168 research outputs found
Asymmetric WIMP dark matter
In existing dark matter models with global symmetries the relic abundance of
dark matter is either equal to that of anti-dark matter (thermal WIMP), or
vastly larger, with essentially no remaining anti-dark matter (asymmetric dark
matter). By exploring the consequences of a primordial asymmetry on the coupled
dark matter and anti-dark matter Boltzmann equations we find large regions of
parameter space that interpolate between these two extremes. Interestingly,
this new asymmetric WIMP framework can accommodate a wide range of dark matter
masses and annihilation cross sections. The present-day dark matter population
is typically asymmetric, but only weakly so, such that indirect signals of dark
matter annihilation are not completely suppressed. We apply our results to
existing models, noting that upcoming direct detection experiments will
constrain a large region of the relevant parameter space.Comment: 32 pages, 6 figures, updated references, updated XENON100 bounds,
typo in figure caption correcte
Noether Symmetry Approach in "Cosmic Triad" Vector Field Scenario
To realize the accelerations in the early and late periods of our universe,
we need to specify potentials for the dominant fields. In this paper, by using
the Noether symmetry approach, we try to find suitable potentials in the
"cosmic triad" vector field scenario. Because the equation of state parameter
of dark energy has been constrained in the range of by observations, we derive the Noether conditions for the vector field
in quintessence, phantom and quintom models, respectively. In the first two
cases, constant potential solutions have been obtained. What is more, a fast
decaying point-like solution with power-law potential is also found for the
vector field in quintessence model. For the quintom case, we find an
interesting constraint on the field potentials,
where and are constants related to the Noether symmetry.Comment: 15 pages, no figures, accepted by Classical and Quantum Gravity
Two loop electroweak corrections to and in the B-LSSM
The rare decays and are important to research new physics beyond standard model. In
this work, we investigate two loop electroweak corrections to and in the minimal
supersymmetric extension of the SM with local gauge symmetry (B-LSSM),
under a minimal flavor violating assumption for the soft breaking terms. In
this framework, new particles and new definition of squarks can affect the
theoretical predictions of these two processes, with respect to the MSSM.
Considering the constraints from updated experimental data, the numerical
results show that the B-LSSM can fit the experimental data for the branching
ratios of and . The
results of the rare decays also further constrain the parameter space of the
B-LSSM.Comment: 33 pages, 9 figures, Published in EPJ
Einstein-aether as a quantum effective field theory
The possibility that Lorentz symmetry is violated in gravitational processes
is relatively unconstrained by experiment, in stark contrast with the level of
accuracy to which Lorentz symmetry has been confirmed in the matter sector. One
model of Lorentz violation in the gravitational sector is Einstein-aether
theory, in which Lorentz symmetry is broken by giving a vacuum expectation
value to a dynamical vector field. In this paper we analyse the effective
theory for quantised gravitational and aether perturbations. We show that this
theory possesses a controlled effective expansion within dimensional
regularisation, that is, for any process there are a finite number of Feynman
diagrams which will contribute to a given order of accuracy. We find that there
is no log-running of the two-derivative phenomenological parameters, justifying
the use of experimental constraints for these parameters obtained over many
orders of magnitude in energy scale. Given the stringent experimental bounds on
two-derivative Lorentz-violating operators, we estimate the size of matter
Lorentz-violation which arises due to loop effects. This amounts to an
estimation of the natural size of coefficients for Lorentz-violating
dimension-six matter operators, which in turn can be used to obtain a new bound
on the two-derivative parameters of this theory.Comment: 21 page
Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj
We present U(1) flavor models for leptophobic Z' with flavor dependent
couplings to the right-handed up-type quarks in the Standard Model, which can
accommodate the recent data on the top forward-backward (FB) asymmetry and the
dijet resonance associated with a W boson reported by CDF Collaboration. Such
flavor-dependent leptophobic charge assignments generally require extra chiral
fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor
symmetry calls for new U(1)'-charged Higgs doublets in order for the SM
fermions to have realistic renormalizable Yukawa couplings. The stringent
constraints from the top FB asymmetry at the Tevatron and the same sign top
pair production at the LHC can be evaded due to contributions of the extra
Higgs doublets. We also show that the extension could realize cold dark matter
candidates.Comment: 40 pages, 10 figures, added 1 figure and extended discussion,
accepted for publication in JHE
Statistical Anisotropy from Anisotropic Inflation
We review an inflationary scenario with the anisotropic expansion rate. An
anisotropic inflationary universe can be realized by a vector field coupled
with an inflaton, which can be regarded as a counter example to the cosmic
no-hair conjecture. We show generality of anisotropic inflation and derive a
universal property. We formulate cosmological perturbation theory in
anisotropic inflation. Using the formalism, we show anisotropic inflation gives
rise to the statistical anisotropy in primordial fluctuations. We also explain
a method to test anisotropic inflation using the cosmic microwave background
radiation (CMB).Comment: 32 pages, 5 figures, invited review for CQG, published versio
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
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