Modern Physics Letters A

Due to thermal radiation process, the temperature of the Schwarzschild black hole diverges at the time the black hole evaporates, while it is natural to expect a vanishing temperature, since the spacetime geometry becomes Minkowskian whose intrinsic temperature is identically zero. Recently, a nonsingular temperature has been proposed in this research line, which follows the Hawking temperature for the large black hole system, at the same time becomes null in the limiting case the black hole mass tends to zero. In this paper, the stability and the phase transition of the quantum-corrected Schwarzschild black hole are investigated based on this modified temperature. For that, the thermodynamic quantities like the local temperature, the heat capacity, and the off-shell free energy are calculated. The results show that the free energy of the black hole follows the characteristic swallow-tail behavior, implying the existence of an unstable intermediate black hole state quickly decaying into the stable small or large black hole.

Recently, some authors have generalized the idea of mimetic gravity to a Randall–Sundrum II braneworld model [L. Randall and R. Sundrum, Phys. Rev. Lett. 83, 3370 (1999); L. Randall and R. Sundrum, Phys. Rev. Lett. 83, 4690 (1999)] and introduced Braneworld Mimetic Cosmology. In this paper, we extend their new cosmological model to brane–anti-brane systems and obtain the explicit form of potential which appeared in their action. This potential depends on the tachyonic fields, the separation distance between two branes and time. On the other hand, our universe is located on one of the branes and its evolution is controlled by the potential between two branes. By passing time and decreasing the separation distance between branes, more energy dissolves into branes and the universe expands. In the following, we presented the physical applications such as late time accelerating phase, inflation model and behavior of perturbations, with respect to brane–anti-brane system. Finally, we briefly discussed the moduli stabilization of the model.

To justify the 20-year old distant Ia Supernova observations which revealed to us that our universe is experiencing a late-time cosmic acceleration, propositions of existence of exotic fluids inside our universe are made. These fluids are assumed to occupy homogeneously the whole space of the universe and to exert negative pressure from inside such that the late-time accelerated expansion is caused. Among the different suggested models of such exotic matters/energy popularly coined as dark matter/dark energy (DE), a well-known and popular process is “introduction of redshift parametrization” of the equation of state (EoS) parameter of these fluids. We, very particularly, take the parametrization proposed by Barboza and Alcaniz (BA) along with the cosmological constant. We use 39 data points for Hubble’s parameter calculated for different redshifts and try to constrain the DE EoS parameters for BA modeling. We then constrain the DE parametrization parameters in the background of Einstein’s general relativity, loop quantum gravity and Horava–Lifshitz gravity one after another. We find the $1\sigma$, $2\sigma$ and $3\sigma$ confidence contours for all these cases and compare them with each other. We try to speculate which gravity is constraining the parameters most and which one is letting the parameters to stay within a larger domain. We tally our results of 557 points Union2 Sample and again compare them for different gravity theories.

Cosmological solutions for covariant canonical gauge theories of gravity are presented. The underlying covariant canonical transformation framework invokes a dynamical spacetime Hamiltonian consisting of the Einstein–Hilbert term plus a quadratic Riemann tensor invariant with a fundamental dimensionless coupling constant $g_1$. A typical time scale related to this constant, $\tau =\sqrt{8\pi G{g}_1}$, is characteristic for the type of cosmological solutions: for $t\ll \tau$, the quadratic term is dominant, the energy–momentum tensor of matter is not covariantly conserved, and we observe modified dynamics of matter and spacetime. On the other hand, for $t\gg \tau$, the Einstein term dominates and the solution converges to classical cosmology. This is analyzed for different types of matter and dark energy with a constant equation of state. While for a radiation-dominated universe solution, the cosmology does not change, we find for a dark energy universe the well-known de-Sitter space. However, we also identify a special bouncing solution (for $k=0$) which for large times approaches the de-Sitter space again. For a dust-dominated universe (with no pressure), deviations are seen only in the early epoch. In late epoch, the solution asymptotically behaves as the standard dust solution.

The geodesics equations on de Sitter (dS) and anti-de Sitter (AdS) spacetimes of any dimensions, are the starting point for deriving the general form of the Boltzmann equation in terms of conserved quantities. The simple equation for the non-equilibrium Marle and Anderson–Witting models are derived and the distributions of the Boltzmann–Marle model on these manifolds are written down first in terms of conserved quantities and then as functions of canonical variables.

In the most arbitrated quantum signatures (AQSs), the signers and verifiers need to perform the quantum key distribution protocols or some other protocols to share secret keys before signing a signature. In some schemes, the entangle states, which are not easily implemented, have to be prepared and distributed among the partners. Based on single photon and one-way functions, a new AQS scheme without entangled states is proposed. In our scheme, the signer generates a quantum signature on the classical message with his/her private key and the one-way function. The arbitrator communicates with the signer through a classical unencrypted channel. The signer and verifier need not perform the key distribution protocol before signing a message. On the other hand, without entangled states, our scheme can reduce the complexity of implementation. Then, our scheme is more efficient than the similar schemes. At the same time, our scheme is secure against forgery attack and disavowal attack.

In this paper, we interpret the dark energy as an effect caused by small-scale inhomogeneities of the universe with the use of the spatial averaged approach of Buchert [Gen. Relat. Gravit. 32, 105 (2000); 33, 1381 (2001)]. The model considered here adopts the Chevallier–Polarski–Linder (CPL) parametrizations of the equation of state of the effective perfect fluid from the backreaction effect. Thanks to the effective geometry introduced by Larena et al. [Phys. Rev. D 79, 083011 (2009)] in their previous work, we confront such backreaction model with the latest type Ia supernova and Hubble parameter observations, coming out with the results that reveal the difference between the Friedmann–Lemaître–Robertson–Walker model and backreaction model.

Considering some modified Newtonian potentials and the Hubble law in writing the total energy of a test mass located at the edge of a flat Friedmann–Robertson–Walker (FRW) universe, we obtain several modified Friedmann equations. Interestingly enough, our study shows that the employed potentials, while some of them have some successes in modeling the spiral galaxies rotation curves, may also address an accelerated universe. This fact indicates that dark energy and dark matter may have some common origins and aspects.

Among many classic heuristic search algorithms, the Grover quantum search algorithm (QSA) can play a role of secondary acceleration. Based on the properties of the two-qubit Grover QSA, a quantum dialogue (QD) protocol is proposed. In addition, our protocol also utilizes the unitary operations and single-particle measurements. The transmitted quantum state (except for the decoy state used for detection) can transmit two-bits of security information simultaneously. Theoretical analysis shows that the proposed protocol has high security.