this presentation requests to CDMS and JPL will be used to explain the basic ideas behind the very powerful VAMDC instrument, its portal and the query possibilities. A new portal to CDMS allows access to all old and new spectroscopic data. In addition CDMS has a number of new features, in particular meaningful quantum numbers, references linked to data points, and improved documentation. In addition, fit files are accessible for download and queries to other databases are possible. Due to the new format the long anticipated unified spectroscopy database including all relevant information is realized. Together with other groups within the VAMDC consortium we are working on common user tools to simplify the access for new customers and to tailor data requests for users with specified needs, e.g. HFS information. The development of CDMS and JPL within the VAMDC infrastructure will allow a much more sophisticated analysis of complex observational data which, e.g., come from the ALMA telescope.

  9. The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC

    NASA Astrophysics Data System (ADS)

    Endres, Christian P.; Schlemmer, Stephan; Schilke, Peter; Stutzki, Jürgen; Müller, Holger S. P.

    2016-09-01

    The Cologne Database for Molecular Spectroscopy, CDMS, was founded 1998 to provide in its catalog section line lists of mostly molecular species which are or may be observed in various astronomical sources (usually) by radio astronomical means. The line lists contain transition frequencies with qualified accuracies, intensities, quantum numbers, as well as further auxiliary information. They have been generated from critically evaluated experimental line lists, mostly from laboratory experiments, employing established Hamiltonian models. Separate entries exist for different isotopic species and usually also for different vibrational states. As of December 2015, the number of entries is 792. They are available online as ascii tables with additional files documenting information on the entries. The Virtual Atomic and Molecular Data Centre, VAMDC, was founded more than 5 years ago as a common platform for atomic and molecular data. This platform facilitates exchange not only between spectroscopic databases related to astrophysics or astrochemistry, but also with collisional and kinetic databases. A dedicated infrastructure was developed to provide a common data format in the various databases enabling queries to a large variety of databases on atomic and molecular data at once. For CDMS, the incorporation in VAMDC was combined with several modifications on the generation of CDMS catalog entries. Here we introduce related changes to the data structure and the data content in the CDMS. The new data scheme allows us to incorporate all previous data entries but in addition allows us also to include entries based on new theoretical descriptions. Moreover, the CDMS entries have been transferred into a mySQL database format. These developments within the VAMDC framework have in part been driven by the needs of the astronomical community to be able to deal efficiently with large data sets obtained with the Herschel Space Telescope or, more recently, with the Atacama Large

  10. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  11. Ionization Readout Electronics for SuperCDMS SNOLAB Employing a HEMT Front-End

    NASA Astrophysics Data System (ADS)

    Partridge, R.

    2014-09-01

    The SuperCDMS SNOLAB experiment seeks to deploy 200 kg of cryogenic Ge detectors employing phonon and ionization readout to identify dark matter interactions. One of the design challenges for the experiment is to provide amplification of the high impedance ionization signal while minimizing power dissipation and noise. This paper describes the design and expected performance of the ionization readout being developed for an engineering model of the SuperCDMS SNOLAB Ge Tower System. The readout features the use of a low-noise HEMT front end transistor operating at 4 K to achieve a power dissipation of 100 W per channel, local grounding to minimize noise injection, and biasing circuitry that allows precise control of the HEMT operating point.

  12. The Search for High Mass WIMPs with the SuperCDMS Experiment

    NASA Astrophysics Data System (ADS)

    Qiu, Hang; SuperCDMS Collaboration

    2016-03-01

    About 26.8% of the universe mass is contributed from dark matter. Weakly Interacting Massive Particle(WIMP) is currently the most promising dark matter candidate. SuperCDMS is one of the leading direct dark matter detection experiments around the world. Its biggest goal is to use semiconductor detectors under the cryogenic condition to detect WIMPs. Both ionization and phonon signals are read out via our detector sensors during the operation periods. The high threshold analysis aims to search for high mass WIMPs based on the data collected in a 2-year-long period of time from the SuperCDMS experiment setup located at the Soudan mine in Minnesota. In today's presentation, I am going to talk about the approaches towards this goal.

  13. Photoneutron Calibration of SuperCDMS Soudan iZIP detectors

    NASA Astrophysics Data System (ADS)

    Iyer, Vijay; SuperCDMS Collaboration

    2017-01-01

    Numerous astrophysical observations have indicated that dark matter constitutes about 27% of the mass and energy content of the universe. Weakly Interacting Massive Particles (WIMPs) are considered the most likely candidates for dark matter. The SuperCDMS (Cryogenic Dark Matter Search) collaboration has pioneered the use of low temperature solid state detectors to search for the rare scattering of WIMPs with an atomic nucleus. An accurate understanding of the nuclear recoil scale is necessary for establishing the WIMP mass scale. Monoenergetic neutrons produced by gamma ray excitation (hence photo-neutrons) can be used to calibrate our detectors. This talk will describe SuperCDMS detectors, discuss the current status and outlook of the photo-neutron calibration that was performed in the Soudan experiment.

  14. The Cologne Database for Molecular Spectroscopy, Cdms, in Times of Herschel, SOFIA, and Alma

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Stutzki, Jürgen; Schlemmer, Stephan

    2009-06-01

    The CDMS provides in its catalog section atomic and molecular line lists for species that have been or may be observed in space by radio astronomical means. The line list of each molecule is gathered in an individual entry; minor isotopologs have separate entries, and the same applies to excited vibrational states with the exception of some diatomic molecules. With 5 to 10 new or updated entries each month, the CDMS catalog has been growing rapidly over the past 10 years: since February 2009, there have been more than 500 entries in the CDMS - with many more entries to be created. Entries are generated from fitting (mostly) laboratory data to accepted Hamiltonian models. Despite many dedicated laboratory spectroscopic investigations in recent years, accurate data is still lacking frequently - in particular at higher frequencies, for minor isotopic species, for excited vibrational states, or for somewhat larger molecules. While high frequency data are of special concern for the Herschel satellite, scheduled to be launched in mid-April 2009, or for the Stratospheric Observatory For Infrared Astronomy (SOFIA), the remaining issues mentioned above are important especially for telecope arrays such as the Atacama Large Millimeter Array (ALMA). The main features of the CDMS catalog will be described, including recent developments concerning new entries as well as available and planned features. In particular, we will discuss issues relevant for generating a consolidated database that also takes into account information from other databases. Attention will be given to laboratory spectroscopic needs for missions such as Herschel and SOFIA on one hand and for ALMA, the Expanded Very Large Array (EVLA), and other facilities on the other, both, in terms of general aspects and in terms of specific examples. Selected contributions from the Cologne spectroscopy laboratories to address these needs will be presented. H. S. P. Müller, S. Thorwirth, D. A. Roth, G. Winnewisser

  15. A modified detector concept for SuperCDMS: The HiZIP and its charge performance

    NASA Astrophysics Data System (ADS)

    Page, Kedar Mohan

    SuperCDMS is a leading direct dark matter search experiment which uses solid state detectors (Ge crystals) at milliKelvin temperatures to look for nuclear recoils caused by dark matter interactions in the detector. 'Weakly Interacting Massive Particles' (WIMPs) are the most favoured dark matter candidate particles. SuperCDMS, like many other direct dark matter search experiments, primarily looks for WIMPs. The measurement of both the ionization and the lattice vibration (phonon) signals from an interaction in the detector allow it to discriminate against electron recoils which are the main source of background for WIMP detection. SuperCDMS currently operates about 9 kgs worth of germanium detectors at the Soudan underground lab in northern Minnesota. In its next phase, SuperCDMS SNOLAB, it plans to use 100-200 kg of target mass (Ge) which would allow it to probe more of the interesting and unexplored parameter space for WIMPs predicted by theoretical models. The SuperCDMS Queen's Test Facility is a detector testing facility which is intended to serve detector testing and detector research and development purposes for the SuperCDMS experiment. A modified detector called the 'HiZIP' (Half-iZIP), which is reduced in complexity in comparison to the currently used iZIP (interleaved Z-sensitive Ionization and Phonon mediated) detectors, is studied in this thesis. The HiZIP detector design also serves to discriminate against background from multiple scatter events occurring close to the surfaces in a single detector. Studies carried out to compare the surface event leakage in the HiZIP detector using limited information from iZIP data taken at SuperCDMS test facility at UC Berkley produce a highly conservative upper limit of 5 out of 10,000 events at 90% confidence level. This upper limit is the best among many different HiZIP configurations that were investigated and is comparable to the upper limit calculated for an iZIP detector in the same way using the same data. A

  16. A modified detector concept for SuperCDMS: The HiZIP and its charge performance

    SciTech Connect

    Page, Kedar Mohan

    2013-01-01

    SuperCDMS (Super Cryogenic Dark Matter Search) is a leading direct dark mat-ter search experiment which uses solid state detectors (Ge crystals) at milliKelvintemperatures to look for nuclear recoils caused by dark matter interactions in the de-tector. `Weakly Interacting Massive Particles' (WIMPs) are the most favoured darkmatter candidate particles. SuperCDMS, like many other direct dark matter searchexperiments, primarily looks for WIMPs. The measurement of both the ionizationand the lattice vibration (phonon) signals from an interaction in the detector allow itto discriminate against electron recoils which are the main source of background forWIMP detection.SuperCDMS currently operates about 9 kg of Ge detectors at the Soudan under-ground lab in northern Minnesota. In its next phase, SuperCDMS SNOLAB plansto use 100-200 kg of target mass (Ge) which would allow it to probe more of theinteresting and and as of yet unexplored parameter space for WIMPs predicted bytheoretical models. The SuperCDMS Queen's Test Facility is a detector test facilitywhich is intended to serve as detector testing and detector research and developmentpurposes for the SuperCDMS experiment.A modifed detector called the HiZIP (Half-iZIP), which is reduced in complex-ity in comparison to the currently used iZIP (interleaved Z-sensitive Ionization and Phonon mediated) detectors, is studied in this thesis. The HiZIP detector designalso serves to discriminate against background from multiple scatter events occurringclose to the surfaces in a single detector. Studies carried out to compare the surfaceevent leakage in the HiZIP detector using limited information from iZIP data takenat SuperCDMS test facility at UC Berkley produce a highly conservative upper limitof 5 out of 10,000 events at 90% condence level. This upper limit is the best amongmany different HiZIP congurations that were investigated and is comparable to theupper limit calculated for an HiZIP detector in the same way using the

  17. Triplet pair amplitude in a trapped s -wave superfluid Fermi gas with broken spin rotation symmetry. II. Three-dimensional continuum case

    NASA Astrophysics Data System (ADS)

    Inotani, Daisuke; Hanai, Ryo; Ohashi, Yoji

    2016-10-01

    We extend our recent work [Y. Endo et al., Phys. Rev. A 92, 023610 (2015)], 10.1103/PhysRevA.92.023610 for a parity-mixing effect in a model of two-dimensional lattice fermions to a realistic three-dimensional ultracold Fermi gas. Including effects of broken local spatial inversion symmetry by a trap potential within the framework of the real-space Bogoliubov-de Gennes theory at T =0 , we point out that an odd-parity p -wave Cooper-pair amplitude is expected to have already been realized in previous experiments on an (even-parity) s -wave superfluid Fermi gas with spin imbalance. This indicates that when one suddenly changes the s -wave pairing interaction to an appropriate p -wave one by using a Feshbach technique in this case, a nonvanishing p -wave superfluid order parameter is immediately obtained, which is given by the product of the p -wave interaction and the p -wave pair amplitude that has already been induced in the spin-imbalanced s -wave superfluid Fermi gas. Thus, by definition, the system is in the p -wave superfluid state, at least just after this manipulation. Since the achievement of a p -wave superfluid state is one of the most exciting challenges in cold Fermi gas physics, our results may provide an alternative approach to this unconventional pairing state. In addition, since the parity-mixing effect cannot be explained as far as one deals with a trap potential in the local density approximation (LDA), it is considered as a crucial example which requires us to go beyond the LDA.

  18. Homogeneous Atomic Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

    2017-03-01

    We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

  19. MRI characteristics are predictive for CDMS in monofocal, but not in multifocal patients with a clinically isolated syndrome

    PubMed Central

    Nielsen, Jessica M; Pohl, Christoph; Polman, Chris H; Barkhof, Frederik; Freedman, Mark S; Edan, Gilles; Miller, David H; Bauer, Lars; Sandbrink, Rupert; Kappos, Ludwig; Uitdehaag, Bernard MJ

    2009-01-01

    Background To diagnose multiple sclerosis (MS), evidence for dissemination in space and time is required. There is no clear definition on how symptoms and signs of a patient indicate clinical dissemination in space. To provide a uniform approach on this subject, a clinical classification system was described recently differentiating patients with mono- and multifocal clinical presentation. Here we assess the predictive value of clinically defined dissemination in space at first presentation for time to clinically definite MS (CDMS). Methods Four hundred and sixty-eight patients with a first episode suggestive of MS were classified as clinically mono- or multifocal by two neurologists blinded to magnetic resonance imaging (MRI) results. These patients were part of the BENEFIT study in which 292 patients were randomized to interferon beta-1b (IFNB-1b) and 176 to placebo. By using Kaplan-Meier statistics the risk for CDMS was studied in mono- and multifocal patients of the placebo group, both with and without taking into account MRI measures of potential prognostic relevance. Results Time to CDMS was similar in monofocal and multifocal patients. In monofocal patients, the risk for CDMS over 2 years was significantly higher when ≥ 9 T2 lesions or at least one Gd-enhancing lesion were present at the first event or 3 or 6 months after the first event. In patients with multifocal presentation, these MRI measures had no significant added value in predicting time to CDMS. Conclusion These data indicate that a carefully performed neurological assessment of symptoms and signs, combined with lesions on MRI, is important for defining the risk of conversion to CDMS. Trial Registration The Benefit trial has been registered under NCT00185211 PMID:19457248

  20. Thermal conductance measurements of bolted copper joints for SuperCDMS

    SciTech Connect

    Schmitt, R.; Tatkowski, Greg; Ruschman, M.; Golwala, S. R.; Kellaris, N.; Daal, M.; Hall, Jeter C.; Hoppe, Eric W.

    2015-09-01

    Joint thermal conductance testing has been undertaken for bolted copper to copper connections from 60 mK to 26 K. This testing was performed to validate an initial design basis for the SuperCDMS experiment, where a dilution refrigerator will be coupled to a cryostat via multiple bolted connections. Copper used during testing was either gold plated or passivated with citric acid to prevent surface oxidation. Results obtained are well fit by a power law regression of joint thermal conductance to temperature and match well with data collected during a literature review.

  1. Search for Low-Mass Weakly Interacting Massive Particles with SuperCDMS

    SciTech Connect

    Agnese, R.; Anderson, Alan J.; Asai, M.; balakishiyeva, D.; Basu Thakur, R.; Bauer, D. A.; Beaty, John; Billard, J.; Borgland, A.; Bowles, M. A.; Brandt, D.; Brink, P. L.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Cerdeno, D. G.; Chagani, H.; Chen, Y.; Cherry, M.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; DeVaney, D.; DeStefano, PC F.; Do Couto E Silva, E.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Hansen, S.; Harris, Harold R.; Hertel, S. A.; Hines, B. A.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kenany, S.; Kennedy, A.; Kiveni, M.; Koch, K.; Leder, A.; Loer, B.; Lopez Asamar, E.; Mahapatra, R.; Mandic, V.; Martinez, C.; McCarthy, K. A.; Mirabolfathi, M.; Moffatt, R. A.; Nelson, R. H.; Novak, L.; Page, K.; Partridge, R.; Pepin, M.; Phipps, A.; Platt, M.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Resch, R. W.; Ricci, Y.; Ruschman, M.; Saab, T.; Sadoulet, B.; Sander, J.; Schmitt, R.; Schneck, K.; Schnee, Richard; Scorza, A.; Seitz, D.; Serfass, B.; Shank, B.; Speller, D.; Tomada, A.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wright, D. H.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2014-06-01

    We report a first search for weakly interacting massive particles (WIMPs) using the background rejection capabilities of SuperCDMS. An exposure of 577 kg-days was analyzed for WIMPs with mass < 30 GeV/c2, with the signal region blinded. Eleven events were observed after unblinding. We set an upper limit on the spin-independent WIMP-nucleon cross section of 1:2 10-42cm2 at 8 GeV/c2. This result is in tension with WIMP interpretations of recent experiments and probes new parameter space for WIMP-nucleon scattering for WIMP masses < 6 GeV/c2.

  2. Thermal conductance measurements of bolted copper joints for SuperCDMS

    DOE PAGES

    Schmitt, R. L.; Tatkowski, G.; Ruschman, M.; ...

    2015-04-28

    Joint thermal conductance testing has been undertaken for bolted copper to copper connections from 60 mK to 26 K. This testing was performed to validate an initial design basis for the SuperCDMS experiment, where a dilution refrigerator will be coupled to a cryostat via multiple bolted connections. Copper used during testing was either gold plated or passivated with citric acid to prevent surface oxidation. Finally, the results we obtained are well fit by a power law regression of joint thermal conductance to temperature and match well with data collected during a literature review.

  3. Measurement of SQUID noise levels for SuperCDMS SNOLAB detectors - Final Paper

    SciTech Connect

    Lee, Maxwell

    2015-08-27

    SuperCDMS SNOLAB is a second generation direct dark matter search. In the SuperCDMS SNOLAB experiment, detectors are able to pick up from signals from dark matter nuclear recoil interactions which occur inside the bulk of the detectors. These interactions produce both phonon and charge signals. HEMTs read out charge signals whereas TES are used to detect phonon signals which are then read out by SQUID amplifiers. SQUID amplifiers must add negligible noise to the TES intrinsic noise which has been previously measured and is approximately 50pA/√Hz down to 100Hz for ease of signal distinguishability in dark matter nuclear interactions. The intrinsic noise level of the SQUID was tested in the SLAC 300mK fridge and determined to provide adequately low levels of noise with a floor of approximately 3pA/√Hz. Furthermore, a 10x amplifier was tested for addition of extraneous noise. This noise was investigated with and without this amplifier, and it was found that it did not add a significant amount of noise to the intrinsic SQUID noise.

  4. Fermi Galactic Center Zoom

    NASA Video Gallery

    This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known...

  5. Fermi at Six Months

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

  6. Fermi, Szilard and Trinity

    ERIC Educational Resources Information Center

    Anderson, Herbert L.

    1974-01-01

    The final installment of the author's recollections of his work with physicists Enrico Fermi, Leo Szilard and others in developing the first controlled nuclear chain reaction and in preparing the test explosion of the first atomic bomb. (GS)

  7. Global analysis of the pMSSM in light of the Fermi GeV excess: prospects for the LHC Run-II and astroparticle experiments

    NASA Astrophysics Data System (ADS)

    Bertone, Gianfranco; Calore, Francesca; Caron, Sascha; Ruiz, Roberto; Kim, Jong Soo; Trotta, Roberto; Weniger, Christoph

    2016-04-01

    We present a new global fit of the 19-dimensional phenomenological Minimal Supersymmetric Standard Model (pMSSM-19) that complies with all the latest experimental results from dark matter indirect, direct and accelerator dark matter searches. We show that the model provides a satisfactory explanation of the excess of gamma rays from the Galactic centre observed by the Fermi Large Area Telescope, assuming that it is produced by the annihilation of neutralinos in the Milky Way halo. We identify two regions that pass all the constraints: the first corresponds to neutralinos with a mass 0~ 80-10 GeV annihilating into WW with a branching ratio of 95%; the second to heavier neutralinos, with mass 0~ 180-20 GeV annihilating into bar tt with a branching ratio of 87%. We show that neutralinos compatible with the Galactic centre GeV excess will soon be within the reach of LHC run-II—notably through searches for charginos and neutralinos, squarks and light smuons—and of Xenon1T, thanks to its unprecedented sensitivity to spin-dependent cross-section off neutrons.

  8. Non-thermal Electron Acceleration in Low Mach Number Collisionless Shocks. II. Firehose-mediated Fermi Acceleration and its Dependence on Pre-shock Conditions

    NASA Astrophysics Data System (ADS)

    Guo, Xinyi; Sironi, Lorenzo; Narayan, Ramesh

    2014-12-01

    Electron acceleration to non-thermal energies is known to occur in low Mach number (Ms <~ 5) shocks in galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Using two-dimensional (2D) particle-in-cell (PIC) plasma simulations, we showed in Paper I that electrons are efficiently accelerated in low Mach number (Ms = 3) quasi-perpendicular shocks via a Fermi-like process. The electrons bounce between the upstream region and the shock front, with each reflection at the shock resulting in energy gain via shock drift acceleration. The upstream scattering is provided by oblique magnetic waves that are self-generated by the electrons escaping ahead of the shock. In the present work, we employ additional 2D PIC simulations to address the nature of the upstream oblique waves. We find that the waves are generated by the shock-reflected electrons via the firehose instability, which is driven by an anisotropy in the electron velocity distribution. We systematically explore how the efficiency of wave generation and of electron acceleration depend on the magnetic field obliquity, the flow magnetization (or equivalently, the plasma beta), and the upstream electron temperature. We find that the mechanism works for shocks with high plasma beta (gsim 20) at nearly all magnetic field obliquities, and for electron temperatures in the range relevant for galaxy clusters. Our findings offer a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  9. Non-thermal electron acceleration in low Mach number collisionless shocks. II. Firehose-mediated Fermi acceleration and its dependence on pre-shock conditions

    SciTech Connect

    Guo, Xinyi; Narayan, Ramesh; Sironi, Lorenzo

    2014-12-10

    Electron acceleration to non-thermal energies is known to occur in low Mach number (M{sub s} ≲ 5) shocks in galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Using two-dimensional (2D) particle-in-cell (PIC) plasma simulations, we showed in Paper I that electrons are efficiently accelerated in low Mach number (M{sub s} = 3) quasi-perpendicular shocks via a Fermi-like process. The electrons bounce between the upstream region and the shock front, with each reflection at the shock resulting in energy gain via shock drift acceleration. The upstream scattering is provided by oblique magnetic waves that are self-generated by the electrons escaping ahead of the shock. In the present work, we employ additional 2D PIC simulations to address the nature of the upstream oblique waves. We find that the waves are generated by the shock-reflected electrons via the firehose instability, which is driven by an anisotropy in the electron velocity distribution. We systematically explore how the efficiency of wave generation and of electron acceleration depend on the magnetic field obliquity, the flow magnetization (or equivalently, the plasma beta), and the upstream electron temperature. We find that the mechanism works for shocks with high plasma beta (≳ 20) at nearly all magnetic field obliquities, and for electron temperatures in the range relevant for galaxy clusters. Our findings offer a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  10. A COMPREHENSIVE ANALYSIS OF FERMI GAMMA-RAY BURST DATA. II. E{sub p} EVOLUTION PATTERNS AND IMPLICATIONS FOR THE OBSERVED SPECTRUM-LUMINOSITY RELATIONS

    SciTech Connect

    Lu Ruijing; Wei Junjie; Liang Enwei; Lue Lianzhong; Zhang Binbin; Lue Houjun; Zhang Bing; Lei Weihua E-mail: zhang@physics.unlv.edu

    2012-09-10

    We present a time-resolved spectral analysis of 51 long and 11 short bright gamma-ray bursts (GRBs) observed with the Fermi/Gamma-Ray Burst Monitor, paying special attention to E{sub p} evolution within each burst. Among eight single-pulse long GRBs, five show an evolution from hard to soft, while three show intensity tracking. The multi-pulse long GRBs have more complicated patterns. Statistically, the hard-to-soft evolution pulses tend to be more asymmetric than the intensity-tracking ones, with a steeper rising wing than the falling wing. Short GRBs have E{sub p} tracking intensity exclusively with the 16 ms time-resolution analysis. We performed a simulation analysis and suggest that for at least some bursts, the late intensity-tracking pulses could be a consequence of overlapping hard-to-soft pulses. However, the fact that the intensity-tracking pattern exists in the first pulse of the multi-pulse long GRBs and some single-pulse GRBs, suggests that intensity tracking is an independent component, which may operate in some late pulses as well. For the GRBs with measured redshifts, we present a time-resolved E{sub p} - L{sub {gamma},iso} correlation analysis and show that the scatter of the correlation is comparable to that of the global Amati/Yonetoku relation. We discuss the predictions of various radiation models regarding E{sub p} evolution, as well as the possibility of a precessing jet in GRBs. The data pose a great challenge to each of these models, and hold the key to unveiling the physics behind GRB prompt emission.

  11. FermiGrid

    SciTech Connect

    Yocum, D.R.; Berman, E.; Canal, P.; Chadwick, K.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; /Fermilab

    2007-05-01

    As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.

  12. Fermi TGF detection map

    NASA Video Gallery

    Fermi’s Gamma-ray Burst Monitor detected 130 TGFs from August 2008 to the end of 2010. Thanks to instrument tweaks, the team has been able to improve the detection rate to several TGFs per week. ...

  13. Interaction quenches of Fermi gases

    SciTech Connect

    Uhrig, Goetz S.

    2009-12-15

    It is shown that the jump in the momentum distribution of Fermi gases evolves smoothly for small and intermediate times once an interaction between the fermions is suddenly switched on. The jump does not vanish abruptly. The loci in momentum space where the jumps occur are those of the noninteracting Fermi sea. No relaxation of the Fermi surface geometry takes place.

  14. Design and performance of a modular low-radioactivity readout system for cryogenic detectors in the CDMS experiment

    NASA Astrophysics Data System (ADS)

    Akerib, D. S.; Barnes, P. D., Jr.; Brink, P. L.; Cabrera, B.; Clarke, R. M.; Gaitskell, R. J.; Golwala, S. R.; Huber, M. E.; Kurylowicz, M.; Mandic, V.; Martinis, J. M.; Meunier, P.; Mirabolfathi, N.; Nam, S. W.; Perillo-Isaac, M.; Saab, T.; Sadoulet, B.; Schnee, R. W.; Seitz, D. N.; Shutt, T.; Smith, G. W.; Stockwell, W. K.; Sundqvist, K. M.; White, S.

    2008-07-01

    The Cryogenic Dark Matter Search (CDMS) experiment employs ultra-cold solid-state detectors to search for rare events resulting from WIMP-nucleus scattering. An innovative detector packaging and readout system has been developed to meet the unusual combination of requirements for: low temperature, low radioactivity, low energy threshold, and large channel count. Features include use of materials with low radioactivity such as multi-layer KAPTON laminates for circuit boards; immunity to microphonic noise via a vacuum coaxial wiring design, manufacturability, and modularity. The detector readout design had to accommodate various electronic components which have to be operated in close proximity to the detector as well maintaining separate individual temperatures (ranging from 600 mK to 150 K) in order to achieve optimal noise performance. The paper will describe the general electrical, thermal, and mechanical designs of the CDMS readout system, as well as presenting the theoretical and measured performance of the detector readout channels.

  15. Geant4 Simulations of the SuperCDMS iZIP Detector Charge Carrier Propagation and FET Readout

    NASA Astrophysics Data System (ADS)

    Agnese, R.; Brandt, D.; Asai, M.; Cabrera, B.; Leman, S.; McCarthy, K.; Redl, P.; Saab, T.; Wright, D.

    2014-09-01

    The SuperCDMS experiment aims to directly detect dark matter particles called WIMPs (weakly interacting massive particles). The detectors measure phonon and ionization energy due to nuclear and electron recoils from incident particles. The SuperCDMS Detector Monte Carlo group uses Geant4 to simulate electron-hole pairs () and low temperature phonons. We use these simulations in order to study energy deposition in the detectors. Phonons and electron-hole pairs are tracked in a crystal detector. Because of the band structure of the crystals, the electrons undergo oblique propagation. The charge electrodes on each side of the detector are biased at different voltages while the phonon sensors are grounded. This creates a nearly uniform electric field through the bulk of the detector, with a complex shape near the surfaces. The electric field is calculated from interpolating on a tetrahedral mesh. The resulting TES phonon readout, as well as the FET charge readout are simulated. To calculate the FET readout, the Shockley-Ramo theorem is applied to simulate the current in the FET. The goal of this paper is to describe the theory and implementation of calculating the electric field, performing the charge carrier propagation, and simulating the FET readout of the SuperCDMS detectors.

  16. Fermi-liquid theory of ultracold trapped Fermi gases: Implications for pseudogap physics and other strongly correlated phases

    SciTech Connect

    Chien, Chih-Chun; Levin, K.

    2010-07-15

    We show how Fermi-liquid theory can be applied to ultracold Fermi gases, thereby expanding their ''simulation'' capabilities to a class of problems of interest to multiple physics subdisciplines. We introduce procedures for measuring and calculating position-dependent Landau parameters. This lays the groundwork for addressing important controversial issues: (i) the suggestion that thermodynamically, the normal state of a unitary gas is indistinguishable from a Fermi liquid and (ii) that a fermionic system with strong repulsive contact interactions is associated with either ferromagnetism or localization; this relates as well to {sup 3}He and its p-wave superfluidity.

  17. Chiral non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2014-07-01

    A non-Fermi liquid state without time-reversal and parity symmetries arises when a chiral Fermi surface is coupled with a soft collective mode in two space dimensions. The full Fermi surface is described by a direct sum of chiral patch theories, which are decoupled from each other in the low-energy limit. Each patch includes low-energy excitations near a set of points on the Fermi surface with a common tangent vector. General patch theories are classified by the local shape of the Fermi surface, the dispersion of the critical boson, and the symmetry group, which form the data for distinct universality classes. We prove that a large class of chiral non-Fermi liquid states exists as stable critical states of matter. For this, we use a renormalization group scheme where low-energy excitations of the Fermi surface are interpreted as a collection of (1+1)-dimensional chiral fermions with a continuous flavor labeling the momentum along the Fermi surface. Due to chirality, the Wilsonian effective action is strictly UV finite. This allows one to extract the exact scaling exponents although the theories flow to strongly interacting field theories at low energies. In general, the low-energy effective theory of the full Fermi surface includes patch theories of more than one universality classes. As a result, physical responses include multiple universal components at low temperatures. We also point out that, in quantum field theories with extended Fermi surface, a noncommutative structure naturally emerges between a coordinate and a momentum which are orthogonal to each other. We show that the invalidity of patch description for Fermi liquid states is tied with the presence of UV/IR mixing associated with the emergent noncommutativity. On the other hand, UV/IR mixing is suppressed in non-Fermi liquid states due to UV insensitivity, and the patch description is valid.

  18. Fermi arc electronic structure and Chern numbers in the type-II Weyl semimetal candidate MoxW1-xTe2

    SciTech Connect

    Belopolski, Ilya; Xu, Su-Yang; Ishida, Yukiaki; Pan, Xingchen; Yu, Peng; Sanchez, Daniel S.; Zheng, Hao; Neupane, Madhab; Alidoust, Nasser; Chang, Guoqing; Chang, Tay-Rong; Wu, Yun; Bian, Guang; Huang, Shin-Ming; Lee, Chi-Cheng; Mou, Daixiang; Huang, Lunan; Song, You; Wang, Baigeng; Wang, Guanghou; Yeh, Yao-Wen; Yao, Nan; Rault, Julien E.; Le Fèvre, Patrick; Bertran, François; Jeng, Horng-Tay; Kondo, Takeshi; Kaminski, Adam; Lin, Hsin; Liu, Zheng; Song, Fengqi; Shin, Shik; Hasan, M. Zahid

    2016-08-15

    It has recently been proposed that electronic band structures in crystals can give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that Mo x W 1 - x Te 2 may realize such a type-II Weyl fermion. Here, we first show theoretically that it is crucial to access the band structure above the Fermi level ε F to show a Weyl semimetal in Mo x W 1 - x Te 2 . Then, we study Mo x W 1 - x Te 2 by pump-probe ARPES and we directly access the band structure > 0.2 eV above ε F in experiment. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. We propose that a future study of Mo x W 1 - x Te 2 by pump-probe ARPES may directly pinpoint the Fermi arc. Our work sets the stage for the experimental discovery of the first type-II Weyl semimetal in Mo x W 1 - x Te 2 .

  19. Berry Fermi liquid theory

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yuan; Son, Dam Thanh

    2017-02-01

    We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current-current correlator exactly matches with the result obtained from the kinetic theory.

  20. Conformal Fermi Coordinates

    SciTech Connect

    Dai, Liang; Pajer, Enrico; Schmidt, Fabian E-mail: Enrico.pajer@gmail.com

    2015-11-01

    Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, by removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable effects and ''projection'' terms.

  1. New results from the search for low-mass weakly interacting massive particles with the CDMS low ionization threshold experiment

    SciTech Connect

    Agnese, R.

    2016-02-17

    The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Our results are presented from the second CDMSlite run with an exposure of 70 kg days, which reached an energy threshold for electron recoils as low as 56 eV. Furthermore, a fiducialization cut reduces backgrounds below those previously reported by CDMSlite. Lastly, new parameter space for the WIMP-nucleon spin-independent cross section is excluded forWIMP masses between 1.6 and 5.5 GeV/c2.

  2. New results from the search for low-mass weakly interacting massive particles with the CDMS low ionization threshold experiment

    DOE PAGES

    Agnese, R.

    2016-02-17

    The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Our results are presented from the second CDMSlite run with an exposure of 70 kg days, which reached an energy threshold for electron recoils as low as 56 eV. Furthermore, a fiducialization cut reduces backgrounds below those previously reported by CDMSlite. Lastly, new parameter space for the WIMP-nucleon spin-independent cross section is excluded forWIMP masses between 1.6 and 5.5 GeV/c2.

  3. Second-Order Fermi Acceleration and Emission in Blazar Jets

    NASA Astrophysics Data System (ADS)

    Asano, Katsuaki; Takahara, Fumio; Toma, Kenji; Kusunose, Masaaki; Kakuwa, Jun

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations, adopt it for 1ES 1101-232, and Mrk 421. The Fermi-II model with radial evolution of the electron injection rate and/or diffusion coefficient can reproduce the spectra from the radio to the gamma-ray regime. For Mrk 421, an external radio photon field with a luminosity of 4.9 begin{math} {times} 10 (38) erg s (-1) is required to agree with the observed GeV flux. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

  4. The Fermi Paradox Is Neither Fermi's Nor a Paradox

    NASA Astrophysics Data System (ADS)

    Gray, Robert H.

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist, or suggesting its absence is paradoxical. The claim 'they are not here; therefore they do not exist' was first published by Michael Hart, claiming that interstellar travel and colonization of the galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence-cited in the U. S. Congress as a reason for killing NASA's SETI program on one occasion-but evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox. Keywords: Astrobiology, SETI, Fermi paradox, extraterrestrial life

  5. Geant4 Simulations of SuperCDMS iZip Detector Charge Carrier Propagation and FET Readout

    NASA Astrophysics Data System (ADS)

    Agnese, Rob

    2013-04-01

    The SuperCDMS experiment aims to directly detect dark matter particles called WIMPs (Weakly Interacting Massive Particles). The detectors collect phonon and ionization energy of incident particles for analysis. The SuperCDMS Detector Monte Carlo group is implementing low temperature phonon and ionization simulations in Geant4 in order to study the response of the detectors to incident events. Phonons and electron-hole pairs are tracked in a low temperature crystal detector. The resulting TES phonon readout, as well as the FET charge readout are simulated. The Geant4 framework is well-suited to these tasks. The charge transport in the presence of a complex electric field is performed by calculating a tetrahedral mesh of potentials across the crystal volume. To calculate the FET readout, the Shockley-Ramo theorem is applied to simulate the current in the FET. The focus of this presentation will be on incorporating and using the software package, Qhull, to calculate a tetrahedral mesh from known potentials and then using barycentric coordinates to perform a linear interpolation to calculate the field. After calculating the field at each charge carrier's position, the Shockley-Ramo theorem is applied and the previous triangulation technique is performed to simulate the FET response

  6. Anisotropic non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2016-11-01

    We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.

  7. The Statistical Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Maccone, C.

    In this paper is provided the statistical generalization of the Fermi paradox. The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book Habitable planets for man (1964). The statistical generalization of the original and by now too simplistic Dole equation is provided by replacing a product of ten positive numbers by the product of ten positive random variables. This is denoted the SEH, an acronym standing for “Statistical Equation for Habitables”. The proof in this paper is based on the Central Limit Theorem (CLT) of Statistics, stating that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable (Lyapunov form of the CLT). It is then shown that: 1. The new random variable NHab, yielding the number of habitables (i.e. habitable planets) in the Galaxy, follows the log- normal distribution. By construction, the mean value of this log-normal distribution is the total number of habitable planets as given by the statistical Dole equation. 2. The ten (or more) astrobiological factors are now positive random variables. The probability distribution of each random variable may be arbitrary. The CLT in the so-called Lyapunov or Lindeberg forms (that both do not assume the factors to be identically distributed) allows for that. In other words, the CLT "translates" into the SEH by allowing an arbitrary probability distribution for each factor. This is both astrobiologically realistic and useful for any further investigations. 3. By applying the SEH it is shown that the (average) distance between any two nearby habitable planets in the Galaxy may be shown to be inversely proportional to the cubic root of NHab. This distance is denoted by new random variable D. The relevant probability density function is derived, which was named the "Maccone distribution" by Paul Davies in

  8. The fermi paradox is neither Fermi's nor a paradox.

    PubMed

    Gray, Robert H

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.

  9. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  10. Quantum Oscillations from Fermi Arcs

    NASA Astrophysics Data System (ADS)

    Pereg-Barnea, Tamar; Refael, Gil; Franz, Marcel; Weber, Heidi; Seradjeh, Babak

    2009-03-01

    Recent experiments[1] in a variety of High Tc superconductors revel 1/B oscillations in the vortex-liquid state. The period of oscillations in underdoped samples is short and can be translated, via the Onsager relation to an area in k-space which makes up a few percents of the Brillouin zone. Quantum oscillations are usually thought of as arising from closed orbits in momentum space along the Fermi surface and are used to measure the Fermi vector. Thus, the observation of quantum oscillations in the cuprates seems to be at odds with the observation of Fermi arcs in ARPES experiments[2] due to their fragmented Fermi surface topology. In this talk we show that quantum oscillations can arise from a partially gapped Fermi surface. We adopt a phenomenological model of arcs which terminate at a regime with a superconducting gap of d-wave symmetry to describe the pseudo gap phase. Without invoking any additional order, quantization of energy is found well below the gap maximum. Semiclassically the quantization condition arises from closed orbits in real-space. When translated to momentum space, the area enclosed by the orbits is much smaller than that of the full Fermi surface. [1]N. Doiron-Leyaraud et al. nature 447, 565 (2007) [2]Kanigel et al. Nature Physics 2 447 (2006)

  11. Dedicated Searches for Low and High Mass Wimps with the SuperCDMS Soudan iZIP Detectors

    SciTech Connect

    Welliver, Bradford

    2016-01-01

    Recent cosmological evidence suggests most of the mass of the universe takes the form of a type of particle that we have not been able to directly detect. Nearly 80 years that have elapsed since the rst hints of this dark matter started to appear from astronomers without any direct detection. The high precision era of cosmology and unifying models of particle physics developed in the 20 th century have presented us with an exciting mystery at the intersection of these two elds that needs to be solved. SuperCDMS Soudan operates specialized germanium detectors (iZIPs) that are cooled to milliKelvin temperatures deep underground in the Soudan Underground Laboratory with the hope of detecting a rare collision between dark matter and a nucleus. A search for low-mass dark matter comes with multiple unique challenges since the background discrimination abilities of these detectors becomes less powerful at the low energies needed to probe low-mass dark matter since the signal to noise ratio deteriorates. Using a sophisticated background model via a pulse rescaling technique, SuperCDMS Soudan was able to produce a world leading exclusion limit on low-mass dark matter. Effort is to extend the analysis to higher masses require long running times during which many aspects of the detectors or the environment can change. Additional challenges are offered by the powerful background discrimination ability of the iZIP. The background distributions are well separated from the signal region, meaning most of the leakage arises from low-probability tails of the background distributions. In the absence of an enormous dataset, extrapolations from the bulk of the distribution are required. While attempting to obtain a model of gamma induced electron-recoils leaking into the signal region of the detector from high radius a curious asymmetry between the sides of the detectors was discovered potentially indicating an electronics or detector design problem. This thesis describes the physics

  12. Dedicated searches for low and high mass wimps with the SuperCDMS Soudan iZIP detectors

    NASA Astrophysics Data System (ADS)

    Welliver, Bradford C., Jr.

    Recent cosmological evidence suggests most of the mass of the universe takes the form of a type of particle that we have not been able to directly detect. Nearly 80 years that have elapsed since the first hints of this dark matter started to appear from astronomers without any direct detection. The high precision era of cosmology and unifying models of particle physics developed in the 20th century have presented us with an exciting mystery at the intersection of these two fields that needs to be solved. SuperCDMS Soudan operates specialized germanium detectors (iZIPs) that are cooled to milliKelvin temperatures deep underground in the Soudan Underground Laboratory with the hope of detecting a rare collision between dark matter and a nucleus. A search for low-mass dark matter comes with multiple unique challenges since the background discrimination abilities of these detectors becomes less powerful at the low energies needed to probe low-mass dark matter since the signal to noise ratio deteriorates. Using a sophisticated background model via a pulse rescaling technique, SuperCDMS Soudan was able to produce a world leading exclusion limit on low-mass dark matter. Effort is to extend the analysis to higher masses require long running times during which many aspects of the detectors or the environment can change. Additional challenges are offered by the powerful background discrimination ability of the iZIP. The background distributions are well separated from the signal region, meaning most of the leakage arises from low-probability tails of the background distributions. In the absence of an enormous dataset, extrapolations from the bulk of the distribution are required. While attempting to obtain a model of gamma induced electron-recoils leaking into the signal region of the detector from high radius a curious asymmetry between the sides of the detectors was discovered potentially indicating an electronics or detector design problem. This thesis describes the

  13. The Fermiac or Fermi's Trolley

    NASA Astrophysics Data System (ADS)

    Coccetti, F.

    2016-03-01

    The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.

  14. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  15. Fermi's β-DECAY Theory

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Throughout his lifetime Enrico Fermi (1901-1954) had considered his 1934 β-decay theory as his most important contribution to theoretical physics. E. Segrè (1905-1989) had vividly written about an episode at the inception of that paper:1...

  16. CCC and the Fermi paradox

    NASA Astrophysics Data System (ADS)

    Gurzadyan, V. G.; Penrose, R.

    2016-01-01

    Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme --of communication by remote civilizations-- may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.

  17. Economics and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Hosek, W. R.

    A resolution of the Fermi paradox is proposed using common economic assumptions that should apply to all intelligent, planet-bound civilizations. It is argued that seemingly rational decisions about resource allocation will lead all civilizations to forego the commitment to interstellar exploration and colonization. Consequently humans have not, and will not, be visited by them and humans will not visit other civilizations.

  18. Fermi's Large Area Telescope (LAT)

    NASA Video Gallery

    Fermi’s Large Area Telescope (LAT) is the spacecraft’s main scientificinstrument. This animation shows a gamma ray (purple) entering the LAT,where it is converted into an electron (red) and a...

  19. STEM education and Fermi problems

    NASA Astrophysics Data System (ADS)

    Holubova, Renata

    2017-01-01

    One of the research areas of Physics education is the study of the educational process. Investigations in this area are aimed for example on the teaching and learning process and its results. The conception of STEM education (Science, Technology, Engineering, and Mathematics) is discussed - it is one possible approach to the preparation of the curriculum and the focus on the educational process at basic and secondary schools. At schools in the Czech Republic STEM is much more realized by the application of interdisciplinary relations between subjects Physics-Nature-Technique. In both conceptions the aim is to support pupils' creativity, critical thinking, cross-curricular links. In this context the possibility of using Fermi problems in teaching Physics was discussed (as an interdisciplinary and constructivist activity). The aim of our research was the analysis of Fermi problems solving strategies, the ability of pupils to solve Fermi problems. The outcome of our analysis was to find out methods and teaching strategies which are important to use in teaching - how to solve qualitative and interdisciplinary tasks in physics. In this paper the theoretical basis of STEM education and Fermi problems will be presented. The outcome of our findings based on the research activities will be discussed so as our experiences from 10 years of Fermi problems competition that takes place at the Science Faculty, Palacky University in Olomouc. Changes in competencies of solving tasks by our students (from the point of view in terms of modern, activating teaching methods recommended by theory of Physics education and other science subjects) will be identified.

  20. Extending the Fermi-LAT Data Processing Pipeline to the Grid

    NASA Astrophysics Data System (ADS)

    Zimmer, S.; Arrabito, L.; Glanzman, T.; Johnson, T.; Lavalley, C.; Tsaregorodtsev, A.

    2012-12-01

    The Data Handling Pipeline (“Pipeline”) has been developed for the Fermi Gamma-Ray Space Telescope (Fermi) Large Area Telescope (LAT) which launched in June 2008. Since then it has been in use to completely automate the production of data quality monitoring quantities, reconstruction and routine analysis of all data received from the satellite and to deliver science products to the collaboration and the Fermi Science Support Center. Aside from the reconstruction of raw data from the satellite (Level 1), data reprocessing and various event-level analyses are also reasonably heavy loads on the pipeline and computing resources. These other loads, unlike Level 1, can run continuously for weeks or months at a time. In addition it receives heavy use in performing production Monte Carlo tasks. In daily use it receives a new data download every 3 hours and launches about 2000 jobs to process each download, typically completing the processing of the data before the next download arrives. The need for manual intervention has been reduced to less than 0.01% of submitted jobs. The Pipeline software is written almost entirely in Java and comprises several modules. The software comprises web-services that allow online monitoring and provides charts summarizing work flow aspects and performance information. The server supports communication with several batch systems such as LSF and BQS and recently also Sun Grid Engine and Condor. This is accomplished through dedicated job control services that for Fermi are running at SLAC and the other computing site involved in this large scale framework, the Lyon computing center of IN2P3. While being different in the logic of a task, we evaluate a separate interface to the Dirac system in order to communicate with EGI sites to utilize Grid resources, using dedicated Grid optimized systems rather than developing our own. More recently the Pipeline and its associated data catalog have been generalized for use by other experiments, and are

  1. Fermi resonance in optical microcavities

    NASA Astrophysics Data System (ADS)

    Yi, Chang-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min

    2015-04-01

    Fermi resonance is a phenomenon of quantum mechanical superposition, which most often occurs between normal and overtone modes in molecular systems that are nearly coincident in energy. We find that scarred resonances in deformed dielectric microcavities are the very phenomenon of Fermi resonance, that is, a pair of quasinormal modes interact with each other due to coupling and a pair of resonances are generated through an avoided resonance crossing. Then the quantum number difference of a pair of quasinormal modes, which is a consequence of quantum mechanical superposition, equals periodic orbits, whereby the resonances are localized on the periodic orbits. We derive the relation between the quantum number difference and the periodic orbits and confirm it in an elliptic, a rectangular, and a stadium-shaped dielectric microcavity.

  2. Enrico Fermi and the Dolomites

    NASA Astrophysics Data System (ADS)

    Battimelli, Giovanni; de Angelis, Alessandro

    2014-11-01

    Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.

  3. Fermi Timing and Synchronization System

    SciTech Connect

    Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D'Auria, G.

    2006-07-19

    The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.

  4. Landau Theory of Helical Fermi Liquids.

    PubMed

    Lundgren, Rex; Maciejko, Joseph

    2015-08-07

    We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.

  5. Pulsar Timing with the Fermi LAT

    DTIC Science & Technology

    2010-12-01

    Pulsar Timing with the Fermi LAT Paul S. Ray∗, Matthew Kerr†, Damien Parent∗∗ and the Fermi PSC‡ ∗Naval Research Laboratory, 4555 Overlook Ave., SW...Laboratory, Washington, DC 20375, USA ‡Fermi Pulsar Search Consortium Abstract. We present an overview of precise pulsar timing using data from the Large...unbinned photon data. In addition to determining the spindown behavior of the pulsars and detecting glitches and timing noise, such timing analyses al

  6. Bioterrorism and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Cooper, Joshua

    2013-04-01

    We proffer a contemporary solution to the so-called Fermi Paradox, which is concerned with conflict between Copernicanism and the apparent paucity of evidence for intelligent alien civilizations. In particular, we argue that every community of organisms that reaches its space-faring age will (1) almost immediately use its rocket-building computers to reverse-engineer its genetic chemistry and (2) self-destruct when some individual uses said technology to design an omnicidal pathogen. We discuss some of the possible approaches to prevention with regard to Homo sapiens' vulnerability to bioterrorism, particularly on a short-term basis.

  7. Superfluid Thomas—Fermi approximation for trapped fermi gases

    NASA Astrophysics Data System (ADS)

    Hernández, E. S.; Capuzzi, P.; Szybisz, L.

    2009-02-01

    We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.

  8. Fermi surface of YBCO by DHVA

    SciTech Connect

    Smith, J.L.; Fowler, C.M.; Freeman, B.L.; Hults, W.L.; King, J.C.; Mueller, F.M.

    1991-01-01

    These proceedings demonstrate how far scientist have come in the last four years of high temperature superconductivity. Knowledge of the energy bands and Fermi surfaces from experiment has come rather late. Photoemission, first showed proof of the validity of the energy band calculations. Positron annihilation, presented by West, after a rough start, is now giving evidence of the Fermi surface. Both of these techniques involve electronic excitations and hence, although they show the Fermi surface, do not put as severe a constraint on various models for superconductivity as does the de Haas-van Alphen (dHvA) effect. This is a true measurement of the electronic ground state in an applied magnetic field where the frequency of oscillatory magnetization yields extremal cross-sectional areas of the Fermi surface. The authors have already reported some of their Fermi surface work at two conferences but present here discussion of several more important aspects of the work. 11 refs., 2 figs.

  9. Cooling and thermometry of atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Onofrio, R.

    2016-11-01

    We review the status of cooling techniques aimed at achieving the deepest quantum degeneracy for atomic Fermi gases. We first discuss some physics motivations, providing a quantitative assessment of the need for deep quantum degeneracy in relevant physics cases, such as the search for unconventional superfluid states. Attention is then focused on the most widespread technique to reach deep quantum degeneracy for Fermi systems, sympathetic cooling of Bose - Fermi mixtures, organizing the discussion according to the specific species involved. Various proposals to circumvent some of the limitations on achieving the deepest Fermi degeneracy, and their experimental realizations, are then reviewed. Finally, we discuss the extension of these techniques to optical lattices and the implementation of precision thermometry crucial to the understanding of the phase diagram of classical and quantum phase transitions in Fermi gases.

  10. Fermi surface measurements of lutetium

    NASA Astrophysics Data System (ADS)

    Johanson, W. R.; Crabtree, G. W.; Schmidt, F. A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101¯0) and (112¯0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  11. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  12. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-01-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of Lutetium at temperatures down to .3K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a non-magnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  13. Deformation quantization of fermi fields

    SciTech Connect

    Galaviz, I. Garcia-Compean, H. Przanowski, M. Turrubiates, F.J.

    2008-04-15

    Deformation quantization for any Grassmann scalar free field is described via the Weyl-Wigner-Moyal formalism. The Stratonovich-Weyl quantizer, the Moyal *-product and the Wigner functional are obtained by extending the formalism proposed recently in [I. Galaviz, H. Garcia-Compean, M. Przanowski, F.J. Turrubiates, Weyl-Wigner-Moyal Formalism for Fermi Classical Systems, arXiv:hep-th/0612245] to the fermionic systems of infinite number of degrees of freedom. In particular, this formalism is applied to quantize the Dirac free field. It is observed that the use of suitable oscillator variables facilitates considerably the procedure. The Stratonovich-Weyl quantizer, the Moyal *-product, the Wigner functional, the normal ordering operator, and finally, the Dirac propagator have been found with the use of these variables.

  14. Quantum Mechanical Models Of The Fermi Shuttle

    SciTech Connect

    Sternberg, James

    2011-06-01

    The Fermi shuttle is a mechanism in which high energy electrons are produced in an atomic collision by multiple collisions with a target and a projectile atom. It is normally explained purely classically in terms of the electron's orbits prescribed in the collision. Common calculations to predict the Fermi shuttle use semi-classical methods, but these methods still rely on classical orbits. In reality such collisions belong to the realm of quantum mechanics, however. In this paper we discuss several purely quantum mechanical calculations which can produce the Fermi shuttle. Being quantum mechanical in nature, these calculations produce these features by wave interference, rather than by classical orbits.

  15. Quantum oscillations from inside the Fermi sea

    NASA Astrophysics Data System (ADS)

    Pal, Hridis K.

    2017-02-01

    Quantum oscillations are conventionally understood to arise from the Fermi level; hence, they are considered to be a proof of the existence of an underlying Fermi surface. In this article we show that in certain situations quantum oscillations can also arise from inside the Fermi sea. We establish this analytically, supporting it with numerical calculations. Possible scenarios where such unusual behavior can occur are pointed out. In particular, in strongly particle-hole asymmetric insulators, models of which have been recently used in the context of the topological Kondo insulator SmB6, we show that the oscillations arise from inside the filled band, and are not related to the gap.

  16. Fermi-liquid theory for unconventional superconductors

    SciTech Connect

    Sauls, J.A.

    1994-12-31

    Fermi liquid theory is used to generate the Ginzburg-Landau free energy functionals for unconventional superconductors belonging to various representations. The parameters defining the GL functional depend on Fermi surface anisotropy, impurity scattering and the symmetry class of the pairing interaction. As applications the author considers the basic models for the multiple superconducting phases of UPt{sub 3}. An important prediction of the leading order Fermi liquid theory for the two-dimensional representations of the hexagonal symmetry group is that the zero-field equilibrium state exhibits spontaneously broken time-reversal symmetry.

  17. Quantum chaos on a critical Fermi surface.

    PubMed

    Patel, Aavishkar A; Sachdev, Subir

    2017-02-21

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  18. Fermi's Conundrum: Proliferation and Closed Societies

    NASA Astrophysics Data System (ADS)

    Teller, Wendy; Westfall, Catherine

    2007-04-01

    On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.

  19. Fermi: physicist with a capital F

    NASA Astrophysics Data System (ADS)

    Cobal, Marina

    2016-12-01

    Enrico Fermi – one of the great physicists of the 21st century – was a beacon for every Italian student of physics. This is wonderfully captured in The Pope of Physics by Gino Segrè and Bettina Hoerlin.

  20. Fermi Proves Supernova Remnants Make Cosmic Rays

    NASA Video Gallery

    The husks of exploded stars produce some of the fastest particles in the cosmos. New findings by NASA's Fermi show that two supernova remnants accelerate protons to near the speed of light. The pro...

  1. Fermi Sees Antimatter-Hurling Thunderstorms

    NASA Video Gallery

    NASA's Fermi Gamma-ray Space Telescope has detected beams of antimatter launched by thunderstorms. Acting like enormous particle accelerators, the storms can emit gamma-ray flashes, called TGFs, an...

  2. Fermi discovers giant bubbles in Milky Way

    NASA Video Gallery

    Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have recently discovered a gigantic, mysterious structure in our galaxy. This feature looks like a pair of bubbles extending above...

  3. Fermi Surface of the Most Dilute Superconductor

    NASA Astrophysics Data System (ADS)

    Lin, Xiao; Zhu, Zengwei; Fauqué, Benoît; Behnia, Kamran

    2013-04-01

    The origin of superconductivity in bulk SrTiO3 is a mystery since the nonmonotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. Here, employing the Nernst effect, an extremely sensitive probe of tiny bulk Fermi surfaces, we show that, down to concentrations as low as 5.5×1017cm-3, the system has both a sharp Fermi surface and a superconducting ground state. The most dilute superconductor currently known therefore has a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. The occurrence of a superconducting instability in an extremely small, single-component, and barely anisotropic Fermi surface implies strong constraints for the identification of the pairing mechanism.

  4. A fast algorithm for finding point sources in the Fermi data stream: FermiFAST

    NASA Astrophysics Data System (ADS)

    Asvathaman, Asha; Omand, Conor; Barton, Alistair; Heyl, Jeremy S.

    2017-04-01

    We present a new and efficient algorithm for finding point sources in the photon event data stream from the Fermi Gamma-Ray Space Telescope, FermiFAST. The key advantage of FermiFAST is that it constructs a catalogue of potential sources very fast by arranging the photon data in a hierarchical data structure. Using this structure, FermiFAST rapidly finds the photons that could have originated from a potential gamma-ray source. It calculates a likelihood ratio for the contribution of the potential source using the angular distribution of the photons within the region of interest. It can find within a few minutes the most significant half of the Fermi Third Point Source catalogue (3FGL) with nearly 80 per cent purity from the 4 yr of data used to construct the catalogue. If a higher purity sample is desirable, one can achieve a sample that includes the most significant third of the Fermi 3FGL with only 5 per cent of the sources unassociated with Fermi sources. Outside the Galactic plane, all but eight of the 580 FermiFAST detections are associated with 3FGL sources. And of these eight, six yield significant detections of greater than 5σ when a further binned likelihood analysis is performed. This software allows for rapid exploration of the Fermi data, simulation of the source detection to calculate the selection function of various sources and the errors in the obtained parameters of the sources detected.

  5. High-redshift Fermi blazars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tagliaferri, G.; Foschini, L.; Ghirlanda, G.; Tavecchio, F.; Della Ceca, R.; Haardt, F.; Volonteri, M.; Gehrels, N.

    2011-02-01

    With the release of the first-year Fermi catalogue, the number of blazars detected above 100 MeV lying at high redshift has been largely increased. There are 28 blazars at z > 2 in the `clean' sample. All of them are flat spectrum radio quasars. We study and model their overall spectral energy distribution in order to find the physical parameters of the jet-emitting region, and for all of them, we estimate their black hole masses and accretion rates. We then compare the jet with the accretion disc properties, setting these sources in the broader context of all the other bright γ-ray or hard X-ray blazars. We confirm that the jet power correlates with the accretion luminosity. We find that the high-energy emission peak shifts to smaller frequencies as the observed luminosity increases, according to the blazar sequence, making the hard X-ray band the most suitable for searching the most-luminous and distant blazars.

  6. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2017-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  7. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center Team

    2016-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  8. Time-dependent Models for Blazar Emission with the Second-order Fermi Acceleration

    NASA Astrophysics Data System (ADS)

    Asano, Katsuaki; Takahara, Fumio; Kusunose, Masaaki; Toma, Kenji; Kakuwa, Jun

    2014-01-01

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 1038 erg s-1, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

  9. Time-dependent models for blazar emission with the second-order Fermi acceleration

    SciTech Connect

    Asano, Katsuaki; Takahara, Fumio; Toma, Kenji; Kusunose, Masaaki; Kakuwa, Jun

    2014-01-01

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101–232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10{sup 38} erg s{sup –1}, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

  10. Search for low-mass weakly interacting massive particles using voltage-assisted calorimetric ionization detection in the SuperCDMS experiment.

    PubMed

    Agnese, R; Anderson, A J; Asai, M; Balakishiyeva, D; Basu Thakur, R; Bauer, D A; Billard, J; Borgland, A; Bowles, M A; Brandt, D; Brink, P L; Bunker, R; Cabrera, B; Caldwell, D O; Cerdeno, D G; Chagani, H; Cooley, J; Cornell, B; Crewdson, C H; Cushman, P; Daal, M; Di Stefano, P C F; Doughty, T; Esteban, L; Fallows, S; Figueroa-Feliciano, E; Godfrey, G L; Golwala, S R; Hall, J; Harris, H R; Hertel, S A; Hofer, T; Holmgren, D; Hsu, L; Huber, M E; Jastram, A; Kamaev, O; Kara, B; Kelsey, M H; Kennedy, A; Kiveni, M; Koch, K; Loer, B; Lopez Asamar, E; Mahapatra, R; Mandic, V; Martinez, C; McCarthy, K A; Mirabolfathi, N; Moffatt, R A; Moore, D C; Nadeau, P; Nelson, R H; Page, K; Partridge, R; Pepin, M; Phipps, A; Prasad, K; Pyle, M; Qiu, H; Rau, W; Redl, P; Reisetter, A; Ricci, Y; Saab, T; Sadoulet, B; Sander, J; Schneck, K; Schnee, R W; Scorza, S; Serfass, B; Shank, B; Speller, D; Villano, A N; Welliver, B; Wright, D H; Yellin, S; Yen, J J; Young, B A; Zhang, J

    2014-01-31

    SuperCDMS is an experiment designed to directly detect weakly interacting massive particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this Letter, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage-assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for ten live days at the Soudan Underground Laboratory. A low energy threshold of 170  eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6  GeV/c2.

  11. A Search for Low-Mass Weakly Interacting Massive Particles Using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment

    SciTech Connect

    Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Bowles, M. A.; Brandt, D.; Brink, P. L.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Cerdeno, D. G.; Chagani, H.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; Di Stefano, P. C.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Harris, H. R.; Hertel, S. A.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Kiveni, M.; Koch, K.; Loer, B.; Lopez Asamar, E.; Mahapatra, R.; Mandic, V.; Martinez, C.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Moore, D. C.; Nadeau, P.; Nelson, R. H.; Page, K.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redi, P.; Reisetter, A.; Ricci, Y.; Saab, T.; Sadoulet, B.; Sander, J.; Schneck, K.; Schnee, Richard; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Villano, A. N.; Welliver, B.; Wright, D. H.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2014-01-27

    SuperCDMS is an experiment designed to directly detect weakly interacting massive particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this Letter, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage-assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for ten live days at the Soudan Underground Laboratory. A low energy threshold of (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c2.

  12. Search for Low-Mass Weakly Interacting Massive Particles Using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment

    SciTech Connect

    Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Bowles, M. A.; Brandt, D.; Brink, P. L.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Cerdeno, D. G.; Chagani, H.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hertel, S. A.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Kiveni, M.; Koch, K.; Loer, B.; Lopez Asamar, E.; Mahapatra, R.; Mandic, V.; Martinez, C.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Moore, D. C.; Nadeau, P.; Nelson, R. H.; Page, K.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Saab, T.; Sadoulet, B.; Sander, J.; Schneck, K.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Villano, A. N.; Welliver, B.; Wright, D. H.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2014-01-01

    SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this paper, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage- assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for 10 live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c2.

  13. Upgrading Fermi Without Traveling to Space

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-02-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% and nobody had to travel to space to make it happen! The difference instead stems from remarkable improvement to the software used to analyze Fermi-LATs data, and it has resulted in a new high-energy map of our sky.Animation (click to watch!) comparing the Pass 7 to the Pass 8 Fermi-LAT analysis, in a region in the constellation Carina. Pass 8 provides more accurate directions for incoming gamma rays, so more of them fall closer to their sources, creating taller spikes and a sharper image. [NASA/DOE/Fermi LAT Collaboration]Pass 8Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector with a flux that can be 10,000 times larger! is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.Pass 8 is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.Map of the High-Energy SkySky map of the sources in the 2FHL catalog, classified by their most likely association. Click for a better look! [Ackermann et al. 2016]The first result from the

  14. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2015-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. The reference manual gives details of the options available for each tool. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide information on recent updates incorporated in the Science Tools as well as upcoming changes that will be included in the upcoming release of the Science Tools in early 2015.

  15. Pairing in a dry Fermi sea

    NASA Astrophysics Data System (ADS)

    Maier, T. A.; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-06-01

    In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  16. Topology of Fermi surfaces and anomaly inflows

    NASA Astrophysics Data System (ADS)

    Adem, Alejandro; Camarena, Omar Antolín; Semenoff, Gordon W.; Sheinbaum, Daniel

    2016-11-01

    We derive a rigorous classification of topologically stable Fermi surfaces of non-interacting, discrete translation-invariant systems from electronic band theory, adiabatic evolution and their topological interpretations. For systems on an infinite crystal it is shown that there can only be topologically unstable Fermi surfaces. For systems on a half- space and with a gapped bulk, our derivation naturally yields a K -theory classification. Given the d - 1-dimensional surface Brillouin zone X s of a d-dimensional half-space, our result implies that different classes of globally stable Fermi surfaces belong in K -1 (Xs) for systems with only discrete translation-invariance. This result has a chiral anomaly inflow interpretation, as it reduces to the spectral flow for d = 2. Through equivariant homotopy methods we extend these results for symmetry classes AI, AII, C and D and discuss their corresponding anomaly inflow interpretation.

  17. The Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, Dave; McEnery, Julie

    2011-01-01

    This slide presentation reviews the Gamma Ray Astronomy as enhanced by the Fermi Gamma Ray Space Telescope and Radio Astronomy as a synergistic relationship. Gamma rays often represent a significant part of the energy budget of a source; therefore, gamma-ray studies can be critical to understanding physical processes in such sources. Radio observations offer timing and spatial resolutions vastly superior to anything possible with gamma-ray telescopes; therefore radio is often the key to understanding source structure. Gamma-ray and radio observations can complement each other, making a great team. It reviews the Fermi Guest Investigator (GI) program, and calls for more cooperative work that involves Fermi and the Very Long Baseline Array (VLBA), a system of ten radio telescopes.

  18. Renormalization group flow for noncommutative Fermi liquids

    SciTech Connect

    Estrada-Jimenez, Sendic; Garcia-Compean, Hugo; Wu Yongshi

    2011-06-15

    Some recent studies of the AdS/CFT correspondence for condensed matter systems involve the Fermi liquid theory as a boundary field theory. Adding B-flux to the boundary D-branes leads in a certain limit to the noncommutative Fermi liquid, which calls for a field theory description of its critical behavior. As a preliminary step to more general consideration, the modification of the Landau's Fermi liquid theory due to noncommutativity of spatial coordinates is studied in this paper. We carry out the renormalization of interactions at tree level and one loop in a weakly coupled fermion system in two spatial dimensions. Channels ZS, ZS' and BCS are discussed in detail. It is shown that while the Gaussian fixed-point remains unchanged, the BCS instability is modified due to the space noncommutativity.

  19. Fermi's Paradox Is a Daunting Problem, Under Whatever Label

    NASA Astrophysics Data System (ADS)

    Čirković, Milan M.

    2016-10-01

    Gray (2015) argued that the Fermi paradox (FP) is a misnomer, and it is not a valid paradox. Gray also speculated that the argument was misattributed to Fermi, whose lunchtime remarks did not pertain to the existence of extraterrestrial intelligence, but to the feasibility of interstellar travel. Instead, the paradox is ascribed to Hart and Tipler, and it is further suggested that the paradox is not a real problem or research subject and should not be used in debates about SETI projects. The arguments given are unpersuasive, ahistorical, and, in at least one instance, clearly hinge on literalistic and uncharitable reading of evidence. Instead, I argue the following three points: (i) Contrary to Gray's assertion, the historical issue of naming of ideas or concepts is completely divorced from their epistemic status. (ii) FP is easily and smoothly generalized into the Great Silence paradox, so it makes no sense either theoretically or empirically to separate the two. (iii) In sharp contrast to the main implication of Gray's paper, FP has become more aggravated lately due to advances in astrobiology.

  20. Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Huaisong; Gao, Deheng; Feng, Shiping

    2017-03-01

    One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.

  1. Fermi surface determination from momentum density projections

    NASA Astrophysics Data System (ADS)

    Leitner, Michael; Weber, Josef Andreas; Ceeh, Hubert

    2016-06-01

    The problem of determining a metal’s Fermi surface from measured projections of the electron or electron/positron momentum densities, such as those obtained by Compton scattering or angular correlation of positron annihilation radiation, respectively, is examined in a Bayesian formulation. A consistent approach with an explicit treatment of the Fermi surface already at the reconstruction stage is presented, and its advantages compared to previous practice are discussed. A validation of the proposed method on simulated data shows its systematic accuracy to be very satisfactory and its statistical precision on modest experimental data to be surprisingly good.

  2. Supernova Remnants with Fermi Large Area Telescope

    NASA Astrophysics Data System (ADS)

    Caragiulo, M.; Di Venere, L.

    2017-03-01

    The Large Area Telescope (LAT), on-board the Fermi satellite, proved to be, after 8 years of data taking, an excellent instrument to detect and observe Supernova Remnants (SNRs) in a range of energies running from few hundred MeV up to few hundred GeV. It provides essential information on physical processes that occur at the source, involving both accelerated leptons and hadrons, in order to understand the mechanisms responsible for the primary Cosmic Ray (CR) acceleration. We show the latest results in the observation of Galactic SNRs by Fermi-LAT.

  3. Information-driven societies and Fermi's paradox

    NASA Astrophysics Data System (ADS)

    Lampton, Michael

    2013-10-01

    Fermi's paradox is founded on the idea that one or more Galactic extraterrestrial civilizations (ETCs) existed long ago and sustained exploration for millions of years, but in spite of their advanced knowledge, they could not find a way to explore the Galaxy other than with fleets of starships or self replicating probes. Here, I question this second assumption: if advanced technology generally allows long-distance remote sensing, and if ETCs were motivated by gaining information rather than conquest or commerce, then such voyages would be unnecessary, thereby resolving Fermi's paradox.

  4. MASTER: OT detection during Fermi trigger inspection

    NASA Astrophysics Data System (ADS)

    Popova, E.; Lipunov, V.; Buckley, D.; Gorbovskoy, E.; Tiurina, N.; Balanutsa, P.; Kuznetsov, A.; Kornilov, V.; Chazov, V.; Vlasenko, D.; Vladimirov, V.; Gress, O.; Ivanov, K.; Potter, S.; Gabovich, A.

    2016-11-01

    During inspection of Fermi trigger 501261070 ( (Ra,Dec)=47.190,-47.210; GRB_ERROR_radius=3.27deg, GRB_TIME=2016/11/19 15:11:06.40UT http://gcn.gsfc.nasa.gov/other/501261070.fermi ) MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 03h 22m 52.70s -48d 29m 10.9s on 2016-11-19 21:17:17.878UT with unfiltered m_OT=17.8 (mlim=19.7).

  5. Higher-spin charges in Hamiltonian form. II. Fermi fields

    NASA Astrophysics Data System (ADS)

    Campoleoni, A.; Henneaux, M.; Hörtner, S.; Leonard, A.

    2017-02-01

    We build the asymptotic higher-spin charges associated with "improper" gauge transformations for fermionic higher-spin gauge fields on Anti de Sitter backgrounds of arbitrary dimension. This is achieved within the canonical formalism. We consider massless fields of spin s+1/2, described by a symmetric spinor-tensor of rank s in the Fang-Fronsdal approach. We begin from a detailed analysis of the spin 5/2 example, for which we cast the Fang-Fronsdal action in Hamiltonian form, we derive the charges and we propose boundary conditions on the canonical variables that secure their finiteness. We then extend the computation of charges and the characterisation of boundary conditions to arbitrary half-integer spin. Our construction generalises to higher-spin fermionic gauge fields the known Hamiltonian derivation of supercharges in AdS supergravity.

  6. Enrico: Python package to simplify Fermi-LAT analysis

    NASA Astrophysics Data System (ADS)

    Sanchez, David; Deil, Christoph

    2015-01-01

    Enrico analyzes Fermi data. It produces spectra (model fit and flux points), maps and lightcurves for a target by editing a config file and running a python script which executes the Fermi science tool chain.

  7. Non-uniform drag force on the Fermi accelerator model

    NASA Astrophysics Data System (ADS)

    Tavares, Danila F.; Leonel, Edson D.; Costa Filho, R. N.

    2012-11-01

    Some dynamical properties of a particle suffering the action of a generic drag force are obtained for a dissipative Fermi Acceleration model. The dissipation is introduced via a viscous drag force, like a gas, and is assumed to be proportional to a power of the velocity: F∝-vγ. The dynamics is described by a two-dimensional nonlinear area-contracting mapping obtained via the solution of Newton’s second law of motion. We prove analytically that the decay of high energy is given by a continued fraction which recovers the following expressions: (i) linear for γ=1; (ii) exponential for γ=2; and (iii) second-degree polynomial type for γ=1.5. Our results are discussed for both the complete version and the simplified version. The procedure used in the present paper can be extended to many different kinds of system, including a class of billiards problems.

  8. Automatic Cloud Bursting under FermiCloud

    SciTech Connect

    Wu, Hao; Shangping, Ren; Garzoglio, Gabriele; Timm, Steven; Bernabeu, Gerard; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin; Noh, Seo-Young

    2013-01-01

    Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied

  9. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGES

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; ...

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scatteringmore » creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.« less

  10. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  11. FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG

    SciTech Connect

    Nolan, P. L.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Abdo, A. A.; Ackermann, M.; Antolini, E.; Bonamente, E.; Atwood, W. B.; Belfiore, A.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D.; Bignami, G. F. E-mail: Gino.Tosti@pg.infn.it E-mail: tburnett@u.washington.edu; and others

    2012-04-01

    We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.

  12. Fermi Large Area Telescope Second Source Catalog

    NASA Technical Reports Server (NTRS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M; Allafort, A.; Antolini, E; Bonnell, J.; Cannon, A.; Celik O.; Corbet, R.; Davis, D. S.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Harding, A. K.; Hays, E.; Johnson, T. E.; McConville, W.; McEnery, J. E; Perkins, J. S.; Racusin, J. L; Scargle, J. D.; Stephens, T. E.; Thompson, D. J.; Troja, E.

    2012-01-01

    We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 11eV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.

  13. Radio core dominance of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

    2016-07-01

    During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are < log Rrangle = 0.99±0.87 for FDBs and < log Rrangle = -0.62±1.15 for the non-FDBs. A K-S test shows that the probability for the two distributions of FDBs and non-FDBs to come from the same parent distribution is near zero (P =9.12×10^{-52}). Secondly, we also investigated the variability index (V.I.) in the γ-ray band for FDBs, and we found V.I.=(0.12 ±0.07) log R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0

  14. FermiGrid - experience and future plans

    SciTech Connect

    Chadwick, K.; Berman, E.; Canal, P.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Timm, S.; Yocum, D.; /Fermilab

    2007-09-01

    Fermilab supports a scientific program that includes experiments and scientists located across the globe. In order to better serve this community, Fermilab has placed its production computer resources in a Campus Grid infrastructure called 'FermiGrid'. The FermiGrid infrastructure allows the large experiments at Fermilab to have priority access to their own resources, enables sharing of these resources in an opportunistic fashion, and movement of work (jobs, data) between the Campus Grid and National Grids such as Open Science Grid and the WLCG. FermiGrid resources support multiple Virtual Organizations (VOs), including VOs from the Open Science Grid (OSG), EGEE and the Worldwide LHC Computing Grid Collaboration (WLCG). Fermilab also makes leading contributions to the Open Science Grid in the areas of accounting, batch computing, grid security, job management, resource selection, site infrastructure, storage management, and VO services. Through the FermiGrid interfaces, authenticated and authorized VOs and individuals may access our core grid services, the 10,000+ Fermilab resident CPUs, near-petabyte (including CMS) online disk pools and the multi-petabyte Fermilab Mass Storage System. These core grid services include a site wide Globus gatekeeper, VO management services for several VOs, Fermilab site authorization services, grid user mapping services, as well as job accounting and monitoring, resource selection and data movement services. Access to these services is via standard and well-supported grid interfaces. We will report on the user experience of using the FermiGrid campus infrastructure interfaced to a national cyberinfrastructure--the successes and the problems.

  15. Fermi and Non-Fermi Liquid Behavior in Quantum Impurity Systems: Conserving Slave Boson Theory

    NASA Astrophysics Data System (ADS)

    Kroha, Johann; Woelfle, Peter

    1998-12-01

    The question of Fermi liquid vs. non-Fermi liquid behavior induced by strong correlations is one of the prominent problems in metallic local moment systems. As standard models for such systems, the SU(N)× SU(M) Anderson impurity models exhibit both Fermi liquid and non-Fermi liquid behavior, depending on their symmetry. Taking the Anderson model as an example, these lectures first give an introduction to the auxiliary boson method to describe correlated systems governed by a strong, short-range electronic repulsion. It is then shown how to include the relevant low-lying excitations (coherent spin flip and charge fluctuation processes), while preserving the local gauge symmetry of the model. This amounts to a conserving T-matrix approximation (CTMA). We prove a cancellation theorem showing that the CTMA incorporates all leading and subleading infrared singularities at any given order in a self-consistent loop expansion of the free energy. As a result, the CTMA recovers the correct infrared behavior of the auxiliary particle propagators, indicating that it correctly describes both the Fermi and the non-Fermi liquid regimes of the Anderson model.

  16. Continuous transitions between composite Fermi liquid and Landau Fermi liquid: A route to fractionalized Mott insulators

    NASA Astrophysics Data System (ADS)

    Barkeshli, Maissam; McGreevy, John

    2012-08-01

    One of the most successful theories of a non-Fermi-liquid metallic state is the composite Fermi-liquid (CFL) theory of the half-filled Landau level. In this paper, we study continuous quantum phase transitions out of the CFL state and into a Landau Fermi liquid, in the limit of no disorder and fixed particle number. This transition can be induced by tuning the bandwidth of the Landau level relative to the interaction energy, for instance through an externally applied periodic potential. We find a transition to the Landau Fermi liquid through a gapless Mott insulator with a Fermi surface of neutral fermionic excitations. In the presence of spatial symmetries, we also find a direct continuous transition between the CFL and the Landau Fermi liquid. The transitions have a number of characteristic observable signatures, including the presence of two crossover temperature scales, resistivity jumps, and vanishing compressibility. When the composite fermions are paired instead, our results imply quantum critical points between various non-Abelian topological states, including the ν=1/2 Moore-Read Pfaffian [Ising × U(1) topological order], a version of the Kitaev B phase (Ising topological order), and paired electronic superconductors. To study such transitions, we use a projective construction of the CFL, which goes beyond the conventional framework of flux attachment to include a broader set of quantum fluctuations. These considerations suggest a possible route to fractionalized Mott insulators by starting with fractional quantum Hall states and tuning the Landau-level bandwidth.

  17. Fermi energy instability in resonant tunneling

    NASA Astrophysics Data System (ADS)

    Claro, Francisco; Inkoferer, Jutta; Obermeir, Gustav

    2001-03-01

    In resonant tunneling two different instabilities may arise induced by the electron-electron interaction, depending on whether the conduction channel is at the emitter Fermi energy, or at the bottom of the emitter Fermi sea. The latter leads to a well understood multistable regime in the device characteristics. The former was found in the past for the case when a magnetic field is present in the direction of the current flow*. We shall show that the external field is not required, and that actually the instability can take place in the presence of zero, one and two dimensional quantum wells. Supported in part by FONDECYT 1990425 and Catedra Presidencial en Ciencias *P.Orellana, E.Anda and F.Claro, Phys.Rev.Lett. 79, 1118 (1997)

  18. Stokes paradox in electronic Fermi liquids

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew

    2017-03-01

    The Stokes paradox is the statement that in a viscous two-dimensional fluid, the "linear response" problem of fluid flow around an obstacle is ill posed. We present a simple consequence of this paradox in the hydrodynamic regime of a Fermi liquid of electrons in two-dimensional metals. Using hydrodynamics and kinetic theory, we estimate the contribution of a single cylindrical obstacle to the global electrical resistance of a material, within linear response. Momentum relaxation, present in any realistic electron liquid, resolves the classical paradox. Nonetheless, this paradox imprints itself in the resistance, which can be parametrically larger than predicted by Ohmic transport theory. We find a remarkably rich set of behaviors, depending on whether or not the quasiparticle dynamics in the Fermi liquid should be treated as diffusive, hydrodynamic, or ballistic on the length scale of the obstacle. We argue that all three types of behavior are observable in present day experiments.

  19. High Energy Neutrinos from the Fermi Bubbles

    SciTech Connect

    Lunardini, Cecilia; Razzaque, Soebur

    2012-06-01

    Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma-ray emission in spectrum and spatial extent. Its highest energy part, above 20–50 TeV, is observable at a kilometer-scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South Pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

  20. High energy neutrinos from the Fermi bubbles.

    PubMed

    Lunardini, Cecilia; Razzaque, Soebur

    2012-06-01

    Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma-ray emission in spectrum and spatial extent. Its highest energy part, above 20-50 TeV, is observable at a kilometer-scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South Pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

  1. Operation of FERMI FELs for users

    NASA Astrophysics Data System (ADS)

    Svandrlik, M.

    2015-05-01

    The FERMI seeded free electron laser facility, located at the Elettra laboratory in Trieste (Italy), has been operated for user experiments in the past years using the first FEL line, FEL-1, covering the VUV - EVU spectral range (100 - 20 nm). After the conclusion of the commissioning for the soft-X ray FEL line, FEL-2, the facility is now ready to provide the scientific community with intense FEL pulses (<10 μJ) characterized by a high degree of coherence and spectral stability in the whole range from 100 nm down to 4 nm. We report about the recent achievement of FERMI FELs and our experience with operations for user requiring specific FEL configurations.

  2. Unconventional Fermi surface in an insulating state

    NASA Astrophysics Data System (ADS)

    Tan, B. S.; Hsu, Y.-T.; Zeng, B.; Hatnean, M. Ciomaga; Harrison, N.; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J.-H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-01

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  3. Probing Magnetized Turbulence in the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Lund, Kelsey; Hales, Christopher A.; Su, Meng

    2017-01-01

    Fermi-LAT observations have revealed giant, sharply defined gamma-ray structures emanating from the Galactic center known as the Fermi bubbles. They extend ~50 degrees (~8.5 kpc) above and below the plane of the Milky Way. Their origin is uncertain but thought to be related to an energetic event such as accretion onto Sgr A* or a burst of nuclear star formation. We analyzed archival radio measurements of Faraday rotation toward extragalactic sources and detected a signature of the bubbles at the shock boundary to the Galactic halo. To confirm these preliminary findings we performed new radio observations with the Karl G. Jansky Very Large Array (JVLA). We discuss the findings of our observations, the shock energetics of the bubbles and their implications for nuclear Galactic activity.

  4. Unconventional Fermi surface in an insulating state

    SciTech Connect

    Harrison, Neil; Tan, B. S.; Hsu, Y. -T.; Zeng, B.; Hatnean, M. Ciomaga; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J. -H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-17

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. As a result, the quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  5. "Permanence" - An Adaptationist Solution to Fermi's Paradox?

    NASA Astrophysics Data System (ADS)

    Cirkovic, Milan M.

    A new solution of Fermi's paradox sketched by SF writer Karl Schroeder in his 2002. novel Permanence is investigated. It is argued that this solution is tightly connected with adaptationism - a widely discussed working hypothesis in evolutionary biology. Schroeder's hypothesis has important ramifications for astrobiology, SETI projects, and future studies. Its weaknesses should be explored without succumbing to the emotional reactions often accompanying adaptationist explanations.

  6. First Light on GRBs with Fermi

    DTIC Science & Technology

    2010-08-04

    components at LAT energies, and the line-of-death problem [21] cannot be easily explained within the framework of such a model , as noted already in...30] using a GRB model [31] with different star formation rate factors for GRBs [31, 32, 33]. If UHECRs originate from long duration GRBs, then the...leptonic models are pitted against hadronic models , and found to be energetically favored. Interpretation of the Fermi data on GRBs helps establish

  7. FERMI-LAT Observations of Galatic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2010-01-01

    This slide presentation reviews the use of the Large Area Telescope on the Fermi Observatory observations of Galactic Transients. LAT all-sky monitoring is producing spectacular results for the GeV transient sky: (1) New blazars and unidentified transients (2) Probing the jet of the Cygnus X-3 microquasar (3) Discovery of gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula.

  8. Ideas by Szilard, physics by Fermi

    SciTech Connect

    Lanouette, W.

    1992-12-01

    An excerpt from William Lanouette's book Genius in the shadows: A biography of Leo Szilard, the man behind the bomb (with Bela Silard). This article covers Szilard's life from early 1933, when he first began contemplating fleeing Germany, to the first self-sustaining nuclear chain reaction on December 2, 1942, and includes a description of his partnership with Enrico Fermi. Part of a series of articles in this magazine commemorating the 50th anniversary of the first controlled chain reaction.

  9. Pairing in a dry Fermi sea

    SciTech Connect

    Maier, Thomas A.; Staar, Peter; Mishra, V.; Chatterjee, Utpal; Campuzano, J. C.; Scalapino, Douglas J.

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  10. Cinema, Fermi problems and general education

    NASA Astrophysics Data System (ADS)

    Efthimiou, C. J.; Llewellyn, R. A.

    2007-05-01

    During the past few years the authors have developed a new approach to the teaching of physical science, a general education course typically found in the curricula of nearly every college and university. This approach, called Physics in Films (Efthimiou and Llewellyn 2006 Phys. Teach. 44 28-33), uses scenes from popular films to illustrate physical principles and has excited student interest and improved student performance. A similar approach at the senior/high-school level, nicknamed Hollywood Physics, has been developed by Chandler (2006 Phys. Teach. 44 290-2 2002 Phys. Teach. 40 420-4). The two approaches may be considered complementary as they target different student groups. The analyses of many of the scenes in Physics in Films are a direct application of Fermi calculations—estimates and approximations designed to make solutions of complex and seemingly intractable problems understandable to the student non-specialist. The intent of this paper is to provide instructors with examples they can use to develop skill in recognizing Fermi problems and making Fermi calculations in their own courses.

  11. Fermi/GBM Results of Magnetars

    NASA Technical Reports Server (NTRS)

    Kouveliotou, chryssa

    2011-01-01

    Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

  12. Signatures of an annular Fermi sea

    NASA Astrophysics Data System (ADS)

    Jo, Insun; Liu, Yang; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.; Winkler, R.

    2017-01-01

    The concept of a Fermi surface, the constant-energy surface containing all the occupied electron states in momentum, or wave-vector (k ) , space plays a key role in determining electronic properties of conductors. In two-dimensional (2D) carrier systems, the Fermi surface becomes a contour which, in the simplest case, encircles the occupied states. In this case, the area enclosed by the contour, which we refer to as the Fermi sea (FS), is a simple disk. Here we report the observation of an FS with a new topology, namely, an FS in the shape of an annulus. Such an FS is expected in a variety of 2D systems where the energy band dispersion supports a ring of extrema at finite k , but its experimental observation has been elusive. Our study provides (1) theoretical evidence for the presence of an annular FS in 2D hole systems confined to wide GaAs quantum wells and (2) experimental signatures of the onset of its occupation as an abrupt rise in the sample resistance, accompanied by a sudden appearance of Shubnikov-de Haas oscillations at an unexpectedly high frequency whose value does not simply correspond to the (negligible) density of holes contained within the annular FS.

  13. A Probabilistic Analysis of the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Solomonides, Evan; Terzian, Yervant

    2016-06-01

    The Fermi paradox uses an appeal to the mediocrity principle to make it seem counterintuitive that humanity has not been contacted by extraterrestrial intelligence. A numerical, statistical analysis was conducted to determine whether this apparent loneliness is, in fact, unexpected. An inequality was derived to relate the frequency of life arising and developing technology on a suitable planet in the galaxy; the average length of time since the first broadcast of such a civilization; and a constant term. An analysis of the sphere reached thus far by human communication was also conducted, considering our local neighborhood and planets of particular interest. These analyses both conclude that the Fermi paradox is not, in fact, unexpected. By the mediocrity principle and numerical modeling, it is actually unlikely that the Earth would have been reached by extraterrestrial communication at this point. We predict that under 1% of the galaxy has been reached at all thus far, and we do not anticipate to be reached until approximately 50% of stars/planets have been reached. We offer a prediction that we should not expect this until at least 1,500 years in the future. Thus the Fermi paradox is not a shocking observation- or lack thereof- and humanity may very well be contacted within our species’ lifespan (we can begin to expect to be contacted 1,500 years in the future).

  14. The Sustainability Solution To The Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Haqq-Misra, J. D.; Baum, S. D.

    No present observations suggest a technologically advanced extraterrestrial intelligence (ETI) has spread through the galaxy. However, under commonplace assumptions about galactic civilization formation and expansion, this absence of observation is highly unlikely. This improbability is the heart of the Fermi Paradox. The Fermi Paradox leads some to conclude that humans have the only advanced civilization in this galaxy, either because civilization formation is very rare or because intelligent civilizations inevitably destroy themselves. In this paper, we argue that this conclusion is premature by introducing the “Sustainability Solution” to the Fermi Paradox, which questions the Paradox's assumption of faster ( e.g. exponential) civilization growth. Drawing on insights from the sustainability of human civilization on Earth, we propose that faster-growth may not be sustainable on the galactic scale. If this is the case, then there may exist ETI that have not expanded throughout the galaxy or have done so but collapsed. These possibilities have implications for both searches for ETI and for human civilization management.

  15. Pairing in a dry Fermi sea

    PubMed Central

    Maier, T. A; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-01-01

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and −k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability. PMID:27312569

  16. Pairing in a dry Fermi sea

    DOE PAGES

    Maier, Thomas A.; Staar, Peter; Mishra, V.; ...

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  17. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; ...

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  18. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    SciTech Connect

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui -Hua

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  19. Probing the Contact Locally in a Trapped Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Paudel, Rabin; Sagi, Yoav; Drake, Tara; Jin, Deborah

    2013-03-01

    The inherent density inhomogeneity of a trapped gas can complicate interpretation of experiments and can wash out sharp features. This is especially important for a Fermi gas, where interaction effects as well as the local Fermi energy, or Fermi momentum, depend on the density. We report on experiments that use optical pumping with shaped light beams to spatially select the center part of a trapped gas for probing. This technique is compatible with momentum resolved measurements. For a weakly interacting Fermi gas of 40K atoms, we present measurements of the momentum distribution that reveal for the first time a sharp Fermi surface. We then apply this technique to a strongly interacting Fermi gas at the Feshbach resonance, where we measured the temperature dependence of the Tan's contact locally in the trapped gas.

  20. [Analysis of spectral intensity of fermi resonance of molecules].

    PubMed

    Jiang, Yong-heng; Gao, Shu-qin; Li, Zhan-long; Cao, Biao; Li, Zuo-wei

    2010-01-01

    Raman spectra of liquid carbon disulfide (CS) and carbon tetrachloride (CCl4) were measured. And the spectral intensity was analyzed using the J. F. Bertran theory and the group theory. The rule about Fermi resonance was obtained from the Raman spectra of carbon disulfide (CS) and carbon tetrachloride (CCL4): (1) The energy can transfer between a fundamental and an overtone frequency about Fermi resonance; the two spectra have the same intensity. The spectral intensity of the two spectra was equal (R=1) about Fermi resonance, when the difference between fundamental of Fermi resonance and overtone of Fermi resonance was very small. (2) The intensity of overtone is stronger than that of fundamental's. (3) The spectrum of Fermi resonance was observed, but the fundamental frequency was not. This article has very good reference value for the assignments in the molecular structure and the research of contents.

  1. Fermi Surface Evolution and Luttinger Theorem in NaxCoO2: A Systematic Photoemission Study

    SciTech Connect

    Yang, H. B.; Pan, Z. H.; Sekharan, A. K. P.; Sato, T.; Souma, S.; Takahashi, T.; Jin, Rongying; Sales, Brian C; Mandrus, David; Fedorov, A. V.; Wang, Z.; Ding, H.

    2005-01-01

    We report a systematic angle-resolved photoemission study on Na{sub x}CoO{sub 2} for a wide range of Na concentrations (0.3 {le} x {le} 0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around {Gamma} and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e{prime}{sub g} band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to sink below the Fermi energy in a manner almost independent of the doping and temperature.

  2. Fermi Large Area Telescope First Source Catalog

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Belli, F.; Berenji, B.; Bisello, D.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T. H.; Busetto, G.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Campana, R.; Canadas, B.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Ceccanti, M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Cillis, A. N.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Corbet, R.; Davis, D. S.; DeKlotz, M.; den Hartog, P. R.; Dermer, C. D.; de Angelis, A.; de Luca, A.; de Palma, F.; Digel, S. W.; Dormody, M.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Fabiani, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Healey, S. E.; Hill, A. B.; Horan, D.; Hughes, R. E.; Iafrate, G.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Landriu, D.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Marangelli, B.; Marelli, M.; Massaro, E.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Minuti, M.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakajima, H.; Nakamori, T.; Naumann-Godo, M.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paccagnella, A.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Pinchera, M.; Piron, F.; Porter, T. A.; Poupard, L.; Rainò, S.; Rando, R.; Ray, P. S.; Razzano, M.; Razzaque, S.; Rea, N.; Reimer, A.; Reimer, O.; Reposeur, T.; Ripken, J.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Romani, R. W.; Roth, M.; Sadrozinski, H. F.-W.; Salvetti, D.; Sanchez, D.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Scolieri, G.; Sgrò, C.; Shaw, M. S.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Starck, J.-L.; Stephens, T. E.; Striani, E.; Strickman, M. S.; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinebra, F.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Van Etten, A.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wallace, E.; Wang, P.; Watters, K.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Ziegler, M.; Fermi LAT Collaboration

    2010-06-01

    We present a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), during the first 11 months of the science phase of the mission, which began on 2008 August 4. The First Fermi-LAT catalog (1FGL) contains 1451 sources detected and characterized in the 100 MeV to 100 GeV range. Source detection was based on the average flux over the 11 month period, and the threshold likelihood Test Statistic is 25, corresponding to a significance of just over 4σ. The 1FGL catalog includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and power-law spectral fits as well as flux measurements in five energy bands for each source. In addition, monthly light curves are provided. Using a protocol defined before launch we have tested for several populations of gamma-ray sources among the sources in the catalog. For individual LAT-detected sources we provide firm identifications or plausible associations with sources in other astronomical catalogs. Identifications are based on correlated variability with counterparts at other wavelengths, or on spin or orbital periodicity. For the catalogs and association criteria that we have selected, 630 of the sources are unassociated. Care was taken to characterize the sensitivity of the results to the model of interstellar diffuse gamma-ray emission used to model the bright foreground, with the result that 161 sources at low Galactic latitudes and toward bright local interstellar clouds are flagged as having properties that are strongly dependent on the model or as potentially being due to incorrectly modeled structure in the Galactic diffuse emission.

  3. Fermi surface and electron correlation effects of ferromagnetic iron

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Hoinkis, M.; Rotenberg, Eli; Blaha, P.; Claessen, R.

    2005-10-01

    The electronic band structure of bulk ferromagnetic iron is explored by angle-resolved photoemission for electron correlation effects. Fermi surface cross sections as well as band maps are contrasted with density functional calculations. The Fermi vectors and band parameters obtained from photoemission and their prediction from band theory are analyzed in detail. Generally good agreement is found for the Fermi surface. A bandwidth reduction for shallow bands of ˜30% is observed. Additional strong quasiparticle renormalization effects are found near the Fermi level, leading to a considerable mass enhancement. The role of electronic correlation effects and the electronic coupling to magnetic excitations is discussed in view of the experimental results.

  4. Stability and single-particle properties of bosonized Fermi liquids

    NASA Astrophysics Data System (ADS)

    Houghton, A.; Kwon, H.-J.; Marston, J. B.

    1994-07-01

    We study the stability and single-particle properties of Fermi liquids in spatial dimensions greater than one via bosonization. For smooth nonsingular Fermi-liquid interactions we obtain Shankar's renormalization-group flows to second order in the BCS coupling and reproduce well-known results for quasiparticle lifetimes. We demonstrate by explicit calculation that spin-charge separation does not occur when the Fermi-liquid interactions are regular. We also explore the relationship between quantized bosonic excitations and zero-sound modes and present a concise derivation of both the spin and the charge collective-mode equations. Finally we discuss some aspects of singular Fermi-liquid interactions.

  5. Nonlocal Poisson-Fermi model for ionic solvent.

    PubMed

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  6. Note on Generalized Fermi-Dirac Function and Its Derivatives

    NASA Astrophysics Data System (ADS)

    Gong, Zhigang; Zejda, Ladislav; Däppen, Werner

    2000-04-01

    Generalized Fermi-Dirac function and its derivatives are important in evaluating the thermodynamic functions of partially degenerate electrons in hot stellar plasmas. Because of the nature of the Fermi-Dirac functions, analytic expressions are only available for certain extreme cases, and regular numeric methods fail when degeneracy and temperature are relatively high (but not high enough to use approximative formulae). In this paper, recursion relations of the generalized Fermi-Dirac function are discussed, and an effective numerical method to evaluate the derivatives of the generalized Fermi-Dirac function is given, following the Aparicio (1998) scheme. Finally, accuracy and domain of reliability of some popular analytic approximations are investigated.

  7. Nonlocal Poisson-Fermi model for ionic solvent

    NASA Astrophysics Data System (ADS)

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  8. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R. D.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed 79 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds.

  9. Fermi-LAT Observations of Galactic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2011-01-01

    This slide presentation reviews the observations of Galactic transients by the Large Area Telescope (LAT) on the Fermi Gamma Ray Space Telescope. The LAT is producing spectacular results for the GeV transient sky, some of which are shown and reviewed. Some of the results in the GeV range that are discussed in this presentation are: (1) New blazars and unidentified transients (2) the jet of the Cygnus X-3 microquasar (3) gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula

  10. Bragg spectroscopy of strongly interacting Fermi gases

    NASA Astrophysics Data System (ADS)

    Lingham, M. G.; Fenech, K.; Peppler, T.; Hoinka, S.; Dyke, P.; Hannaford, P.; Vale, C. J.

    2016-10-01

    This article provides an overview of recent developments and emerging topics in the study of two-component Fermi gases using Bragg spectroscopy. Bragg scattering is achieved by exposing a gas to two intersecting laser beams with a slight frequency difference and measuring the momentum transferred to the atoms. By varying the Bragg laser detuning, it is possible to measure either the density or spin response functions which characterize the basic excitations present in the gas. Specifically, one can measure properties such as the dynamic and static structure factors, Tan's universal contact parameter and observe signatures for the onset of pair condensation locally within a gas.

  11. Transport phenomena in correlated quantum liquids: Ultracold Fermi gases and F/N junctions

    NASA Astrophysics Data System (ADS)

    Li, Hua

    Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal-metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low

  12. Fermi LAT Observations of LS 5039

    SciTech Connect

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B.M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R.D.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; /more authors..

    2012-03-29

    The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 {+-} 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300 GeV) of 4.9 {+-} 0.5(stat) {+-} 1.8(syst) x 10{sup -7} photon cm{sup -2} s{sup -1}, with a cutoff at 2.1 {+-} 0.3(stat) {+-} 1.1(syst) GeV and photon index {Gamma} = 1.9 {+-} 0.1(stat) {+-} 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.

  13. Pair condensation in a finite Fermi system

    SciTech Connect

    Sambataro, M.

    2007-05-15

    The lowest seniority-zero eigenstates of an exactly solvable multilevel pairing Hamiltonian for a finite Fermi system are examined at different pairing regimes. After briefly reviewing the form of the eigenstates in the Richardson formalism, we discuss a different representation of these states in terms of the collective pairs resulting from the diagonalization of the Hamiltonian in a space of two degenerate time-reversed fermions. We perform a two-fold analysis by working both in the fermionic space of these collective pairs and in a space of corresponding elementary bosons. On the fermionic side, we monitor the variations which occur, with increasing the pairing strength, in the structure of both these collective pairs and the lowest eigenstates. On the bosonic side, after reviewing a fermion-boson mapping procedure, we construct exact images of the fermion eigenstates and study their wave function. The analysis allows a close examination of the phenomenon of pair condensation in a finite Fermi system and gives new insights into the evolution of the lowest (seniority-zero) excited states of a pairing Hamiltonian from the unperturbed regime up to a strongly interacting one.

  14. Fermi level stabilization energy in cadmium oxide

    SciTech Connect

    Speaks, D. T.; Mayer, M. A.; Yu, K. M.; Mao, S. S.; Haller, E. E.; Walukiewicz, W.

    2010-04-08

    We have studied the effects of high concentrations of native point defects on the electrical and optical properties of CdO. The defects were introduced by irradiation with high energy He+, Ne+, Ar+ and C+ ions. Increasing the irradiation damage with particles heavier than He+ increases the electron concentration until a saturation level of 5x1020 cm-3 is reached. In contrast, due to the ionic character and hence strong dynamic annealing of CdO, irradiation with much lighter He+ stabilizes the electron concentration at a much lower level of 1.7x1020 cm-3. A large shift of the optical absorption edge with increasing electron concentration in irradiated samples is explained by the Burstein-Moss shift corrected for electron-electron and electron-ion interactions. The saturation of the electron concentration and the optical absorption edge energy are consistent with a defect induced stabilization of the Fermi energy at 1 eV above the conduction band edge. The result is in a good agreement with previously determined Fermi level pinning energies on CdO surfaces. The results indicate that CdO shares many similarities with InN, as both materials exhibit extremely large electron affinities and an unprecedented propensity for n-type conductivity.

  15. Orientifolding of the ABJ Fermi gas

    NASA Astrophysics Data System (ADS)

    Okuyama, Kazumi

    2016-03-01

    The grand partition functions of ABJ theory can be factorized into even and odd parts under the reflection of fermion coordinate in the Fermi gas approach. In some cases, the even/odd part of ABJ grand partition function is equal to that of {N}=5O(n)× USp({n}^') theory, hence it is natural to think of the even/odd projection of grand partition function as an orientifolding of ABJ Fermi gas system. By a systematic WKB analysis, we determine the coefficients in the perturbative part of grand potential of such orientifold ABJ theory. We also find the exact form of the first few "half-instanton" corrections coming from the twisted sector of the reflection of fermion coordinate. For the Chern-Simons level k = 2 ,4 ,8 we find closed form expressions of the grand partition functions of orientifold ABJ theory, and for k = 2 , 4 we prove the functional relations among the grand partition functions conjectured in arXiv:1410.7658.

  16. Lasing in Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Kochereshko, Vladimir P.; Durnev, Mikhail V.; Besombes, Lucien; Mariette, Henri; Sapega, Victor F.; Askitopoulos, Alexis; Savenko, Ivan G.; Liew, Timothy C. H.; Shelykh, Ivan A.; Platonov, Alexey V.; Tsintzos, Simeon I.; Hatzopoulos, Z.; Savvidis, Pavlos G.; Kalevich, Vladimir K.; Afanasiev, Mikhail M.; Lukoshkin, Vladimir A.; Schneider, Christian; Amthor, Matthias; Metzger, Christian; Kamp, Martin; Hoefling, Sven; Lagoudakis, Pavlos; Kavokin, Alexey

    2016-01-01

    Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling.

  17. Fermi's Paradox - The Last Challenge For Copernicanism?

    NASA Astrophysics Data System (ADS)

    Cirkovic, M. M.

    2009-06-01

    We review Fermi's paradox (or the "Great Silence" problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi's paradox is certain to tell us something about the future of humanity. Already more than three quarters of century old puzzle -- and a quarter of century since the last major review paper in the field by G. David Brin -- has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built in various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypotheses gives, on the balance, the strongest justification to optimism regarding our current and near-future SETI efforts.

  18. Density functional theory for atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Ma, Ping Nang; Pilati, Sebastiano; Troyer, Matthias; Dai, Xi

    2012-08-01

    The interplay between interaction and inhomogeneity for electrons in solids generates many interesting phenomena, including insulating and metallic behaviour, magnetism, superconductivity, quantum criticality and more exotic phases. Many of the same phenomena appear in ultracold fermionic atoms in optical lattices, which provide clean, controlled and tunable `quantum simulators' to explore the intriguing physics of fermionic systems. Although density functional theory (DFT) is widely used to calculate material properties, it has not yet been applied to cold atomic gases in optical lattices. Here we present a new density functional for short-range interactions (as opposed to Coulomb interactions of electrons), which renders DFT suitable for atomic Fermi gases. This grants us access to an extensive toolset, previously developed for materials simulations, to calculate the static and dynamic properties of atomic Fermi gases in optical lattices and external potentials. Ultracold atom quantum simulators can in turn be used to explore limitations of DFT functionals, and to further improve hybrid functionals, thus forming a bridge between materials simulations and atomic physics.

  19. Lasing in Bose-Fermi mixtures

    PubMed Central

    Kochereshko, Vladimir P.; Durnev, Mikhail V.; Besombes, Lucien; Mariette, Henri; Sapega, Victor F.; Askitopoulos, Alexis; Savenko, Ivan G.; Liew, Timothy C. H.; Shelykh, Ivan A.; Platonov, Alexey V.; Tsintzos, Simeon I.; Hatzopoulos, Z.; Savvidis, Pavlos G.; Kalevich, Vladimir K.; Afanasiev, Mikhail M.; Lukoshkin, Vladimir A.; Schneider, Christian; Amthor, Matthias; Metzger, Christian; Kamp, Martin; Hoefling, Sven; Lagoudakis, Pavlos; Kavokin, Alexey

    2016-01-01

    Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling. PMID:26822483

  20. Fermi (nee GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steve

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  1. Fermi (Formerly GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  2. Fermi Mission Results, Status, and Plans

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  3. The first Fermi LAT supernova remnant catalog

    DOE PAGES

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidatesmore » falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.« less

  4. Ther FERMI FEL project at TRIESTE

    SciTech Connect

    Walker, R.P.; Bulfone, D.; Cargnello, F.

    1995-12-31

    The goal of the FERMI project - Free Electron Radiation and Matching Instrumentation - is to construct a new user facility for FEL radiation beams covering a broad spectral range (2-250 {mu}m) to complement the high brightness VUV/Soft-Xray radiation available from the ELETTRA synchrotron radiation facility at Trieste. A unique feature of the project will be the possibility of carrying out {open_quote}pump-probe{close_quote} experiments using synchronized radiation beams from FERMI and ELETTRA on the same sample. The project was launched at a meeting with Italian FEL experts held in Trieste on the 18th November 1994, chaired by C. Rubbia, as a collaboration between Sincrotrone Trieste, ENEA (Frascati), INFN (Frascati) and the University of Naples (Department of Electronic Engineering). The facility will make use of an existing linac, that forms part of the ELETTRA injection system, and a hall into which the beam can be extracted. In addition, for the first phase of the project equipment will be used from the suspended INFN/ENEA {open_quote}SURF{close_quote} FEL experiment, including the undulator, beam transport magnets and optical cavity. In this first International FEL Conference report on the project, we summarize the main features of the project, concentrating in particular on the most recent activities, including: results of measurements of the linac beam in the FEL mode of operation, further studies of the electron beam transport system including possibilities for bunch length manipulations, and further numerical calculations of the FEL performance.

  5. Fermi Liquid Instabilities in the Spin Channel

    SciTech Connect

    Wu, Congjun; Sun, Kai; Fradkin, Eduardo; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-16

    We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves (F{sub l}{sup a} (l > 0)). The ordered phases are classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-phases. The Fermi surfaces in the {alpha}-phases exhibit spontaneous anisotropic distortions, while those in the {beta}-phases remain circular or spherical with topologically non-trivial spin configurations in momentum space. In the {alpha}-phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have nearly isotropic underdamped dispersion relation at small propagating wavevectors. Due to the coupling to the Goldstone modes, the spin wave spectrum develops resonance peaks in both the {alpha} and {beta}-phases, which can be detected in inelastic neutron scattering experiments. In the p-wave channel {beta}-phase, a chiral ground state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.

  6. Massive Fermi gas in the expanding universe

    NASA Astrophysics Data System (ADS)

    Trautner, Andreas

    2017-03-01

    The behavior of a decoupled ideal Fermi gas in a homogeneously expanding three-dimensional volume is investigated, starting from an equilibrium spectrum. In case the gas is massless and/or completely degenerate, the spectrum of the gas can be described by an effective temperature and/or an effective chemical potential, both of which scale down with the volume expansion. In contrast, the spectrum of a decoupled massive and non-degenerate gas can only be described by an effective temperature if there are strong enough self-interactions such as to maintain an equilibrium distribution. Assuming perpetual equilibration, we study a decoupled gas which is relativistic at decoupling and then is red-shifted until it becomes non-relativistic. We find expressions for the effective temperature and effective chemical potential which allow us to calculate the final spectrum for arbitrary initial conditions. This calculation is enabled by a new expansion of the Fermi-Dirac integral, which is for our purpose superior to the well-known Sommerfeld expansion. We also compute the behavior of the phase space density under expansion and compare it to the case of real temperature and real chemical potential. Using our results for the degenerate case, we also obtain the mean relic velocity of the recently proposed non-thermal cosmic neutrino background.

  7. Blue Fermi flat spectrum radio quasars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Foschini, L.; Sbarrato, T.; Ghirlanda, G.; Maraschi, L.

    2012-09-01

    Many blazars detected by the Fermi satellite, observed spectroscopically in the optical, are line-less, and have been classified as BL Lac objects. Optical-ultraviolet (UV) photometry of nearly 100 of them allowed us to determine the redshift for a handful of objects and redshift upper limits in the great majority. A few of these are candidates to be 'blue quasars', namely flat spectrum radio quasars whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies. In turn, this requires relatively weak radiative cooling, a condition that can be met if the main radiative dissipation of the jet power occurs outside the broad-line region. We confirm this hypothesis by studying and modelling the spectral energy distributions of the four 'blue quasars' recently discovered. Furthermore, we discuss the distribution of Fermi blazars in the γ-ray spectral index-γ-ray luminosity plane, and argue that 'blue quasars' objects are a minority within the blazar populations.

  8. Spectral functions in ultracold Fermi gases

    NASA Astrophysics Data System (ADS)

    Schneider, William; Randeria, Mohit

    2011-03-01

    We study the fermion spectral function in the superfluid state across the BEC-BCS crossover and in the normal Fermi liquid phase in highly imbalanced Fermi gases. We focus on features that can be measured in momentum-resolved radio frequency spectroscopy experiments. We go beyond mean field theory and include the effects of Gaussian order parameter fluctuations in a manner that gives excellent agreement with asymptotically exact results for the T = 0 equation of state in the BEC and BCS limits, as well as quantum Monte Carlo (QMC) results near unitarity. We show that sharp Bogoliubov quasiparticles, with a substantial coherent spectral weight, exist near unitarity. We argue that this is true generally even beyond the Gaussian approximation. In addition, quasiparticle scattering and interaction with collective modes produces incoherent spectral weight. We show that the dispersion is strongly renormalized at unitarity with its minimum shifted up from its mean field value √{ 2 mμ } and compare our results with existing QMC data. We discuss how the spectral function changes qualitatively compared with its mean field form as 1 / (kF a) increases and the chemical potential changes sign. Supported by NSF-DMR 0706203 and ARO W911NF-08-1-0338.

  9. THE SPECTRAL INDEX PROPERTIES OF FERMI BLAZARS

    SciTech Connect

    Fan, J. H.; Yang, J. H.; Yuan, Y. H.; Wang, J.; Gao, Y.

    2012-12-20

    In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi {gamma}-ray data is compiled to investigate the correlation both between the X-ray spectral index and the {gamma}-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes {alpha}{sub X}, {alpha}{sub {gamma}}, {alpha}{sub X{gamma}}, and {alpha}{sub {gamma}X{gamma}} for different subclasses. We also investigated the correlation between the X-ray and the {gamma}-ray luminosity. The following results have been obtained. Our analysis indicates that an anti-correlation exists between the X-ray and the {gamma}-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs.

  10. LETTERS AND COMMENTS: Enrico Fermi: a great teacher

    NASA Astrophysics Data System (ADS)

    Lan, Boon Leong

    2002-09-01

    Enrico Fermi was not only a great theoretical and experimental physicist but a great teacher as well. This article highlights Fermi's approaches in both his formal and informal teaching, and as a thesis advisor. The great teacher inspires - William Arthur Ward

  11. 76 FR 1197 - Detroit Edison Company, FERMI 2; Exemption

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-07

    ... From the Federal Register Online via the Government Publishing Office NUCLEAR REGULATORY COMMISSION Detroit Edison Company, FERMI 2; Exemption 1.0 Background Detroit Edison Company (DECo) (the licensee) is the holder of Facility Operating License No. NFP-43 which authorizes operation of the Fermi...

  12. Collisional Properties of a Polarized Fermi Gas with Resonant Interactions

    SciTech Connect

    Bruun, G. M.; Recati, A.; Stringari, S.; Pethick, C. J.; Smith, H.

    2008-06-20

    Highly polarized mixtures of atomic Fermi gases constitute a novel Fermi liquid. We demonstrate how information on thermodynamic properties may be used to calculate quasiparticle scattering amplitudes even when the interaction is resonant and apply the results to evaluate the damping of the spin dipole mode. We estimate that under current experimental conditions the mode would be intermediate between the hydrodynamic and collisionless limits.

  13. "Where is Everybody?" An Account of Fermi's Question

    DOE R&D Accomplishments Database

    Jones, E. M.

    1985-03-01

    Enrico Fermi's famous question, now central to debates about the prevalence of extraterrestrial civilizations, arose during a luncheon conversation with Emil Konopinski, Edward Teller, and Herbert York in the summer of 1950. Fermi's companions on that day have provided accounts of the incident.

  14. Changing Horses in Midstream: Fermi LAT Computing and SCons

    NASA Astrophysics Data System (ADS)

    Bogart, J. R.; Golpayegani, N.

    2011-07-01

    (For the Fermi LAT Collaboration) Several years into GLAST (now Fermi) offline software development it became evident we would need a replacement for our original build system, the Configuration Management Tool (CMT) developed at CERN, in order to support Mac users and to keep pace with newer compilers and operating system versions on our traditional platforms, Linux and Windows. The open source product SCons emerged as the only viable alternative and development began in earnest several months before Fermi's successful launch in June of 2008. Over two years later the conversion is nearing completion. This paper describes the conversion to and our use of SCons, concentrating on the resulting environment for users and developers and how it was achieved. Topics discussed include SCons and its interaction with Fermi code, GoGui, a cross-platform gui for Fermi developers, and issues specific to Windows developer support.

  15. Momentum sharing in imbalanced Fermi systems

    DOE PAGES

    Hen, O.; Sargsian, M.; Weinstein, L. B.; ...

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron starsmore » and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.« less

  16. Momentum sharing in imbalanced Fermi systems

    SciTech Connect

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.

  17. Multiwavelength Challenges in the Fermi Era

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2010-01-01

    The gamma-ray surveys of the sky by AGILE and the Fermi Gamma-ray Space Telescope offer both opportunities and challenges for multiwavelength and multi-messenger studies. Gamma-ray bursts, pulsars, binary sources, flaring Active Galactic Nuclei, and Galactic transient sources are all phenomena that can best be studied with a wide variety of instruments simultaneously or contemporaneously. From the gamma-ray side, a principal challenge is the latency from the time of an astrophysical event to the recognition of this event in the data. Obtaining quick and complete multiwavelength coverage of gamma-ray sources of interest can be difficult both in terms of logistics and in terms of generating scientific interest.

  18. High Energy Neutrinos from the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Razzaque, Soebur; Lunardini, Cecilia

    2012-03-01

    Recent discovery of two gamma-ray emitting bubble-shaped structures (Fermi Bubbles) at the Galactic center opens up a possibility to detect high-energy neutrinos from them as well, if the observed gamma rays have hadronic origin. This new predicted Galactic neutrino flux is hard, following gamma-ray data, compared to the atmospheric neutrino flux and can be detected with a kilometer scale neutrino telescope in the northern hemisphere, such as the planned KM3NeT, above 20-50 TeV. IceCube Neutrino Observatory at the South pole can also provide interesting constraints on the flux model. A detection or exclusion of this neutrino flux can discriminate between a leptonic or hadronic origin of the gamma-rays, as well as bring unique information on the activities at the Galactic center.

  19. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; von Kienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed more than 77 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds. The energy spectra of some TGFs have strong 511 keV positron annihilation lines, indicating that these TGFs contain a large fraction of positrons

  20. Fermi's golden rule in the Wigner representation

    NASA Astrophysics Data System (ADS)

    Segev, Bilha

    2003-06-01

    When Fermi's golden rule (FGR) is studied in the Wigner representation, the transition rate from an initial pure state or from an initial thermal distribution into a quasicontinuum manifold of degenerate states is given by an overlap integral of Wigner functions in phase space. In the semiclassical limit the transition rate is obtained by integrating over the regions in phase space where the energy difference between the initial and final potential surfaces is equal to the available energy. The integral is weighted by the initial probability density to be at that phase-space region. The classical limit of FGR is thus both simple and intuitive. In one dimension a relation to the Landau-Zener-Stuckelberg formula is established. The multi-dimensional case is considered by induction, proving that for separable multi-dimensional systems deviations of the logarithm of the transition rate from its classical limit scale at worst linearly with the dimension.

  1. Fermi liquid viscosity in a finite geometry

    NASA Technical Reports Server (NTRS)

    Jaffe, J. E.

    1979-01-01

    Forced flow of a Fermi liquid is studied for a cell geometry consisting of two planes with a separation on the order of the mean free path. An approximate transport equation is used to derive an integral equation for the velocity profile, which is solved numerically. Results for the total flux through the cell, which determines the dissipation, are given as a function of the Knudsen number kappa (ratio of cell thickness to mean free path). Effects of specular reflection at the boundaries are considered. It is found that the dissipation has a minimum at kappa of 1/2, and behaves linearly for kappa not less than 3. Implications for present experimentation are discussed.

  2. The Mirage of the Fermi Scale

    NASA Astrophysics Data System (ADS)

    Antipin, Oleg; Sannino, Francesco; Tuominen, Kimmo

    2013-09-01

    The discovery of a light Higgs boson at Large Hadron Collider may be suggesting that we need to revise our model building paradigms to understand the origin of the weak scale. We explore the possibility that the Fermi scale is not fundamental but rather a derived one, i.e. a low energy mirage. We show that this scenario emerges in a very natural way in models previously used to break the electroweak symmetry dynamically and suggest a simple dynamical framework for this idea. In our model the electroweak scale results from the interplay between two very high energy scales, one typically of the order of ΛUV 1010GeV and the other around MU 1016GeV, although other values are also possible.

  3. Fermi liquid viscosity in a finite geometry

    NASA Technical Reports Server (NTRS)

    Jaffe, J. E.

    1979-01-01

    Forced flow of a Fermi liquid is studied for a cell geometry consisting of two planes with a separation on the order of mean free path. An approximate transport equation is used to derive an integral equation for the velocity profile, which is solved numerically. Results for the total flux through the cell, which determines the dissipation, are given as a function of the Knudsen number N (ratio of cell thickness to mean free path). Effects of specular reflection at the boundaries are considered. It is found that the dissipation has a minimum at N approximately equal to 1/2, and behaves linearly for N greater than or equal to 3. Implications for present experimentation are discussed.

  4. Entanglement rules for holographic Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Roychowdhury, Dibakar

    2016-08-01

    In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

  5. The Gamma-ray Universe through Fermi

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2012-01-01

    Gamma rays, the most powerful form of light, reveal extreme conditions in the Universe. The Fermi Gamma-ray Space Telescope and its smaller cousin AGILE have been exploring the gamma-ray sky for several years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge ga.nuna-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

  6. Pairing phenomena in strongly correlated Fermi liquids

    NASA Astrophysics Data System (ADS)

    Krotscheck, E.; Smith, R. A.; Jackson, A. D.

    1981-12-01

    The correlated-basis-function method is extended to deal with pairing phenomena in strongly correlated Fermi liquids. With a variational ansatz for the model wave function we derive the "correlated" analog of the conventional Bardeen-Cooper-Schrieffer (or Balian-Werthamer), Anderson-Brinkman-Morel theory of pairing. A suitable (and well-controlled) set of approximations brings the theory into a form identical to the conventional theories, but with the bare interaction replaced by a weak effective interaction and the bare single-particle energies replaced by an effective single-particle spectrum. As usual, liquid 3He provides a very stringent test of the theory, as both the interaction and the experimental facts are pretty clear. The variational estimates for the pairing interaction are improved by nonorthogonal perturbation theory. We find the expected enhancement of the attraction in P waves, although the restriction to effective two-body interactions appears to be insufficient to generate P-wave pairing.

  7. The Gamma-ray Sky with Fermi

    NASA Technical Reports Server (NTRS)

    Thompson, David

    2012-01-01

    Gamma rays reveal extreme, nonthermal conditions in the Universe. The Fermi Gamma-ray Space Telescope has been exploring the gamma-ray sky for more than four years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge gamma-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

  8. From ultracold Fermi Gases to Neutron Stars

    NASA Astrophysics Data System (ADS)

    Salomon, Christophe

    2012-02-01

    Ultracold dilute atomic gases can be considered as model systems to address some pending problem in Many-Body physics that occur in condensed matter systems, nuclear physics, and astrophysics. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold Bose and Fermi gases [1,2,3]. This method allows stringent tests of recent many-body theories. For attractive spin 1/2 fermions with tunable interaction (^6Li), we will show that the gas thermodynamic properties can continuously change from those of weakly interacting Cooper pairs described by Bardeen-Cooper-Schrieffer theory to those of strongly bound molecules undergoing Bose-Einstein condensation. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas. Surprisingly, the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory [3] and we localize the superfluid phase transition. A detailed comparison with theories including recent Monte-Carlo calculations will be presented. Moving away from the unitary gas, the Lee-Huang-Yang and Lee-Yang beyond-mean-field corrections for low density bosonic and fermionic superfluids are quantitatively measured for the first time. Despite orders of magnitude difference in density and temperature, our equation of state can be used to describe low density neutron matter such as the outer shell of neutron stars. [4pt] [1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, Nature 463, 1057 (2010) [0pt] [2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, Science 328, 729 (2010) [0pt] [3] S. Nascimbène, N. Navon, S. Pilati, F. Chevy, S. Giorgini, A. Georges, and C. Salomon, Phys. Rev. Lett. 106, 215303 (2011)

  9. Thomas-Fermi and Thomas-Fermi-Dirac models in two-dimension - Effect of strong quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    De, Sanchari; Chakrabarty, Somenath

    2017-01-01

    Using Thomas-Fermi (TF) and Thomas-Fermi-Dirac (TFD) models, we have investigated the properties of electron gas inside two-dimensional (2D) Wigner-Seitz (WS) cells in presence of a strong orthogonal quantizing magnetic field. The electron-electron Coulomb exchange interaction in quasi-2D case is obtained. The exact form of exchange term in 2D is derived making the width of the system tending to zero. Further, using the exchange term, the Thomas-Fermi-Dirac equation in 2D is established. It has been observed that only the ionized WS cell can have finite radius in the Thomas-Fermi model, even in presence of a strong quantizing magnetic field. On the other hand, in the Thomas-Fermi-Dirac model a neutral WS cell can have finite radius.

  10. Sub-saturation matter in compact stars: Nuclear modelling in the framework of the extended Thomas-Fermi theory

    SciTech Connect

    Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

    2015-02-24

    A recently introduced analytical model for the nuclear density profile [1] is implemented in the Extended Thomas-Fermi (ETF) energy density functional. This allows to (i) shed a new light on the issue of the sign of surface symmetry energy in nuclear mass formulas, as well as to (ii) show the importance of the in-medium corrections to the nuclear cluster energies in thermodynamic conditions relevant for the description of core-collapse supernovae and (proto)-neutron star crust.

  11. Looking for the Northern Fermi Bubble with HAWC

    NASA Astrophysics Data System (ADS)

    Ayala, Hugo; Zhou, Hao; Huentemeyer, Petra; HAWC Collaboration

    2016-03-01

    The Fermi Bubbles were discovered in the GeV gamma-ray data from the Fermi Telescope in 2010. They extend up to 55° above and below the Galactic Center forming two large and homogeneous regions of spectrally hard gamma-ray emission. Understanding the mechanisms which produce the observed hard spectrum will help understand the origin of the Fermi Bubbles. Both hadronic and leptonic models can describe the spectrum of the bubbles, though the leptonic model can explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff between 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain their spectrum. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With a large field of view and good sensitivity to spatially extended sources, HAWC is the ground-based observatory best suited to detect extended regions like the Fermi Bubbles. We present a search for emission from the Fermi Bubble visible to HAWC.

  12. Towards a complete Fermi surface in underdoped high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  13. Fermi Gamma-Ray Space Telescope Science Overview

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    After more than 2 years of science operations, the Fermi Gamma-ray Space Telescope continues to survey the high-energy sky on a daily basis. In addition to the more than 1400 sources found in the first Fermi Large Area Telescope Catalog (I FGL), new results continue to emerge. Some of these are: (1) Large-scale diffuse emission suggests possible activity from the Galactic Center region in the past; (2) a gamma-ray nova was found, indicating particle acceleration in this binary system; and (3) the Crab Nebula, long thought to be a steady source, has varied in the energy ranges seen by both Fermi instruments.

  14. Fermi Large Area Telescope Bright Gamma-ray Source List

    SciTech Connect

    Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Band, D.L.; Barbiellini, Guido; Bastieri, Denis; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bignami, G.F.; Bloom, Elliott D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brigida, M.; Bruel, P.; Burnett, Thompson H.; /more authors..

    2009-05-15

    Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

  15. Physics of ultracold Fermi gases revealed by spectroscopies

    NASA Astrophysics Data System (ADS)

    Törmä, Päivi

    2016-04-01

    This article provides a brief review of how various spectroscopies have been used to investitage many-body quantum phenomena in the context of ultracold Fermi gases. In particular, work done with RF spectroscopy, Bragg spectroscopy and lattice modulation spectroscopy is considered. The theoretical basis of these spectroscopies, namely linear response theory in the many-body quantum physics context is briefly presented. Experiments related to the BCS-BEC crossover, imbalanced Fermi gases, polarons, possible pseudogap and Fermi liquid behaviour and measuring the contact are discussed. Remaining open problems and goals in the field are sketched from the perspective how spectroscopies could contribute.

  16. X.509 Authentication/Authorization in FermiCloud

    SciTech Connect

    Kim, Hyunwoo; Timm, Steven

    2014-11-11

    We present a summary of how X.509 authentication and authorization are used with OpenNebula in FermiCloud. We also describe a history of why the X.509 authentication was needed in FermiCloud, and review X.509 authorization options, both internal and external to OpenNebula. We show how these options can be and have been used to successfully run scientific workflows on federated clouds, which include OpenNebula on FermiCloud and Amazon Web Services as well as other community clouds. We also outline federation options being used by other commercial and open-source clouds and cloud research projects.

  17. Degenerate Fermi gas perturbations at standard background cosmology

    SciTech Connect

    Bernardini, A.E.; Perico, E.L.D. E-mail: elduarte@ifi.unicamp.br

    2011-01-01

    The hypothesis of a tiny fraction of the cosmic inventory evolving cosmologically as a degenerate Fermi gas test fluid at some dominant cosmological background is investigated. Our analytical results allow for performing preliminary computations to the evolution of perturbations for relativistic and non-relativistic test fluids. The density fluctuation, δ, the fluid velocity divergence, θ, and an explicit expression for the dynamics of the shear stress, σ, are obtained for a degenerate Fermi gas in the background regime of radiation. Extensions to the dominance of matter and to the ΛCDM cosmological background are also investigated and lessons concerning the formation of large structures of degenerate Fermi gas are depicted.

  18. Mapping the Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial Extent of the Northern Fermi Bubble

    NASA Astrophysics Data System (ADS)

    Bordoloi, Rongmon; Fox, Andrew J.; Lockman, Felix J.; Wakker, Bart P.; Jenkins, Edward B.; Savage, Blair D.; Hernandez, Svea; Tumlinson, Jason; Bland-Hawthorn, Joss; Kim, Tae-Sun

    2017-01-01

    We report new observations from a systematic, spectroscopic, ultraviolet absorption-line survey that maps the spatial and kinematic properties of the high velocity gas in the Galactic Center (GC) region. We examine the hypothesis that this gas traces the biconical nuclear outflow. We use an ultraviolet spectra of 47 background QSOs and halo stars projected inside and outside the northern Fermi Bubble from the Hubble Space Telescope to study the incidence of high velocity absorption around it. We use five lines of sight inside the northern Fermi Bubble to constrain the velocity and column densities of outflowing gas traced by O i, Al ii, C ii, C iv, Si ii, Si iii, Si iv, and other species. We find that all five lines of sight inside the northern Fermi Bubble exhibit blueshifted high velocity absorption components, whereas only 9 out of the 42 lines of sight outside the northern Fermi Bubble exhibit blueshifted high velocity absorption components. The observed outflow velocity profile decreases with Galactic latitude and radial distance (R) from the GC. The observed blueshifted velocities change from {v}{GSR}=-265 {km} {{{s}}}-1 at R ≈ 2.3 kpc to {v}{GSR}=-91 {km} {{{s}}}-1 at R ≈ 6.5 kpc. We derive the metallicity of the entrained gas along the 1H1613-097 sightline, one that passes through the center of the northern Fermi Bubble, finding [O/H] ≳ ‑0.54 ± 0.15. A simple kinematic model, tuned to match the observed absorption component velocities along the five lines of sight inside the Bubble, constrains the outflow velocities to ≈1000–1300 {km} {{{s}}}-1, and the age of the outflow to be ∼6–9 Myr. We estimate a minimum mass outflow rate for the nuclear outflow to be ≳ 0.2{M}ȯ {{yr}}-1. Combining the age and mass outflow rates, we determine a minimum mass of total UV-absorbing cool gas entrained in the Fermi Bubbles to be ≳ 2× {10}6 {M}ȯ .

  19. NASA's Fermi Shows How Active Galaxies Can Be

    NASA Video Gallery

    Active galaxies called blazars make up the largest class of objects detected by Fermi's Large Area Telescope (LAT). Massive black holes in the hearts of these galaxies fire particle jets in our dir...

  20. Chandra and Swift Observations of Unidentified Fermi-LAT Objects

    NASA Astrophysics Data System (ADS)

    Donato, Davide; Cheung, T.; Gehrels, N.

    2010-03-01

    In the last year we targeted some of the unidentified Fermi-LAT objects (UFOs) at high Galactic latitude with Chandra and Swift in order to determine the basic properties (positions, fluxes, hardness ratios) of all X-ray sources within the Fermi-LAT localization circles. These satellites enable us to detect the X-ray conterparts with a flux limit that is at least an order of magnitude lower than achieved in extant RASS data and to further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources. Here we present the results obtained with 5 Chandra pointings of high Galactic latitude UFOs in the Fermi-LAT 3-months bright source list. The association of detected X-ray sources within the improved 11-months Fermi-LAT localization circles with available optical and radio observations is discussed.

  1. GRBs in the Era of Swift and Fermi

    NASA Technical Reports Server (NTRS)

    Racusin, Judy

    2011-01-01

    Utilizing both Swift and Fermi to study GRBs provides us with a unique broad spectral and temporal window into both prompt emission and afterglow studies. Swift has provided key information from GRB follow-up of LAT detected bursts) that has led to ground-based redshift measurements and afterglow broadband light curves and SEDs. We study the X-ray and optical afterglows of Fermi-LAT detected bursts in the context of the hundreds of GRBs discovered by Swift over the last 7 years) in order to better understand the origin of the high-energy gamma-rays. We also briefly describe the efforts to best facilitate joint Swift-Fermi observations. These initial results demonstrate the synergy between Swift and Fermi) and hint at the many interesting discoveries to come.

  2. Renormalization group and the superconducting susceptibility of a Fermi liquid

    SciTech Connect

    Parameswaran, S. A.; Sondhi, S. L.; Shankar, R.

    2010-11-15

    A free Fermi gas has, famously, a superconducting susceptibility that diverges logarithmically at zero temperature. In this paper we ask whether this is still true for a Fermi liquid and find that the answer is that it does not. From the perspective of the renormalization group for interacting fermions, the question arises because a repulsive interaction in the Cooper channel is a marginally irrelevant operator at the Fermi liquid fixed point and thus is also expected to infect various physical quantities with logarithms. Somewhat surprisingly, at least from the renormalization group viewpoint, the result for the superconducting susceptibility is that two logarithms are not better than one. In the course of this investigation we derive a Callan-Symanzik equation for the repulsive Fermi liquid using the momentum-shell renormalization group, and use it to compute the long-wavelength behavior of the superconducting correlation function in the emergent low-energy theory. We expect this technique to be of broader interest.

  3. Fermi and LIGO Hone in on Gravity Wave Source

    NASA Video Gallery

    Fermi's GBM saw a fading X-ray source at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of t...

  4. Generalized Fermi-Dirac functions and derivatives: properties and evaluation

    NASA Astrophysics Data System (ADS)

    Gong, Z.; Zejda, L.; Däppen, W.; Aparicio, J. M.

    2001-05-01

    The generalized Fermi-Dirac functions and their derivatives are important in evaluating the thermodynamic quantities of partially degenerate electrons in hot dense stellar plasmas. New recursion relations of the generalized Fermi-Dirac functions have been found. An effective numerical method to evaluate the derivatives of the generalized Fermi-Dirac functions up to third order with respect to both degeneracy and temperature is then proposed, following Aparicio [Ap.J.S.S. 117 (1998) 627]. A Fortran program based on this method, together with a sample test case, is provided. Accuracy and domain of reliability of some other, popularly used analytic approximations of the generalized Fermi-Dirac functions for extreme conditions are investigated and compared with our results.

  5. Manipulating superconductivity in ruthenates through Fermi surface engineering

    NASA Astrophysics Data System (ADS)

    Hsu, Yi-Ting; Cho, Weejee; Rebola, Alejandro Federico; Burganov, Bulat; Adamo, Carolina; Shen, Kyle M.; Schlom, Darrell G.; Fennie, Craig J.; Kim, Eun-Ah

    2016-07-01

    The key challenge in superconductivity research is to go beyond the historical mode of discovery-driven research. We put forth a new strategy, which is to combine theoretical developments in the weak-coupling renormalization-group approach with the experimental developments in lattice-strain-driven Fermi surface engineering. For concreteness we theoretically investigate how superconducting tendencies will be affected by strain engineering of ruthenates' Fermi surface. We first demonstrate that our approach qualitatively reproduces recent experiments under uniaxial strain. We then note that the order of a few percent strain, readily accessible to epitaxial thin films, can bring the Fermi surface close to van Hove singularity. Using the experimental observation of the change in the Fermi surface under biaxial epitaxial strain and ab initio calculations, we predict Tc for triplet pairing to be maximized by getting close to the van Hove singularities without tuning on to the singularity.

  6. Thermal properties of three Fermi pulsars

    NASA Astrophysics Data System (ADS)

    Danilenko, A.; Karpova, A.; Kirichenko, A.; Shibanov, Y.; Shternin, P.; Zharikov, S.; Zyuzin, D.

    2014-07-01

    We analysed thermal properties of the Fermi pulsars J0357+3205, J1741-2054, and J0633+0632 using data from the XMM-Newton and Chandra archives. The X-ray spectra of all three pulsars can be fitted by sum of thermal and power-law components. For J1741-2054, the thermal component is best described by a blackbody model whose normalization suggests that the thermal emission comes from the bulk of the neutron star surface. The effective temperature of 60 eV, which is rather large for a pulsar as old as J1741-2054, makes it similar to the well-studied pulsar B1055-52, one of ``the three musketeers''. The thermal components of PSRs J0357+3205 and J0633+0632 can be equally well described by blackbody or the hydrogen atmosphere models. In the former case the normalizations suggest hot polar cap as thermal emission origin and only upper limits on the neutron stars surface temperatures can be computed. For the hydrogen atmosphere models, the normalizations are in agreement with emission coming from a substantial part of neutron star surface. Thermal properties of the pulsars are confronted with similar data on other isolated neutron stars and predictions of the neutron star cooling theory.

  7. The nuclear Thomas-Fermi model

    SciTech Connect

    Myers, W.D.; Swiatecki, W.J.

    1994-08-01

    The statistical Thomas-Fermi model is applied to a comprehensive survey of macroscopic nuclear properties. The model uses a Seyler-Blanchard effective nucleon-nucleon interaction, generalized by the addition of one momentum-dependent and one density-dependent term. The adjustable parameters of the interaction were fitted to shell-corrected masses of 1654 nuclei, to the diffuseness of the nuclear surface and to the measured depths of the optical model potential. With these parameters nuclear sizes are well reproduced, and only relatively minor deviations between measured and calculated fission barriers of 36 nuclei are found. The model determines the principal bulk and surface properties of nuclear matter and provides estimates for the more subtle, Droplet Model, properties. The predicted energy vs density relation for neutron matter is in striking correspondence with the 1981 theoretical estimate of Friedman and Pandharipande. Other extreme situations to which the model is applied are a study of Sn isotopes from {sup 82}Sn to {sup 170}Sn, and the rupture into a bubble configuration of a nucleus (constrained to spherical symmetry) which takes place when Z{sup 2}/A exceeds about 100.

  8. The Nuclear Thomas-Fermi Model

    DOE R&D Accomplishments Database

    Myers, W. D.; Swiatecki, W. J.

    1994-08-01

    The statistical Thomas-Fermi model is applied to a comprehensive survey of macroscopic nuclear properties. The model uses a Seyler-Blanchard effective nucleon-nucleon interaction, generalized by the addition of one momentum-dependent and one density-dependent term. The adjustable parameters of the interaction were fitted to shell-corrected masses of 1654 nuclei, to the diffuseness of the nuclear surface and to the measured depths of the optical model potential. With these parameters nuclear sizes are well reproduced, and only relatively minor deviations between measured and calculated fission barriers of 36 nuclei are found. The model determines the principal bulk and surface properties of nuclear matter and provides estimates for the more subtle, Droplet Model, properties. The predicted energy vs density relation for neutron matter is in striking correspondence with the 1981 theoretical estimate of Friedman and Pandharipande. Other extreme situations to which the model is applied are a study of Sn isotopes from {sup 82}Sn to {sup 170}Sn, and the rupture into a bubble configuration of a nucleus (constrained to spherical symmetry) which takes place when Z{sup 2}/A exceeds about 100.

  9. General physical properties of bright Fermi blazars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Foschini, L.; Ghirlanda, G.; Maraschi, L.; Celotti, A.

    2010-02-01

    We studied all blazars of known redshift detected by the Fermi satellite during its first 3-month survey. For the majority of them, pointed Swift observations ensure a good multiwavelength coverage, enabling us to reliably construct their spectral energy distributions (SEDs). We model the SEDs using a one-zone leptonic model and study the distributions of the derived interesting physical parameters as a function of the observed γ-ray luminosity. We confirm previous findings concerning the relation of the physical parameters with source luminosity which are at the origin of the blazar sequence. The SEDs allow to estimate the luminosity of the accretion disc for the majority of broad emitting line blazars, while for the lineless BL Lac objects in the sample upper limits can be derived. We find a positive correlation between the jet power and the luminosity of the accretion disc in broad-line blazars. In these objects, we argue that the jet must be proton dominated, and that the total jet power is of the same order of (or slightly larger than) the disc luminosity. We discuss two alternative scenarios to explain this result.

  10. Angular correlations near the Fermi energy

    SciTech Connect

    Fox, D.; Cebra, D.A.; Karn, J.; Parks, C.; Pradhan, A.; Vander Molen, A.; van der Plicht, J.; Westfall, G.D.; Wilson, W.K.; Tickle, R.S.; and others

    1988-07-01

    Angular correlations between light particles have been studied to probe the extent to which a thermally equilibrated system is formed in heavy ion collisions near the Fermi energy. Single-light-particle inclusive energy spectra and two-particle large-angle correlations were measured for 40 and 50 MeV/nucleon C+C, Ag, and Au. The single-particle inclusive energy spectra are well fit by a three moving source parametrization. Two-particle large-angle correlations are shown to be consistent with emission from a thermally equilibrated source when the effects of momentum conservation are considered. Single-particle inclusive spectra and light-particle correlations at small relative momentum were measured for 35 MeV/nucleon N+Ag. Source radii were extracted from the two-particle correlation functions and were found to be consistent with previous measurements using two-particle correlations and the coalescence model. The temperature of the emitting source was extracted from the relative populations of states using the quantum statistical model and was found to be 4.8/sub -2.4//sup +2.8/ MeV, compared to the 14 MeV temperature extracted from the slopes of the kinetic energy spectra.

  11. Strongly interacting isotopic Bose-Fermi mixture immersed in a Fermi sea

    SciTech Connect

    Wu, Cheng-Hsun; Santiago, Ibon; Park, Jee Woo; Ahmadi, Peyman; Zwierlein, Martin W.

    2011-07-15

    We have created a triply quantum-degenerate mixture of bosonic {sup 41}K and two fermionic species {sup 40}K and {sup 6}Li. The boson is shown to be an efficient coolant for the two fermions, spurring hopes for the observation of fermionic superfluids with imbalanced masses. We observe multiple heteronuclear Feshbach resonances, in particular a wide s-wave resonance for the combination {sup 41}K-{sup 40}K, opening up studies of strongly interacting isotopic Bose-Fermi mixtures. For large imbalance in the local densities of different species, we enter the polaronic regime of dressed impurities immersed in a bosonic or fermionic bath.

  12. Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas

    SciTech Connect

    Sanner, Christian; Su, Edward J.; Keshet, Aviv; Gommers, Ralf; Shin, Yong-il; Huang Wujie; Ketterle, Wolfgang

    2010-07-23

    We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

  13. Spin waves in a persistent spin-current Fermi liquid

    SciTech Connect

    Feldmann, J. D.; Bedell, K. S.

    2010-06-15

    We report two theoretical results for transverse spin waves, which arise in a system with a persistent spin current. Using Fermi liquid theory, we introduce a spin current in the ground state of a polarized or unpolarized Fermi liquid, and we derive the resultant spin waves using the Landau kinetic equation. The resulting spin waves have a q{sup 1} and q{sup 1/2} dispersion to leading order for the polarized and unpolarized systems, respectively.

  14. FERMI: A Flexible Expert Reasoner with Multi-Domain Inferencing.

    DTIC Science & Technology

    2014-09-26

    representation systems. In particular, FERMI uses schemas, (Brachman, 1979, Minsky, 1975, 1975, Fox , 1979, Bobrow, 1977)data structures composed of...if-added demons in the CONNIVER system (Sussman, 1975), and continuing through KAL (Bobrow, 1977) and SRL (Wright & Fox , 1983, 1983). FERMI’s schemas...language SRL ( Fox , 1979, Wright & Fox , 1983, 1983) in which isa links cause automatic inheritance of all the slots and their associated knowledge

  15. Insulating behavior of a trapped ideal Fermi gas.

    PubMed

    Pezzè, L; Pitaevskii, L; Smerzi, A; Stringari, S; Modugno, G; de Mirandes, E; Ferlaino, F; Ott, H; Roati, G; Inguscio, M

    2004-09-17

    We investigate theoretically and experimentally the center-of-mass motion of an ideal Fermi gas in a combined periodic and harmonic potential. We find a crossover from a conducting to an insulating regime as the Fermi energy moves from the first Bloch band into the band gap of the lattice. The conducting regime is characterized by an oscillation of the cloud about the potential minimum, while in the insulating case the center of mass remains on one side of the potential.

  16. Fermi Large Area Telescope Operations: Progress Over 4 Years

    SciTech Connect

    Cameron, Robert A.; /SLAC

    2012-06-28

    The Fermi Gamma-ray Space Telescope was launched into orbit in June 2008, and is conducting a multi-year gamma-ray all-sky survey, using the main instrument on Fermi, the Large Area Telescope (LAT). Fermi began its science mission in August 2008, and has now been operating for almost 4 years. The SLAC National Accelerator Laboratory hosts the LAT Instrument Science Operations Center (ISOC), which supports the operation of the LAT in conjunction with the Mission Operations Center (MOC) and the Fermi Science Support Center (FSSC), both at NASA's Goddard Space Flight Center. The LAT has a continuous output data rate of about 1.5 Mbits per second, and data from the LAT are stored on Fermi and transmitted to the ground through TDRS and the MOC to the ISOC about 10 times per day. Several hundred computers at SLAC are used to process LAT data to perform event reconstruction, and gamma-ray photon data are subsequently delivered to the FSSC for public release with a few hours of being detected by the LAT. We summarize the current status of the LAT, and the evolution of the data processing and monitoring performed by the ISOC during the first 4 years of the Fermi mission, together with future plans for further changes to detected event data processing and instrument operations and monitoring.

  17. Spectrum-splitting approach for Fermi-operator expansion in all-electron Kohn-Sham DFT calculations

    NASA Astrophysics Data System (ADS)

    Motamarri, Phani; Gavini, Vikram; Bhattacharya, Kaushik; Ortiz, Michael

    2017-01-01

    We present a spectrum-splitting approach to conduct all-electron Kohn-Sham density functional theory (DFT) calculations by employing Fermi-operator expansion of the Kohn-Sham Hamiltonian. The proposed approach splits the subspace containing the occupied eigenspace into a core subspace, spanned by the core eigenfunctions, and its complement, the valence subspace, and thereby enables an efficient computation of the Fermi-operator expansion by reducing the expansion to the valence-subspace projected Kohn-Sham Hamiltonian. The key ideas used in our approach are as follows: (i) employ Chebyshev filtering to compute a subspace containing the occupied states followed by a localization procedure to generate nonorthogonal localized functions spanning the Chebyshev-filtered subspace; (ii) compute the Kohn-Sham Hamiltonian projected onto the valence subspace; (iii) employ Fermi-operator expansion in terms of the valence-subspace projected Hamiltonian to compute the density matrix, electron density, and band energy. We demonstrate the accuracy and performance of the method on benchmark materials systems involving silicon nanoclusters up to 1330 electrons, a single gold atom, and a six-atom gold nanocluster. The benchmark studies on silicon nanoclusters revealed a staggering fivefold reduction in the Fermi-operator expansion polynomial degree by using the spectrum-splitting approach for accuracies in the ground-state energies of ˜10-4Ha/atom with respect to reference calculations. Further, numerical investigations on gold suggest that spectrum splitting is indispensable to achieve meaningful accuracies, while employing Fermi-operator expansion.

  18. Fermi acceleration in the randomized driven Lorentz gas and the Fermi-Ulam model.

    PubMed

    Karlis, A K; Papachristou, P K; Diakonos, F K; Constantoudis, V; Schmelcher, P

    2007-07-01

    Fermi acceleration of an ensemble of noninteracting particles evolving in a stochastic two-moving wall variant of the Fermi-Ulam model (FUM) and the phase randomized harmonically driven periodic Lorentz gas is investigated. As shown in [A. K. Karlis, P. K. Papachristou, F. K. Diakonos, V. Constantoudis, and P. Schmelcher, Phys. Rev. Lett. 97, 194102 (2006)], the static wall approximation, which ignores scatterer displacement upon collision, leads to a substantial underestimation of the mean energy gain per collision. In this paper, we clarify the mechanism leading to the increased acceleration. Furthermore, the recently introduced hopping wall approximation is generalized for application in the randomized driven Lorentz gas. Utilizing the hopping approximation the asymptotic probability distribution function of the particle velocity is derived. Moreover, it is shown that, for harmonic driving, scatterer displacement upon collision increases the acceleration in both the driven Lorentz gas and the FUM by the same amount. On the other hand, the investigation of a randomized FUM, comprising one fixed and one moving wall driven by a sawtooth force function, reveals that the presence of a particular asymmetry of the driving function leads to an increase of acceleration that is different from that gained when symmetrical force functions are considered, for all finite number of collisions. This fact helps open up the prospect of designing accelerator devices by combining driving laws with specific symmetries to acquire a desired acceleration behavior for the ensemble of particles.

  19. No indications of axionlike particles from Fermi

    SciTech Connect

    Belikov, Alexander V.; Goodenough, Lisa; Hooper, Dan

    2011-03-15

    As very high energy (> or approx. 100 GeV) gamma rays travel over cosmological distances, their flux is attenuated through interactions with the extragalactic background light. Observations of distant gamma ray sources at energies between {approx}200 GeV and a few TeV by ground-based gamma-ray telescopes such as HESS, however, have motivated the possibility that the universe is more transparent to very high energy photons than had been anticipated. One proposed explanation for this is the existence of axionlike particles (ALPs) which gamma rays can efficiently oscillate into, enabling them to travel cosmological distances without attenuation. In this article, we use a state-of-the-art model for the extragalactic background light (which is somewhat lower at {approx}{mu}m wavelengths than in previous models) and data from the Fermi Gamma Ray Space Telescope to calculate the spectra at 1-100 GeV of two gamma-ray sources, 1ES1101-232 at redshift z=0.186 and H2356-309 at z=0.165, in conjunction with the measurements of ground-based telescopes, to test the ALP hypothesis. We find that these observations can be well fit by an intrinsic power-law source spectrum with indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that no ALPs or other exotic physics is necessary to explain the observed degree of attenuation. While this does not exclude the possibility that ALPs are involved in the cosmological propagation of gamma rays, it does reduce the motivation for such new physics.

  20. Destruction of the Fermi surface due to pseudogap fluctuations in correlated systems

    NASA Astrophysics Data System (ADS)

    Sadovskii, M. V.; Kuchinskii, E. Z.; Nekrasov, I. A.

    2007-09-01

    Pseudogap phenomena in strongly correlated systems have essential spatial length scale dependence [M.V. Sadovskii, Physics - Uspekhi 44 (2001) 515]. To merge pseudogap physics and strong electron correlations we generalize the dynamical-mean field theory (DMFT) [A. Georges, G. Kotliar, W. Krauth, M.J. Rozenberg, Rev. Mod. Phys. 68 (1996) 13]. Dependence on correlation length of pseudogap fluctuations via additional (momentum dependent) self-energy Σk is included into conventional DMFT equations. The self-energy Σk describes non-local dynamical correlations induced either by short-ranged collective SDW-like antiferromagnetic spin or CDW-like charge fluctuations [J. Schmalian, D. Pines, B. Stojkovic, Phys. Rev. B 60 (1999) 667; E.Z. Kuchinskii, M.V. Sadovskii, JETP 88 (1999) 347]. Weakly doped one-band Hubbard model with repulsive Coulomb interaction on a square lattice with nearest and next nearest neighbour hopping is numerically investigated within this generalized DMFT + Σk approach [E.Z. Kuchinskii, I.A. Nekrasov, M.V. Sadovskii, JETP Lett. 82 (2005) 198; M.V. Sadovskii, I.A. Nekrasov, E.Z. Kuchinskii, Th. Prushke, V.I. Anisimov, Phys. Rev. B 72 (2005) 155105]. Both types of strongly correlated metals, namely (i) doped Mott insulator and (ii) the case of bandwidth W < U ( U - value of local Coulomb interaction) were considered. Energy dispersions, quasiparticle damping, spectral functions and ARPES spectra calculated within DMFT + Σk, all show a pseudogap effects close to the Fermi level of quasiparticle band. Finally we demonstrate the qualitative picture of quasiparticle band dispersion, Fermi surface “destruction” and “Fermi arcs” formation due to pseudogap fluctuations, which agrees well with observations by ARPES.

  1. The Spectral Energy Distributions of Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Yang, J. H.; Liu, Y.; Luo, G. Y.; Lin, C.; Yuan, Y. H.; Xiao, H. B.; Zhou, A. Y.; Hua, T. X.; Pei, Z. Y.

    2016-10-01

    In this paper, multiwavelength data are compiled for a sample of 1425 Fermi blazars to calculate their spectral energy distributions (SEDs). A parabolic function, {{log}}{(ν {F}ν )={P}1({{log}}ν -{P}2)}2+{P}3, is used for SED fitting. Synchrotron peak frequency ({log}{ν }{{p}}), spectral curvature (P1), peak flux ({ν }{{p}}{F}{ν {{p}}}), and integrated flux (ν {F}ν ) are successfully obtained for 1392 blazars (461 flat-spectrum radio quasars [FSRQs], 620 BL Lacs [BLs], and 311 blazars of uncertain type [BCUs]; 999 sources have known redshifts). Monochromatic luminosity at radio 1.4 GHz, optical R band, X-ray at 1 keV and γ-ray at 1 GeV, peak luminosity, integrated luminosity, and effective spectral indices of radio to optical ({α }{{RO}}) and optical to X-ray ({α }{{OX}}) are calculated. The “Bayesian classification” is employed to log {ν }{{p}} in the rest frame for 999 blazars with available redshift, and the results show that three components are enough to fit the log {ν }{{p}} distribution; there is no ultra-high peaked subclass. Based on the three components, the subclasses of blazars using the acronyms of Abdo et al. are classified, and some mutual correlations are also studied. Conclusions are finally drawn as follows: (1) SEDs are successfully obtained for 1392 blazars. The fitted peak frequencies are compared with common sources from available samples. (2) Blazars are classified as low synchrotron peak sources if log {ν }{{p}}({Hz})≤slant 14.0, intermediate synchrotron peak sources if 14.0\\lt {log} {ν }{{p}}({Hz})≤slant 15.3, and high synchrotron peak sources if {log} {ν }{{p}}({Hz})\\gt 15.3. (3) Gamma-ray emissions are strongly correlated with radio emissions. Gamma-ray luminosity is also correlated with synchrotron peak luminosity and integrated luminosity. (4) There is an anticorrelation between peak frequency and peak luminosity within the whole blazar sample. However, there is a marginally positive correlation for high

  2. The Equation of State of a Strongly Interacting Fermi Gas

    NASA Astrophysics Data System (ADS)

    Navon, Nir; Nascimbène, Sylvain; Jiang, Kaijun; Chevy, Frédéric; Salomon, Christophe

    2010-03-01

    In this talk, we will present recent experimental work on the thermodynamics of strongly interacting Fermi gases. We have developed a general method to probe with high precision the Equation of State (EoS) of locally homogeneous ultracold gases [1]. This allows stringent tests of recent many-body theories. First, we focus on the finite-temperature EoS of the unpolarized unitary gas. Precise thermometry is provided by adding to the Fermi gas of ^6Li a trace of bosonic ^7Li. We show that the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory and we localize the superfluid transition. Second, we address the zero-temperature EoS of the spin-polarized system. Surprisingly, despite strong interactions, the polarized phase behaves as a mixture of two ideal gases: a Fermi gas of majority atoms and a non-interacting gas of dressed quasi-particles, the Fermi polarons. Finally, we will report on work in progress on the extension of our study to the BEC-BCS crossover [2]. [4pt] [1] S. Nascimbene and N. Navon, K. Jiang, F. Chevy, C. Salomon, arXiv:0911.0747, Nature (in press, 2010) [0pt] [2] N. Navon and S. Nascimbene, F. Chevy, C. Salomon, in preparation (2010)

  3. Model for overscreened Kondo effect in ultracold Fermi gas

    NASA Astrophysics Data System (ADS)

    Kuzmenko, I.; Kuzmenko, T.; Avishai, Y.; Kikoin, K.

    2015-04-01

    The feasibility of realizing the overscreened Kondo effect in ultracold Fermi gas of atoms with spin s ≥ 3/2 in the presence of a localized magnetic impurity atom is proved realistic. Specifying (as a mere example) a system of ultracold 22Na Fermi gas and a trapped 6Li impurity, the mechanism of exchange interaction between the Na and Li atoms is elucidated and the exchange constant is found to be positive (antiferromagnetic). The corresponding exchange Hamiltonian is derived, and the Kondo temperature is estimated at the order of 500 nK. Within a weak-coupling renormalization group scheme, it is shown that the coupling renormalizes to the non-Fermi-liquid fixed point. An observable displaying multichannel features even in the weak-coupling regime is the impurity magnetization that is negative for T ≫TK and becomes positive with decreasing temperature.

  4. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    DOE PAGES

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

  5. Searches for Axionlike Particles with the Fermi Large Area Telescope

    NASA Astrophysics Data System (ADS)

    Albert, Andrea; Meyer, Manuel; Sanchez-Conde, Miguel; Wood, Matthew; LAT Collaboration

    2017-01-01

    Axionlike particles (ALPs) are dark-matter candidates that occur in a variety of extensions of the Standard Model. These particles could leave signatures in gamma rays, due to the coupling of ALPs to photons in external electromagnetic fields. To date, observations with Fermi Large Area Telescope (LAT) provide the strongest constraints on the photon-ALP coupling for ALP masses between 0.5 and 20 neV. Here, we summarize these constraints and present the sensitivity to detect an ALP induced gamma-ray burst from a Galactic core-collapse supernova. ALPs would be produced in the stellar medium via the Primakoff effect and convert into gamma rays in the Galactic magnetic field. Fermi LAT observations would be able to probe couplings where ALPs could constitute the entirety of dark matter. Below 1 neV, the Fermi-LAT sensitivity would surpass that of future laboratory experiments by one order of magnitude.

  6. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  7. Bosonic models with Fermi-liquid kinematics: realizations and properties

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul; Gopalakrishnan, Sarang; Lamacraft, Austen

    2011-03-01

    We consider models of interacting bosons in which the single-particle kinetic energy achieves its minimum on a surface in momentum space. The kinematics of such models resembles that resulting from Pauli blocking in Fermi liquids; therefore, Shankar's renormalization-group treatment of Fermi liquids can be adapted to investigate phase transitions in these bosonic systems. We explore possible experimental realizations of such models in cold atomic gases: e.g., via spin-orbit coupling, multimode-cavity-mediated interactions, and Cooper pairing of Fermi gases in spin-dependent lattices. We address the phase structure and critical behavior of the resulting models within the framework of Ref., focusing in particular on Bose-Einstein condensation and on quantum versions of the Brazovskii transition from a superfluid to a supersolid.

  8. Time evolution of excitations in normal Fermi liquids

    NASA Astrophysics Data System (ADS)

    Pavlyukh, Y.; Rubio, A.; Berakdar, J.

    2013-05-01

    We inspect the initial and the long-time evolution of excitations in Fermi liquids by analyzing the time structure of the electron spectral function. Focusing on the short-time limit we study the electron-boson model for the homogeneous electron gas and apply the first-order (in boson propagator) cumulant expansion of the electron Green's function. In addition to a quadratic decay in time upon triggering the excitation, we identify nonanalytic terms in the time expansion similar to those found in the Fermi edge singularity phenomenon. We also demonstrate that the exponential decay in time in the long-time limit is inconsistent with the GW approximation for the self-energy. The background for this is the Paley-Wiener theorem of complex analysis. To reconcile with the Fermi liquid behavior an inclusion of higher order diagrams (in the screened Coulomb interaction) is required.

  9. Enrico Fermi - And the Revolutions of Modern Physics

    NASA Astrophysics Data System (ADS)

    Cooper, Dan

    1999-02-01

    In 1938, at the age of 37, Enrico Fermi was awarded the Nobel Prize in Physics. That same year he emigrated from Italy to the United States and, in the course of his experiments, discovered nuclear fission--a process which forms the basis of nuclear power and atomic bombs. Soon the brilliant physicist was involved in the top secret race to produce the deadliest weapon on Earth. He created the first self-sustaining chain reaction, devised new methods for purifying plutonium, and eventually participated in the first atomic test. This compelling biography traces Fermis education in Italy, his meteoric career in the scientific world, his escape from fascism to America, and the ingenious experiments he devised and conducted at the University of Rome, Columbia University, and the Los Alamos laboratory. The book also presents a mini-course in quantum and nuclear physics in an accessible, fast-paced narrative that invokes all the dizzying passion of Fermis brilliant discoveries.

  10. Exploring the association of Fermi sources with young stellar objects

    NASA Astrophysics Data System (ADS)

    Munar-Adrover, P.; Paredes, J. M.; Romero, G. E.

    2011-11-01

    Massive protostars have associated bipolar outflows which can produce strong shocks when interact with the surrounding medium. In these conditions particle acceleration at relativistic velocities can occur leading to gamma ray emission, as some theoretical models predict. To identify young stellar objects (YSO) that may emit gamma rays we have crossed the Fermi First Year Catalog with some catalogs of known YSOs, and we have conducted Montecarlo simulations to find the probability of chance coincidence. With this crossing we obtained a list of YSOs spatially coincident with Fermi sources that may show gamma ray emission. Our results indicate that about 70% of the candidates should be gamma-ray sources with a confidence of 5 sigma. We have studied the coincidences one by one to check the viability of these YSOs as potential counterparts of Fermi sources and plan further detailed observations of few of them.

  11. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    SciTech Connect

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.

  12. Discovery of a Weyl fermion semimetal and topological Fermi arcs

    NASA Astrophysics Data System (ADS)

    Xu, Su-Yang; Belopolski, Ilya; Alidoust, Nasser; Neupane, Madhab; Bian, Guang; Zhang, Chenglong; Sankar, Raman; Chang, Guoqing; Yuan, Zhujun; Lee, Chi-Cheng; Huang, Shin-Ming; Zheng, Hao; Ma, Jie; Sanchez, Daniel S.; Wang, BaoKai; Bansil, Arun; Chou, Fangcheng; Shibayev, Pavel P.; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid

    2015-08-01

    A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, tantalum arsenide (TaAs). Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl fermion nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.

  13. Complexity and Fermi surface deformation in compressed lithium

    NASA Astrophysics Data System (ADS)

    Rodriguez-Prieto, A.; Bergara, A.; Silkin, V. M.; Echenique, P. M.

    2006-11-01

    Recently reported structural complexity and enhanced temperature superconducting transitions in lithium under pressure have increased the interest in light alkalies, otherwise considered as simple and well-known systems under normal conditions. Here we present an analysis of the pressure-induced Fermi surface deformation in lithium and its relation to the observed complexity. According to our calculations, the Fermi surface becomes increasingly anisotropic with pressure and at 8GPa contacts the Brillouin zone boundary inducing a Hume-Rothery mechanism explaining the bcc-fcc transition. Around 30GPa increasing cooper-like necks and an extended nesting are observed in the Fermi surface in the fcc phase, enhancing the electronic susceptibility response function and inducing a strong phonon softening. This softening, besides preluding the transition to complex structures and providing a better understanding of the observed superconductivity, is expected to induce other yet unexplored anomalies in compressed lithium.

  14. FERMI@Elettra FEL Design Technical Optimization Final Report

    SciTech Connect

    Fawley, William; Penn, Gregory; Allaria, Enrico; De Ninno,Giovanni; Graves, William

    2006-07-31

    This is the final report of the FEL Design Group for the Technical Optimization Study for the FERMI{at}ELETTRA project. The FERMI{at}ELETTRA project is based on the principle of harmonic upshifting of an initial ''seed'' signal in a single pass, FEL amplifier employing multiple undulators. There are a number of FEL physics principles which underlie this approach to obtaining short wavelength output: (1) the energy modulation of the electron beam via the resonant interaction with an external laser seed (2) the use of a chromatic dispersive section to then develop a strong density modulation with large harmonic overtones (3) the production of coherent radiation by the microbunched beam in a downstream radiator. Within the context of the FERMI project, we discuss each of these elements in turn.

  15. Superfluidity of heated Fermi systems in the static fluctuation approximation

    SciTech Connect

    Khamzin, A. A.; Nikitin, A. S.; Sitdikov, A. S.

    2015-10-15

    Superfluidity properties of heated finite Fermi systems are studied in the static fluctuation approximation, which is an original method. This method relies on a single and controlled approximation, which permits taking correctly into account quasiparticle correlations and thereby going beyond the independent-quasiparticle model. A closed self-consistent set of equations for calculating correlation functions at finite temperature is obtained for a finite Fermi system described by the Bardeen–Cooper–Schrieffer Hamiltonian. An equation for the energy gap is found with allowance for fluctuation effects. It is shown that the phase transition to the supefluid state is smeared upon the inclusion of fluctuations.

  16. Fermi surface, magnetic, and superconducting properties in actinide compounds

    NASA Astrophysics Data System (ADS)

    Ōnuki, Yoshichika; Settai, Rikio; Haga, Yoshinori; Machida, Yo; Izawa, Koichi; Honda, Fuminori; Aoki, Dai

    2014-08-01

    The de Haas-van Alphen effect, which is a powerful method to explore Fermi surface properties, has been observed in cerium, uranium, and nowadays even in neptunium and plutonium compounds. Here, we present the results of several studies concerning the Fermi surface properties of the heavy fermion superconductors UPt3 and NpPd5Al2, and of the ferromagnetic pressure-induced superconductor UGe2, together with those of some related compounds for which fascinating anisotropic superconductivity, magnetism, and heavy fermion behavior has been observed. xml:lang="fr"

  17. Fermi Bubbles: an elephant in the gamma-ray sky

    NASA Astrophysics Data System (ADS)

    Malyshev, Dmitry

    2017-03-01

    The Fermi bubbles are one of the most remarkable features in the gamma-ray sky revealed by the Fermi Large Area Telescope (LAT). The nature of the gamma-ray emission and the origin of the bubbles are still open questions. In this note, we will review some basic features of leptonic and hadronic modes of gamma-ray production. At the moment, gamma rays are our best method to study the bubbles, but in order to resolve the origin of the bubbles multi-wavelength and multi-messenger observations will be crucial.

  18. Exotic Paired States with Anisotropic Spin-Dependent Fermi Surfaces

    SciTech Connect

    Feiguin, Adrian E.; Fisher, Matthew P. A.

    2009-07-10

    We propose a model for realizing exotic paired states in cold Fermi gases by using a spin-dependent optical lattice to engineer mismatched Fermi surfaces for each hyperfine species. The BCS phase diagram shows a stable paired superfluid state with coexisting pockets of momentum space with gapless unpaired carriers, similar to the Sarma state in polarized mixtures, but in our case the system is unpolarized. We propose the possible existence of an exotic 'Cooper-pair Bose-metal' phase, which has a gap for single fermion excitations but gapless and uncondensed 'Cooper-pair' excitations residing on a 'Bose surface' in momentum space.

  19. MASTER-OAFA: Fermi GRB faded optical counterpart detection

    NASA Astrophysics Data System (ADS)

    Pogrosheva, T.; Lipunov, V.; Podesta, R.; Levato, H.; Buckley, D.; Gorbovskoy, E.; Tiurina, N.; Balanutsa, P.; Kuznetsov, A.; Gress, O.; Kornilov, V.; Vladimirov, V.; Chazov, V.; Gorbunov, I.; Krylov, A.; Shumkov, V.; Kuvshinov, D.

    2017-02-01

    During Fermi GBM 508295323 trigger ( GRB_TIME: 2017-02-09 01:08:38.08 UT https://gcn.gsfc.nasa.gov/other/508295323.fermi ) inspection MASTER-OAFA auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered new OT source (Podesta et al. GCN #20650) at (RA, Dec) = 07h 23m 07.30s -52d 14m 46.6s on 2017-02-09 02:07:07.478UT with unfiltered m_OT=17.4 (mlimit=18.1m).

  20. Hydrodynamics in a Degenerate, Strongly Attractive Fermi Gas

    NASA Technical Reports Server (NTRS)

    Thomas, John E.; Kinast, Joseph; Hemmer, Staci; Turlapov, Andrey; O'Hara, Ken; Gehm, Mike; Granade, Stephen

    2004-01-01

    In summary, we use all-optical methods with evaporative cooling near a Feshbach resonance to produce a strongly interacting degenerate Fermi gas. We observe hydrodynamic behavior in the expansion dynamics. At low temperatures, collisions may not explain the expansion dynamics. We observe hydrodynamics in the trapped gas. Our observations include collisionally-damped excitation spectra at high temperature which were not discussed above. In addition, we observe weakly damped breathing modes at low temperature. The observed temperature dependence of the damping time and hydrodynamic frequency are not consistent with collisional dynamics nor with collisionless mean field interactions. These observations constitute the first evidence for superfluid hydrodynamics in a Fermi gas.

  1. Harper Operator, Fermi Curves and Picard-Fuchs Equation

    NASA Astrophysics Data System (ADS)

    Li, Dan

    2014-05-01

    This paper is a continuation of the work on the spectral problem of the Harper operator using algebraic geometry. We continue to discuss the local monodromy of algebraic Fermi curves based on Picard-Lefschetz formula. The density of states over approximating components of Fermi curves satisfies a Picard-Fuchs equation. By the property of Landen transformation, the density of states has a Lambert series as the quarter period. A q-expansion of the energy is derived from a mirror map as in the B-model.

  2. Pairing and condensation in a resonant Bose-Fermi mixture

    NASA Astrophysics Data System (ADS)

    Fratini, Elisa; Pieri, Pierbiagio

    2010-05-01

    We study by diagrammatic means a Bose-Fermi mixture, with boson-fermion coupling tuned by a Fano-Feshbach resonance. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling. Such quantum critical point depends very weakly on the population imbalance and, for vanishing boson densities, coincides with that found for the polaron-molecule transition in a strongly imbalanced Fermi gas, thus bridging two quite distinct physical systems.

  3. Strongly Interacting Fermi Gases: Current Issues and Future Prospects

    NASA Astrophysics Data System (ADS)

    Ho, Tin-Lun Jason

    2005-03-01

    There has been rapid development in the study of interacting atomic Fermi gases last year. In this talk, I shall discuss the issues brought forth by current experiments with regard to the nature of the newly found pair condensate, the universal thermodynamic and dynamical features in strongly interacting regime, and new methods of probing strongly interacting physics not possible in solid state environment. In the last part of the talk, I shall discuss the exciting theoretical possibilities associating with the latest experimental progress on producing molecules with higher orbital angular momentum, and on strongly interacting Fermi gases in optical lattices. In collaboration with Roberto Diener.

  4. ROLE OF NUCLEONIC FERMI SURFACE DEPLETION IN NEUTRON STAR COOLING

    SciTech Connect

    Dong, J. M.; Zuo, W.; Lombardo, U.; Zhang, H. F.

    2016-01-20

    The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties that determine the neutron star (NS) thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions are calculated within the Brueckner–Hartree–Fock approach, employing the AV18 two-body force supplemented by a microscopic three-body force. Neutrino emissivity, heat capacity, and in particular neutron {sup 3}PF{sub 2} superfluidity, turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young NSs are significantly slowed.

  5. The radio-γ-ray connection in Fermi blazars

    NASA Astrophysics Data System (ADS)

    Ghirlanda, G.; Ghisellini, G.; Tavecchio, F.; Foschini, L.; Bonnoli, G.

    2011-05-01

    We study the correlation between the γ-ray flux (Fγ), averaged over the first 11 months of the Fermi survey and integrated above 100 MeV, and the radio flux density (Fr at 20 GHz) of Fermi sources associated with a radio counterpart in the 20-GHz Australia Telescope Compact Array (AT20G) survey. Considering the blazars detected in both bands, the correlation is highly significant and has the form Fγ∝F0.85±0.04r, similar to BL Lacertae objects and flat-spectrum radio quasars. However, only a small fraction (˜1/15) of the AT20G radio sources with flat radio spectra are detected by Fermi. To understand if this correlation is real, we examine the selection effects introduced by the flux limits of both the radio and the γ-ray surveys, and the importance of variability of the γ-ray flux. After accounting for these effects, we find that the radio-γ-ray flux correlation is real, but its slope is steeper than the observed one, that is, Fγ∝Fδr with δ in the range 1.25-1.5. The observed Fγ-Fr correlation and the fraction of radio sources detected by Fermi are reproduced assuming a long-term γ-ray flux variability, following a lognormal probability distribution with standard deviation σ≥ 0.5 (corresponding to Fγ varying by at least a factor of 3). Such a variability is compatible, even if not necessarily equal, with what is observed when comparing, for the sources in common, the EGRET and the Fermi γ-ray fluxes (even if the Fermi fluxes are averaged over ˜1 yr). Another indication of variability is the non-detection of 12 out of 66 EGRET blazars by Fermi, despite its higher sensitivity. We also study the strong linear correlation between the γ-ray and the radio luminosity of the 144 AT20G-Fermi associations with known redshift and show, through partial correlation analysis, that it is statistically robust. Two possible implications of these correlations are discussed: the contribution of blazars to the extragalactic γ-ray background and the prediction

  6. String theory, quantum phase transitions, and the emergent Fermi liquid.

    PubMed

    Cubrović, Mihailo; Zaanen, Jan; Schalm, Koenraad

    2009-07-24

    A central problem in quantum condensed matter physics is the critical theory governing the zero-temperature quantum phase transition between strongly renormalized Fermi liquids as found in heavy fermion intermetallics and possibly in high-critical temperature superconductors. We found that the mathematics of string theory is capable of describing such fermionic quantum critical states. Using the anti-de Sitter/conformal field theory correspondence to relate fermionic quantum critical fields to a gravitational problem, we computed the spectral functions of fermions in the field theory. By increasing the fermion density away from the relativistic quantum critical point, a state emerges with all the features of the Fermi liquid.

  7. The AGN Jet Model of the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Guo, Fulai

    2017-01-01

    The nature and origin of the Fermi bubbles detected in the inner Galaxy remain elusive. In this paper, we briefly discuss some recent theoretical and observational developments, with a focus on the AGN jet model. Analogous to radio lobes observed in massive galaxies, the Fermi bubbles could be naturally produced by a pair of opposing jets emanating nearly along the Galaxy's rotation axis from the Galactic center. Our two-fluid hydrodynamic simulations reproduce quite well the bubble location and shape, and interface instabilities at the bubble surface could be effectively suppressed by shear viscosity. We briefly comment on some potential issues related to our model, which may lead to future progress.

  8. Magnetic moments and non-Fermi-liquid behavior in quasicrystals

    NASA Astrophysics Data System (ADS)

    Andrade, Eric

    Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures, leading to a power-law distribution of Kondo temperatures, accompanied by a non-Fermi-liquid behavior, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. This work was supported by FAPESP (Brazil) Grant No. 2013/00681-8.

  9. Fermi problem with artificial atoms in circuit QED.

    PubMed

    Sabín, Carlos; del Rey, Marco; García-Ripoll, Juan José; León, Juan

    2011-10-07

    We propose a feasible experimental test of a 1D version of the Fermi problem using superconducting qubits. We give an explicit nonperturbative proof of strict causality in this model, showing that the probability of excitation of a two-level artificial atom with a dipolar coupling to a quantum field is completely independent of the other qubit until signals from it may arrive. We explain why this is in perfect agreement with the existence of nonlocal correlations and previous results which were used to claim apparent causality problems for Fermi's two-atom system.

  10. Spontaneous separation of large-spin Fermi gas in the harmonic trap: a density functional study

    PubMed Central

    Sun, Zongli; Gu, Qiang

    2016-01-01

    The component separation of the trapped large-spin Fermi gas is studied within density functional theory. The ground state and ferromagnetic transition in the gas, with and without the spin mixing collision, are calculated. In the absence of spin mixing, two patterns of separation are observed as the interaction between atoms increases, whereas only one of them corresponds to a ferromagnetic transition. The phase diagram suggests that the pattern which the system chooses depends on the interaction strength in the collision channels. With the presence of spin mixing, the distribution of phase region changes because of the interplay between different collision channels. Specifically, the spin exchange benefits the FM transition, while it suppresses the component separation of CS-II pattern. PMID:27549012

  11. Life on the edge: a beginner’s guide to the Fermi surface

    NASA Astrophysics Data System (ADS)

    Dugdale, S. B.

    2016-05-01

    The concept of the Fermi surface is at the very heart of our understanding of the metallic state. Displaying intricate and often complicated shapes, the Fermi surfaces of real metals are both aesthetically beautiful and subtly powerful. A range of examples is presented of the startling array of physical phenomena whose origin can be traced to the shape of the Fermi surface, together with experimental observations of the particular Fermi surface features.

  12. Working with Fermi at Chicago and Los Alamos

    NASA Astrophysics Data System (ADS)

    Garwin, Richard L.

    2010-02-01

    I discuss my experience with Enrico Fermi as student and fellow faculty member at Chicago and with him as consultants to the Los Alamos Scientific Laboratory in 1950-1952. The talk shares observations about this great physicist and exemplary human being. )

  13. Unidentified EGRET sources and their possible Fermi counterparts

    NASA Astrophysics Data System (ADS)

    Lyapin, A. R.; Arkhangelskaja, I. V.; Larin, D. S.

    2017-01-01

    Unidentified EGRET sources from 3EG catalog have been analyzed. Preliminary data analysis has shown at least 23 of these sources coincide with those in 3FGL Fermi catalogue within 1, 2 and 3 sigma error intervals of the coordinates and fluxes. Their properties are discussed in the presented work. Even 3-sigma difference allows supposing sources similarity because of more than 3-sigma distinctions in values of fluxes between identified EGRET sources and their Fermi counterparts. For instance, the coincidence between 3EG J1255-0549 and 3FGL J1256.1-0547 was reported in Fermi catalogues 1FGL, 2FGL, 3FGL. However, these sources fluxes (in units of 10‑8 photons × cm‑2 × s‑1) in the energy band E > 100 MeV were 179.7 ± 6.7 (3EG), 44.711 ± 0.724 (3FGL), 53.611 ± 0.997 (2FGL) and 67.939 ± 1.861 (1FGL). Such effect was observed for sufficient portion of identified EGRET sources. It could cause by troubles of particles identification by Fermi/LAT trigger system. Very often charged particles recognized as gamma-quanta because of wrong backsplash analysis. Nevertheless, gammas counts as charged particles due analogous reason and rejected during ground data processing. For example, it appears as geomagnetic modulation presence on gamma-quanta count rate latitudinal profiles in energy band E > 20 MeV.

  14. Landau-Khalatnikov phonon damping in strongly interacting Fermi gases

    NASA Astrophysics Data System (ADS)

    Kurkjian, Hadrien; Castin, Yvan; Sinatra, Alice

    2016-11-01

    We derive the phonon damping rate due to the four-phonon Landau-Khalatnikov process in low-temperature strongly interacting Fermi gases using quantum hydrodynamics, correcting and extending the original calculation of Landau and Khalatnikov (Zh. Eksp. Teor. Fiz., 19 (1949) 637). Our predictions can be tested in state-of-the-art experiments with cold atomic gases in the collisionless regime.

  15. Constraining decaying dark matter with Fermi LAT gamma-rays

    SciTech Connect

    Zhang, Le; Sigl, Günter; Weniger, Christoph; Maccione, Luca; Redondo, Javier E-mail: christoph.weniger@desy.de E-mail: redondo@mppmm.mpg.de

    2010-06-01

    High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constrain dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraints. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess.

  16. Landau quantization and Fermi velocity renormalization in twisted graphene bilayers

    NASA Astrophysics Data System (ADS)

    Yin, Long-Jing; Qiao, Jia-Bin; Wang, Wen-Xiao; Zuo, Wei-Jie; Yan, Wei; Xu, Rui; Dou, Rui-Fen; Nie, Jia-Cai; He, Lin

    2015-11-01

    Currently there is a lively discussion concerning Fermi velocity renormalization in twisted bilayers and several contradicted experimental results are reported. Here we study electronic structures of the twisted bilayers by scanning tunneling microscopy (STM) and spectroscopy (STS). The interlayer coupling strengths between the adjacent bilayers are measured according to energy separations of two pronounced low-energy van Hove singularities (VHSs) in the STS spectra. We demonstrate that there is a large range of values for the interlayer interaction not only in different twisted bilayers, but also in twisted bilayers with the same rotation angle. Below the VHSs, the observed Landau quantization in the twisted bilayers is identical to that of massless Dirac fermions in graphene monolayer, which allows us to measure the Fermi velocity directly. Our result indicates that the Fermi velocity of the twisted bilayers depends remarkably on both the twisted angles and the interlayer coupling strengths. This removes the discrepancy about the Fermi velocity renormalization in the twisted bilayers and provides a consistent interpretation of all current data.

  17. Fermi level stabilization energy in group III-nitrides

    SciTech Connect

    Li, S.X.; Yu, K.M.; Wu, J.; Jones, R.E.; Walukiewicz, W.; AgerIII, J.W.; Shan, W.; Haller, E.E.; Lu, Hai; Schaff, William J.

    2005-01-07

    Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi Stabilization Energy (E{sub FS}), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E{sub FS} is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.

  18. Where Was Everybody? Olaf Stapledon and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Baxter, S.

    In 1948 Olaf Stapledon gave an address to the BIS in which he summarised his vision of mankind's cosmic future: `One can imagine some sort of cosmical community of worlds ...' One might ask, however, since the universe is vastly older than mankind, why races on other worlds have not already built such a community. This is a `Fermi Paradox' question. The Paradox is based on the observation that there has been time for extraterrestrial intelligence to arise and colonise the Galaxy many times over, yet we see no sign of such endeavours. In this paper Stapledon's novels are retrospectively analysed from the point of view of the Fermi Paradox. In Last and First Men (1930) humanity is forever isolated because life and mind are rare in the Galaxy, and interstellar distances are too large ever to be traversed. These are classic candidate Fermi `solutions'. The `solution' implicit in Star Maker (1937) might be criticised in that it posits that humanity lives at a special epoch, with the cosmically transforming development of interstellar travel occurring a `mere' ten billion years after mankind, in a universe supposedly ~200bn years old. Stapledon died in 1950, the year the Paradox was formulated, and was probably unaware of the Paradox. However to apply retrospectively Fermi thinking to Stapledon's cosmologies is to gain a new insight into the author's philosophy.

  19. Magnetic breakdown in an array of overlapping Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Kadigrobov, A. M.; Radić, D.; Bjeliš, A.

    2015-03-01

    We develop a theoretical framework for a magnetic breakdown in an array of circular two-dimensional bands with a finite overlap of neighboring Fermi surfaces due to the presence of a presumably weak periodic potential, and apply the obtained results to the electron bands in carbon honeycomb structures of doped graphene and intercalated graphite compounds. In contrast to the standard treatment, inaugurated more than fifty years ago by Slutskin and Kadigrobov, with electron semiclassical trajectories encircling significantly overlapping Fermi surfaces, we examine a configuration in which bands are related in a way that the Fermi surfaces only slightly overlap, forming internal band pockets with areas of the size comparable to the area of the quantum magnetic flux for a given external magnetic field. Such band configuration has to be treated quantum mechanically. The calculation leads to the results for magnetic breakdown coefficients comprising an additional large factor with respect to the standard results, proportional to the ratio of the Fermi energy and the cyclotron energy. Also, these coefficients show oscillating dependence on energy, as well as on the wave number of periodic potential. Both mentioned elements enable the adjustment of the preferred wave vector of possible magnetic breakdown induced density wave instability at the highest possible critical temperature.

  20. Disordered Fermi liquid in epitaxial graphene from quantum transport measurements.

    PubMed

    Lara-Avila, Samuel; Tzalenchuk, Alexander; Kubatkin, Sergey; Yakimova, Rositza; Janssen, T J B M; Cedergren, Karin; Bergsten, Tobias; Fal'ko, Vladimir

    2011-10-14

    We have performed magnetotransport measurements on monolayer epitaxial graphene and analyzed them in the framework of the disordered Fermi liquid theory. We have separated the electron-electron and weak-localization contributions to resistivity and demonstrated the phase coherence over a micrometer length scale, setting the limit of at least 50 ps on the spin relaxation time in this material.

  1. Fermi surface behavior in the ABJM M2-brane theory

    NASA Astrophysics Data System (ADS)

    DeWolfe, Oliver; Henriksson, Oscar; Rosen, Christopher

    2015-06-01

    We calculate fermionic Green's functions for states of the three-dimensional Aharony-Bergman-Jafferis-Maldacena M2-brane theory at large N using the gauge-gravity correspondence. We embed extremal black brane solutions in four-dimensional maximally supersymmetric gauged supergravity, obtain the linearized Dirac equations for each spin-1 /2 mode that cannot mix with a gravitino, and solve these equations with infalling boundary conditions to calculate retarded Green's functions. For generic values of the chemical potentials, we find Fermi surfaces with universally non-Fermi liquid behavior, matching the situation for four-dimensional N =4 super-Yang-Mills. Fermi surface singularities appear and disappear discontinuously at the point where all chemical potentials are equal, reminiscent of a quantum critical point. One limit of parameter space has zero entropy at zero temperature, and fermionic fluctuations are perfectly stable inside an energy region around the Fermi surface. An ambiguity in the quantization of the fermions is resolved by supersymmetry.

  2. 75 FR 15748 - Detroit Edison Company; Fermi 2; Exemption

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-30

    ... From the Federal Register Online via the Government Publishing Office NUCLEAR REGULATORY COMMISSION Detroit Edison Company; Fermi 2; Exemption 1.0 Background Detroit Edison Company (the licensee) is... five requirements specified in Enclosure 1 of the Detroit Edison letter dated December 23, 2009,...

  3. All-Sky Monitoring of Variable Sources with Fermi GBM

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Cherry, Michael L.; Case, Gary L.; Camero-Arranz, Ascension; Chaplin, Vandiver; Connaughton, Valerie; Finger, Mark H.; Jenke, Pater; Rodi, James C.; Baumgartner, Wayne H.; Beklen, Elif; Bhat, P. Narayana; Briggs, Michael S.; Gehrels, Neil; Greiner, Jochen; Jahoda, Keith; Kippen, R. Marc; Kouveliotou, Chryssa; Krimm, Hans A.; Kuulkers, Erik; Lund, Niels; Meegan, Charles A.; Natalucci, Lorenzo; Paciesas, William S.; Preece, Robert

    2011-01-01

    This slide presentation reviews the monitoring of variable sources with the Fermi Gamma Ray Burst Monitor (GBM). It reviews the use of the Earth Occultation technique, the observations of the Crab Nebula with the GBM, and the comparison with other satellite's observations. The instruments on board the four satellites indicate a decline in the Crab from 2008-2010.

  4. A picosecond accuracy relativistic VLBI model via Fermi normal coordinates

    NASA Technical Reports Server (NTRS)

    Shahid-Saless, Bahman; Hellings, Ronald W.; Ashby, Neil

    1991-01-01

    Fermi normal coordinates are used to construct transformations relating solar system barycentric coordinates to local inertial geocentric coordinates. Relativistic corrections to terrestrial VLBI measurements are calculated, and this formalism is developed to include corrections needed for picosecond accuracy. A calculation of photon time delay which includes effects arising from the motion of gravitational sources is given.

  5. Global Structure of Isothermal Diffuse X-Ray Emission along the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Kataoka, J.; Tahara, M.; Totani, T.; Sofue, Y.; Inoue, Y.; Nakashima, S.; Cheung, C. C.

    2015-07-01

    In our previous works, we found absorbed thermal X-ray plasma with kT ≃ 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes | l| < 20° and latitude 5°≲ | b| < 60°, covering the whole extent of the Fermi bubbles. We show that the plasma temperature is constant at kT ≃ 0.30 ± 0.07 keV, while the emission measure (EM) varies by an order of magnitude, increasing toward the Galactic center (i.e., low | b| ) with enhancements at the North Polar Spur (NPS), SE-claw, and NW-clump features. Moreover, the EM distribution of kT ≃ 0.30 keV plasma is highly asymmetric in the northern and southern bubbles. Although the association of the X-ray emission with the bubbles is not conclusive, we compare the observed EM properties with simple models assuming (i) a filled halo without bubbles, whose gas density follows a hydrostatic isothermal model (King profile), and (ii) a bubble-in-halo in which two identical bubbles expand into the halo, forming thick shells of swept halo gas. We argue that the EM profile in the north (b > 0°) favors (ii), whereas that of the south (b < 0°) is rather close to (i), but a weak excess signature is clearly detected also in the south like NPS (South Polar Spur). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles’ axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial conditions.

  6. Dependence of the Fermi energy upon neutron excess

    NASA Astrophysics Data System (ADS)

    Jeukenne, J.-P.; Mahaux, C.; Sartor, R.

    1991-05-01

    The Fermi energy EF is defined as the negative of the average between the separation energies of a nucleon from the (A+1)- and A-nucleon systems. In the independent-particle limit, EF is the average between the energies of the last occupied and of the first unoccupied shell-model orbits. For mass numbers 40<~A<~208, the experimental neutron Fermi energies EFn increase approximately linearly with increasing asymmetry parameter η=(N-Z)/A. In contrast, the experimental proton Fermi energies EFp are, on the average, nearly independent of η when the average single-particle Coulomb energy EC is subtracted, the quantity EFp-EC decreases linearly with increasing η, with a slope whose modulus differs from that found for EFn. These features are analyzed in the framework of two mean-field models; they both include an isoscalar and an isovector central component, as well as a Coulomb correction in the case of protons. From the comparison between the n-208Pb and p-208Pb mean fields, it is derived that the depth of the symmetry potential is nearly independent of energy in the domain 15<~E<~50 MeV, in close agreement with a recent phenomenological study of the global optical-model potential for nuclei with mass numbers 40<=A<=208. In the vicinity of the Fermi energy, the isoscalar and isovector components are assumed to have Woods-Saxon radial shapes and linearly energy-dependent depths. In both models, the depth of the symmetry potential is taken equal to (23.2-0.46E) MeV. In the first model, all the parameters are extracted from a recent dispersion relation analysis of the mean fields felt by neutrons and protons in 208Pb; then, the calculated neutron Fermi energies are in good agreement with the experimental values but the calculated proton Fermi energies are larger than the experimental values, except for the lead isotopes. The second model incorporates, in addition, information derived from dispersion relation analyses of the n-40Ca and n-90Zr potentials; its main

  7. 75 FR 81316 - Detroit Edison Company; FERMI 2; Environmental Assessment and Finding of No Significant Impact

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-27

    ... the Final Environmental Statement for the Enrico Fermi Atomic Power Plant, Unit 2, NUREG-0769, dated... COMMISSION Detroit Edison Company; FERMI 2; Environmental Assessment and Finding of No Significant Impact The... Edison Company (the licensee), for operation of Fermi 2, located in Monroe County, Michigan....

  8. Nonanalytic corrections to the Fermi-liquid behavior

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Maslov, Dmitrii L.

    2003-10-01

    The issue of nonanalytic corrections to the Fermi-liquid behavior is revisited. Previous studies have indicated that the corrections to the Fermi-liquid forms of the specific heat and the static spin susceptibility (CFL∝T, χFLs=const) are nonanalytic in D⩽3 and scale as δC(T)∝TD, χs(T)∝TD-1, and χs(Q)∝QD-1, with extra logarithms in D=3 and 1. It is shown that these nonanalytic corrections originate from the universal singularities in the dynamical bosonic response functions of a generic Fermi liquid. In contrast to the leading, Fermi-liquid forms which depend on the interaction averaged over the Fermi surface, the nonanalytic corrections are parametrized by only two coupling constants, which are the components of the interaction potential at momentum transfers q=0 and q=2pF. For three-dimensional (3D) systems, a recent result of Belitz, Kirkpatrick, and Vojta for the spin susceptibility is reproduced and the issue why a nonanalytic momentum dependence, χs(Q,T=0)-χFLs∝Q2log Q, is not paralleled by a nonanalyticity in the T dependence [χs(0,T)-χFLs]∝T2 is clarified. For 2D systems, explicit forms of C(T)-CFL∝T2, χ(Q,T=0)-χFL∝|Q|, and χ(0,T)-χFL∝T are obtained. It is shown that earlier calculations of the temperature dependences in two dimensions are incomplete.

  9. Vibrational lifetime and Fermi resonance in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Fendt, A.; Fischer, S. F.; Kaiser, W.

    1981-05-01

    The energy decay of CH-stretching modes of the molecules CHCl 3 ,CH 2Cl 2, CH 3COCH 3, CH 3OH, and CH 3CH 2OH is measured in the liquid state. The observed lifetime very between 1.5 and 65 ps. A theoretical analysis points to the importance of Fermi resonance in the vibrational relaxation process. Quantitative comparison between theory and experiments is presented for the individual molecules. The strong variation of the lifetime for CH-stretching modes of various molecules may be understood if several effects are taken into account. First and most important is the influence of the Fermi resonances. Without the anharmonic mixing of the initial state, the overtone of the CH-bending modes and/or a higher order combination tone, one would predict lifetimes which are more than an order of magnitude longer than the observed lifetimes. This effect has been discussed earlier in detail for methylhalides by Zygan-Maus and Fischer [11] and, more recently, it has been incorporated in elaborate discussions for triatomic molecules like CO 2 by several authors [12]. A second factor to be considered for the interpretation is the rapi energy redistribution between different CH-stretching states was found theoretically to be faster than the further decay process by an order of magnitude [6, 11]. Experimentally, this effect was verified in this note for CH 2Cl 2 by the observation that the decay time was the same regardl whether the symmetric or the asymmetric CH-stretching mode was excited. This effect leads to a lengthening of the observed decay process. There is a bottleneck effect. Finally, we have shown that location and width of the final state are important parameters for the interpretation of the depopulatio lifetime. The empirical determination of these effects is not free of uncertainties. Very strong Fermi resonance can lead to rapid energy exchange during the exc process. In this case there is no bottleneck effect and it is difficult to detect the pathway of the energy

  10. A Southern Sky Survey with Fermi LAT and ASKAP

    SciTech Connect

    Cameron, Robert A.; /SLAC /KIPAC, Menlo Park

    2010-04-29

    We present the prospects for a future joint gamma-ray and radio survey of southern hemisphere sources using the Fermi Large Area Telescope (LAT) and the upcoming Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. ASKAP is a next generation radio telescope designed to perform surveys at GHz frequencies at a much higher survey speed than previous radio telescopes, and is scheduled to start engineering observations in 2011. The survey capabilities of both Fermi LAT and ASKAP are described, and the planned science surveys for ASKAP are summarized. We give some expected details of the Variable and Slow Transient (VAST) survey using ASKAP, which will search for transients on timescales from 5 seconds to years. Some observational properties of faint and transient sources seen at gamma-ray and radio wavelengths are summarized, and prospects and strategies for using ASKAP survey data for LAT source counterpart identification are summarized.

  11. DPA Cross Section Library FermiDPA 1.0

    SciTech Connect

    Pronskikh, V. S.; Mokhov, N. V.

    2013-06-05

    DPA cross section library FermiDPA 1.0 based on the industry standard NRT model calculations is described. The library contains DPA cross sections for neutrons in the energy range 10$^{-5}$ eV 20 (150) MeV. Calculations used neutron-induced reaction cross sections from ENDFB-VII database of evaluated nuclear data. The NJOY99 nuclear data processing system's module HEATR was applied to calculate NRT model radiation damage cross sections. The FermiDPA 1.0 library is a database of 395 text files (for 395 known isotopes) with DPA cross sections. It is code-independent and can be implemented in any transport code.

  12. THE FIVE YEAR FERMI/GBM MAGNETAR BURST CATALOG

    SciTech Connect

    Collazzi, A. C.; Kouveliotou, C.; Horst, A. J. van der; Younes, G. A.; Kaneko, Y.; Göğüş, E.; Lin, L.; Granot, J.; Finger, M. H.; Chaplin, V. L.; Huppenkothen, D.; Watts, A. L.; Kienlin, A. von; Baring, M. G.; Gruber, D.; Bhat, P. N.; Gibby, M. H.; and others

    2015-05-15

    Since launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has detected many hundreds of bursts from magnetar sources. While the vast majority of these bursts have been attributed to several known magnetars, there is also a small sample of magnetar-like bursts of unknown origin. Here, we present the Fermi/GBM magnetar catalog, providing the results of the temporal and spectral analyses of 440 magnetar bursts with high temporal and spectral resolution. This catalog covers the first five years of GBM magnetar observations, from 2008 July to 2013 June. We provide durations, spectral parameters for various models, fluences, and peak fluxes for all the bursts, as well as a detailed temporal analysis for SGR J1550–5418 bursts. Finally, we suggest that some of the bursts of unknown origin are associated with the newly discovered magnetar 3XMM J185246.6+0033.7.

  13. Quantum dynamics of impurities coupled to a Fermi sea

    NASA Astrophysics Data System (ADS)

    Parish, Meera M.; Levinsen, Jesper

    2016-11-01

    We consider the dynamics of an impurity atom immersed in an ideal Fermi gas at zero temperature. We focus on the coherent quantum evolution of the impurity following a quench to strong impurity-fermion interactions, where the interactions are assumed to be short range like in cold-atom experiments. To approximately model the many-body time evolution, we use a truncated basis method, where at most two particle-hole excitations of the Fermi sea are included. When the system is initially noninteracting, we show that our method exactly captures the short-time dynamics following the quench, and we find that the overlap between initial and final states displays a universal nonanalytic dependence on time in this limit. We further demonstrate how our method can be used to compute the impurity spectral function, as well as describe many-body phenomena involving coupled impurity spin states, such as Rabi oscillations in a medium or highly engineered quantum quenches.

  14. Emergent Fermi sea in a system of interacting bosons

    NASA Astrophysics Data System (ADS)

    Wu, Ying-Hai; Jain, J. K.

    2015-06-01

    An understanding of the possible ways in which interactions can produce fundamentally new emergent many-body states is a central problem of condensed-matter physics. We ask if a Fermi sea can arise in a system of bosons subject to contact interaction. Based on exact diagonalization studies and variational wave functions, we predict that such a state is likely to occur when a system of two-component bosons in two dimensions, interacting via a species-independent contact interaction, is exposed to a synthetic magnetic field of strength that corresponds to a filling factor of unity. The fermions forming the SU(2) singlet Fermi sea are bound states of bosons and quantized vortices, formed as a result of the repulsive interaction between bosons in the lowest Landau level.

  15. Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases

    SciTech Connect

    Osterloh, Klaus; Barberan, Nuria; Lewenstein, Maciej

    2007-10-19

    We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling {nu}=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.

  16. Fermi Science Support Center Data Servers and Archive

    NASA Astrophysics Data System (ADS)

    Reustle, Alexander; FSSC, LAT Collaboration

    2017-01-01

    The Fermi Science Support Center (FSSC) provides the scientific community with access to Fermi data and other products. The Gamma-Ray Burst Monitor (GBM) data is stored at NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) and is accessible through their searchable Browse web interface. The Large Area Telescope (LAT) data is distributed through a custom FSSC interface where users can request all photons detected from a region on the sky over a specified time and energy range. Through its website the FSSC also provides planning and scheduling products, such as long and short term observing timelines, spacecraft position and attitude histories, and exposure maps. We present an overview of the different data products provided by the FSSC, how they can be accessed, and statistics on the archive usage since launch.

  17. Higgs Mode in a Trapped Superfluid Fermi Gas

    NASA Astrophysics Data System (ADS)

    Tokimoto, Jun; Tsuchiya, Shunji; Nikuni, Tetsuro

    2017-03-01

    In quantum many-body systems with spontaneous breaking of a continuous symmetry, Higgs modes emerge as collective amplitude oscillations of order parameters. Recently, Higgs modes have been observed in superconductors and in Bose gases in optical lattices. However, it has yet to be observed in Fermi gases. In the present paper, we use the time-dependent Bogoliubov-de Gennes equations to investigate Higgs amplitude oscillations of the superfluid order parameter in a trapped Fermi gas induced by a sudden changes of the { s} -wave scattering length. In particular, we investigate the Higgs mode with different values of the initial scattering length and discuss how the frequency and damping of the Higgs mode changes around the unitarity regime.

  18. Fluctuation theory of Rashba Fermi gases: Gaussian and beyond

    NASA Astrophysics Data System (ADS)

    Shenoy, Vijay B.; Vyasanakere, Jayantha P.

    Fermi gases with generalized Rashba spin orbit coupling induced by a synthetic gauge field have the potential of realizing many interesting states such as rashbon condensates and topological phases. Here we address the key open problem of the fluctuation theory of such systems and demonstrate that beyond-Gaussian effects are essential to capture finite temperature physics of such systems. We obtain their phase diagram by constructing an approximate non-Gaussian theory. We conclusively establish that spin-orbit coupling can enhance the exponentially small transition temperature (Tc) of a weakly attracting superfluid to the order of Fermi temperature, paving a pathway towards high Tc superfluids. Work supported by CSIR, DST, DAE and IUSSTF.

  19. The Second Fermi Large Area Telescope GRB Catalog

    NASA Astrophysics Data System (ADS)

    Kocevski, Daniel; Fermi Large Area Telescope Collaboration

    2017-01-01

    The high-energy emission from gamma-ray bursts (GRBs) is a formidable probe of extreme physics, requiring rapid variability from highly relativistic sources. Despite the advancements in our understanding of GRBs through observations by NASA's Swift and Fermi spacecraft, many fundemental questions regarding the particle acceleration and radiative processes associated with these events remain unanswered. Here we present the most extensive search for emission from GRBs above 40 MeV performed by the Fermi Large Area Telescope (LAT). The resulting catalog includes more than 130 detections and represents an improvement in the detection efficency of GRBs at high-energies of over 50% compared to the first LAT GRB catalog. We utilize this improved sensativity to characterize the high-energy emission from GRBs and review how these observations further our understanding of the nature of these events.

  20. Unconventional fermi surface instabilities in the kagome Hubbard model.

    PubMed

    Kiesel, Maximilian L; Platt, Christian; Thomale, Ronny

    2013-03-22

    We investigate the competing Fermi surface instabilities in the kagome tight-binding model. Specifically, we consider on-site and short-range Hubbard interactions in the vicinity of van Hove filling of the dispersive kagome bands where the fermiology promotes the joint effect of enlarged density of states and nesting. The sublattice interference mechanism devised by Kiesel and Thomale [Phys. Rev. B 86, 121105 (2012)] allows us to explain the intricate interplay between ferromagnetic fluctuations and other ordering tendencies. On the basis of the functional renormalization group used to obtain an adequate low-energy theory description, we discover finite angular momentum spin and charge density wave order, a twofold degenerate d-wave Pomeranchuk instability, and f-wave superconductivity away from van Hove filling. Together, this makes the kagome Hubbard model the prototypical scenario for several unconventional Fermi surface instabilities.

  1. The simplified Fermi accelerator in classical and quantum mechanics

    NASA Astrophysics Data System (ADS)

    Karner, Gunther

    1994-11-01

    We review the simplified classical Fermi acceleration mechanism and construct a quantum counterpart by imposing time-dependent boundary conditions on solutions of the "free" Schrödinger equation at the unit interval. We find similiar dynamical features in the sense that limiting KAM curves, respectively purely singular quasienergy spectrum, exist(s) for sufficiently smooth "wall oscillations" (typically of C 2 type). In addition, we investigate quantum analogs to local approximations of the Fermi map both in its quasiperiodic and irregular phase space regions. In particular, we find pure point q.e. spectrum in the former case and conjecture that "random boundary conditions" are necessary to model a quantum analog to the chaotic regime of the classical accelerator.

  2. The Five Year Fermi/GBM Magnetar Burst Catalog

    NASA Astrophysics Data System (ADS)

    Collazzi, A. C.; Kouveliotou, C.; van der Horst, A. J.; Younes, G. A.; Kaneko, Y.; Göğüş, E.; Lin, L.; Granot, J.; Finger, M. H.; Chaplin, V. L.; Huppenkothen, D.; Watts, A. L.; von Kienlin, A.; Baring, M. G.; Gruber, D.; Bhat, P. N.; Gibby, M. H.; Gehrels, N.; McEnery, J.; van der Klis, M.; Wijers, R. A. M. J.

    2015-05-01

    Since launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has detected many hundreds of bursts from magnetar sources. While the vast majority of these bursts have been attributed to several known magnetars, there is also a small sample of magnetar-like bursts of unknown origin. Here, we present the Fermi/GBM magnetar catalog, providing the results of the temporal and spectral analyses of 440 magnetar bursts with high temporal and spectral resolution. This catalog covers the first five years of GBM magnetar observations, from 2008 July to 2013 June. We provide durations, spectral parameters for various models, fluences, and peak fluxes for all the bursts, as well as a detailed temporal analysis for SGR J1550-5418 bursts. Finally, we suggest that some of the bursts of unknown origin are associated with the newly discovered magnetar 3XMM J185246.6+0033.7.

  3. Quasi-two-dimensional Fermi gases at finite temperatures

    NASA Astrophysics Data System (ADS)

    Fischer, Andrea M.; Parish, Meera M.

    2014-12-01

    We consider a Fermi gas with short-range attractive interactions that is confined along one direction by a tight harmonic potential. For this quasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of state, radiofrequency spectrum, and the superfluid critical temperature Tc using a mean-field theory that accounts for all the energy levels of the harmonic confinement. Our calculation for Tc provides a natural generalization of the Thouless criterion to the quasi-2D geometry, and it correctly reduces to the 3D expression derived from the local density approximation in the limit where the confinement frequency ωz→0 . Furthermore, our results suggest that Tc can be enhanced by relaxing the confinement and perturbing away from the 2D limit.

  4. Fermi GBM Observations of Terrestrial Gamma-Ray Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    This slide presentation explores the relationship between Terrestrial Gamma-Ray Flashes (TGF) and lightning. Using data from the World-Wide Lightning Location Network (WWLLN), and the gamma ray observations from Fermi's Gamma-ray Burst Monitor (GBM), the study reviews any causal relationship between TGFs and lightning. The conclusion of the study is that the TGF and lightning are simultaneous with out a causal relationship.

  5. Momentum Resolved Radio Frequency Spectroscopy in Trapped Fermi Gases

    SciTech Connect

    Chen Qijin; Levin, K.

    2009-05-15

    We address recent momentum-resolved radio frequency (rf) spectroscopy experiments, showing how they yield more stringent tests than other comparisons with theory, associated with the ultracold Fermi gases. We demonstrate that, by providing a clear dispersion signature of pairing, they remove the ambiguity plaguing the interpretation of previous rf experiments. Our calculated spectral intensities are in semiquantitative agreement with the data. Even in the presence of a trap, the spectra are predicted to exhibit two BCS-like branches.

  6. Nonperturbative effects on the ferromagnetic transition in repulsive Fermi gases

    NASA Astrophysics Data System (ADS)

    He, Lianyi; Huang, Xu-Guang

    2012-04-01

    It is generally believed that a dilute spin-(1)/(2) Fermi gas with repulsive interactions can undergo a ferromagnetic phase transition to a spin-polarized state at a critical gas parameter (kFa)c. Previous theoretical predictions of the ferromagnetic phase transition have been based on the perturbation theory, which treats the gas parameter as a small number. On the other hand, Belitz, Kirkpatrick, and Vojta (BKV) have argued that the phase transition in clean itinerant ferromagnets is generically of first order at low temperatures, due to the correlation effects that lead to a nonanalytic term in the free energy. The second-order perturbation theory predicts a first-order phase transition at (kFa)c=1.054, consistent with the BKV argument. However, since the critical gas parameter is expected to be of order O(1), perturbative predictions may be unreliable. In this paper we study the nonperturbative effects on the ferromagnetic phase transition by summing the particle-particle ladder diagrams to all orders in the gas parameter. We consider a universal repulsive Fermi gas where the effective range effects can be neglected, which can be realized in a two-component Fermi gas of 6Li atoms by using a nonadiabatic field switch to the upper branch of a Feshbach resonance with a positive s-wave scattering length. Our theory predicts a second-order phase transition, which indicates that ferromagnetic transition in dilute Fermi gases is possibly a counterexample to the BKV argument. The predicted critical gas parameter (kFa)c=0.858 is in good agreement with the recent quantum Monte Carlo result (kFa)c=0.86 for a nearly zero-range potential [S. Pilati , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.030405 105, 030405 (2010)]. We also compare the spin susceptibility with the quantum Monte Carlo result and find good agreement.

  7. High Energy Astrophysics with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    This slide presentation reviews some of the findings of the Large Area Telescope (LAT) aboard the Fermi Observatory. It includes information about the LAT, and the Gamma-Ray Burst Monitor (GBM), detection of the quiet sun and the moon in gamma rays, Pulsars observed by the observatory, Globular Star Clusters, Active Galactic Nucleus, and Gamma-Ray Bursts, with specific information about GRB 080916C.

  8. Processing GPS Receiver Data for Improved Fermi GLAST Navigation

    NASA Technical Reports Server (NTRS)

    Woodard, Mark A.

    2008-01-01

    Fermi GLAST s 5-year mission objectives: a) Explore the most extreme environments in the Universe. b) Search for signs of new laws of physics and what composes the mysterious Dark Matter. c) Explain how black holes accelerate immense jets of material to nearly light speed. d) Help crack the mysteries of gamma-ray bursts. e) Answer long-standing questions across a broad range of topics, including solar flares, pulsars and the origin of cosmic rays.

  9. Spreader Design for FERMI@Elettra Free Electron Laser

    SciTech Connect

    Zholents, A.; Bacescu, D.; Chow, K.; Diviacco, B.; Ferianis, M.; Di Mitri, S.; Wells, R.

    2007-01-18

    In this note we describe a conceptual design of a part ofthe electron beam delivery system for FERMI@Elettra free electron laser(FEL) located between the end of the linac and the entrance to the FEL.This part includes the emittance diagnostic section, the electron beamswitchyard for two FELs called spreader and matching sections. The designmeets various constrains imposed by the existing and planned buildingboundaries, desire for utilization of existing equipment and demands forvarious diagnostic instruments.

  10. Branching ratio for sup 10 C superallowed Fermi. beta. decay

    SciTech Connect

    Nagai, Y.; Kunihiro, K.; Toriyama, T.; Harada, S.; Torii, Y.; Yoshida, A. ); Nomura, T.; Tanaka, J. ); Shinozuka, T. )

    1991-01-01

    The branching ratio for {sup 10}C superallowed Fermi {beta} decay has been measured accurately by a newly developed method. The result is 1.473{plus minus}0.007 %. The {ital Ft} value is derived as 3065.4{plus minus}14.7 sec, which is consistent with the {ital Ft} values determined accurately for heavier nuclei and with predictions of conserved vector current hypothesis. The method developed here can be applied to the high precision {beta}-{gamma} spectroscopy.

  11. Diagnosing alternative conceptions of Fermi energy among undergraduate students

    NASA Astrophysics Data System (ADS)

    Sharma, Sapna; Ahluwalia, Pardeep Kumar

    2012-07-01

    Physics education researchers have scientifically established the fact that the understanding of new concepts and interpretation of incoming information are strongly influenced by the preexisting knowledge and beliefs of students, called epistemological beliefs. This can lead to a gap between what students actually learn and what the teacher expects them to learn. In a classroom, as a teacher, it is desirable that one tries to bridge this gap at least on the key concepts of a particular field which is being taught. One such key concept which crops up in statistical physics/solid-state physics courses, and around which the behaviour of materials is described, is Fermi energy (εF). In this paper, we present the results which emerged about misconceptions on Fermi energy in the process of administering a diagnostic tool called the Statistical Physics Concept Survey developed by the authors. It deals with eight themes of basic importance in learning undergraduate solid-state physics and statistical physics. The question items of the tool were put through well-established sequential processes: definition of themes, Delphi study, interview with students, drafting questions, administration, validity and reliability of the tool. The tool was administered to a group of undergraduate students and postgraduate students, in a pre-test and post-test design. In this paper, we have taken one of the themes i.e. Fermi energy of the diagnostic tool for our analysis and discussion. Students’ responses and reasoning comments given during interview were analysed. This analysis helped us to identify prevailing misconceptions/learning gaps among students on this topic. How spreadsheets can be effectively used to remove the identified misconceptions and help appreciate the finer nuances while visualizing the behaviour of the system around Fermi energy, normally sidestepped both by the teachers and learners, is also presented in this paper.

  12. Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2012-01-01

    Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

  13. Exploring the thermodynamics of a universal Fermi gas.

    PubMed

    Nascimbène, S; Navon, N; Jiang, K J; Chevy, F; Salomon, C

    2010-02-25

    One of the greatest challenges in modern physics is to understand the behaviour of an ensemble of strongly interacting particles. A class of quantum many-body systems (such as neutron star matter and cold Fermi gases) share the same universal thermodynamic properties when interactions reach the maximum effective value allowed by quantum mechanics, the so-called unitary limit. This makes it possible in principle to simulate some astrophysical phenomena inside the highly controlled environment of an atomic physics laboratory. Previous work on the thermodynamics of a two-component Fermi gas led to thermodynamic quantities averaged over the trap, making comparisons with many-body theories developed for uniform gases difficult. Here we develop a general experimental method that yields the equation of state of a uniform gas, as well as enabling a detailed comparison with existing theories. The precision of our equation of state leads to new physical insights into the unitary gas. For the unpolarized gas, we show that the low-temperature thermodynamics of the strongly interacting normal phase is well described by Fermi liquid theory, and we localize the superfluid transition. For a spin-polarized system, our equation of state at zero temperature has a 2 per cent accuracy and extends work on the phase diagram to a new regime of precision. We show in particular that, despite strong interactions, the normal phase behaves as a mixture of two ideal gases: a Fermi gas of bare majority atoms and a non-interacting gas of dressed quasi-particles, the fermionic polarons.

  14. Fermi: The Gamma-Ray Large Area Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  15. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2015-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  16. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10 seconds of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  17. Fermi: The Gamma-Ray Large Area Telescope Mission Status

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  18. Ugo Fano, Enrico Fermi, and spectral line shapes

    NASA Astrophysics Data System (ADS)

    Clark, Charles W.

    2005-03-01

    Ugo Fano's 1961 paper on spectral line shapes^1 was recently ranked as the third highest in citation impact of all papers published in the entire Physical Review series.^2 In the course of preparing an article for a NIST Centennial volume,^3 I became interested in the history of the results presented in Fano’s seminal paper, and will present my findings in this talk. An amusing sidelight concerns the role played by Enrico Fermi in the development of the famous ``Fano profile'' formula. I had been told this story by Fano when I was his graduate student, but uncertain of my recollection of the details, I did not publish it in his obituary.^4 I later learned that the archives of the Royal Society of London contain Fano's own written version of the tale, which will be presented in this talk. The story sheds light on the nature of Enrico Fermi's interactions with his students, and confirms accounts concerning the way in which he did his theoretical work.^5 ^1 U. Fano,``Effects of Configuration Interaction on Intensities and Phase Shifts,'' Phys. Rev. 124, 1866-1878 (1961)^2 S. Redner, physics/0407137 (2004)^3 http://nvl.nist.gov/pub/nistpubs/sp958-lide/116-119.pdf^4 C. W. Clark, Nature 410, 164 (2001)^5 F. Rasetti, in Collected Papers, vol. I, E. Fermi (University of Chicago Press, 1962), p. 178

  19. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    PubMed

    Kargarian, Mehdi; Randeria, Mohit; Lu, Yuan-Ming

    2016-08-02

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at [Formula: see text] where gapless states on the side surfaces are protected only near [Formula: see text] We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2 Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

  20. Radio-weak BL Lac Objects in the Fermi Era

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Marchesini, E. J.; D’Abrusco, R.; Masetti, N.; Andruchow, I.; Smith, Howard A.

    2017-01-01

    The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]–[4.6]–[12] μm color–color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.

  1. Fermi LAT Limits on Primordial Black Hole Evaporation

    NASA Astrophysics Data System (ADS)

    Johnson, Chistian; Malyshev, Dmitry; Funk, Stefan; Ritz, Steven; Fermi LAT Collaboration

    2017-01-01

    Primordial black holes (PBHs) of sufficiently small mass emit gamma rays in the Fermi Large Area Telescope (LAT) energy range. PBHs with lifetimes shorter than the Fermi observation time will appear as moving point sources with gamma-ray emission that becomes harder and brighter with time until the PBH completely evaporates. Previous searches for gamma rays from PBHs have focused on either short time scale bursts or the contribution of PBH bursts to the isotropic diffuse emission. Here we use Fermi LAT point source catalogs to search for PBH candidates that evaporate on a time scale of several years. In addition to looking for the spectral signatures of a PBH, we also develop an algorithm to detect proper motion. There are a few unassociated point sources with spectra consistent with PBH evaporation; however, none of these sources show significant proper motion. We derive a conservative limit on PBH evaporation rate in the vicinity of the Earth by using a threshold on the gamma-ray flux above 10 GeV such that there are no sources above this threshold with spectra consistent with Hawking radiation from PBHs. The derived limit is more stringent than the limits obtained with ground-based gamma-ray observatories.

  2. The First FERMI-LAT Gamma-Ray Burst Catalog

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Burgess, J. Michael; Buson, S.; Byrne, D.; Caliandro, G. A.; Ferrara, E. C.; Gehrels, N.; Guiriec, S.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Racusin, J. L.; Thompson, D. J.; Kouveliotou, C.

    2013-01-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy great than (20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above approximately 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  3. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    PubMed Central

    Kargarian, Mehdi; Randeria, Mohit

    2016-01-01

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments. PMID:27436895

  4. Fermi Large Area Telescope as a Galactic Supernovae Axionscope.

    PubMed

    Meyer, M; Giannotti, M; Mirizzi, A; Conrad, J; Sánchez-Conde, M A

    2017-01-06

    In a Galactic core-collapse supernova (SN), axionlike particles (ALPs) could be emitted via the Primakoff process and eventually convert into γ rays in the magnetic field of the Milky Way. From a data-driven sensitivity estimate, we find that, for a SN exploding in our Galaxy, the Fermi Large Area Telescope (LAT) would be able to explore the photon-ALP coupling down to g_{aγ}≃2×10^{-13}  GeV^{-1} for an ALP mass m_{a}≲10^{-9}  eV. These values are out of reach of next generation laboratory experiments. In this event, the Fermi LAT would probe large regions of the ALP parameter space invoked to explain the anomalous transparency of the Universe to γ rays, stellar cooling anomalies, and cold dark matter. If no γ-ray emission were to be detected, Fermi-LAT observations would improve current bounds derived from SN 1987A by more than 1 order of magnitude.

  5. Quadratic Fermi node in a 3D strongly correlated semimetal

    DOE PAGES

    Kondo, Takeshi; Nakayama, M.; Chen, R.; ...

    2015-12-07

    We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour ismore » predicted, for which we observe some evidence. Lastly, our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.« less

  6. Dark Matter Searches with the Fermi Large Area Telescope

    SciTech Connect

    Meurer, Christine

    2008-12-24

    The Fermi Gamma-Ray Space Telescope, successfully launched on June 11th, 2008, is the next generation satellite experiment for high-energy gamma-ray astronomy. The main instrument, the Fermi Large Area Telescope (LAT), with a wide field of view (>2 sr), a large effective area (>8000 cm{sup 2} at 1 GeV), sub-arcminute source localization, a large energy range (20 MeV-300 GeV) and a good energy resolution (close to 8% at 1 GeV), has excellent potential to either discover or to constrain a Dark Matter signal. The Fermi LAT team pursues complementary searches for signatures of particle Dark Matter in different search regions such as the galactic center, galactic satellites and subhalos, the milky way halo, extragalactic regions as well as the search for spectral lines. In these proceedings we examine the potential of the LAT to detect gamma-rays coming from Weakly Interacting Massive Particle annihilations in these regions with special focus on the galactic center region.

  7. Fermi Large Area Telescope as a Galactic Supernovae Axionscope

    NASA Astrophysics Data System (ADS)

    Meyer, M.; Giannotti, M.; Mirizzi, A.; Conrad, J.; Sánchez-Conde, M. A.

    2017-01-01

    In a Galactic core-collapse supernova (SN), axionlike particles (ALPs) could be emitted via the Primakoff process and eventually convert into γ rays in the magnetic field of the Milky Way. From a data-driven sensitivity estimate, we find that, for a SN exploding in our Galaxy, the Fermi Large Area Telescope (LAT) would be able to explore the photon-ALP coupling down to ga γ≃2 ×10-13 GeV-1 for an ALP mass ma≲10-9 eV . These values are out of reach of next generation laboratory experiments. In this event, the Fermi LAT would probe large regions of the ALP parameter space invoked to explain the anomalous transparency of the Universe to γ rays, stellar cooling anomalies, and cold dark matter. If no γ -ray emission were to be detected, Fermi-LAT observations would improve current bounds derived from SN 1987A by more than 1 order of magnitude.

  8. A Mobile Data Application for the Fermi Mission

    NASA Astrophysics Data System (ADS)

    Stephens, Thomas E.; Science Support Center, Fermi

    2014-01-01

    With the ever increasing use of smartphones and tablets among scientists and the world at large, it becomes increasingly important for projects and missions to have mobile friendly access to their data. This access could come in the form of mobile friendly websites and/or native mobile applications that allow the users to explore or access the data. The Fermi Gamma-ray Space Telescope mission has begun work along the latter path. In this poster I present the current version of the Fermi Data Portal, a native mobile application for both Android and iOS devices that allows access to various high level public data products from the Fermi Science Support Center (FSSC), the Gamma-ray Coordinate Network (GCN), and other sources. While network access is required to download data, most of the data served by the app are stored locally and are available even when a network connection is not available. This poster discusses the application's features as well as the development experience and lessons learned so far along the way.

  9. A Mobile Data Application for the Fermi Mission

    NASA Astrophysics Data System (ADS)

    Stephens, T. E.

    2013-10-01

    With the ever increasing use of smartphones and tablets among scientists and the world at large, it becomes increasingly important for projects and missions to have mobile friendly access to their data. This access could come in the form of mobile friendly websites and/or native mobile applications that allow the users to explore or access the data. The Fermi Gamma-ray Space Telescope Mission has begun work along the latter path. In this poster I present the initial version of the Fermi Mobile Data Portal, a native application for both Android and iOS devices that allows access to various high level public data products from the Fermi Science Support Center (FSSC), the Gamma-ray Coordinate Network (GCN), and other sources. While network access is required to download data, most of the data served by the app are stored locally and are available even when a network connection is not available. This poster discusses the application's features as well as the development experience and lessons learned so far along the way.

  10. Observation of Weyl nodes and Fermi arcs in tantalum phosphide

    PubMed Central

    Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.

    2016-01-01

    A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910

  11. Topologically nontrivial Fermi regions and their novel electromagnetic response properties

    NASA Astrophysics Data System (ADS)

    Lee, Ching Hua; Zhang, Xiao

    In the last decade, there has been a surge of interest in the application of topology to condensed matter physics. So far, most studies have been concerned with the novel properties that arise due to nontrivial band topology, i.e Quantum Anomalous Hall and Z2 topological insulators (TIs). In this talk, I shall describe another context where nontrivial topology also leads to interesting, measurable effects. Within the semi-classical Boltzmann approach, it can be shown that a topologically nontrivial Fermi sea region generically exhibits a non-monotonic nonlinear electromagnetic response in the limit of low chemical potential. Such topologically nontrivial regions of filled states can arise in experimentally realized TI heterostructures or materials with large Rashba splitting, i.e. BiTeI, where the Fermi sea is not simply connected. A non-monotonic electromagnetic response implies regimes of negative differential resistance, which have important applications in technologies involving microwave generation, like motion sensing and radio astronomy. We hope that nontrivial Fermi sea topology will hence provide another route for the realization of such technologies.

  12. Quadratic Fermi node in a 3D strongly correlated semimetal

    SciTech Connect

    Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E. -G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

    2015-12-07

    We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Lastly, our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.

  13. Quadratic Fermi node in a 3D strongly correlated semimetal

    PubMed Central

    Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E.-G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

    2015-01-01

    Strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states. PMID:26640114

  14. Fermi-LAT detection of ongoing gamma-ray activity from the new gamma-ray source Fermi J1654-1055 (PMN J1632-1052)

    NASA Astrophysics Data System (ADS)

    Kocevski, D.; Ajello, M.; Buson, S.; Buehler, R.; Giomi, M.

    2016-02-01

    During the week between February 8 and 15, 2016, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray activity from a new transient source, Fermi J1654-1055.

  15. The physical properties of Fermi TeV BL Lac objects' jets

    NASA Astrophysics Data System (ADS)

    Ding, N.; Zhang, X.; Xiong, D. R.; Zhang, H. J.

    2017-01-01

    We investigate the physical properties of Fermi TeV BL Lac objects' jets by modelling the quasi-simultaneous spectral energy distribution of 29 Fermi TeV BL Lacs in the frame of a one-zone leptonic synchrotron self-Compton model. Our main results are the following. (i) There is a negative correlation between B and δ in our sample, which suggests that B and δ are dependent on each other mainly in the Thomson regime. (ii) There are negative correlations between νsy and r, the νIC and r, which is a signature of the energy-dependent statistical acceleration or the stochastic acceleration. There is a significant correlation between r and s, which suggests that the curvature of the electron energy distribution is attributed to the energy-dependent statistical acceleration mechanism. (iii) By assuming one proton per relativistic electron, we estimate the jet power and radiative power. A size relation Pe ˜ Pp > Pr ≳ PB is found in our sample. The Pe > PB suggests that the jets are particle dominated, and the Pe ˜ Pp means that the mean energy of relativistic electrons approaches mp/me. There are not significant correlations between Pjet and black hole mass in high or low state with a subsample of 18 sources, which suggests that the jet power weakly depends on the black hole mass. (iv) There is a correlation between the changes in the flux density at 1 TeV and the changes in the γpeak, which suggests that the change/evolution of electron energy distribution may be mainly responsible for the flux variation.

  16. Two-dimensional vibrational spectroscopy of the amide I band of crystalline acetanilide: Fermi resonance, conformational substates, or vibrational self-trapping?

    NASA Astrophysics Data System (ADS)

    Edler, J.; Hamm, P.

    2003-08-01

    Two-dimensional infrared (2D-IR) spectroscopy is applied to investigate acetanilide, a molecular crystal consisting of quasi-one-dimensional hydrogen bonded peptide units. The amide-I band exhibits a double peak structure, which has been attributed to different mechanisms including vibrational self-trapping, a Fermi resonance, or the existence of two conformational substates. The 2D-IR spectrum of crystalline acetanilide is compared with that of two different molecular systems: (i) benzoylchloride, which exhibits a strong symmetric Fermi resonance and (ii) N-methylacetamide dissolved in methanol which occurs in two spectroscopically distinguishable conformations. Both 2D-IR spectra differ significantly from that of crystalline acetanilide, proving that these two alternative mechanisms cannot account for the anomalous spectroscopy of crystalline acetanilide. On the other hand, vibrational self-trapping of the amide-I band can naturally explain the 2D-IR response.

  17. Competition Between Pairing and Ferromagnetic Instabilities in Ultracold Fermi Gases Near Feshbach Resonances

    DTIC Science & Technology

    2010-05-13

    In- ternational School of Physics “ Enrico Fermi ”, Course CLXIV, 5 Varenna, 20-30 June 2006, edited by M. Inguscio, W. Ketterle, and C. Salomon (IOS...Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances David Pekker1, Mehrtash Babadi1...MA 02139, USA We study the quench dynamics of a two-component ultracold Fermi gas from the weak into the strong inter- action regime, where the

  18. Fermi-LAT detection of the Galactic nova TCP J18102829-2729590

    NASA Astrophysics Data System (ADS)

    Li, Kwan-Lok; Chomiuk, Laura

    2016-11-01

    Fermi-LAT detection of the Galactic nova TCP J18102829-2729590 Following the discovery of the nova in Sagittarius TCP J18102829-2729590 (CBAT 2016 10 20.383; ATel #9658), we triggered an one-week Fermi ToO (observation number: 090603-1-1; PI: Laura Chomiuk) from 2016-10-25 as part of our Fermi-LAT monitoring campaign for Galactic novae (ATel #9311).

  19. The Hamiltonian structure of Dirac's equation in tensor form and its Fermi quantization

    NASA Technical Reports Server (NTRS)

    Reifler, Frank; Morris, Randall

    1992-01-01

    Currently, there is some interest in studying the tensor forms of the Dirac equation to elucidate the possibility of the constrained tensor fields admitting Fermi quantization. We demonstrate that the bispinor and tensor Hamiltonian systems have equivalent Fermi quantizations. Although the tensor Hamiltonian system is noncanonical, representing the tensor Poisson brackets as commutators for the Heisenberg operators directly leads to Fermi quantization without the use of bispinors.

  20. The Spectrum and Morphology of the Fermi Bubbles

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazini, R.; Bissaldi, E.; Brandt, T. J.; Ferrara, E. C.; Guiriec, S.; Harding, A. K.; Hayes, E.; Kocevski, D.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Troja, E.

    2014-01-01

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55 deg above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7 sigma significance. The power law with an exponential cutoff has an index of 1.90+/-0.2 and a cutoff energy of 110+/- 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4(+)2.4(-0.9 ) 10(exp 37) erg s-1. We confirm a significant enhancement of gamma-ray emission in the south-eastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4(+)3.7(-)2.6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons t the gamma-ray data well. In the IC scenario, the synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 micro-G.

  1. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    NASA Astrophysics Data System (ADS)

    Kargarian, Mehdi; Randeria, Mohit; Lu, Yuan-Ming

    2016-08-01

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q),k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0.kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

  2. Prospects for Fermi Particle Acceleration at Coronal Magnetic Reconnection Sites

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V.

    2015-12-01

    The mechanism of first order Fermi acceleration of particles interacting with the converging magnetized flows at a reconnection site was introduced recently in an attempt to predict the energy distribution of particles resulting from violent reconnection in galactic microquasars. More careful consideration of this mechanism showed that the spectral index of accelerated particles is related to the total plasma compression within a reconnection region, similar to that in the formulation for diffusive shock acceleration. In the solar context, reconnection regions producing strong compression could be the source of suprathermal "seed particles". A hard spectrum of such suprathermal particles is believed to be necessary to initiate the particle acceleration process at low Mach number coronal mass ejection shocks close to the Sun where the gradual solar energetic particle events originate. As a first step to investigate the efficiency of Fermi acceleration, we explore the degree of plasma compression that can be achieved at reconnection sites in the solar corona. This work presents a set of 2D two-temperature resistive MHD simulations of the dynamics of several magnetic configurations within a range of lower corona plasma parameters. Energy transport processes in the MHD model include anisotropic thermal conduction for electrons and ions and radiative cooling. Magnetic configurations considered are a Harris current sheet, a force-free current sheet, a flux rope sitting above an arcade of magnetic loops, and two merging flux ropes. We demonstrate that only for some magnetic topologies, corresponding in particular to 3D magnetic nulls, the compression ratio, sufficient for first order Fermi acceleration in the reconnection region, can be achieved. These represent the potential sites in the solar corona where a hard seed particle energetic spectrum could be produced.

  3. Determination of CKM Matrix Elements with Superallowed Fermi Decays^*.

    NASA Astrophysics Data System (ADS)

    Fujikawa, Brian

    1996-10-01

    The u-d element (V_ud) of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix is a fundamental parameter of the Standard Model of Electroweak Interactions. Its most precise determination comes from nuclear physics experiments, in particular, from measurements of superallowed Fermi beta decays. Precise knowledge of V_ud will allow a variety of tests of the Standard Model, in addition to placing a number of important constraints on astrophysics and cosmology. These measurements, which require both precision nuclear physics experiments and state of the art theoretical nuclear physics calculations, have been made for a variety of nuclei ranging from ^14O to ^54Co. The u-d element obtained from these measurements are in statistical agreement and the average value obtained implies a non-unitary CKM matrix, which if correct, would require exotic extensions to the Standard Model. Unfortunately the theoretical calculations of the isospin breaking corrections, which are necessary to extract V_ud, are controversial. In order to resolve this controversy, much effort has recently been invested in measuring V_ud from the superallowed Fermi decay of ^10C, where the isospin breaking corrections are expected to be small. This is a very challenging experiment, since it requires the precision measurement of very small branching ratios in a high background environment. I will report on the current status of the determination of V_ud emphasizing the recent experimental effort to measure V_ud from the superallowed Fermi decay of ^10C. ^*Supported by the U.S. D.O.E. under Contracts No. W-31-109-ENG-38 and No. DE-AC03-76SF00098.

  4. Fermi surface reconstruction in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Taillefer, Louis

    2009-03-01

    The recent observation of quantum oscillations in underdoped high-Tc superconductors (1), combined with their negative Hall coefficient at low temperature (2), reveals that the Fermi surface of hole-doped cuprates includes a small electron pocket. This strongly suggests that the large hole Fermi surface characteristic of the overdoped regime undergoes a reconstruction caused by the onset of some order which breaks translational symmetry. Here we consider the possibility that this order is ``stripe'' order, a form of combined charge / spin modulation observed most clearly in materials like Eu- doped and Nd-doped LSCO. In these materials, the onset of stripe order coincides with major changes in transport properties (3), providing strong evidence that stripe order is indeed the cause of Fermi-surface reconstruction. We identify the critical doping where this reconstruction occurs and show that the temperature dependence of transport coefficients at that doping is typical of metals at a quantum critical point (4). We discuss an interpretation of the pseudogap as a fluctuating precursor of the stripe-ordered phase.This work was performed in collaboration with L. Balicas, D.A. Bonn, J. Chang, O. Cyr-Choinière, R. Daou, N. Doiron- Leyraud, W.N. Hardy, N.E. Hussey, F. Lalibert'e, D. LeBoeuf, S.Y. Li, R. Liang, C. Proust, H. Takagi, and J.S. Zhou.(1) N. Doiron-Leyraud et al., Nature 447, 565 (2007).(2) D. LeBoeuf et al., Nature 450, 533 (2007).(3) R. Daou et al., Nature Physics, in press (DOI 10.1038/nphys1109); http://arXiv.org/abs/0806.2881.(4) R. Daou et al., to be published; http://arXiv.org/abs/0810.4280.

  5. Virial Expansion for a Strongly Correlated Fermi Gas

    NASA Astrophysics Data System (ADS)

    Hu, Hui

    2011-03-01

    Few-body physics can give considerable insight into the challenging many-body problem. A concrete example is the exact Tan relations linking the ``hard'' (few-body) physics at short distance, large-momentum and high frequency to the ``soft'' physics of the equation of state via a contact parameter. This has been demonstrated clearly using the operator product expansion (OPE) method which separates in a natural way few-body from many-body physics. In this talk, we present another example: the quantum virial expansion that bridges few-body and many-body physics. At large temperatures, the properties of a strongly correlated Fermi gas, either static or dynamic, can be expanded in terms of virial coefficients or expansion functions, calculable from the few-fermion solutions. For the equation of state in the resonant unitarity limit, we obtain for the first time an accurate third order virial coefficient. This has been experimentally verified in a measurement at ENS (Paris). For the single-particle spectral function, we demonstrate that an expansion up to second order is able to explain the main features of momentum-resolved RF spectroscopy in a resonantly interacting Fermi gas, as recently reported by JILA. We also obtain a virial expansion of the dynamic structure function, as measured at Swinburne University (Melbourne), and check that the second order expansion functions give the correct OPE coefficients in the limit of large momentum and frequency. The important feature of this expansion is the existence of a small parameter, the fugacity, even for strong interactions. In the future, we anticipate that higher-order virial expansions of dynamic properties such as the single-particle spectral function may provide useful insights into clarifying the debate on the pseudo-gap issue in resonantly interacting Fermi gases.

  6. The spectrum and morphology of the Fermi bubbles

    SciTech Connect

    Ackermann, M.; Buehler, R.; Albert, A.; Blandford, R. D.; Bloom, E. D.; Bottacini, E.; Caliandro, G. A.; Cameron, R. A.; Atwood, W. B.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D.; Buson, S.; Bissaldi, E.; Brandt, T. J.; Bregeon, J.; and others

    2014-09-20

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55° above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10° in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7σ significance. The power law with an exponential cutoff has an index of 1.9 ± 0.2 and a cutoff energy of 110 ± 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4{sub −0.9}{sup +2.4}×10{sup 37} erg s{sup –1}. We confirm a significant enhancement of gamma-ray emission in the southeastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4{sub −2.6}{sup +3.7} deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons fit the gamma-ray data well. In the IC scenario, synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 μG.

  7. Spectral properties of 438 GRBs detected by Fermi/GBM

    NASA Astrophysics Data System (ADS)

    Nava, L.; Ghirlanda, G.; Ghisellini, G.; Celotti, A.

    2011-06-01

    We present the results of the spectral analysis of the public data of 438 gamma ray bursts (GRBs) detected by the Fermi Gamma ray Burst Monitor (GBM) up to March 2010. For 432 bursts we could fit the time-integrated spectrum. In 318 cases we could reliably constrain the peak energy Eobs_peak of their νFν spectrum by analyzing their time-integrated spectrum between 8 keV and 35 MeV. Eighty percent of these spectra are fitted by a power-law with an exponential cutoff, and the remaining with the Band function. Among these 318 GRBs, 274 belong to the long GRB class and 44 to the short. Long GRBs have a typical peak energy Eobs_peak ~ 160 keV and low-energy spectral index α ~ - 0.92. Short GRBs have a harder peak energy (Eobs_peak ~ 490 keV) and a harder low-energy spectral index (α ~ -0.50) than long bursts. For each Fermi GRB we also analyzed the spectrum corresponding to the peak flux of the burst. On average, the peak spectrum has a harder low-energy spectral index than the corresponding time-integrated spectrum for the same burst, but similar Eobs_peakṪhe spectral parameters derived in our analysis of Fermi/GBM bursts are globally consistent with those reported in the GRB Cicular Network (GCN) archive after December 2008, while we found systematic differences in the low-energy power-law index for earlier bursts. Tables 2-5 are available in electronic form at http://www.aanda.org

  8. FERMI view of the TeV blazar Markarian 421

    SciTech Connect

    Paneque, D; Raino, S.; Chiang, J.; Mazziotta, M.N.; Tramacere, A.; /SLAC /KIPAC, Menlo Park /CIFS, Turin

    2010-08-26

    The high energy component of the TeV blazar Markarian 421 has been extensively studied since the beginning of the 90s, when the source was first detected at gamma-rays with EGRET and the Whipple Telescope, yet the source is still far from being understood. The high sensitivity, large dynamic range, and excellent time coverage of the Fermi Large Area Telescope (LAT), all representing significant advances over previous gamma-ray observations, will play a key role in the elucidation of the physical processes underlying the high energy emission of this blazar. In this presentation we show the results from almost 6 months (4 August 2008 to 20 January 2009) of observation with LAT. We report significant flux/spectral variability on a range of time scales from weeks to days, and an energy spectrum from 0.1 GeV to 300 GeV, overlapping with the energy ranges covered by the current generation of Cherenkov Telescopes. Results on the observations of the BLLac object Markarian 421 collected in the first months of operation of the Fermi satellite have been presented. Light curves on weekly and daily timescales have been shown, as well as the results of the spectral analysis in the energy range between 100 MeV and 300 GeV, covered for the first time by a satellite experiment overlapping the lower energy observations from Cherenkov telescopes on earth. These results are still preliminary and will be enriched and completed soon by a forthcoming publication. The results shown here demonstrate the great performance of Fermi-LAT to study the gamma-emission from Mrk421 (and blazars in general) over a large dynamic range and also on short timescales, which is expected to be of key importance for the study of the emission of the source in a coordinated way with other instruments covering other energy ranges.

  9. Critical Zeeman splitting of a unitary Fermi superfluid

    SciTech Connect

    He Lianyi; Zhuang Pengfei

    2011-05-01

    We determine the critical Zeeman energy splitting of a homogeneous Fermi superfluid at unitary in terms of the Fermi energy {epsilon}{sub F} according to recent experimental results in Laboratoire Kastler Brossel (LKB)-Lhomond. Based on the universal equations of state for the superfluid and normal phases, we show that there exist two critical fields H{sub c1} and H{sub c2}, between which a superfluid-normal mixed phase is energetically favored. Universal formulas for the critical fields and the critical population imbalance P{sub c} are derived. We have found a universal relation between the critical fields and the critical imbalances: H{sub c1}={gamma}{xi}{epsilon}{sub F} and H{sub c2}=(1+{gamma}P{sub c}){sup 2/3}H{sub c1}, where {xi} is the universal constant and {gamma} is the critical value of the chemical potential imbalance in the grand canonical ensemble. Since {xi}, {gamma}, and P{sub c} have been measured in the experiments, we can determine the critical Zeeman fields without the detailed information of the equation of state for the polarized normal phase. Using the experimental data from LKB-Lhomond, we have found H{sub c1{approx_equal}}0.37{epsilon}{sub F} and H{sub c2{approx_equal}}0.44{epsilon}{sub F}. Our result of the polarization P as a function of the Zeeman field H/{epsilon}{sub F} is in good agreement with the data extracted from the experiments. We also give an estimation of the critical magnetic field for dilute neutron matter at which the matter gets spin polarized, assuming the properties of the dilute neutron matter are close to those of the unitary Fermi gas.

  10. CLUSTERING OF γ-RAY-SELECTED 2LAC FERMI BLAZARS

    SciTech Connect

    Allevato, V.; Finoguenov, A.; Cappelluti, N.

    2014-12-20

    We present the first measurement of the projected correlation function of 485 γ-ray-selected blazars, divided into 175 BL Lacertae (BL Lacs) and 310 flat-spectrum radio quasars (FSRQs) detected in the 2 year all-sky survey by the Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with log M{sub h} = 13.35{sub −0.14}{sup +0.20} and log M{sub h} = 13.40{sub −0.19}{sup +0.15} h {sup –1} M {sub ☉}, respectively, at low (z ∼ 0.4) and high (z ∼ 1.2) redshift. In terms of clustering properties, these results suggest that BL Lacs and FSRQs are similar objects residing in the same dense environment typical of galaxy groups, despite their different spectral energy distributions, power, and accretion rates. We find no difference in the typical bias and hosting halo mass between Fermi blazars and radio-loud active galactic nuclei (AGNs), supporting the unification scheme simply equating radio-loud objects with misaligned blazar counterparts. This similarity in terms of the typical environment they preferentially live in, suggests that blazars tend to occupy the center of DMHs, as already pointed out for radio-loud AGNs. This implies, in light of several projects looking for the γ-ray emission from DM annihilation in galaxy clusters, a strong contamination from blazars to the expected signal from DM annihilation.

  11. Teaching theoretical physics: The cases of Enrico Fermi and Ettore Majorana

    NASA Astrophysics Data System (ADS)

    De Gregorio, Alberto; Esposito, Salvatore

    2007-09-01

    We report on theoretical courses by Enrico Fermi and Ettore Majorana, which give evidence of the first appearance and further development of quantum mechanics teaching in Italy. On the basis of original documents, we compare Fermi and Majorana's approaches. A detailed analysis is made of Fermi's course on theoretical physics attended by Majorana in 1927-28. Three (previously unknown) programs on advanced physics courses submitted by Majorana to the University of Rome between 1933 and 1936 and the course he taught in Naples in 1938 complete our analysis. Fermi's phenomenological approach resounded in Majorana, who combined it with a deeper theoretical approach, closer to the contemporary way of presenting quantum mechanics.

  12. Generalized Thomas-Fermi equations as the Lampariello class of Emden-Fowler equations

    NASA Astrophysics Data System (ADS)

    Rosu, Haret C.; Mancas, Stefan C.

    2017-04-01

    A one-parameter family of Emden-Fowler equations defined by Lampariello's parameter p which, upon using Thomas-Fermi boundary conditions, turns into a set of generalized Thomas-Fermi equations comprising the standard Thomas-Fermi equation for p = 1 is studied in this paper. The entire family is shown to be non integrable by reduction to the corresponding Abel equations whose invariants do not satisfy a known integrability condition. We also discuss the equivalent dynamical system of equations for the standard Thomas-Fermi equation and perform its phase-plane analysis. The results of the latter analysis are similar for the whole class.

  13. Detroit Edison's Fermi 1 - Preparation for Reactor Removal

    SciTech Connect

    Swindle, Danny

    2008-01-15

    This paper is intended to provide information about the ongoing decommissioning tasks at Detroit Edison's Fermi 1 plant, and in particular, the work being performed to prepare the reactor for removal and disposal. In 1972 Fermi 1 was shutdown and the fuel returned to the Atomic Energy Commission. By the end of 1975, a retirement plan was prepared, the bulk sodium removed, and the plant placed in a safe store condition. The plant systems were left isolated with the sodium containing systems inert with carbon dioxide in an attempt to form a carbonate layer, thus passivating the underlying reactive sodium. In 1996, Detroit Edison determined to evaluate the condition of the plant and to make recommendations in relation to the Fermi 1 future plans. At the end of 1997 approval was obtained to remove the bulk asbestos and residual alkali-metals (i.e., sodium and sodium potassium (NaK)). In 2000, full nuclear decommissioning of the plant was approved. To date, the bulk asbestos insulation has been removed, and the only NaK remaining is located in six capillary instrument tubes. The remaining sodium is contained within the reactor, two of the three primary loops, and miscellaneous removed pipes and equipment to be processed. The preferred method for removing or reacting sodium at Fermi 1 is by injecting superheated steam into a heated, nitrogen inert system. The byproducts of this reaction are caustic sodium hydroxide, hydrogen gas, and heat. The decision was made to separate the three primary loops from the reactor for better control prior to processing each loop and the reactor separately. The first loop has already been processed. The main focus is now to process the reactor to allow removal and disposal of the Class C waste prior to the anticipated June 2008 closure of the Barnwell radioactive waste disposal facility located in South Carolina. Lessons learnt are summarized and concern: the realistic schedule and adherence to the schedule, time estimates, personnel

  14. The Fermi-Pasta-Ulam Problem in the Thermodynamic Limit

    NASA Astrophysics Data System (ADS)

    Ponno, Antonio

    In the present contribution we justify and discuss the scaling laws characterizing the first phase of the energy transfer from large to small spatial scales in a chain of nonlinear oscillators (the so-called Fermi-Pasta-Ulam α-model). By means of qualitative estimates, we show that large scale initial excitations (long wavelength Fourier modes) produce injection of energy into smaller scales on times t > τc ˜ ɛ-3/4 and up to a cutoff spatial scale ell c ˜ ɛ-1/4, where ɛ is the energy per degree of freedom of the system.

  15. PHOTOMETRICALLY TRIGGERED KECK SPECTROSCOPY OF FERMI BL LACERTAE OBJECTS

    SciTech Connect

    Shaw, Michael S.; Romani, Roger W.

    2013-11-01

    We report on Keck spectra of 10 Fermi blazars. J0622+3326, previously unobserved, is shown to be a flat-spectrum radio quasar at redshift z = 1.062. The others are known BL Lac type objects that have resisted previous attempts to secure redshifts. Using a photometric monitoring campaign with the 0.76 m Katzman Automatic Imaging Telescope at Lick Observatory, we identified epochs when the relativistic jet emission was fainter than usual, thus triggering the Keck spectroscopy. This strategy gives improved sensitivity to stars and ionized gas in the host galaxy, thereby providing improved redshift constraints for seven of these sources.

  16. Dependence of Kambersky damping on Fermi level and spin orientation

    SciTech Connect

    Qu, T.; Victora, R. H.

    2014-05-07

    Kambersky damping represents the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction. It is demonstrated that, for bcc Fe-based transition metal alloys, the logarithm of the energy loss is proportional to the density of states at the Fermi level. Both inter and intraband damping are calculated for spins at arbitrary angle to the previously examined [001] direction. Although the easy axis 〈100〉 shows isotropic relaxation and achieves the minimum damping value of 0.002, other directions, such as 〈110〉, show substantial anisotropic damping.

  17. Geometrically frustrated coarsening dynamics in spinor Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Phuc, Nguyen Thanh; Momoi, Tsutomu; Furukawa, Shunsuke; Kawaguchi, Yuki; Fukuhara, Takeshi; Ueda, Masahito

    2017-01-01

    Coarsening dynamics theory describes equilibration of a broad class of systems. By studying the relaxation of a periodic array of microcondensates immersed in a Fermi gas, which mediates long-range spin interactions to simulate frustrated classical magnets, we show that coarsening dynamics can be suppressed by geometrical frustration. The system is found to eventually approach a metastable state which is robust against random field noise and characterized by finite correlation lengths together with the emergence of topologically stable Z2 vortices. We find universal scaling laws with no thermal-equilibrium analog that relate the correlation lengths and the number of vortices to the degree of frustration in the system.

  18. Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices.

    PubMed

    Cramer, M; Eisert, J; Illuminati, F

    2004-11-05

    We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices.

  19. Composite Fermi liquids in the lowest Landau level

    NASA Astrophysics Data System (ADS)

    Wang, Chong; Senthil, T.

    2016-12-01

    We study composite Fermi liquid (CFL) states in the lowest Landau level (LLL) limit at a generic filling ν =1/n . We begin with the old observation that, in compressible states, the composite fermion in the lowest Landau level should be viewed as a charge-neutral particle carrying vorticity. This leads to the absence of a Chern-Simons term in the effective theory of the CFL. We argue here that instead a Berry curvature should be enclosed by the Fermi surface of composite fermions, with the total Berry phase fixed by the filling fraction ϕB=-2 π ν . We illustrate this point with the CFL of fermions at filling fractions ν =1 /2 q and (single and two-component) bosons at ν =1 /(2 q +1 ) . The Berry phase leads to sharp consequences in the transport properties including thermal and spin Hall conductances. We emphasize that these results only rely on the LLL limit and do not require particle-hole symmetry, which is present microscopically only for fermions at ν =1 /2 . Nevertheless, we show that the existing LLL theory of the composite Fermi liquid for bosons at ν =1 does have an emergent particle-hole symmetry. We interpret this particle-hole symmetry as a transformation between the empty state at ν =0 and the boson integer quantum hall state at ν =2 . This understanding enables us to define particle-hole conjugates of various bosonic quantum Hall states which we illustrate with the bosonic Jain and Pfaffian states. For bosons at ν =1 we construct paired non-Abelian states distinct from both the standard bosonic Pfaffian and its particle hole conjugate and show how they may arise naturally out of the neutral vortex composite Fermi liquid. The bosonic particle-hole symmetry can be realized exactly on the surface of a three-dimensional boson topological insulator. We also show that with the particle-hole and spin S U (2 ) rotation symmetries, there is no gapped topological phase for bosons at ν =1 . Finally we comment on systems that are not strictly in the

  20. Minimax rational approximation of the Fermi-Dirac distribution

    DOE PAGES

    Moussa, Jonathan E.

    2016-10-27

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ–1)) poles to achieve an error tolerance ϵ at temperature β–1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δocc, the occupied energy interval. Furthermore, this is particularly beneficial when Δ >> Δocc, such as in electronic structure calculations that use a large basis set.

  1. Laser cooling of a trapped two-component Fermi gas

    SciTech Connect

    Idziaszek, Z.; Santos, L.; Lewenstein, M.; Baranov, M.

    2003-04-01

    We study the collective Raman cooling of a trapped two-component Fermi gas using quantum master equation in the festina lente regime, where the heating due to photon reabsorption can be neglected. The Monte Carlo simulations show that three-dimensional temperatures of the order of 0.008T{sub F} can be achieved. We analyze the heating related to background losses, and show that our laser-cooling scheme can maintain the temperature of the gas without significant additional losses.

  2. Orbital Non-Fermi-Liquid Behavior in Cubic Ruthenates

    NASA Astrophysics Data System (ADS)

    Laad, M. S.; Bradarić, I.; Kusmartsev, F. V.

    2008-03-01

    We peruse various anomalous physical responses of the cubic (ferromagnetic SrRuO3 and paramagnetic CaRuO3) ruthenates, such as fractional power-law conductivity, anomalous Raman line shapes, and Hall currents. We show how these exciting power-law observations are naturally described within a new, local (orbital) non-Fermi-liquid state arising from strong, multiorbital Coulomb interactions. Introducing a multiorbital, correlated model treated within the dynamical mean-field theory, we also find two distinct relaxation rates for relaxation of transport in complete agreement with experiment.

  3. Orbital non-fermi-liquid behavior in cubic ruthenates.

    PubMed

    Laad, M S; Bradarić, I; Kusmartsev, F V

    2008-03-07

    We peruse various anomalous physical responses of the cubic (ferromagnetic SrRuO3 and paramagnetic CaRuO3) ruthenates, such as fractional power-law conductivity, anomalous Raman line shapes, and Hall currents. We show how these exciting power-law observations are naturally described within a new, local (orbital) non-Fermi-liquid state arising from strong, multiorbital Coulomb interactions. Introducing a multiorbital, correlated model treated within the dynamical mean-field theory, we also find two distinct relaxation rates for relaxation of transport in complete agreement with experiment.

  4. SETI Before Marconi - Sunlight Beacons and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Baxter, S.

    The strategies underlying the search for extraterrestrial intelligence are generally predicated on a model of civilisations with telecommunications technology searching for evidence of each other and making contact accordingly. It is argued that there is at least one plausible signalling type detectable to pre-radio civilisations: naked-eye `sunlight beacons'. A motive for attempting such communication could be the remote detection of the injection of greenhouse and other waste gases into a planetary atmosphere as a result of agricultural and early industrial activities. We may have been detectable, and contactable, since the Neolithic. An absence of such contacts is therefore a deepening of the Fermi Paradox.

  5. The Fermi-Pasta-Ulam problem: fifty years of progress.

    PubMed

    Berman, G P; Izrailev, F M

    2005-03-01

    A brief review of the Fermi-Pasta-Ulam (FPU) paradox is given, together with its suggested resolutions and its relation to other physical problems. We focus on the ideas and concepts that have become the core of modern nonlinear mechanics, in their historical perspective. Starting from the first numerical results of FPU, both theoretical and numerical findings are discussed in close connection with the problems of ergodicity, integrability, chaos and stability of motion. New directions related to the Bose-Einstein condensation and quantum systems of interacting Bose-particles are also considered.

  6. Exploring the association of Fermi sources with Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Munar-Adrover, P.; Paredes, J. M.; Romero, G. E.

    2011-02-01

    Massive protostars have associated bipolar outflows which can produce strong shocks when interact with the surrounding medium. Some theoretical models predict that particle acceleration at relativistic velocities can occur leading to gamma ray emission. In order to identify young stellar objects (YSO) that might emit gamma rays, we have crossed the Fermi First Year Catalog with catalogs of known YSOs, obtaining a set of candidates by spatial correlation. We have conducted Montecarlo simulations to find the probability of chance coincidence. Our results indicate that ~70% of the candidates should be gamma-ray sources with a confidence of ~5σ.

  7. Quantum phase transition in Bose-Fermi mixtures

    SciTech Connect

    Ludwig, D.; Moroz, S.; Wetterich, C.; Floerchinger, S.

    2011-09-15

    We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero temperature. Within a quantum field theoretical model, a two-step Gaussian approximation allows us to capture the main features of the quantum phase diagram. We show that a repulsive boson-boson interaction is necessary for thermodynamic stability. The quantum phase diagram is mapped in chemical-potential and density space, and both first- and second-order quantum phase transitions are found. We discuss typical characteristics of the first-order transition, such as hysteresis or a droplet formation of the condensate, which may be searched for experimentally.

  8. Dark matter annihilation and the PAMELA, FERMI, and ATIC anomalies

    SciTech Connect

    El Zant, A. A.; Okada, H.; Khalil, S.

    2010-06-15

    If dark matter annihilation accounts for the tantalizing excess of cosmic ray electron/positrons, as reported by the PAMELA, ATIC, HESS, and FERMI observatories, then the implied annihilation cross section must be relatively large. This results, in the context of standard cosmological models, in very small relic dark matter abundances that are incompatible with astrophysical observations. We explore possible resolutions to this apparent conflict in terms of nonstandard cosmological scenarios; plausibly allowing for large cross sections, while maintaining relic abundances in accord with current observations.

  9. Pushing the Limits: High Redshift Fermi-LAT Blazars

    NASA Astrophysics Data System (ADS)

    Ojha, Roopesh; Gasparrini, Dario; Lott, Benoit; Cutini, Sara; Fermi-LAT Collaboration

    2016-01-01

    High-redshift blazars detected by the Fermi Large Area Telescope (LAT) are of great astrophysical import as they are extreme objects whose energetics remain a mystery. Such blazars are intrinsically interesting since they inform us about the evolution of gamma-ray blazars and are, by definition, some of the more luminous blazars in the LAT sample. They are also an excellent tool to study the EBL and thus the gamma-ray horizon. We present the latest high redshift blazar detections in the LAT and discuss some of their implications.

  10. Spin response of a normal Fermi liquid with noncentral interactions

    SciTech Connect

    Pethick, C. J.; Schwenk, A.

    2009-11-15

    We consider the spin response of a normal Fermi liquid with noncentral interactions under conditions intermediate between the collisionless and hydrodynamic regimes. This problem is of importance for calculations of neutrino properties in dense matter. By expressing the deviation of the quasiparticle distribution function from equilibrium in terms of eigenfunctions of the transport equation under the combined influence of collisions and an external field, we derive a closed expression for the spin-density-spin-density response function and compare its predictions with that of a relaxation-time approximation. Our results indicate that the relaxation-time approximation is reliable for neutrino properties under astrophysically relevant conditions.

  11. Scattering properties of weakly-bound dimers of Fermi atoms

    NASA Astrophysics Data System (ADS)

    Petrov, Dmitry

    2005-03-01

    We discuss the behavior of weakly bound bosonic dimers formed in a two-component Fermi gas with a large positive scattering length for the interspecies interaction. We present a theoretical approach for solving a few-body scattering problem and describe the physics of dimer-dimer elastic and inelastic scattering. We explain why these diatomic molecules, while in the highest ro-vibrational level, are characterized by remarkable collisional stability. Co-authors are Christophe Salomon, LKB, Ecole Normale Superieure, Paris, France; Georgy Shlyapnikov, LPTMS, University of South Paris, Orsay, France.

  12. Minimax rational approximation of the Fermi-Dirac distribution

    SciTech Connect

    Moussa, Jonathan E.

    2016-10-27

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ–1)) poles to achieve an error tolerance ϵ at temperature β–1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δocc, the occupied energy interval. Furthermore, this is particularly beneficial when Δ >> Δocc, such as in electronic structure calculations that use a large basis set.

  13. Condensate fraction of a two-dimensional attractive Fermi gas

    SciTech Connect

    Salasnich, Luca

    2007-07-15

    We investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers.

  14. Gamma Ray Bursts in the Swift-Fermi Era

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Razzaque, Soebur

    2013-01-01

    Gamma-ray bursts (GRBs) are among the most violent occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole birth. They are highly luminous events and provide excellent probes of the distant universe. GRB research has greatly advanced over the past 10 years with the results from Swift, Fermi and an active follow-up community. In this review we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglows.

  15. Spectral function and kinetic equation for a normal Fermi liquid

    SciTech Connect

    Arshad, M.; Siddique, I.; Kondratyev, A. S.

    2007-08-01

    On the basis of the Kadanoff-Baym (KB) version of the time-dependent Green's function method, an Ansatz for the approximation of a spectral function is offered. The Ansatz possesses all the advantages of quasiparticle and extended quasiparticle approximations and satisfies the KB equation for a spectral function in the case of slightly nonequilibrium system when disturbances in space and time are taken into consideration in the gradient approximation. This feature opens opportunities for the microscopic derivation of the Landau kinetic equation for the quasiparticle distribution function of the normal Fermi liquid and provides the widening of these equations' temperature range of validity.

  16. Realizing type-II Weyl points in an optical lattice

    NASA Astrophysics Data System (ADS)

    Shastri, Kunal; Yang, Zhaoju; Zhang, Baile

    2017-01-01

    The recent discovery of the Lorentz symmetry-violating "type-II" Weyl semimetal phase has renewed interest in the study of Weyl physics in condensed-matter systems. However, tuning the exceptional properties of this novel state has remained a challenge. Optical lattices, created using standing laser beams, provide a convenient platform to tune tunneling parameters continuously in time. In this paper, we propose a generalized two level system exhibiting type-II Weyl points that can be realized using ultracold atoms in an optical lattice. The system is engineered using a three-dimensional lattice with complex π phase tunneling amplitudes. Various unique properties of the type-II Weyl semimetal such as open Fermi surface, anomalous chirality, and topological Fermi arcs can be probed using the proposed optical lattice scheme.

  17. Correlations in the low-density Fermi gas: Fermi-liquid state, dimerization, and Bardeen-Cooper-Schrieffer pairing

    NASA Astrophysics Data System (ADS)

    Fan, H. H.; Krotscheck, E.; Lichtenegger, T.; Mateo, D.; Zillich, R. E.

    2015-08-01

    We present ground-state calculations for low-density Fermi gases described by two model interactions, an attractive square-well potential and a Lennard-Jones potential, of varying strength. We use the optimized Fermi-hypernetted chain integral equation method, which has been proved to provide, in the density regimes of interest here, an accuracy of better than 1%. We first examine the low-density expansion of the energy and compare it with the exact answer of H. Huang and C. N. Yang [Phys. Rev. 105, 767 (1957), 10.1103/PhysRev.105.767]. It is shown that a locally correlated wave function of the Jastrow-Feenberg type does not recover the quadratic term in the expansion of the energy in powers of a0kF , where a0 is the vacuum s -wave scattering length and kF the Fermi wave number. The problem is cured by adding second-order perturbation corrections in a correlated basis. Going to higher densities and/or more strongly coupled systems, we encounter an instability of the normal state of the system which is characterized by a divergence of the in-medium scattering length. We interpret this divergence as a phonon-exchange-driven dimerization of the system, similar to what occurs at zero density when the vacuum scattering length a0 diverges. We then study, in the stable regime, the superfluid gap and its dependence on the density and the interaction strength. We identify two corrections to low-density expansions: One is medium corrections to the pairing interaction, and the other is finite-range corrections. We show that the most important finite-range corrections are a direct manifestation of the many-body nature of the system.

  18. Born-Kothari condensation in an ideal Fermi gas

    NASA Astrophysics Data System (ADS)

    Ghosh, Arnab; Ray, Deb Shankar

    2017-02-01

    ``Condensation" in Fermi-Dirac statistics [D. S. Kothari and B. Nath, Nature 151, 420 (1943), 10.1038/151420a0], which appears as a natural consequence of Born's reciprocity principle [M. Born, Proc. R. Soc. London A 165, 291 (1938), 10.1098/rspa.1938.0060; M. Born, Nature 141, 328 (1938), 10.1038/141327a0], is examined from a theoretical perspective. Since fermions obey the Pauli exclusion principle, it is conceptually different from Bose-Einstein condensation, which permits macroscopic occupation of bosons at the single-particle level below a critical temperature. Yet, in accordance with the Cahill and Glauber [Phys. Rev. A 59, 1538 (1999)], 10.1103/PhysRevA.59.1538 formulation for fermionic fields, and in close kinship to bosonic fields, we have shown that in analogy to Bose-Einstein condensation, it is possible to associate an intrinsic notion of symmetry breaking and the thermodynamic "order parameter" to characterize the foregoing hitherto unexplored phenomenon in an ideal Fermi-Dirac gas as condensation-like coherence within fermions.

  19. Intrinsic Correlations for Flaring Blazars Detected by Fermi

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Yang, J. H.; Xiao, H. B.; Lin, C.; Constantin, D.; Luo, G. Y.; Pei, Z. Y.; Hao, J. M.; Mao, Y. W.

    2017-02-01

    Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ-ray luminosity is strongly correlated with other intrinsic luminosities.

  20. Tunable Fermi level and hedgehog spin texture in gapped graphene

    NASA Astrophysics Data System (ADS)

    Varykhalov, A.; Sánchez-Barriga, J.; Marchenko, D.; Hlawenka, P.; Mandal, P. S.; Rader, O.

    2015-07-01

    Spin and pseudospin in graphene are known to interact under enhanced spin-orbit interaction giving rise to an in-plane Rashba spin texture. Here we show that Au-intercalated graphene on Fe(110) displays a large (~230 meV) bandgap with out-of-plane hedgehog-type spin reorientation around the gapped Dirac point. We identify two causes responsible. First, a giant Rashba effect (~70 meV splitting) away from the Dirac point and, second, the breaking of the six-fold graphene symmetry at the interface. This is demonstrated by a strong one-dimensional anisotropy of the graphene dispersion imposed by the two-fold-symmetric (110) substrate. Surprisingly, the graphene Fermi level is systematically tuned by the Au concentration and can be moved into the bandgap. We conclude that the out-of-plane spin texture is not only of fundamental interest but can be tuned at the Fermi level as a model for electrical gating of spin in a spintronic device.

  1. THREE MILLISECOND PULSARS IN FERMI LAT UNASSOCIATED BRIGHT SOURCES

    SciTech Connect

    Ransom, S. M.; Ray, P. S.; Wolff, M. T.; Grove, J. E.; Camilo, F.; Roberts, M. S. E.; Celik, Oe.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Cheung, C. C.; Abdo, A. A.; Kerr, M.; Pennucci, T.; Cognard, I.; Freire, P. C. C.; Desvignes, G.; Donato, D. E-mail: Paul.Ray@nrl.navy.mil

    2011-01-20

    We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and {gamma}-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind {gamma}-ray pulsation searches. They seem to be relatively normal, nearby ({<=}2 kpc) MSPs. These observations, in combination with the Fermi detection of {gamma}-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient {gamma}-ray producers. The {gamma}-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of {approx}10{sup 30}-10{sup 31} erg s{sup -1} are typical of the rare radio MSPs seen in X-rays.

  2. Multi-wavelength emission from the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Ko, Chung-Ming; Dogiel, V. A.; Chernyshov, Dmitry; Cheng, K. S.

    The source of electrons responsible for the nonthermal emissions from the Fermi Bubbles, such as gamma rays and microwave, still awaits successful explanation. These electrons should be accelerated in-situ because of the efficient energy loss by inverse Compton and synchrotron processes. In this contribution, we analyse electron acceleration or re-acceleration by the shocks and turbulence produced by tidal disruption of stars by the supermassive black hole at the Galactic center. We consider two different scenarios. The first involved stochastic acceleration of electrons directly from the background plasma (in which the seeds are KeV electrons). The model can explain the observed gamma-ray microwave fluxes but only in a very restricted parameter space. The second is the re-acceleration of GeV electrons originated from the supernova remnants in the Galactic plane that diffuse into the Bubbles. This model produces the Fermi-LAT gamma-ray result but the microwave spectrum is steeper than the observed one.

  3. The First Fermi-LAT Supernova Remnant Catalog

    NASA Astrophysics Data System (ADS)

    Brandt, T. J.; Fermi-LAT Collaboration

    2015-04-01

    The Fermi Gamma-ray Space Telescope's Large Area Telescope (Fermi-LAT) has shed new light on many types of Galactic objects, including many individual Supernova Remnants (SNRs). The spectral detection of hadronic gamma-ray emission from two SNRs, suggesting acceleration of cosmic ray (CR) protons, is an example of individual studies providing clues to characteristics that may be common to all SNRs. To uniformly determine SNR properties, we have developed the first systematic survey of SNRs from 1 to 100 GeV. From the 279 known radio SNRs, we found more than 100 GeV candidates, 31 of which are likely and 14 of which are marginally counterparts. These candidates span a wide range of multiwavelength properties, providing a critical context for complementary, in depth individual studies. Modeling this multiwavelength data demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from hadronic and leptonic particle populations in these objects. Together with the > 240 upper limits on GeV emission at the radio position and extension, our results also enable us to indirectly constrain SNRs' aggregate ability to accelerate CRs, and with direct measurements, will additionally enable a better understanding of CR origins.

  4. Two-fluid hydrodynamics in strongly interacting Fermi gases

    NASA Astrophysics Data System (ADS)

    Taylor, Edward

    2010-03-01

    Landau's theory of two-fluid hydrodynamics provides an exact description of the finite-temperature, low-energy dynamics of all strongly interacting superfluids described by a two-component order parameter. Reliable solutions of the two-fluid equations in trapped Fermi gases through the BCS-BEC crossover are crucial for extracting information about the equation of state and transport coefficients from experiments in the superfluid phase. In this talk, I will present new accurate variational solutions for the first and second sound frequencies in a trapped Fermi gas at unitarity, highlighting similarities with superfluid Helium-4 as well as some surprising differences [1.]. I will also discuss proposals to detect these modes in experiments. For the uniform gas, we show that at temperatures of order 0.7Tc and higher, second sound enters with comparable weight to first sound in the dynamic structure factor, in agreement with the recent results of Arahata and Nikuni on the propagation of density pulses [2.].[1.] E. Taylor, H. Hu, X.-J. Liu, L. P. Pitaevskii, A. Griffin, and S. Stringari, Phys. Rev. A 80, 053601 (2009).[2.] E. Arahata and T. Nikuni, Phys. Rev. A 80, 043613 (2009).

  5. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, J. L.; Oates, S. R.; Schady, P.; Burrows, D. N.; de Pasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multiwavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  6. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.; Oates, S. R.; Schady, P.; Burrows, D. N.; dePasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Troja, E.; Vasileiou, V.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi -LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust dataset of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT detected GRBs and the well studied, fainter, less energetic GRBs detected by Swift -BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi -GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  7. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith I.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  8. Tan's distributions and Fermi-Huang pseudopotential in momentum space

    NASA Astrophysics Data System (ADS)

    Valiente, Manuel

    2012-01-01

    The long-standing question of finding the momentum representation for the s-wave zero-range interaction in three spatial dimensions is here solved. This is done by expressing a certain distribution, introduced in a formal way in [S. Tan, Ann. Phys. (NY)APNYA60003-491610.1016/j.aop.2008.03.004 323, 2952 (2008)], explicitly. The resulting form of the Fourier-transformed pseudopotential remains very simple. Operator forms for the so-called Tan's selectors, which, together with Fermi-Huang pseudopotential, largely simplify the derivation of Tan's universal relations for the Fermi gas, are here derived and are also very simple. A momentum cutoff version of the pseudopotential is also provided, and with this no apparent contradiction to the notion of integrals in Tan's methods is left. The equivalence, even at the intermediate-step level, between the pseudopotential approach and momentum-space renormalization of the bare Dirac delta interaction is then shown by using the explicit form of the cutoff pseudopotential.

  9. Simulating strongly correlated electrons with a strongly interacting Fermi gas

    SciTech Connect

    Thomas, John E.

    2013-05-28

    The quantum many-body physics of strongly-correlated fermions is studied in a degenerate, strongly- interacting atomic Fermi gas, first realized by our group with DOE support in 2002. This system, which exhibits strong spin pairing, is now widely studied and provides an important paradigm for testing predictions based on state-of-the-art many-body theory in fields ranging from nuclear matter to high temperature superfluidity and superconductivity. As the system is strongly interacting, both the superfluid and the normal fluid are nontrivial and of great interest. A central part of our program on Fermi gases is the connection between the study of thermodynamics, supported by DOE and the study of hydrodynamic transport, supported by NSF. This connection is especially interesting in view of a recent conjecture from the string theory community on the concept of nearly perfect normal fluids, which exhibit a minimum ratio of shear viscosity to entropy density in strongly-interacting, scale-invariant systems.

  10. The likely Fermi detection of the supernova remnant RCW 103

    SciTech Connect

    Xing, Yi; Wang, Zhongxiang; Zhang, Xiao; Chen, Yang

    2014-02-01

    We report on the results from our γ-ray analysis of the supernova remnant (SNR) RCW 103 region. The data were taken with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. An extended source is found at a position consistent with that of RCW 103 and its emission was only detected above 1 GeV (10σ significance), with a power-law spectrum with a photon index of 2.0 ± 0.1. We obtain its 1-300 GeV spectrum and the total flux gives a luminosity of 8.3 × 10{sup 33} erg s{sup –1} at a source distance of 3.3 kpc. Given the positional coincidence and property similarities of this source with other SNRs, we identify it as the likely Fermi γ-ray counterpart to RCW 103. Including radio measurements of RCW 103, the spectral energy distribution (SED) is modeled by considering emission mechanisms based on both hadronic and leptonic scenarios. We find that models in the two scenarios can reproduce the observed SED, while in the hadronic scenario the existence of SNR-molecular cloud interactions is suggested as a high density of the target protons is required.

  11. FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE VELA PULSAR

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Bartelt, J.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bogart, J. R.; Atwood, W. B.; Bagagli, R.; Baldini, L.; Bellardi, F.; Bellazzini, R.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bisello, D.; Baughman, B. M. E-mail: massimiliano.razzano@pi.infn.it

    2009-05-10

    The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new {gamma}-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E {>=} 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of {gamma} = 1.51{sup +0.05} {sub -0.04} with an exponential cutoff at E{sub c} = 2.9 {+-} 0.1 GeV. Spectral fits with generalized cutoffs of the form e{sup -(E/E{sub c}){sup b}} require b {<=} 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.

  12. Revised Thomas-Fermi approximation for singular potentials

    NASA Astrophysics Data System (ADS)

    Dufty, James W.; Trickey, S. B.

    2016-08-01

    Approximations for the many-fermion free-energy density functional that include the Thomas-Fermi (TF) form for the noninteracting part lead to singular densities for singular external potentials (e.g., attractive Coulomb). This limitation of the TF approximation is addressed here by a formal map of the exact Euler equation for the density onto an equivalent TF form characterized by a modified Kohn-Sham potential. It is shown to be a "regularized" version of the Kohn-Sham potential, tempered by convolution with a finite-temperature response function. The resulting density is nonsingular, with the equilibrium properties obtained from the total free-energy functional evaluated at this density. This new representation is formally exact. Approximate expressions for the regularized potential are given to leading order in a nonlocality parameter, and the limiting behavior at high and low temperatures is described. The noninteracting part of the free energy in this approximation is the usual Thomas-Fermi functional. These results generalize and extend to finite temperatures the ground-state regularization by R. G. Parr and S. Ghosh [Proc. Natl. Acad. Sci. U.S.A. 83, 3577 (1986), 10.1073/pnas.83.11.3577] and by L. R. Pratt, G. G. Hoffman, and R. A. Harris [J. Chem. Phys. 88, 1818 (1988), 10.1063/1.454105] and formally systematize the finite-temperature regularization given by the latter authors.

  13. Shells, orbit bifurcations, and symmetry restorations in Fermi systems

    NASA Astrophysics Data System (ADS)

    Magner, A. G.; Koliesnik, M. V.; Arita, K.

    2016-11-01

    The periodic-orbit theory based on the improved stationary-phase method within the phase-space path integral approach is presented for the semiclassical description of the nuclear shell structure, concerning themain topics of the fruitful activity ofV.G. Soloviev. We apply this theory to study bifurcations and symmetry breaking phenomena in a radial power-law potential which is close to the realistic Woods-Saxon one up to about the Fermi energy. Using the realistic parametrization of nuclear shapes we explain the origin of the double-humped fission barrier and the asymmetry in the fission isomer shapes by the bifurcations of periodic orbits. The semiclassical origin of the oblate-prolate shape asymmetry and tetrahedral shapes is also suggested within the improved periodic-orbit approach. The enhancement of shell structures at some surface diffuseness and deformation parameters of such shapes are explained by existence of the simple local bifurcations and new non-local bridge-orbit bifurcations in integrable and partially integrable Fermi-systems. We obtained good agreement between the semiclassical and quantum shell-structure components of the level density and energy for several surface diffuseness and deformation parameters of the potentials, including their symmetry breaking and bifurcation values.

  14. Low-lying excitations in a strongly interacting Fermi gas

    NASA Astrophysics Data System (ADS)

    Vale, Christopher; Hoinka, Sascha; Dyke, Paul; Lingham, Marcus

    2016-05-01

    We present measurements of the low-lying excitation spectrum of a strongly interacting Fermi gas across the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover using Bragg spectroscopy. By focussing the Bragg lasers onto the central volume of the cloud we can probe atoms at near-uniform density allowing measurement of the homogeneous density-density response function. The Bragg wavevector is set to be approximately half of the Fermi wavevector to probe the collective response. Below the superfluid transition temperature the Bragg spectra dominated by the Bogoliubov-Anderson phonon mode. Single particle excitations become visible at energies greater than twice the pairing gap. As interactions are tuned from the BCS to BEC regime the phonon and single particle modes separate apart and both the pairing gap and speed of sound can be directly read off in certain regions of the crossover. Single particle pair-breaking excitations become heavily suppressed as interactions are tuned from the BCS to BEC regimes.

  15. Fermi GBM Counterparts to LIGO Gravitational-Wave Candidates

    NASA Astrophysics Data System (ADS)

    Burns, Eric; Blackburn, Lindy; Briggs, Michael Stephen; Camp, Jordan; Christensen, Nelson; Connaughton, Valerie; Goldstein, Adam; Littenberg, Tyson; Racusin, Judith L.; Shawhan, Peter S.; Pound Singer, Leo; Veitch, John; Zhang, Binbin

    2016-04-01

    As the advanced configuration of the Laser Interferometer Gravitational-wave Observatory has begun operations, we eagerly anticipate the detection of gravitational waves (GW) with LIGO in coincidence with a gamma-ray signal from the Fermi Gamma-ray Burst Monitor (GBM). The most likely source is a short Gamma-Ray Burst (GRB) arising from the merger of two compact objects. With its broad sky coverage, GBM triggers and localizes more short GRBs than other active space missions, ~40 each year. Combining GBM and LIGO localization uncertainty regions may provide a smaller target to look for the GW host. A joint GBM-LIGO detection increases the confidence in the GW detection and helps characterize the parameters of the merger. Offline searches for weak GRBs that fail to trigger onboard Fermi indicate that additional short GRBs can be detected in the GBM data. I will discuss the implementation and expected benefits of joint searches to detect and localize GW candidates. I will also explore how the non-detection in the GBM data of a signal consistent with GW candidates in the LIGO data can affect follow-up strategies for counterpart searches by other observers.

  16. The first Fermi LAT supernova remnant catalog

    SciTech Connect

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidates falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.

  17. High-redshift Fermi blazars observed by GROND and Swift

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Nardini, M.; Tagliaferri, Greiner, J.; Schady, P.; Rau, A.; Foschini, L.; Tavecchio, F.; Ghirlanda, G.; Sbarrato, T.

    2013-01-01

    We observed five γ-ray-loud blazars at redshift greater than 2 with the X-Ray Telescope (XRT) and the UltraViolet and Optical Telescope (UVOT) on-board the Swift satellite, and the Gamma-Ray burst Optical Near-Infrared Detector (GROND) instrument. These observations were quasi-simultaneous, usually within a few hours. For four of these blazars, the near-IR to UV data show the presence of an accretion disc, and we could reliably estimate its accretion rate and black hole mass. One of them, PKS 1348+007, was found in an extraordinarily high IR-optical state, almost two orders of magnitude brighter than at the epoch of the Sloan Digital Sky Survey observations. For all the five quasars, the physical parameters of the jet-emitting zone, derived by applying a one-zone emission model, are similar to that found for the bulk of other γ-ray-loud quasars. With our observations, we have X-ray data for the full sample of blazars at z > 2 present in the Fermi 2-year (2LAC) catalogue. This allows us to have a rather complete view of the spectral energy distribution of all high-redshift Fermi blazars, and to draw some conclusions about their properties, and especially about the relation between the accretion rate and the jet power.

  18. Three Millisecond Pulsars in Fermi LAT Unassociated Bright Sources

    NASA Technical Reports Server (NTRS)

    Ransom, S. M.; Ray, P. S.; Camilo, F.; Roberts, M. S. E.; Celik, O.; Wolff, M. T.; Cheung, C. C.; Kerr, M.; Pennucci, T.; DeCesar, M. E.; Cognard, I.; Lyne, A. G.; Stappers, B. W.; Freire, P. C. C.; Grove, J. E.; Abdo, A. A.; Desvignes, G.; Donato, D.; Ferrara, E. C.; Gehrels, N.; Guillemot, L.; Gwon, C.; Johnston, S.; Harding, A. K.; Thompson, D. J.

    2010-01-01

    We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and gamma-ray millisecond pulsar (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind gamma-ray pulsation searches. They seem to be relatively normal, nearby (<= 2 kpc) MSPs. These observations, in combination with the Fermi detection of gamma-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient gamma-ray producers. The gamma-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few Ge V, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of approx 10(exp 30) - 10(exp 31) erg/s are typical of the rare radio MSPs seen in X-rays.

  19. Enhanced photogalvanic current in topological insulators via Fermi energy tuning

    NASA Astrophysics Data System (ADS)

    Okada, Ken N.; Ogawa, Naoki; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S.; Kawasaki, Masashi; Tokura, Yoshinori

    2016-02-01

    We achieve the enhancement of the circular photogalvanic effect arising from the photoinjection of spins in topological insulator thin films by tuning the Fermi level (EF) . A series of (Bi1-xSbx) 2Te3 thin films were tailored so that the Fermi energy ranges above 0.34 eV to below 0.29 eV of the Dirac point, i.e., from the bulk conduction band bottom to the valence band top through the bulk in-gap surface-Dirac cone. The circular photogalvanic current, indicating a flow of spin-polarized surface-Dirac electrons, shows a pronounced peak when the EF is set near the Dirac point and is also correlated with the carrier mobility. Our observation reveals that there are substantial scatterings between the surface-Dirac and bulk state electrons in the generation process of spin-polarized photocurrent, which can be avoided by designing the electronic structure in topological insulators.

  20. Detecting superlight dark matter with Fermi-degenerate materials

    NASA Astrophysics Data System (ADS)

    Hochberg, Yonit; Pyle, Matt; Zhao, Yue; Zurek, Kathryn M.

    2016-08-01

    We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O (keV). Detection of suc light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O (meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ˜ 10-3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in order to detect the small energy deposits from the dark matter scatterings. Considering a wide variety of constraints, from dark matter self-interactions to the cosmic microwave background, we show that models consistent with cosmological/astrophysical and terrestrial constraints are observable with such detectors. A wider range of viable models with dark matter mass below an MeV is available if dark matter or mediator properties (such as couplings or masses) differ at BBN epoch or in stellar interiors from those in superconductors. We also show that metal targets pay a strong in-medium suppression for kinetically mixed mediators; this suppression is alleviated with insulating targets.

  1. Thermal conductivity and sound attenuation in dilute atomic Fermi gases

    SciTech Connect

    Braby, Matt; Chao Jingyi; Schaefer, Thomas

    2010-09-15

    We compute the thermal conductivity and sound attenuation length of a dilute atomic Fermi gas in the framework of kinetic theory. Above the critical temperature for superfluidity, T{sub c}, the quasiparticles are fermions, whereas below T{sub c}, the dominant excitations are phonons. We calculate the thermal conductivity in both cases. We find that at unitarity the thermal conductivity {kappa} in the normal phase scales as {kappa}{proportional_to}T{sup 3/2}. In the superfluid phase we find {kappa}{proportional_to}T{sup 2}. At high temperature the Prandtl number, the ratio of the momentum and thermal diffusion constants, is 2/3. The ratio increases as the temperature is lowered. As a consequence we expect sound attenuation in the normal phase just above T{sub c} to be dominated by shear viscosity. We comment on the possibility of extracting the shear viscosity of the dilute Fermi gas at unitarity using measurements of the sound absorption length.

  2. Remarkable paramagnetic features of Fermi-Dirac-Pauli plasmas

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2011-07-01

    In this paper by using the relativistic magnetic susceptibility of a Fermi-Dirac (relativistically degenerate) plasma, quantum magnetohydrodynamics model is used to investigate the propagation of spin-induced (SI) magnetosonic nonlinear excitations in a normally and relativistically degenerate dense electron-ion plasma in the presence of the spin magnetization effect. Based on the conventional pseudopotential method the matching criterion for the evolution of SI solitary structures is evaluated. It is found that, the plasma mass density and strength of the magnetic field have significant effects on excitation and evolution of magnetosonic nonlinear structures in Fermi-Dirac plasmas. Only rarefactive SI magnetosonic solitary structures are found to excite in such plasmas. Furthermore, fundamental differences are shown to exist in magnetosonic soliton dynamics in the two distinct plasma degeneracy regimes, which are due to interplay between the negative pressure-like paramagnetism and positive relativistic degeneracy pressure of electrons. Current investigation can help better understand the electron spin effects on nonlinear wave propagations in strongly magnetized dense astrophysical objects such as white dwarfs and pulsar magnetospheres.

  3. Ultracold Fermi gases with emergent SU(N) symmetry

    NASA Astrophysics Data System (ADS)

    Cazalilla, Miguel A.; Rey, Ana Maria

    2014-12-01

    We review recent experimental and theoretical progress on ultracold alkaline-earth Fermi gases with emergent SU(N) symmetry. Emphasis is placed on describing the ground-breaking experimental achievements of recent years. The latter include (1) the cooling to below quantum degeneracy of various isotopes of ytterbium and strontium, (2) the demonstration of optical Feshbach resonances and the optical Stern-Gerlach effect, (3) the realization of a Mott insulator of 173Yb atoms, (4) the creation of various kinds of Fermi-Bose mixtures and (5) the observation of many-body physics in optical lattice clocks. On the theory side, we survey the zoo of phases that have been predicted for both gases in a trap and loaded into an optical lattice, focusing on two and three dimensional systems. We also discuss some of the challenges that lie ahead for the realization of such phases such as reaching the temperature scale required to observe magnetic and more exotic quantum orders. The challenge of dealing with collisional relaxation of excited electronic levels is also discussed.

  4. Probing the Southern Fermi Bubble in Ultraviolet Absorption

    NASA Astrophysics Data System (ADS)

    Karim, Md. Tanveer; Fox, Andrew; Jenkins, Edward B.

    2017-01-01

    The Fermi Bubbles are two giant gamma-ray emitting lobes, extending 55° below and above the Galactic Center, that were discovered in 2010. While the Northern Bubble has been extensively studied in ultraviolet (UV) absorption, little is known about the UV properties of the Southern Bubble. We use UV absorption-line spectra from the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) to probe the Southern Fermi Bubble using two sightlines to background AGN, one passing inside the Bubble (RBS 1768) and one passing just outside (RBS 2000). We used VPFIT, a Voigt profile fitting program to detect the existence of high-velocity absorption components and to measure the column density of different metal ions. We detected two high-velocity absorption components in both sightlines; one at vLSR = -150 km s-1 and one at vLSR = 160 km s-1. We determined that the component at vLSR = 160 km s-1 is due to the Magellanic Stream. Absorption is seen in ions of silicon, carbon and aluminium. The discovery that the high-velocity component is present in both sightlines shows that cool gas can extend further from the Galactic plane than the gamma-ray emitting regions. This could indicate past outflow activity prior to the creation of the Southern Bubble. This project was supported in part by the NSF REU grant AST-1358980 and by the Nantucket Maria Mitchell Association.

  5. Feshbach resonances in ultracold Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Bortolotti, Daniele Carlo Enrico

    In the wake of successful experiments in Fermi condensates, experimental attention is broadening to include resonant interactions in degenerate Bose-Fermi mixtures. In this thesis we wish to study the equilibrium properties of the fermionic molecules that can be created in such a mixture. To this end, we first discuss the two body properties of the system, and introduce the model Hamiltonian we use to describe the resonant physics, highlighting its virtues, as well as its limitations. We then proceed by analyzing the mean field solution of this model, by studying both the equilibrium problem, and the non-equilibrium equations of motion, thus developing a powerful language to discuss the system. We then highlight the limitations of the mean-field approach, and develop a numerically tractable generalized version of this theory, which is able to correctly describe the two-body properties of the system in the low-density limit. Finally, we study the properties of the system using this generalized mean-field theory, by first analyzing the two-body scattering matrix in the many-body environment, assessing its complex poles in order to understand the stability properties of the Feshbach molecules in the gas. Secondly we solve the equilibrium equations self-consistently, to study the molecular populations and density distributions at equilibrium, as a function of external bias magnetic field.

  6. LaBaNiO4: a Fermi glass

    NASA Astrophysics Data System (ADS)

    Schilling, A.; Dell'Amore, R.; Karpinski, J.; Bukowski, Z.; Medarde, M.; Pomjakushina, E.; Müller, K. A.

    2009-01-01

    Polycrystalline samples of LaSr1-xBaxNiO4 show a crossover from a state with metallic transport properties for x = 0 to an insulating state as x\\to 1 . The end member LaBaNiO4 with a nominal nickel Ni 3d7 configuration might therefore be regarded as a candidate for an antiferromagnetic insulator. However, we do not observe any magnetic ordering in LaBaNiO4 down to 1.5 K, and despite its insulating transport properties several other physical properties of LaBaNiO4 resemble those of metallic LaSrNiO4. Based on an analysis of electrical and thermal-conductivity data as well as magnetic-susceptibility and low-temperature specific-heat measurements, we suggest that LaBaNiO4 is a Fermi glass with a finite electron density of states at the Fermi level but these states are localized.

  7. Fermi surface pockets in the underdoped cuprate YBa2Cu4O8, - are they present in low magnetic fields?

    NASA Astrophysics Data System (ADS)

    Cooper, J. R.; Matusiak, M.; Loram, J. W.; Yelland, E. A.; Dabrowski, B.

    2008-03-01

    The observations of quantum oscillations in the underdoped cuprate superconductors, ortho-II YBa2Cu3O6.5 [1] and YBa2Cu4O8 (Y124) [2] at very high magnetic fields and low temperatures could lead to improved understanding of cuprate superconductivity. This will be especially true if the small Fermi surface (FS) pockets are still present at higher temperatures and lower magnetic fields. As pointed out in ref. [2] the pockets appear to have low Fermi energies ˜ 300 K, and could therefore give rise to T-dependent magnetic anisotropy in the normal state associated with Landau-Peierls diamagnetism. We report susceptibility anisotropy data for Y124 crystals up to 300 K, and discuss whether these data and zero field heat capacity data, are consistent with the properties of the FS pockets obtained from high field measurements. [1] N. Doiron-Leyraud, et al., Nature 447,565 (2007) [2] E.A. Yelland et al. arXiv:cond-mat/07070057.

  8. Fulde-Ferrell-Larkin-Ovchinnikov states and quantum oscillations in mesoscopic superconductors and superfluid ultracold Fermi gases

    SciTech Connect

    Samokhvalov, A. V.; Mel'nikov, A. S.; Buzdin, A. I.

    2010-11-01

    We have studied the distinctive features of the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability and phase transitions in two-dimensional (2D) mesoscopic superconductors placed in magnetic field of arbitrary orientation and rotating superfluid Fermi gases with imbalanced state populations. Using a generalized version of the phenomenological Ginzburg-Landau theory we have shown that the FFLO states are strongly modified by the effect of the trapping potential confining the condensate. The phenomenon of the inhomogeneous state formation is determined by the interplay of three length scales: (i) length scale of the FFLO instability; (ii) 2D system size; (iii) length scale associated with the orbital effect caused either by the Fermi condensate rotation or magnetic field component applied perpendicular to the superconducting disk. We have studied this interplay and resulting quantum oscillation effects in both superconducting and superfluid finite-size systems with FFLO instability and described the hallmarks of the FFLO phenomenon in a restricted geometry. The finite size of the system is shown to affect strongly the conditions of the observability of switching between the states with different vorticities.

  9. Observations and Interpretation of Behind the Limb Solar Flares Detected by Fermi-LAT and Other Instruments

    NASA Astrophysics Data System (ADS)

    Petrosian, Vahe; Omodei, Nicola; Pesce-Rollins, Melissa; Rubio da Costa, Fatima; Liu, Wei

    2015-04-01

    The Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing > 30 MeV gamma-rays. During the past active period of the Sun the LAT has detected more than 40 flares up to GeV energies some of which occur behind the limb as determined by STEREO observations. We will present the observations on two such flares with significant flux of > 100 MeV (and some indication of 1 to 10 MeV detected by Fermi-GBM) gamma-rays coming from the visible disk while the flare and associated CMEs are initiated in active regions tens of degrees behind the visible limb of the Sun. We will consider acceleration of particles, their transport and radiative signatures, and the transfer of these radiation in the solar atmosphere to distinguish between (i) acceleration in the low corona, in a high corona trap, and/or in the CME driven shock; (ii) between continuous and prompt acceleration; and (iii) between electron bremsstrahlung and decay of pions produced by accelerated ions.

  10. The novel metallic states of the cuprates: Topological Fermi liquids and strange metals

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir; Chowdhury, Debanjan

    2016-12-01

    We review ideas on the nature of the metallic states of the hole-doped cuprate high temperature superconductors, with an emphasis on the connections between the Luttinger theorem for the size of the Fermi surface, topological quantum field theories (TQFTs), and critical theories involving changes in the size of the Fermi surface. We begin with the derivation of the Luttinger theorem for a Fermi liquid, using momentum balance during a process of flux insertion in a lattice electronic model with toroidal boundary conditions. We then review the TQFT of the ℤ spin liquid, and demonstrate its compatibility with the toroidal momentum balance argument. This discussion leads naturally to a simple construction of "topological" Fermi liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge liquid (ACL). We present arguments for a description of the pseudogap metal of the cuprates using ℤ-FL* or ℤ-ACL states with Ising-nematic order. These pseudogap metal states are also described as Higgs phases of a SU(2) gauge theory. The Higgs field represents local antiferromagnetism, but the Higgs-condensed phase does not have long-range antiferromagnetic order: the magnitude of the Higgs field determines the pseudogap, the reconstruction of the Fermi surface, and the Ising-nematic order. Finally, we discuss the route to the large Fermi surface Fermi liquid via the critical point where the Higgs condensate and Ising nematic order vanish, and the application of Higgs criticality to the strange metal.

  11. Pulsars above 10 GeV: Fermi LAT Observations and Questions

    NASA Technical Reports Server (NTRS)

    Thomson, Dave

    2012-01-01

    The success of the Fermi Large Area Telescope in studying gamma-ray pulsars offers hints about future work above 10 GeV. The infrastructure for discovering pulsars will be similar between LAT and any future telescope. Some of the Fermi LAT results suggest intriguing questions about the future of high-energy pulsar studies.

  12. Farm batch system and Fermi inter-process communication and synchronization toolkit

    SciTech Connect

    Mandrichenko, I.V.

    2001-02-20

    Farms Batch System (FBS) was developed as a batch process management system for off-line Run II data processing at Fermilab. FBS will manage PC farms composed of up to 250 nodes and scalable to 1000 nodes with disk capacity of up to several TB. FBS allows users to start arrays of parallel processes on multiple computers. It uses a simplified resource counting method load balancing. FBS has been successfully used for more than a year at Fermilab by fixed target experiments and will be used for collider experiment off-line data processing. Fermi Inter-Process Communication toolkit (FIPC) was designed as a supplement product for FBS that helps establish synchronization and communication between processes running in a distributed batch environment. However, FIPC is an independent package, and can be used with other batch systems, as well as in a non-batch environment. FIPC provides users with a variety of global distributed objects such as semaphores, queues and string variables. Other types of objects can be easily added to FIPC. FIPC has been running on several PC farms at Fermilab for half a year and is going to be used by CDF for off-line data processing.

  13. Physics of our Days: Cooling and thermometry of atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Onofrio, R.

    2017-02-01

    We review the status of cooling techniques aimed at achieving the deepest quantum degeneracy for atomic Fermi gases. We first discuss some physics motivations, providing a quantitative assessment of the need for deep quantum degeneracy in relevant physics cases, such as the search for unconventional superfluid states. Attention is then focused on the most widespread technique to reach deep quantum degeneracy for Fermi systems, sympathetic cooling of Bose–Fermi mixtures, organizing the discussion according to the specific species involved. Various proposals to circumvent some of the limitations on achieving the deepest Fermi degeneracy, and their experimental realizations, are then reviewed. Finally, we discuss the extension of these techniques to optical lattices and the implementation of precision thermometry crucial to the understanding of the phase diagram of classical and quantum phase transitions in Fermi gases.

  14. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    PubMed Central

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-01-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier–Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence. PMID:27845342

  15. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    NASA Astrophysics Data System (ADS)

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-11-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier-Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence.

  16. Electronic structure model of the hidden order and Fermi surface gapping in URu2Si2

    NASA Astrophysics Data System (ADS)

    Oppeneer, Peter; Elgazzar, Saad; Rusz, Jan; Suzuki, Michi-To; Mydosh, John

    2009-03-01

    The hidden order (HO) in the heavy-fermion superconductor URu2Si2 has been studied for more than 20 years, without that the nature of this unusual phase could be uncovered. We present a microscopic explanation for the mechanism of the hidden order, on the basis of state-of-the-art electronic structure calculations. In particular, we show that our calculations explain very well all the known properties of the paramagnetic and large moment antiferromagnetic (LMAF) phases. Exploiting the known experimental equivalence between the Fermi surface properties of the LMAF and HO phases, we identify the Fermi surface ``hot spots'' where a Fermi surface instability is lifted through spontaneous symmetry breaking, causing a surprisingly large Fermi surface gapping. We quantify that symmetry breaking through collective modes of antiferromagnetic moment excitations can induce a substantial Fermi surface gapping that consistently explains the transport properties and entropy loss of the HO phase.

  17. Temperature dependence of the universal contact parameter in a unitary Fermi gas.

    PubMed

    Kuhnle, E D; Hoinka, S; Dyke, P; Hu, H; Hannaford, P; Vale, C J

    2011-04-29

    The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.

  18. Quantum oscillations from surface Fermi arcs in Weyl and Dirac semimetals.

    PubMed

    Potter, Andrew C; Kimchi, Itamar; Vishwanath, Ashvin

    2014-10-20

    In a magnetic field, electrons in metals repeatedly traverse closed magnetic orbits around the Fermi surface. The resulting oscillations in the density of states enable powerful experimental techniques for measuring a metal's Fermi surface structure. On the other hand, the surface states of Weyl semimetals consist of disjoint, open Fermi arcs raising the question of whether they can be observed by standard quantum oscillatory techniques. Here, we find that the open Fermi arcs participate in unusual closed magnetic orbits by traversing the bulk of the sample to connect opposite surfaces. These orbits have anomalous features that are impossible for conventional surface states, and result in quantum oscillations that contain observable signatures of the topological character of the bulk Weyl semimetal. We also apply our predictions to the compounds Cd3As2 and Na3Bi that were recently proposed to be three-dimensional Dirac (doubled Weyl) semimetals, and propose experimental signatures of their possible Fermi arc states.

  19. Fermi Liquid Behavior in Quasi 1-D Conductors via Angular Magnetoresistance Oscillations

    NASA Astrophysics Data System (ADS)

    Lee, I. J.; Naughton, M. J.

    1998-03-01

    A body of evidence appears to be developing which suggests that electronic conduction in the q1D TMTSF molecular conductors can not be explained solely by Fermi liquid theory. Recent magnetotransport(G.M. Danner and P.M. Chaikin, Phys. Rev. Lett., 75), 4690 (1995). and photoemission(F. Zwick, et al. al.,) Phys. Rev. Lett., 79, 3982 (1997). experiments even point to a lack of a Fermi surface. We present angular-dependent magnetoresistance data on (TMTSF)_2PF6 under pressure, accompanied by calculations/simulations based on Boltzman transport (which explicitly require the existence of a Fermi surface). Based on rather good agreement between the two results, we maintain that a Fermi liquid description works, at least for the pressures employed. We will attempt to define the parameter space where Fermi liquid theory works, and where other (e.g. Luttinger) theories may be required.

  20. A New View of the High Energy Gamma-ray Sky with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2010-01-01

    This slide presentation reviews some of the findings that have been made possible by the use of the Fermi Gamma-ray Space Telescope. It describes the current status of the Fermi Telescope and reviews some of the science highlights.

  1. Momentum and spin transport properties of spin polarized Fermi systems

    NASA Astrophysics Data System (ADS)

    Wei, Lijuan

    We carried out experiments on a spin polarized 3He- 4He mixture with 3He concentration x 3 = 6.26 x 10-4, and on pure 3He liquid. Spin polarization affects the transport properties of these Fermi systems. The effect on momentum transport was studied by using a vibrating-wire viscometer to measure viscosity of the 3He-4He mixture over the temperature range 6.09 mK--100 mK in 7.96 T and 1.00 T magnetic fields. A large viscosity increase was observed upon application of the 7.96 T magnetic field for temperature T < TF(TF = 19.5 mK is the Fermi temperature). The observed viscosity is in very good agreement with theoretical calculations for a dilute Fermi gas by Jeon and Mullin [1988, 1989] and Mullin and Jeon [1992]. The polarization effect on spin transport was investigated by measuring the transverse diffusion coefficient D ⊥ in pure 3He liquid at saturated vapor pressure and at 15.85 bar over the temperature range 4.5 mK--159 mK in a 7.96 T magnetic field. We used a pulsed NMR spin echo technique in a field gradient of 16.0 G/cm to do the measurements and fits to the Leggett equations [1970] to obtain D⊥. For T < 20 mK, we found D⊥ is less than measured in earlier experiments at lower magnetic fields. D⊥ does not increase with decreasing temperature as 1/T2, but appears to approach a constant as T → 0 while it is expected that the longitudinal spin diffusion coefficient D∥ ∝ 1/ T2. This is called spin diffusion anisotropy and it was observed for the first time in our 3He liquid experiments. The anisotropy temperature we determined for 3He liquid was Ta = 16.4 +/- 2.2 mK at saturated vapor pressure and in a 7.96 T magnetic field. The transverse spin diffusion in 3 He results agree qualitatively with theories proposed by Meyerovich and Musaeflan [1992, 1994]. They also agree qualitatively with theories proposed by Golosov and Ruckenstein [1995, 1998] by extrapolation of the dilute theory to a strongly interacting system.

  2. FERMI LAT DISCOVERY OF EXTENDED GAMMA-RAY EMISSIONS IN THE VICINITY OF THE HB 3 SUPERNOVA REMNANT

    SciTech Connect

    Katagiri, H.; Yoshida, K.; Ballet, J.; Hewitt, J. W.; Kubo, H. E-mail: 13nm169s@gmail.com

    2016-02-20

    We report the discovery of extended gamma-ray emission measured by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) HB 3 (G132.7+1.3) and the W3 II complex adjacent to the southeast of the remnant. W3 is spatially associated with bright {sup 12}CO (J = 1–0) emission. The gamma-ray emission is spatially correlated with this gas and the SNR. We discuss the possibility that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields. The decay of neutral pions produced in nucleon–nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray emission. The emission from W3 is consistent with irradiation of the CO clouds by the cosmic rays accelerated in HB 3.

  3. One-dimensional Fermi accelerator model with moving wall described by a nonlinear van der Pol oscillator.

    PubMed

    Botari, Tiago; Leonel, Edson D

    2013-01-01

    A modification of the one-dimensional Fermi accelerator model is considered in this work. The dynamics of a classical particle of mass m, confined to bounce elastically between two rigid walls where one is described by a nonlinear van der Pol type oscillator while the other one is fixed, working as a reinjection mechanism of the particle for a next collision, is carefully made by the use of a two-dimensional nonlinear mapping. Two cases are considered: (i) the situation where the particle has mass negligible as compared to the mass of the moving wall and does not affect the motion of it; and (ii) the case where collisions of the particle do affect the movement of the moving wall. For case (i) the phase space is of mixed type leading us to observe a scaling of the average velocity as a function of the parameter (χ) controlling the nonlinearity of the moving wall. For large χ, a diffusion on the velocity is observed leading to the conclusion that Fermi acceleration is taking place. On the other hand, for case (ii), the motion of the moving wall is affected by collisions with the particle. However, due to the properties of the van der Pol oscillator, the moving wall relaxes again to a limit cycle. Such kind of motion absorbs part of the energy of the particle leading to a suppression of the unlimited energy gain as observed in case (i). The phase space shows a set of attractors of different periods whose basin of attraction has a complicated organization.

  4. Interface Superconductivity in Cuprates Defies Fermi-Liquid Description

    SciTech Connect

    Radović, Zoran; Vanević, Mihajlo; Wu, Jie; Bollinger, Anthony T.; Božović, Ivan

    2016-07-26

    La2-xSrxCuO4/La2CuO4 bilayers show interface superconductivity that originates from accumulation and depletion of mobile charge carriers across the interface. Surprisingly, the doping level can be varied broadly (within the interval 0.15 < x < 0.47) without affecting the transition temperature, which stays essentially constant and equal to that in optimally doped material, Tc ≈ 40 K. Here we argue that this finding implies that doping up to the optimum level does not shift the chemical potential, unlike in ordinary Fermi liquids. Lastly, we discuss possible physical scenarios that can give doping-independent chemical potential in the pseudogap regime: electronic phase separation, formation of charge-density waves, strong Coulomb interactions, or self-trapping of mobile charge carriers.

  5. Interface Superconductivity in Cuprates Defies Fermi-Liquid Description

    DOE PAGES

    Radović, Zoran; Vanević, Mihajlo; Wu, Jie; ...

    2016-07-26

    La2-xSrxCuO4/La2CuO4 bilayers show interface superconductivity that originates from accumulation and depletion of mobile charge carriers across the interface. Surprisingly, the doping level can be varied broadly (within the interval 0.15 < x < 0.47) without affecting the transition temperature, which stays essentially constant and equal to that in optimally doped material, Tc ≈ 40 K. Here we argue that this finding implies that doping up to the optimum level does not shift the chemical potential, unlike in ordinary Fermi liquids. Lastly, we discuss possible physical scenarios that can give doping-independent chemical potential in the pseudogap regime: electronic phase separation, formationmore » of charge-density waves, strong Coulomb interactions, or self-trapping of mobile charge carriers.« less

  6. Fermi GBM Observations of Terrestrial Gamma-ray Flashes

    SciTech Connect

    Briggs, Michael S.

    2011-09-21

    Terrestrial Gamma-ray Flashes are short pulses of energetic radiation associated with thunderstorms and lightning. While the Gamma-ray Burst Monitor (GBM) on Fermi was designed to observe gamma-ray bursts, its large BGO detectors are excellent for observing TGFs. Using GBM, TGF pulses are seen to either be symmetrical or have faster rise time than fall times. Some TGFs are resolved into double, partially overlapping pulses. Using ground-based radio observations of lightning from the World Wide Lightning Location Network (WWLLN), TGFs and their associated lightning are found to be simultaneous to {approx_equal}40 {mu} s. The lightning locations are typically within 300 km of the sub-spacecraft point.

  7. Interacting preformed Cooper pairs in resonant Fermi gases

    SciTech Connect

    Gubbels, K. B.; Stoof, H. T. C.

    2011-07-15

    We consider the normal phase of a strongly interacting Fermi gas, which can have either an equal or an unequal number of atoms in its two accessible spin states. Due to the unitarity-limited attractive interaction between particles with different spin, noncondensed Cooper pairs are formed. The starting point in treating preformed pairs is the Nozieres-Schmitt-Rink (NSR) theory, which approximates the pairs as being noninteracting. Here, we consider the effects of the interactions between the Cooper pairs in a Wilsonian renormalization-group scheme. Starting from the exact bosonic action for the pairs, we calculate the Cooper-pair self-energy by combining the NSR formalism with the Wilsonian approach. We compare our findings with the recent experiments by Harikoshi et al. [Science 327, 442 (2010)] and Nascimbene et al. [Nature (London) 463, 1057 (2010)], and find very good agreement. We also make predictions for the population-imbalanced case, which can be tested in experiments.

  8. Electron-ion coupling in semiconductors beyond Fermi's golden rule

    NASA Astrophysics Data System (ADS)

    Medvedev, Nikita; Li, Zheng; Tkachenko, Victor; Ziaja, Beata

    2017-01-01

    In the present work, a theoretical study of electron-phonon (electron-ion) coupling rates in semiconductors driven out of equilibrium is performed. Transient change of optical coefficients reflects the band gap shrinkage in covalently bonded materials, and thus, the heating of atomic lattice. Utilizing this dependence, we test various models of electron-ion coupling. The simulation technique is based on tight-binding molecular dynamics. Our simulations with the dedicated hybrid approach (XTANT) indicate that the widely used Fermi's golden rule can break down describing material excitation on femtosecond time scales. In contrast, dynamical coupling proposed in this work yields a reasonably good agreement of simulation results with available experimental data.

  9. Fermi gamma-ray imaging of a radio galaxy.

    PubMed

    Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, Ł; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

    2010-05-07

    The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.

  10. SLAC All Access: Fermi Gamma-ray Space Telescope

    SciTech Connect

    Romani, Roger

    2013-05-31

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  11. Fermi-surface reconstruction by stripe order in cuprate superconductors

    PubMed Central

    Laliberté, F.; Chang, J.; Doiron-Leyraud, N.; Hassinger, E.; Daou, R.; Rondeau, M.; Ramshaw, B.J.; Liang, R.; Bonn, D.A.; Hardy, W.N.; Pyon, S.; Takayama, T.; Takagi, H.; Sheikin, I.; Malone, L.; Proust, C.; Behnia, K.; Taillefer, Louis

    2011-01-01

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa2Cu3Oy (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La1.8−xEu0.2SrxCuO4 (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates. PMID:21847106

  12. Contact interaction in an unitary ultracold Fermi gas

    SciTech Connect

    Pessoa, Renato; Gandolfi, Stefano; Vitiello, S. A.; Schmidt, Kevin E.

    2015-12-16

    An ultracold Fermi atomic gas at unitarity presents universal properties that in the dilute limit can be well described by a contact interaction. By employing a guiding function with correct boundary conditions and making simple modifications to the sampling procedure we are able to calculate the properties of a true contact interaction with the diffusion Monte Carlo method. The results are obtained with small variances. Our calculations for the Bertsch and contact parameters are in excellent agreement with published experiments. The possibility of using a more faithful description of ultracold atomic gases can help uncover additional features of ultracold atomic gases. In addition, this work paves the way to perform quantum Monte Carlo calculations for other systems interacting with contact interactions, where the description using potentials with finite effective range might not be accurate.

  13. Contact interaction in an unitary ultracold Fermi gas

    DOE PAGES

    Pessoa, Renato; Gandolfi, Stefano; Vitiello, S. A.; ...

    2015-12-16

    An ultracold Fermi atomic gas at unitarity presents universal properties that in the dilute limit can be well described by a contact interaction. By employing a guiding function with correct boundary conditions and making simple modifications to the sampling procedure we are able to calculate the properties of a true contact interaction with the diffusion Monte Carlo method. The results are obtained with small variances. Our calculations for the Bertsch and contact parameters are in excellent agreement with published experiments. The possibility of using a more faithful description of ultracold atomic gases can help uncover additional features of ultracold atomicmore » gases. In addition, this work paves the way to perform quantum Monte Carlo calculations for other systems interacting with contact interactions, where the description using potentials with finite effective range might not be accurate.« less

  14. Fermi-surface reconstruction by stripe order in cuprate superconductors.

    PubMed

    Laliberté, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, B J; Liang, R; Bonn, D A; Hardy, W N; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, Louis

    2011-08-16

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)O(y) (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.

  15. Isospin-mixing correction for fp-shell Fermi transitions

    SciTech Connect

    Ormand, W.E.; Brown, B.A.

    1995-10-01

    Isospin-mixing corrections for superallowed Fermi transitions in fp-shell nuclei are computed within the framework of the shelf model. The study includes a re-evaluation of three nuclei that are part of the set of nine accurately measured transitions and five new cases that are expected to be measured in the future at radioactive-beam facilities. For the heavier fp-shell nuclei, both the configuration mixing term, {delta}{sub IM}, and the radial-overlap mis-match correction, {delta}{sub RO}, are much larger than in the case of the previous nine transitions. For the nine accurately measured transitions, excellent agreement with the CVC hypothesis is found. but the CKM matrix is found to violate the unitarity condition at the level of 3 {sigma}.

  16. Ultrasonic probe of the AuZn Fermi surface.

    SciTech Connect

    Svitelskiy, O.; Suslov, A. V.; Singleton, J. M.; Lashley, J. C.

    2005-01-01

    We, for the first time, apply the ultrasonic pulse-echo technique to explore the Fermi surface of the martensite phase of the single crystalline AuZn shape memory alloy. The ultrasonic measurements were performed in the magnetic fields of up to 45 T in the temperature range of 0.07 < T < 300 K. In the martensite phase (T < 64 K), the oscillations of the speed of the longitudinal sound wave propagating in the (110) direction indicated a strong acoustic de Haas - van Alphen effect. In addition to the earlier described oscillations with frequencies of 1140 and 4720 Tesla, we observed a new frequency of 120 Tesla, which was predicted theoretically. Corresponding effective masses were in favorable agreement with those expected from band structure calculations.

  17. q-Breathers and the Fermi-Pasta-Ulam problem.

    PubMed

    Flach, S; Ivanchenko, M V; Kanakov, O I

    2005-08-05

    The Fermi-Pasta-Ulam (FPU) paradox consists of the non-equipartition of energy among normal modes of a weakly anharmonic atomic chain model. In the harmonic limit each normal mode corresponds to a periodic orbit in phase space and is characterized by its wave number q. We continue normal modes from the harmonic limit into the FPU parameter regime and obtain persistence of these periodic orbits, termed here q-breathers (QB). They are characterized by time periodicity, exponential localization in the q-space of normal modes and linear stability up to a size-dependent threshold amplitude. Trajectories computed in the original FPU setting are perturbations around these exact QB solutions. The QB concept is applicable to other nonlinear lattices as well.

  18. Correlation between -ray flux density and redshift for Fermi blazars

    NASA Astrophysics Data System (ADS)

    Xiao, Hu-Bing; Pei, Zhi-Yuan; Xie, Hong-Jing; Hao, Jing-Meng; Yang, Jiang-He; Yuan, Yu-Hai; Liu, Yi; Fan, Jun-Hui

    2015-09-01

    Blazars are strong -ray emitters, the -ray emissions are likely strongly beamed, therefore, one should use the intrinsic (de-beamed) emissions to investigate its emission nature. In this work, we compiled a sample of Fermi blazars with available beaming Doppler factors, , to investigate the correlation between -ray flux density, , and redshift, . The analysis shows that there is no correlation between and for the observed -ray flux density, but there is a clear strong correlation between the intrinsic flux densities, and . We also discussed the relationship of -ray luminosity and short time scale for the observed data and the intrinsic data. Our analysis suggests that the intrinsic -ray flux density obeys the flux density and redshift relation, and the jet in -rays maybe a continuous case. The intrinsic luminosity and the short time scales obey the Elliot and Shapiro relation and Abramowicz and Nobili relation as well.

  19. The γ-ray spectral changes in Fermi blazars

    NASA Astrophysics Data System (ADS)

    Yang, Jianghe; Fan, Junhui; Nie, Jianjun; Yang, Rushu; Tuo, Manxian; Zhang, Yuelian

    2017-02-01

    Based upon Fermi 2FGL and 3FGL catalogues, a sample of 842 blazars (hereinto 356 FSRQs, 486 BL Lac objects) is collected to discuss the changes of γ-ray photon spectral indices and brightness from 2FGL to 3FGL blazars. Our results indicate that the distributions of γ-ray photon spectral indices and luminosities between 2FGL and 3FGL have no obvious difference; The photon spectral indices and γ-ray luminosity from 2FGL are closely correlated with that from 3FGL respectively; There are close anti-relations between the change of photon spectral indices and the change of luminosity for FSRQs and BL Lac objects samples and for sub-class samples of HBLs, IBLs and LBLs, which suggests that the spectrum becomes flat when the source becomes bright.

  20. Global topology of Weyl semimetals and Fermi arcs

    NASA Astrophysics Data System (ADS)

    Mathai, Varghese; Thiang, Guo Chuan

    2017-03-01

    We provide a manifestly topological classification scheme for generalised Weyl semimetals, in any spatial dimension and with arbitrary Weyl surfaces which may be non-trivially linked. The classification naturally incorporates that of Chern insulators. Our analysis refines, in a mathematically precise sense, some well-known 3D constructions to account for subtle but important global aspects of the topology of semimetals. Using a fundamental locality principle, we derive a generalized charge cancellation condition for the Weyl surface components. We analyse the bulk-boundary correspondence under a duality transformation, which reveals explicitly the topological nature of the resulting surface Fermi arcs. We also analyse the effect of moving Weyl points on the bulk and boundary topological semimetal invariants.

  1. Nuclear physics. Momentum sharing in imbalanced Fermi systems.

    PubMed

    Hen, O; Sargsian, M; Weinstein, L B; Piasetzky, E; Hakobyan, H; Higinbotham, D W; Braverman, M; Brooks, W K; Gilad, S; Adhikari, K P; Arrington, J; Asryan, G; Avakian, H; Ball, J; Baltzell, N A; Battaglieri, M; Beck, A; May-Tal Beck, S; Bedlinskiy, I; Bertozzi, W; Biselli, A; Burkert, V D; Cao, T; Carman, D S; Celentano, A; Chandavar, S; Colaneri, L; Cole, P L; Crede, V; D'Angelo, A; De Vita, R; Deur, A; Djalali, C; Doughty, D; Dugger, M; Dupre, R; Egiyan, H; El Alaoui, A; El Fassi, L; Elouadrhiri, L; Fedotov, G; Fegan, S; Forest, T; Garillon, B; Garcon, M; Gevorgyan, N; Ghandilyan, Y; Gilfoyle, G P; Girod, F X; Goetz, J T; Gothe, R W; Griffioen, K A; Guidal, M; Guo, L; Hafidi, K; Hanretty, C; Hattawy, M; Hicks, K; Holtrop, M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkanov, B I; Isupov, E L; Jiang, H; Jo, H S; Joo, K; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, F J; Koirala, S; Korover, I; Kuhn, S E; Kubarovsky, V; Lenisa, P; Levine, W I; Livingston, K; Lowry, M; Lu, H Y; MacGregor, I J D; Markov, N; Mayer, M; McKinnon, B; Mineeva, T; Mokeev, V; Movsisyan, A; Munoz Camacho, C; Mustapha, B; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Niculescu, I; Osipenko, M; Pappalardo, L L; Paremuzyan, R; Park, K; Pasyuk, E; Phelps, W; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Rimal, D; Ripani, M; Ritchie, B G; Rizzo, A; Rosner, G; Roy, P; Rossi, P; Sabatié, F; Schott, D; Schumacher, R A; Sharabian, Y G; Smith, G D; Shneor, R; Sokhan, D; Stepanyan, S S; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tkachenko, S; Ungaro, M; Vlassov, A V; Voutier, E; Walford, N K; Wei, X; Wood, M H; Wood, S A; Zachariou, N; Zana, L; Zhao, Z W; Zheng, X; Zonta, I

    2014-10-31

    The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using (12)C, (27)Al, (56)Fe, and (208)Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

  2. Solitonic Vortex in a Strongly-Interacting Fermi Gas

    NASA Astrophysics Data System (ADS)

    Ku, Mark; Ji, Wenjie; Mukherjee, Biswaroop; Cheuk, Lawrence; Sanchez, Elmer; Yefsah, Tarik; Zwierlein, Martin

    2014-05-01

    We investigate the solitonic excitation observed in our previous experiments [Yefsah et al., Nature 499, 426 (2013)] for a unitary Fermi gas with tomographic imaging. In this work, we directly access the local density of our 3D clouds by imaging a thin layer of atoms, which we achieve with a masked pumping beam that transfers atoms outside of the selected layer into an undetected state. Using the tomographic imaging, which circumvents the density integration along the probing axis, we identify unambiguously this excitation as a solitonic vortex. In particular, we rule out the vortex ring scenario predicted by several theory groups. Our measurements provide a quantitative benchmark for the theories of non-equilibrium dynamics of strongly-interacting superfluids.

  3. Rotating a Rashba-coupled Fermi gas in two dimensions

    NASA Astrophysics Data System (ADS)

    Doko, E.; Subaşı, A. L.; Iskin, M.

    2016-03-01

    We analyze the interplay of adiabatic rotation and Rashba spin-orbit coupling on the BCS-BEC evolution of a harmonically trapped Fermi gas in two dimensions under the assumption that vortices are not excited. First, by taking the trapping potential into account via both the semiclassical and exact quantum-mechanical approaches, we firmly establish the parameter regime where the noninteracting gas forms a ring-shaped annulus. Then, by taking the interactions into account via the BCS mean-field approximation, we study the pair-breaking mechanism that is induced by rotation, i.e., the Coriolis effects. In particular, we show that the interplay allows for the possibility of creating either an isolated annulus of rigidly rotating normal particles that is disconnected from the central core of nonrotating superfluid pairs or an intermediate mediator phase where the superfluid pairs and normal particles coexist as a partially rotating gapless superfluid.

  4. Environmental Survey preliminary report, Fermi National Accelerator Laboratory, Batavia, Illinois

    SciTech Connect

    Not Available

    1988-10-01

    This report presents the preliminary findings from the first phase of the Environmental Survey of the US Department of Energy (DOE) Fermi National Accelerator Laboratory (Fermilab), conducted September 14 through 25, 1987. The Survey is being conducted by an interdisciplinary team of environmental specialists led and managed by the Office of Environment, Safety and Health's Office of Environmental Audit. Individual participants for the Survey team are being supplied by a private contractor. The objective of the Survey is to identify environmental problems and areas of environmental risk associated with Fermilab. The Survey covers all environmental media and all areas of environmental regulation. It is being performed in accordance with the DOE Environmental Survey Manual. This phase of the Survey involves the review of existing site environmental data, observations of the operations performed at Fermilab, and interviews with site personnel. 110 refs., 26 figs., 41 tabs.

  5. Unitary Fermi Gas, ɛ Expansion, and Nonrelativistic Conformal Field Theories

    NASA Astrophysics Data System (ADS)

    Nishida, Yusuke; Son, Dam Thanh

    We review theoretical aspects of unitary Fermi gas (UFG), which has been realized in ultracold atom experiments. We first introduce the ɛ expansion technique based on a systematic expansion in terms of the dimensionality of space. We apply this technique to compute the thermodynamic quantities, the quasiparticle cum, and the criticl temperature of UFG. We then discuss consequences of the scale and conformal invariance of UFG. We prove a correspondence between primary operators in nonrelativistic conformal field theories and energy eigenstates in a harmonic potential. We use this correspondence to compute energies of fermions at unitarity in a harmonic potential. The scale and conformal invariance together with the general coordinate invariance constrains the properties of UFG. We show the vanishing bulk viscosities of UFG and derive the low-energy effective Lagrangian for the superfluid UFG. Finally we propose other systems exhibiting the nonrelativistic scaling and conformal symmetries that can be in principle realized in ultracold atom experiments.

  6. Eta Carinae's first full orbit in the Fermi era

    NASA Astrophysics Data System (ADS)

    Reimer, Olaf; Reitberger, Klaus; Reimer, Anita; Takahashi, Hiromitsu

    2015-08-01

    Eta Carinae, the so-far only colliding wind binary system shining brightly at high-energy gamma-rays, has been observed over the first complete orbit since launch of the Fermi Gamma-ray Space Telescope. This allows us to compare the spatial, temporal and spectral characteristics of the gamma-ray emission to earlier studies and confront predictions about anticipated observational signatures when concluding the full orbit and entering into the next. By analyzing 2024 days of LAT data we were able to improve the spatial association between the nominal location of eta Carinae and the observed gamma-ray location, confirming the two-component spectrum, as well as the spectro-variability seen predominatly above 10 GeV. The observed source characteristics strengthens the case that eta Car remains unique for the otherwise elusive class of gamma-ray sources whose emission can be related to a colliding stellar wind scenario.

  7. Seiberg-Witten theory as a Fermi gas

    NASA Astrophysics Data System (ADS)

    Bonelli, Giulio; Grassi, Alba; Tanzini, Alessandro

    2017-01-01

    We explore a new connection between Seiberg-Witten theory and quantum statistical systems by relating the dual partition function of SU(2) Super Yang-Mills theory in a self-dual Ω background to the spectral determinant of an ideal Fermi gas. We show that the spectrum of this gas is encoded in the zeroes of the Painlevé III_3 τ function. In addition, we find that the Nekrasov partition function on this background can be expressed as an O(2) matrix model. Our construction arises as a four-dimensional limit of a recently proposed conjecture relating topological strings and spectral theory. In this limit, we provide a mathematical proof of the conjecture for the local P^1 × P^1 geometry.

  8. SLAC All Access: Fermi Gamma-ray Space Telescope

    ScienceCinema

    Romani, Roger

    2016-07-12

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  9. Trapped 173Yb Fermi gas across an orbital Feshbach resonance

    NASA Astrophysics Data System (ADS)

    Iskin, M.

    2017-01-01

    Starting with the two-band description of an orbital Feshbach resonance, we study superfluid properties of a trapped 173Yb Fermi gas under the assumptions of a local-density approximation for the trapping potential and a mean-field approximation for the intraband Cooper pairings. In particular, we investigate the competition and interplay between the pair-breaking effect that is caused by the interband detuning energy, and the pair-breaking and thermal-broadening effects that are simultaneously caused by the temperature. We predict several experimental signatures that are directly caused by this interplay including a spatial separation of superfluid and normal phases within the trap, and could play decisive roles in probing two-band superfluidity in these systems.

  10. Observations of Accreting Pulsars with the FERMI-GBM

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen

    2012-01-01

    The Gamma-ray Burst Monitor (GBM) on-board Fermi comprises 12 NaI detectors spanning the 8-1000 keV band and 2 BGO detectors spanning the 100 keV to 40 MeV band. These detectors view the entire unocculted sky, providing long (approximately 40 ks/day) observations of accreting pulsars daily, which allow long-term monitoring of spin-frequencies and pulsed uxes via epoch-folded searches plus daily blind searches for new pulsars. Phase averaged uxes can be measured using the Earth occultation technique. In this talk I will present highlights of GBM accretion-powered pulsar monitoring such as the discovery of a torque reversal in 4U1626-67, a high-energy QPO in A0535+26, and evidence for a stable accretion disk in OAO 1657-415.

  11. Structure of a Quantized Vortex in Fermi Atom Gas

    SciTech Connect

    Machida, Masahiko; Koyama, Tomio

    2006-09-07

    In atomic Fermi gases, the pairing character changes from BCS-like to BEC-like when one decreases the threshold energy of the Feshbach resonance. With this crossover, the system enters the strong-coupling regime through the population enhancement of diatom molecules, and the vortex structure becomes much different from well-known core structures in BCS superfluid since the superfluid order parameter is given by a sum of BCS pairs and BEC molecular condensates. In this paper, we study the structure of a vortex by numerically solving the generalized Bogoliubov-de Gennes equation derived from the fermion-boson model and clarify how the vortex structure changes with the threshold energy of the Feshbach resonance. We find that the diatom boson condensate enhances the matter density depletion inside the vortex core and the discreteness of localized quasi-particle spectrum.

  12. Quantum solitons in the Fermi-Pasta-Ulam model

    NASA Astrophysics Data System (ADS)

    Li, De-Jun; Tang, Bing

    2014-03-01

    In this paper, quantum solitons in the Fermi-Pasta-Ulam (FPU) model are investigated analytically. By using the canonical transform method and number-conserving approximation, we obtain the normal form of the phonon-conserving quantized Hamiltonian. In order to convert the quantized Hamiltonian into the coordinate space, we employ the inverse Fourier transform. With the help of the Hartree approximate and the semidiscrete multiple-scale method, the nonlinear Schrödinger (NLS) equation is derived. The results show that quantum solitons may exist in the FPU model. Moreover, it is found that moving quantum solitons become quantum intrinsic localized modes under certain condition. In addition, we obtain the energy level of quantum solitons, which indicates that the energy of such quantum solitons is quantized.

  13. The cosmic evolution of Fermi BL Lacertae objects

    SciTech Connect

    Ajello, M.; Romani, R. W.; Shaw, M. S.; Healey, S. E.; Michelson, P. F.; Gasparrini, D.; Bolmer, J.; Cotter, G.; Potter, W. J.; Finke, J.; Greiner, J.; Rau, A.; Schady, P.; King, O.; Max-Moerbeck, W.; Readhead, A. C. S.; Richards, J. L. E-mail: rwr@astro.stanford.edu E-mail: gasparrini@asdc.asi.it

    2014-01-01

    Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by Fermi during its first year of operation. We obtained redshift constraints for 206 out of the 211 BL Lac objects in our sample, making it the largest and most complete sample of BL Lac objects available in the literature. We use this sample to determine the luminosity function of BL Lac objects and its evolution with cosmic time. We find that for most BL Lac classes the evolution is positive, with a space density peaking at modest redshift (z ≈ 1.2). Low-luminosity, high-synchrotron-peaked (HSP) BL Lac objects are an exception, showing strong negative evolution, with number density increasing for z ≲ 0.5. Since this rise corresponds to a drop-off in the density of flat-spectrum radio quasars (FSRQs), a possible interpretation is that these HSPs represent an accretion-starved end state of an earlier merger-driven gas-rich phase. We additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the so-called 'blazar sequence'. Finally, by estimating the beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of γ=6.1{sub −0.8}{sup +1.1}, and that most are seen within 10° of the jet axis.

  14. The Thomas–Fermi quark model: Non-relativistic aspects

    SciTech Connect

    Liu, Quan Wilcox, Walter

    2014-02-15

    The first numerical investigation of non-relativistic aspects of the Thomas–Fermi (TF) statistical multi-quark model is given. We begin with a review of the traditional TF model without an explicit spin interaction and find that the spin splittings are too small in this approach. An explicit spin interaction is then introduced which entails the definition of a generalized spin “flavor”. We investigate baryonic states in this approach which can be described with two inequivalent wave functions; such states can however apply to multiple degenerate flavors. We find that the model requires a spatial separation of quark flavors, even if completely degenerate. Although the TF model is designed to investigate the possibility of many-quark states, we find surprisingly that it may be used to fit the low energy spectrum of almost all ground state octet and decuplet baryons. The charge radii of such states are determined and compared with lattice calculations and other models. The low energy fit obtained allows us to extrapolate to the six-quark doubly strange H-dibaryon state, flavor symmetric strange states of higher quark content and possible six quark nucleon–nucleon resonances. The emphasis here is on the systematics revealed in this approach. We view our model as a versatile and convenient tool for quickly assessing the characteristics of new, possibly bound, particle states of higher quark number content. -- Highlights: • First application of the statistical Thomas–Fermi quark model to baryonic systems. • Novel aspects: spin as generalized flavor; spatial separation of quark flavor phases. • The model is statistical, but the low energy baryonic spectrum is successfully fit. • Numerical applications include the H-dibaryon, strange states and nucleon resonances. • The statistical point of view does not encourage the idea of bound many-quark baryons.

  15. Astrobiological phase transition: towards resolution of Fermi's paradox.

    PubMed

    Cirković, Milan M; Vukotić, Branislav

    2008-12-01

    Can astrophysics explain Fermi's paradox or the "Great Silence" problem? If available, such explanation would be advantageous over most of those suggested in literature which rely on unverifiable cultural and/or sociological assumptions. We suggest, instead, a general astrobiological paradigm which might offer a physical and empirically testable paradox resolution. Based on the idea of James Annis, we develop a model of an astrobiological phase transition of the Milky Way, based on the concept of the global regulation mechanism(s). The dominant regulation mechanisms, arguably, are gamma-ray bursts, whose properties and cosmological evolution are becoming well-understood. Secular evolution of regulation mechanisms leads to the brief epoch of phase transition: from an essentially dead place, with pockets of low-complexity life restricted to planetary surfaces, it will, on a short (Fermi-Hart) timescale, become filled with high-complexity life. An observation selection effect explains why we are not, in spite of the very small prior probability, to be surprised at being located in that brief phase of disequilibrium. In addition, we show that, although the phase-transition model may explain the "Great Silence", it is not supportive of the "contact pessimist" position. To the contrary, the phase-transition model offers a rational motivation for continuation and extension of our present-day Search for ExtraTerrestrial Intelligence (SETI) endeavours. Some of the unequivocal and testable predictions of our model include the decrease of extinction risk in the history of terrestrial life, the absence of any traces of Galactic societies significantly older than human society, complete lack of any extragalactic intelligent signals or phenomena, and the presence of ubiquitous low-complexity life in the Milky Way.

  16. Fermi-surface reconstruction by stripe order in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Laliberté, Francis

    2012-02-01

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBCO, application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order [1,2,3]. In another cuprate, Eu-LSCO, the onset of stripe order - a modulation of spin and charge densities - at low temperature is well established [4]. By a comparative study of thermoelectric transport in the cuprates YBCO and Eu-LSCO, we show that the two materials exhibit a very similar process of Fermi-surface reconstruction as a function of temperature and doping [5,6]. This strongly suggests that Fermi-surface reconstruction is caused by stripe order in both cases, compelling evidence that stripe order is a generic tendency of hole-doped cuprates.[4pt] Work done in collaboration with J. Chang, N. Doiron-Leyraud, E. Hassinger, R. Daou, D. LeBoeuf, M. Rondeau, B. J. Ramshaw, R. Liang, D. A. Bonn, W. N. Hardy, S. Pyon, T. Takayama, H. Takagi, I. Sheikin, L. Malone, C. Proust, K. Behnia and L. Taillefer.[4pt] [1] N. Doiron-Leyraud et al., Nature 447, 565 (2007).[0pt] [2] D. LeBoeuf et al., Nature 450, 533 (2007).[0pt] [3] D. LeBoeuf et al., Phys. Rev. B 83, 054506 (2011).[0pt] [4] J. Fink et al., Phys. Rev. B 83, 092503 (2011).[0pt] [5] J. Chang et al., Phys. Rev. Lett. 104, 057005 (2010).[0pt] [6] F. Lalibert'e et al., Nat. Commun. 2, 432 (2011).

  17. FERMI Observations of Gamma -Ray Emission From the Moon

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwoo, W. B.; Baldini, I.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Hays, E.; Thompson, D. J.; McEnery, J. E.; Troja, E.

    2012-01-01

    We report on the detection of high-energy ? -ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmicray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(greater than100 MeV) = (1.04 plus or minus 0.01 [statistical error] plus or minus 0.1 [systematic error]) × 10(sup -6) cm(sup -2) s(sup -1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(greater than100 MeV)˜5×10(sup -7) cm(sup -2) s(sup -1), when solar activity was relatively high. The higher gamma -ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.

  18. Numerical Investigation and Experimental Reproduction of Fermi Acceleration in Laboratory Scale

    NASA Astrophysics Data System (ADS)

    Zhou, M.; Zhai, C.

    2015-12-01

    Fermi acceleration is widely accepted as the mechanism to explain power law of cosmic ray spectrum. Now this mechanism has been developed to first order Fermi acceleration and second order Fermi acceleration. In first order Fermi acceleration, also known as diffusive shock acceleration, particles are confined around the shock through scattering and accelerated by repeatedly crossing shock front. In second order Fermi acceleration, particles gain energy through statistical collisions with interstellar clouds. In this proposed work, we plan to carefully study these two kinds of acceleration numerically and experimentally. We first consider a single relativistic particle and investigate how it gains energy in Fermi-Ulam model and shock wave acceleration model respectively. We investigate collective behavior of particles with different kinds of wall-oscillation functions and try to find an optimal one in terms of efficiency of acceleration. Then, we plan to go further and consider a group of particles statistically, during which we borrow the correct generalization of Maxwell's velocity distribution in special relativity and compare the results with those in cases where we simply use Maxwell-Boltzmann distribution. To this end, we try to provide a scheme to build an accelerator applying both laser technology and mirror effect in Laboratory to reproduce Fermi acceleration, which might be a promising source to obtain high energy particles and further study the mechanism of cosmic rays acceleration.

  19. Universal Fermi liquid crossover and quantum criticality in a mesoscopic system.

    PubMed

    Keller, A J; Peeters, L; Moca, C P; Weymann, I; Mahalu, D; Umansky, V; Zaránd, G; Goldhaber-Gordon, D

    2015-10-08

    Quantum critical systems derive their finite-temperature properties from the influence of a zero-temperature quantum phase transition. The paradigm is essential for understanding unconventional high-Tc superconductors and the non-Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behaviour to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two independent electronic reservoirs. On detuning the exchange couplings we observe the Fermi liquid scale T*, at energies below which the spin is screened conventionally by the more strongly coupled channel. We extract a quadratic dependence of T* on gate voltage close to criticality, and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.

  20. Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Xu, N.; Autès, G.; Matt, C. E.; Lv, B. Q.; Yao, M. Y.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Qian, T.; Yazyev, O. V.; Mesot, J.; Ding, H.; Shi, M.

    2017-03-01

    The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides. While Weyl fermion quasiparticles exist only when the chemical potential is located between two saddle points of the Weyl cone features, the Fermi arc states extend in a larger energy scale and are robust across the bulk Lifshitz transitions associated with the recombination of two nontrivial Fermi surfaces enclosing one Weyl point into a single trivial Fermi surface enclosing two Weyl points of opposite chirality. Therefore, in some systems (e.g., NbP), topological Fermi arc states are preserved even if Weyl fermion quasiparticles are absent in the bulk. Our findings not only provide insight into the relationship between the exotic physical phenomena and the intrinsic bulk band topology in Weyl semimetals, but also resolve the apparent puzzle of the different magnetotransport properties observed in TaAs, TaP, and NbP, where the Fermi arc states are similar.