We propose a novel enhancement mechanism of the curvature perturbations in the nonminimal derivative coupling inflation model with a coupling parameter related to the inflaton field. By considering a special form of the coupling parameter as a function of the inflaton, a period of ultraslow-roll inflation can be realized due to the gravitationally enhanced friction, and the resulting power spectrum of the curvature perturbations has a sharp peak, which is large enough to produce the primordial black holes. Under this mechanism, we can easily obtain a sharp mass spectrum of primordial black holes around specific masses such as O(10)M , O(10 −5 )M , and O(10 −12 )M , which can explain the LIGO events, the ultrashort-timescale microlensing events in OGLE data, and the most of dark matter, respectively.

We perform a cosmological-model-independent test for the distance-duality (DD) relation η(z) = D L (z)(1 + z) −2 /D A (z), where D L and D A are the luminosity distance and angular diameter distance respectively, with a combination of observational data for D L taken from the latest Union2 SNe Ia and that for D A provided by two galaxy clusters samples compiled by De Filippis et al. and Bonamente et al.. Two parameterizations for η(z), i.e., η(z) = 1 + η 0 z and η(z) = 1 + η 0 z/(1 + z), are used. We find that the DD relation can be accommodated at 1σ confidence level (CL) for the De Filippis et al. sample and at 3σ CL for the Bonamente et al. sample. We also examine the DD relation by postulating two more general parameterizations: η(z) = η 0 + η 1 z and η(z) = η 0 + η 1 z/(1 + z), and find that the DD relation is compatible with the results from the De Filippis et al. and the Bonamente et al. samples at 1σ and 2σ CLs, respectively. Thus, we conclude that the DD relation is compatible with present observations.

The quantum lightcone fluctuations in flat spacetimes with compactified spatial dimensions or with boundaries are examined. The discussion is based upon a model in which the source of the underlying metric fluctuations is taken to be quantized linear perturbations of the gravitational field. General expressions are derived, in the transverse trace-free gauge, for the summation of graviton polarization tensors, and for vacuum graviton two-point functions. Because of the fluctuating light cone, the flight time of photons between a source and a detector may be either longer or shorter than the light propagation time in the background classical spacetime. We calculate the mean deviations from the classical propagation time of photons due to the changes in the topology of the flat spacetime. These deviations are in general larger in the directions in which topology changes occur and are typically of the order of the Planck time, but they can get larger as the travel distance increases. PACS number(s): 04.60.-m, 04.62.+v Typeset using REVT E X

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.

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.

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, 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 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.