International Journal of Modern Physics D

Perturbative algebraic quantum field theory (pAQFT) is a mathematically rigorous framework that allows to construct models of quantum field theories (QFTs) on a general class of Lorentzian manifolds. Recently, this idea has been applied also to perturbative quantum gravity (QG), treated as an effective theory. The difficulty was to find the right notion of observables that would in an appropriate sense be diffeomorphism invariant. In this paper, I will outline a general framework that allows to quantize theories with local symmetries (this includes infinitesimal diffeomorphism transformations) with the use of the Batalin–Vilkovisky (BV) formalism. This approach has been successfully applied to effective QG in a recent paper by Brunetti, Fredenhagen and myself. In the same paper, we also proved perturbative background independence of the quantized theory, which is going to be discussed in the present work as well.

The dark matter (DM) parallel session DM2 of the 14th Marcel Grossmann Meeting was enriched by several contributions about the results and the strategies in the study and in the detection of DM particles in the Galactic halo. In the following, an overview of the latest results in this field will be summarized. A particular care will be given to the results obtained by exploiting the model independent DM annual modulation signature for the presence of DM particles in the galactic halo. Results from the other experiments using different procedures, different techniques and different target materials will be shortly addressed as well as implications and experimental perspectives.

It is recognized that very likely the correlation between peak energy $E_p$ and bolometric intensity is intrinsic to GRBs. However, its physical origin is still debated. In this paper, we will discuss a possible interpretation of the correlation in the light of a GRB prompt emission spectral model, grbcomp, proposed in [L. Titarchuk, R. Farinelli, F. Frontera and L. Amati, Astrophys. J. 752 (2012) 116]. grbcomp is essentially a photospheric model for the prompt emission of GRBs. Its main ingredients are a thermal bath of soft seed photons and a subrelativistically expanding outflow plasma, consequence of the star explosion. The emerging spectrum is the result of two phases: first, up to the photospheric radius, Comptonization of a subrelativistic electron outflow with thermal bath of soft photons, then, convolution of the Comptonized photons in the first phase with a Green function. The result of this convolution is consistent with different physical processes, in particular Inverse Compton. grbcomp has been successfully tested using a significant sample of GRB time resolved spectra in the broad energy band from 2keV to 2MeV [F. Frontera, L. Amati, R. Farinelli, S. Dichiara, C. Guidorzi, R. Landi and L. Titarchuk, Astrophys. J. 779 (2013) 175].

The paper deals with phantom scalar field cosmology in Einstein gravity. At first, using Lie symmetry, the coupling function to the kinetic term and the potential function of the scalar field and the equation of state parameter of the matter field are determined and a simple solution is obtained. Subsequently, Noether symmetry is imposed on the Lagrangian of the system. The symmetry vector is obtained and the potential takes a very general form from which potential using Lie symmetry can be obtained as a particular case. Then, we choose a point transformation $(a,\varphi )\to (u,v)$ such that one of the transformed variables (say $u$) is a cyclic for the Lagrangian. Using conserved charge (corresponding to the cyclic coordinate) and the constant of motion, solutions are obtained.

I introduce in $\kappa$-Minkowski noncommutative spacetime the basic tools of quantum differential geometry, namely bicovariant differential calculus, Lie and inner derivatives, the integral, the Hodge-$\ast$ and the metric. I show the relevance of these tools for field theory with an application to complex scalar field, for which I am able to identify a vector-valued four-form which generalizes the energy–momentum tensor. Its closedness is proved, expressing in a covariant form the conservation of energy–momentum.

We explore the possibility of the acoustic analogue of a super-radiance like phenomenon, i.e. the amplification of a sound wave by reflection from the ergo-region of a rotating acoustic black hole in the fluid draining bathtub model in the presence of the pressure to be amplified or reduced in agreement with the value of the parameter $(\gamma =1+\frac{kn{\rho }_0^{n-1}}{c^2})$. We remark that the interval of frequencies depend upon the neo-Newtonian parameter $\gamma$ (${\bar{\mathrm{\Omega }}}_H=\frac{2}{1+\gamma }{\mathrm{\Omega }}_H$) and becomes narrow in this work. As a consequence, the tuning of the neo-Newtonian parameter $(\gamma =1+\frac{kn{\rho }_0^{n-1}}{c^2})$ changes the rate of loss of the acoustic black hole mass.

We propose a novel approach to obtain limitations on the dark energy (DE) and dark matter (DM) coupling. The suggested approach allows us to express the coupling constant in terms of the cosmographic parameters (CPs). It enables us to find constraints on the coupling constant directly based on observational data and to restrict number of numerous models describing interaction in the dark sector.

We study the late-time cosmological evolution of $f(T)$ (where $T$ is the torsion scalar) theories with matter contents consisting of collisional self-interacting matter and radiations. The power law, exponential and logarithmic $f(T)$ models are considered to explore the evolution of Hubble parameter $H(z)$, dark energy (DE) equation of state (EoS) ${\omega }_{\mathrm{\text{DE}}}$ and effective EoS parameter ${\omega }_{\mathrm{\text{eff}}}$. We show that crossing of phantom divide line can be realized in the presence of collisional matter as compared to the results obtained for the choice of noncollisional matter [K. Bamba, C.-Q. Geng, C.-C. Lee and L.-W. Luo, J. Cosmol. Astropart. Phys. 01 (2011) 021; K. Bamba, C.-Q. Geng and C.-C. Lee, arXiv:1008.4036]. The evolutionary behavior of ${\omega }_{\mathrm{\text{DE}}}$ is consistent with the one developed in [P. Wu and H. Yu, Eur. Phys. J. C 71 (2011) 1552] and recent observational data [U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0406 (2004) 008; S. Nesseris and L. Perivolaropoulos, J. Cosmol. Astropart. Phys. 0701 (2007) 018; P. Wu and H. Yu, Phys. Lett. B 643 (2006) 315; U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0702 (2007) 011; H. K. Jassal, J. S. Bagla and T. Padmanabhan, Mon. Not. R. Astron. Soc. 405 (2010) 2639].

We reinterpret the spectral dimension of spacetimes as the scaling of an effective self-energy transition amplitude in quantum field theory (QFT), when the system is probed at a given resolution. This picture has four main advantages: (a) it dispenses with the usual interpretation (unsatisfactory in covariant approaches) where, instead of a transition amplitude, one has a probability density solving a nonrelativistic diffusion equation in an abstract diffusion time; (b) it solves the problem of negative probabilities known for higher-order and nonlocal dispersion relations in classical and quantum gravity; (c) it clarifies the concept of quantum spectral dimension as opposed to the classical one. We then consider a class of logarithmic dispersion relations associated with quantum particles and show that the spectral dimension $d_{\mathrm{\text{S}}}$ of spacetime as felt by these quantum probes can deviate from its classical value, equal to the topological dimension $D$. In particular, in the presence of higher momentum powers it changes with the scale, dropping from $D$ in the infrared (IR) to a value $d_{\mathrm{\text{S}}}^{\mathrm{\text{UV}}}\le D$ in the ultraviolet (UV). We apply this general result to Stelle theory of renormalizable gravity, which attains the universal value $d_{\mathrm{\text{S}}}^{\mathrm{\text{UV}}}=2$ for any dimension $D$.

The ${}^1{S}_0$ nucleon superfluidity in neutron star matter was investigated in the framework of relativistic $\sigma -\omega -\pi -\rho$ model with the tensor couplings of $\omega$ and $\rho$ mesons using the relativistic Hartree–Fock (RHF) approximation. It was found that the tensor couplings of $\omega$ and $\rho$ mesons lead to a clear growth of the ${}^1{S}_0$ neutron pairing gap in the density range where there exists ${}^1{S}_0$ neutron superfluidity. The ${}^1{S}_0$ pairing gap of proton with the tensor couplings of $\omega$ and $\rho$ mesons in the density range of ${\rho }_B=0.0$–$0.079$fm${}^{-3}$ is lower and then in the density range of ${\rho }_B=0.079$–$0.383$fm${}^{-3}$ higher than the corresponding value without the tensor couplings of $\omega$ and $\rho$ mesons. Our results provide a basic to understand the influence of the tensor couplings of $\omega$ and $\rho$ mesons on the cooling properties of neutron star.

A Hubble diagram (HD) has recently been constructed in the redshift range $0\lesssim z\lesssim 6.5$ using a nonlinear relation between the ultraviolet (UV) and X-ray luminosities of quasi stellar objects (QSOs). The Type Ia Supernovae (SN) HD has already provided a high-precision test of cosmological models, but the fact that the QSO distribution extends well beyond the supernova range ($z\lesssim 1.8$), in principle provides us with an important complementary diagnostic whose significantly greater leverage in $z$ can impose tighter constraints on the distance versus redshift relationship. In this paper, we therefore perform an independent test of nine different cosmological models, among which six are expanding, while three are static. Many of these are disfavored by other kinds of observations (including the aforementioned Type Ia SNe). We wish to examine whether the QSO HD confirms or rejects these earlier conclusions. We find that four of these models (Einstein–de Sitter, the Milne universe, the static universe with simple tired light and the static universe with plasma tired light) are excluded at the $>99\%$ C.L. The quasi-steady state model is excluded at $>95\%$ C.L. The remaining four models ($\mathrm{\Lambda }$CDM/$w$CDM, the $R_{\mathrm{\text{h}}}=ct$ universe, the Friedmann open universe and a static universe with a linear Hubble law) all pass the test. However, only $\mathrm{\Lambda }$CDM/$w$CDM and $R_{\mathrm{\text{h}}}=ct$ also pass the Alcock–Paczyński (AP) test. The optimized parameters in $\mathrm{\Lambda }$CDM/$w$CDM are ${\mathrm{\Omega }}_m=0.20_{-0.20}^{+0.24}$ and $w_{\mathrm{\text{de}}}=-1.2_{-\infty }^{+1.6}$ (the dark energy equation-of-state). Combined with the AP test, these values become ${\mathrm{\Omega }}_m=0.38_{-0.19}^{+0.20}$ and $w_{\mathrm{\text{de}}}=-0.28_{-0.40}^{+0.52}$. But whereas this optimization of parameters in $\mathrm{\Lambda }$CDM/$w$CDM creates some tension with their concordance values, the $R_{\mathrm{\text{h}}}=ct$ universe has the advantage of fitting the QSO and AP data without any free parameters.

Quantum radiation properties of nonstationary Kerr–de Sitter (KdS) black hole is investigated using the method of generalized tortoise coordinate transformation. The locations of horizons and the temperature of the thermal radiation as well as the maximum energy of the nonthermal radiation are derived. It is found that the surface gravity and the Hawking temperature depend on both time and different angles. An extra coupling effect is obtained in the thermal radiation spectrum of Maxwell’s electromagnetic field equations which is absent in the thermal radiation spectrum of scalar particles. Further, the chemical potential derived from the thermal radiation spectrum of scalar particle has been found to be equal to the highest energy of the negative energy state of the scalar particle in the nonthermal radiation for KdS black hole. It is also shown that the generalized tortoise coordinate transformation produces a constant term in the expression of the surface gravity and Hawking temperature.