35 research outputs found
Equivalence of modified gravity equation to the Clausius relation
We explicitly show that the equations of motion for modified gravity theories
of -gravity, the scalar-Gauss-Bonnet gravity, -gravity
and the non-local gravity are equivalent to the Clausius relation in
thermodynamics. In addition, we discuss the relation between the expression of
the entropy and the contribution from the modified gravity as well as the
matter to the definition of the energy flux (heat).Comment: 6 pages, no figure, several statements clarified, references adde
Cosmological Constraint and Analysis on Holographic Dark Energy Model Characterized by the Conformal-age-like Length
We present a best-fit analysis on the single-parameter holographic dark
energy model characterized by the conformal-age-like length,
. Based on the Union2 compilation of
557 supernova Ia data, the baryon acoustic oscillation results from the SDSS
DR7 and the cosmic microwave background radiation data from the WMAP7, we show
that the model gives the minimal , which is comparable to
for the CDM model. The single
parameter concerned in the model is found to be . Since the fractional density of dark energy at
, the fraction of dark energy is naturally negligible in the early
universe, at . The resulting constraints on the
present fractional energy density of matter and the equation of state are
\Omega_{m0}=0.286^{+0.019}_{-0.018}^{+0.032}_{-0.028} and
w_{de0}=-1.240^{+0.027}_{-0.027}^{+0.045}_{-0.044} respectively. The model
leads to a slightly larger fraction of matter comparing to the CDM
model. We also provide a systematic analysis on the cosmic evolutions of the
fractional energy density of dark energy, the equation of state of dark energy,
the deceleration parameter and the statefinder. It is noticed that the equation
of state crosses from to , the universe transits from
decelerated expansion () to accelerated expansion () recently, and
the statefinder may serve as a sensitive diagnostic to distinguish the CHDE
model with the CDM model.Comment: 17 pages, 5 figures, minor changes for the fitting data, references
adde
Thermodynamics of cosmological horizons in gravity
We explore thermodynamics of the apparent horizon in gravity with both
equilibrium and non-equilibrium descriptions. We find the same dual
equilibrium/non-equilibrium formulation for as for gravity. In
particular, we show that the second law of thermodynamics can be satisfied for
the universe with the same temperature of the outside and inside the apparent
horizon.Comment: 18 pages, no figure, version accepted for publication in JCA
Large-scale magnetic fields from inflation due to Chern-Simons-like effective interaction
We discuss the generation of large-scale magnetic fields due to the breaking
of the conformal invariance in the electromagnetic field through the -even
dimension-six Chern-Simons-like effective interaction with a fermion current in
inflationary cosmology. It is shown that the magnetic fields on 1Mpc scale with
the field strength of G at the present time can be generated even
for the scale of the effective interaction being the Planck scale.Comment: 13 pages, 2 figures, additional explanations include
Large-scale magnetic fields from inflation due to a -even Chern-Simons-like term with Kalb-Ramond and scalar fields
We investigate the generation of large-scale magnetic fields due to the
breaking of the conformal invariance in the electromagnetic field through the
-even dimension-six Chern-Simons-like effective interaction with a fermion
current by taking account of the dynamical Kalb-Ramond and scalar fields in
inflationary cosmology. It is explicitly demonstrated that the magnetic fields
on 1Mpc scale with the field strength of G at the present time
can be induced.Comment: 18 pages, 6 figures, version accepted for publication in Eur. Phys.
J.
Phase-Space analysis of Teleparallel Dark Energy
We perform a detailed dynamical analysis of the teleparallel dark energy
scenario, which is based on the teleparallel equivalent of General Relativity,
in which one adds a canonical scalar field, allowing also for a nonminimal
coupling with gravity. We find that the universe can result in the
quintessence-like, dark-energy-dominated solution, or to the stiff dark-energy
late-time attractor, similarly to standard quintessence. However, teleparallel
dark energy possesses an additional late-time solution, in which dark energy
behaves like a cosmological constant, independently of the specific values of
the model parameters. Finally, during the evolution the dark energy
equation-of-state parameter can be either above or below -1, offering a good
description for its observed dynamical behavior and its stabilization close to
the cosmological-constant value.Comment: 23 pages, 4 figures, 5 tables, version published at JCA
Unified dark energy thermodynamics: varying w and the -1-crossing
We investigate, in a unified and general way, the thermodynamic properties of
dark energy with an arbitrary, varying equation-of-state parameter w(a). We
find that all quantities are well defined and regular for every w(a), including
at the -1-crossing, with the temperature being negative in the phantom regime
(w(a)-1). The density and
entropy are always positive while the chemical potential can be arbitrary. At
the -1-crossing, both temperature and chemical potential are zero. The
temperature negativity can only be interpreted in the quantum framework. The
regular behavior of all quantities at the -1-crossing, leads to the conclusion
that such a crossing does not correspond to a phase transition, but rather to a
smooth cross-over.Comment: 5 pages, version published in Class. Quant. Gra
Radiative neutrino mass generation and dark energy
We study the models with radiative neutrino mass generation and explore the
relation between the neutrino masses and dark energy. In these models, the
pseudo-Nambu-Goldston bosons (pNGBs) arise at two-loop level via the Majorana
neutrino masses. In particular, we demonstrate that the potential energy of the
pNGB can be the dark energy potential and the observed value of the equation of
state (EoS) parameter of the universe, , , can be realized.Comment: 10 pages, 1 figure, a minor correction in Eq. (17
Phase space analysis of interacting dark energy in f(T) cosmology
In this paper, we examine the interacting dark energy model in
cosmology. We assume dark energy as a perfect fluid and choose a specific
cosmologically viable form . We show that there is one
attractor solution to the dynamical equation of Friedmann equations.
Further we investigate the stability in phase space for a general model
with two interacting fluids. By studying the local stability near the critical
points, we show that the critical points lie on the sheet in the
phase space, spanned by coordinates . From this critical sheet,
we conclude that the coupling between the dark energy and matter .Comment: 13 pages,2 figures, Published in "Central European Journal of
Physics