2,957 research outputs found
Radio Frequency Spectroscopy of Trapped Fermi Gases with Population Imbalance
Motivated by recent experiments, we address, in a fully self consistent
fashion, the behavior and evolution of radio frequency (RF) spectra as
temperature and polarization are varied in population imbalanced Fermi gases.
We discuss a series of scenarios for the experimentally observed zero
temperature pseudogap phase and show how present and future RF experiments may
help in its elucidation. We conclude that the MIT experiments at the lowest
may well reflect ground state properties, but take issue with their claim that
the pairing gap survives up to temperatures of the order of the degeneracy
temperature at unitarity.Comment: 4 page, 3 figures, submitted to PRA Rapi
Decaying Hidden Dark Matter in Warped Compactification
The recent PAMELA and ATIC/Fermi/HESS experiments have observed an excess of
electrons and positrons, but not anti-protons, in the high energy cosmic rays.
To explain this result, we construct a decaying hidden dark matter model in
string theory compactification that incorporates the following two ingredients,
the hidden dark matter scenario in warped compactification and the
phenomenological proposal of hidden light particles that decay to the Standard
Model. In this model, on higher dimensional warped branes, various warped
Kaluza-Klein particles and the zero-mode of gauge field play roles of the
hidden dark matter or mediators to the Standard Model.Comment: 15 pages; v4, several clarifications added, update on Fermi/HESS
result
Dark Matter Model Selection and the ATIC/PPB-BETS anomaly
We argue that we may be able to sort out dark matter models in which
electrons are generated through the annihilation and/or decay of dark matter,
by using a fact that the initial energy spectrum is reflected in the cosmic-ray
electron flux observed at the Earth even after propagation through the galactic
magnetic field. To illustrate our idea we focus on three representative initial
spectra: (i)monochromatic (ii)flat and (iii)double-peak ones. We find that
those three cases result in significantly different energy spectra, which may
be probed by the Fermi satellite in operation or an up-coming cosmic-ray
detector such as CALET.Comment: 19 pages, 8 figure
An ocean coupling potential intensity index for tropical cyclones
© American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 1878–1882, doi:10.1002/grl.50091.Timely and accurate forecasts of tropical cyclones (TCs, i.e., hurricanes and typhoons) are of great importance for risk mitigation. Although in the past two decades there has been steady improvement in track prediction, improvement on intensity prediction is still highly challenging. Cooling of the upper ocean by TC-induced mixing is an important process that impacts TC intensity. Based on detail in situ air-deployed ocean and atmospheric measurement pairs collected during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign, we modify the widely used Sea Surface Temperature Potential Intensity (SST_PI) index by including information from the subsurface ocean temperature profile to form a new Ocean coupling Potential Intensity (OC_PI) index. Using OC_PI as a TC maximum intensity predictor and applied to a 14 year (1998–2011) western North Pacific TC archive, OC_PI reduces SST_PI-based overestimation of archived maximum intensity by more than 50% and increases the correlation of maximum intensity estimation from r2 = 0.08 to 0.31. For slow-moving TCs that cause the greatest cooling, r2 increases to 0.56 and the root-mean square error in maximum intensity is 11 m s−1. As OC_PI can more realistically characterize the ocean contribution to TC intensity, it thus serves as an effective new index to improve estimation and prediction of TC maximum intensity.This work is supported by Taiwan’s National
Science Council and National Taiwan University (grant numbers: NSC 101-
2111-M-002-002-MY2; NSC 101-2628-M-002-001-MY4; 102R7803) and
US Office of Naval Research (ONR) under the Impact of Typhoons on
Pacific (ITOP) program. PB’s support is provided by ONR under
PE 0601153N through NRL Contract N00173-10-C-6019
Models of Little Higgs and Electroweak Precision Tests
The little Higgs idea is an alternative to supersymmetry as a solution to the
gauge hierarchy problem. In this note, I review various little Higgs models and
their phenomenology with emphases on the precision electroweak constraints in
these models.Comment: 16 pages; 4 figures; review submitted to Modern Physics Letter
Dirac gaugino as leptophilic dark matter
We investigate the leptophilic properties of Dirac gauginos in an
R--symmetric N=2 supersymmetric model with extended gauge and Higgs sectors.
The annihilation of Dirac gauginos to leptons requires no chirality flip in the
final states so that it is not suppressed as in the Majorana case. This implies
that it can be sizable enough to explain the positron excess observed by the
PAMELA experiment with moderate or no boost factors. When squark masses are
heavy, the annihilation of Dirac gauginos to hadrons is controlled by their
Higgsino fraction and is driven by the and final states.
Moreover, at variance with the Majorana case, Dirac gauginos with a
non-vanishing higgsino fraction can also have a vector coupling with the
gauge boson leading to a sizable spin--independent scattering cross section off
nuclei. Saturating the current antiproton limit, we show that Dirac gauginos
can leave a signal in direct detection experiments at the level of the
sensitivity of dark matter searches at present and in the near future.Comment: 24 pages, 10 figures, typos corrected, final version published on
JCA
Strongly coupled matter near phase transition
In the Hartree approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism of
the real scalar field theory, we show that for the strongly coupled scalar
system near phase transition, the shear viscosity over entropy density is
small, however, the bulk viscosity over entropy density is large. The large
bulk viscosity is related to the highly nonconformal equation of state. It is
found that the square of the sound velocity near phase transition is much
smaller than the conformal value 1/3, and the trace anomaly at phase transition
deviates far away from 0. These results agree well with the lattice results of
the complex QCD system near phase transition.Comment: 6 pages, 2 figures, 1 table, contributed to the International
Conference on Strangeness in Quark Matter 2008, Beijing, China, 6-10 October
200
The Leptonic Higgs as a Messenger of Dark Matter
We propose that the leptonic cosmic ray signals seen by PAMELA and ATIC
result from the annihilation or decay of dark matter particles via states of a
leptonic Higgs doublet to leptons, linking cosmic ray signals of dark
matter to LHC signals of the Higgs sector. The states of the leptonic Higgs
doublet are lighter than about 200 GeV, yielding large and
event rates at the LHC. Simple models are
given for the dark matter particle and its interactions with the leptonic
Higgs, for cosmic ray signals arising from both annihilations and decays in the
galactic halo. For the case of annihilations, cosmic photon and neutrino
signals are on the verge of discovery.Comment: 34 pages, 9 figures, minor typos corrected, references adde
Dark matter and sub-GeV hidden U(1) in GMSB models
Motivated by the recent PAMELA and ATIC data, one is led to a scenario with
heavy vector-like dark matter in association with a hidden sector
below GeV scale. Realizing this idea in the context of gauge mediated
supersymmetry breaking (GMSB), a heavy scalar component charged under
is found to be a good dark matter candidate which can be searched for direct
scattering mediated by the Higgs boson and/or by the hidden gauge boson. The
latter turns out to put a stringent bound on the kinetic mixing parameter
between and : . For the typical range
of model parameters, we find that the decay rates of the ordinary lightest
neutralino into hidden gauge boson/gaugino and photon/gravitino are comparable,
and the former decay mode leaves displaced vertices of lepton pairs and missing
energy with distinctive length scale larger than 20 cm for invariant lepton
pair mass below 0.5 GeV. An unsatisfactory aspect of our model is that the
Sommerfeld effect cannot raise the galactic dark matter annihilation by more
than 60 times for the dark matter mass below TeV.Comment: 1+15 pages, 4 figures, version published in JCAP, references added,
minor change
Very Long Baseline Neutrino Oscillation Experiment for Precise Measurements of Mixing Parameters and CP Violating Effects
We analyze the prospects of a feasible, Brookhaven National Laboratory based,
very long baseline (BVLB) neutrino oscillation experiment consisting of a
conventional horn produced low energy wide band beam and a detector of 500 kT
fiducial mass with modest requirements on event recognition and resolution.
Such an experiment is intended primarily to determine CP violating effects in
the neutrino sector for 3-generation mixing. We analyze the sensitivity of such
an experiment. We conclude that this experiment will allow determination of the
CP phase and the currently unknown mixing parameter
, if , a value times
lower than the present experimental upper limit. In addition to
and , the experiment has great potential for precise measurements
of most other parameters in the neutrino mixing matrix including , , ,
and the mass ordering of neutrinos through the observation of the matter effect
in the appearance channel.Comment: 12 pages, 10 figure
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