35,924 research outputs found
Testing the Lorentz and CPT Symmetry with CMB polarizations and a non-relativistic Maxwell Theory
We present a model for a system involving a photon gauge field and a scalar
field at quantum criticality in the frame of a Lifthitz-type non-relativistic
Maxwell theory. We will show this model gives rise to Lorentz and CPT violation
which leads to a frequency-dependent rotation of polarization plane of
radiations, and so leaves potential signals on the cosmic microwave background
temperature and polarization anisotropies.Comment: 7 pages, 2 figures, accepted on JCAP, a few references adde
Cyclic cosmology from Lagrange-multiplier modified gravity
We investigate cyclic and singularity-free evolutions in a universe governed
by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as
well as in one. In the scalar case, cyclicity can be induced by a
suitably reconstructed simple potential, and the matter content of the universe
can be successfully incorporated. In the case of -gravity, cyclicity can
be induced by a suitable reconstructed second function of a very
simple form, however the matter evolution cannot be analytically handled.
Furthermore, we study the evolution of cosmological perturbations for the two
scenarios. For the scalar case the system possesses no wavelike modes due to a
dust-like sound speed, while for the case there exist an oscillation
mode of perturbations which indicates a dynamical degree of freedom. Both
scenarios allow for stable parameter spaces of cosmological perturbations
through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio
Bounce and cyclic cosmology in extended nonlinear massive gravity
We investigate non-singular bounce and cyclic cosmological evolutions in a
universe governed by the extended nonlinear massive gravity, in which the
graviton mass is promoted to a scalar-field potential. The extra freedom of the
theory can lead to certain energy conditions violations and drive cyclicity
with two different mechanisms: either with a suitably chosen scalar-field
potential under a given Stuckelberg-scalar function, or with a suitably chosen
Stuckelberg-scalar function under a given scalar-field potential. Our analysis
shows that extended nonlinear massive gravity can alter significantly the
evolution of the universe at both early and late times.Comment: 20 pages, 5 figures, version published at JCA
Gluon Fusion induced Zg and Zgg Productions in the Standard Model at the LHC
We report calculations of the gluon induced Zg and Zgg productions in the
Standard Model at the LHC operating at both 7 TeV and 14 TeV collision energy.
We present total cross sections and differential distributions of the processes
and compare them with the leading and next-to-leading order QCD pp -> Z+1 jet,
Z+2 jets results. Our results show that the gluon induced Zg and Zgg
productions contribute to pp -> Z+1 jet, Z+2 jets at 1% level.Comment: 8 pages, 5 figure
Scalar Perturbations Through Cycles
We analytically and numerically investigate the evolutions of the scalar
perturbations through the cycles with nonsingular bounce. It is found that the
amplitude of the curvature perturbation on large scale will be amplified cycle
by cycle, and the isocurvature perturbations also obtain an amplification, but
the rate of its amplification is slower than that of curvature perturbation,
unless its coupling to the metric perturbation is not negligible.Comment: 7 pages, 10 figure
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