13,723 research outputs found
Testing quantum gravity effects with latest CMB observations
Inspired by quantum gravitational physics, the approach of non-commutative
(NC) phase space leads to a modified dispersion relation of gravitational
waves. This feature, if applied to the very early universe, gives rise to a
modified power spectrum of primordial tensor perturbations with a suppression
of power on large scales. We confront this phenomenon with the BICEP2 and
Planck experiments, and show that inflation with the modified dispersion
relation can simultaneously fit the observations better than the standard
inflationary paradigm. In particular, the numerical result implies that with
the latest cosmological microwave background (CMB) observations, a quantum
gravity modified power spectrum of primordial tensor modes is preferred at a
statistical significance of more than compared with the minimal
model. Our study indicates that the potential tension between the BICEP2 and
Planck data may be resolved by quantum gravity effects.Comment: 5 pages, 2 figures, comments are welcom
Large Nonlocal Non-Gaussianity from a Curvaton Brane
We use a generalized delta N formalism to study the generation of the
primordial curvature perturbation in the curvaton brane scenario inspired by
stringy compactifications. We note that the non-Gaussian features, especially
the trispectra, crucially depend on the decay mechanism in a general curvaton
scenario. Specifically, we study the bispectra and trispectra of the curvaton
brane model in detail to illustrate the importance of curvaton decay in
generating nonlinear fluctuations. When the curvaton brane moves
nonrelativistically during inflation, the shape of non-Gaussianity is local,
but the corresponding size is different from that in the standard curvaton
scenario. When the curvaton brane moves relativistically in inflationary stage,
the shape of non-Gaussianity is of equilateral type.Comment: 24 pages, 2 figure
The Higgs Seesaw Induced Neutrino Masses and Dark Matter
In this paper we propose a possible explanation of the active neutrino
Majorana masses with the TeV scale new physics which also provide a dark matter
candidate. We extend the Standard Model (SM) with a local U(1)' symmetry and
introduce a seesaw relation for the vacuum expectation values (VEVs) of the
exotic scalar singlets, which break the U(1)' spontaneously. The larger VEV is
responsible for generating the Dirac mass term of the heavy neutrinos, while
the smaller for the Majorana mass term. As a result active neutrino masses are
generated via the modified inverse seesaw mechanism. The lightest of the new
fermion singlets, which are introduced to cancel the U(1)' anomalies, can be a
stable particle with ultra flavor symmetry and thus a plausible dark matter
candidate. We explore the parameter space with constraints from the dark matter
relic abundance and dark matter direct detection.Comment: 14 pages, 4 figure
Low-Temperature Enhancement of Semi-annihilation and the AMS-02 Positron Anomaly
Semi-annihilation is a generic feature of particle dark matter that is most
easily probed by cosmic ray experiments. We explore models where the
semi-annihilation cross section is enhanced at late times and low temperatures
by the presence of an s-channel resonance near threshold. The relic density is
then sensitive to the evolution of the dark matter temperature, and we compute
expressions for the associated Boltzmann equation valid in general
semi-annihilating models. At late times, a self-heating effect warms the dark
matter, allowing number-changing processes to remain effective long after
kinetic decoupling of the dark and visible sectors. This allows the
semi-annihilation signal today to be enhanced by up to five orders of magnitude
over the thermal relic cross section. As a case study, we apply this to a dark
matter explanation of the positron excess seen by AMS-02. We see that unlike
annihilating dark matter, our model has no difficulty fitting the data while
also giving the correct relic density. However, constraints from the CMB and
-rays from the galactic centre do restrict the preferred regions of
parameter space.Comment: 32 pages, 5 figures; minor update
Studies of Single Component Fermi Gas near a -wave Resonance with Lowest Order Constrained Variational Method
We study single component Fermi gas near a -wave resonance with the lowest
order constrained variational (LOCV) method. We obtain the energy per particle
for the ground state of single component Fermi gas near a -wave resonance
with LOCV method. We also calculate compressibility of the single component
Fermi gas near a -wave resonance and it shows that near the -wave
resonance, the system would lose its stability and collapse. The two -wave
contacts are also obtained and their variation tendencies with interaction
strength are consistent with recent experimental results
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