In this paper, we propose two new models in f (T ) gravity to realize the crossing of the phantom divide line for the effective equation of state, and we then study the observational constraints on the model parameters. The best fit results suggest that the observations favor a crossing of the phantom divide line.

We study, in the paradigm of open quantum systems, the entanglement dynamics of two uniformly accelerated atoms with the same acceleration perpendicular to the separation. The two-atom system is treated as an open system coupled with a bath of fluctuating massless scalar fields in the Minkowski vacuum, and the master equation that governs its evolution is derived. It has been found that, for accelerated atoms with a nonvanishing separation, entanglement sudden death is a general feature when the initial state is entangled, while for those in a separable initial state, entanglement sudden birth only happens for atoms with an appropriate interatomic separation and sufficiently small acceleration. Remarkably, accelerated atoms can get entangled in certain circumstances while the inertial ones in the Minkowski vacuum cannot. A comparison between the results of accelerated atoms and those of static ones in a thermal bath shows that uniformly accelerated atoms exhibit features distinct from those immersed in a thermal bath at the Unruh temperature in terms of entanglement dynamics.

We study the Brownian motion of a charged test particle coupled to electromagnetic vacuum fluctuations near a perfectly reflecting plane boundary. The presence of the boundary modifies the quantum fluctuations of the electric field, which in turn modifies the motion of the test particle. We calculate the resulting mean squared fluctuations in the velocity and position of the test particle. In the case of directions transverse to the boundary, the results are negative. This can be interpreted as reducing the quantum uncertainty which would otherwise be present.

In this Letter, by reconstructing the $Om$ diagnostic and the deceleration
parameter $q$ from the latest Union2 Type Ia supernova sample with and without
the systematic error along with the baryon acoustic oscillation (BAO) and the
cosmic microwave background (CMB), we study the cosmic expanding history, using
the Chevallier-Polarski-Linder (CPL) parametrization. We obtain that Union2+BAO
favor an expansion with a decreasing of the acceleration at $z<0.3$. However,
once the CMB data is added in the analysis, the cosmic acceleration is found to
be still increasing, indicating a tension between low redshift data and high
redshift one. In order to reduce this tension significantly, two different
methods are considered and thus two different subsamples of Union2 are
selected. We then find that two different subsamples+BAO+CMB give completely
different results on the cosmic expanding history when the systematic error is
ignored, with one suggesting a decreasing cosmic acceleration, the other just
the opposite, although both of them alone with BAO support that the cosmic
acceleration is slowing down. However, once the systematic error is considered,
two different subsamples of Union2 along with BAO and CMB all favor an
increasing of the present cosmic acceleration. Therefore a clear-cut answer on
whether the cosmic acceleration is slowing down calls for more consistent data
and more reliable methods to analyze them.Comment: 17 pages, 6 figures; PLB in pres

We study the thermodynamics and thermodynamic geometry of a five-dimensional Reissner-NordstromAdS black hole in the extended phase space by treating the cosmological constant as being related to the number of colors in the boundary gauge theory and its conjugate quantity as the associated chemical potential. We find that the contribution of the charge of the black hole to the chemical potential is always positive, and the existence of charge makes the chemical potential become positive more easily. We calculate the scalar curvatures of the thermodynamical Weinhold metric, Ruppeiner metric, and Quevedo metric, respectively, in the fixed N 2 case and the fixed q case. We find that in the fixed N 2 case, the divergence of the scalar curvature is related to the divergence of the specific heat with fixed electric potential in the Weinhold metric and Ruppeiner metric, and the divergence of the scalar curvature in the Quevedo metric corresponds to the divergence of the specific heat with fixed electric charge density. In the fixed q case, however, the divergence of the scalar curvature is related to the divergence of the specific heat with fixed chemical potential in the Weinhold metric and Ruppeiner metric, while in the Quevedo metric, the divergence of the scalar curvature corresponds to the divergence of the specific heat with a fixed number of colors and the vanishing of the specific heat with a fixed chemical potential.

We propose a parametrization for the growth index of the linear matter perturbations, γ(z) = γ 0 + z 1+z γ 1 . The growth factor of the perturbations parameterized as Ω γ m is analyzed for both the wCDM model and the DGP model with our proposed form for γ. We find that γ 1 is negative for the wCDM model but is positive for the DGP model. Thus it provides another signature to discriminate them. We demonstrate that Ω γ m with γ taking our proposed form approximates the growth factor very well both at low and high redshfits for both kinds of models. In fact, the error is below 0.03% for the ΛCDM model and 0.18% for the DGP model for all redshifts when Ω m0 = 0.27. Therefore, our parametrization may be robustly used to constrain the growth index of different models with the observational data which include points for redshifts ranging from 0.15 to 3.8, thus providing discriminative signatures for different models.

Massive gravity is a modified theory of general relativity. In this paper, we
study, using a method in which the scale factor changes as a particle in a
"potential", all possible cosmic evolutions in a ghost-free massive gravity. We
find that there exists, in certain circumstances, an oscillating universe or a
bouncing one. If the universe starts at the oscillating region, it may undergo
a number of oscillations before it quantum mechanically tunnels to the bounce
point and then expand forever. But going back to the singularity from the
oscillating region is physically not allowed. So, the big bang singularity can
be successfully resolved. At the same time, we also find that there exists a
stable Einstein static state in some cases. However, the universe can not stay
at this stable state past-eternally since it is allowed to quantum mechanically
tunnel to a big-bang-to-big-crunch region and end with a big crunch. Thus, a
stable Einstein static state universe can not be used to avoid the big bang
singularity in massive gravity.Comment: 36 pages, 30 figures, accepted for publication in PRD. Two references
adde

We study, in the framework of open quantum systems, the geometric phase
acquired by a uniformly accelerated two-level atom undergoing nonunitary
evolution due to its coupling to a bath of fluctuating vacuum electromagnetic
fields in the multipolar scheme. We find that the phase variation due to the
acceleration can be in principle observed via atomic interferometry between the
accelerated atom and the inertial one, thus providing an evidence of the Unruh
effect.Comment: 12 pages, no figure

scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.