119191418
Fluctuations of differential number counts of radio continuum sources
We investigate the differential number counts of sources in radio continuum surveys, including all terms at linear order in cosmological perturbations. Our framework does not assume a specific gauge condition. This general approach allows us to recover gauge invariance explicitly. With the complete derivations of the covariant volume integral on the past light cone, we have identified several contributions in the number counts. To clarify their underlying physics, we present each contribution in terms of scalar, vector and tensor modes. This theoretical framework promises to be widely applicable to continuum radio galaxy surveys to model the expected angular power spectrum and two-point correlation.
118628016
Is the CMB asymmetry due to the kinematic dipole
Parity violation found in the Cosmic Microwave Background (CMB) radiation is a crucial clue for the non-standard cosmological model or the possible contamination of various foreground residuals and/or calibration of the CMB data sets. In this paper, we study the directional properties of the CMB parity asymmetry by excluding the $m=0$ modes in the definition of parity parameters. We find that the preferred directions of the parity parameters coincide with the CMB kinematic dipole, which implies that the CMB parity asymmetry may be connected with the possible contamination of the residual dipole component. We also find that such tendency is not only localized at $l=2,3$, but in the extended multipole ranges up to $l\sim 22$.
36303260
Influence of Lorentz violation on Dirac quasinormal modes in the Schwarzschild black hole spacetime
Using the third-order WKB approximation and monodromy methods, we investigate the influence of the Lorentz violating coefficient b (associated with a special axial-vector bμ field ) on Dirac quasinormal modes in the Schwarzschild black hole spacetime. At fundamental overtone, the real part decreases linearly as the parameter b increases. But the variation of the imaginary part with b becomes more complex. For the larger multiple moment k, the magnitude of the imaginary part increases with the increase of b, which means that the presence of Lorentz violation makes Dirac field damps more rapidly. At high overtones, it is found that the real part of highly-damped quasinormal frequency does not tend to zero, which is quite different from the asymptotic Dirac quasinormal modes without Lorentz violation.
119260243
Holographic superconductors in the AdS black-hole spacetime with a global monopole
Abstract We study holographic superconductors in the Schwarzschild–AdS black hole with a global monopole through a charged complex scalar field. We calculate the condensates of the charged operators in the dual conformal field theories (CFTs) and discuss the effects of the global monopole on the condensation formation. Moreover, we compute the electric conductive using the probe approximation and find that the properties of the conductive are quite similar to those in the Schwarzschild–AdS black hole. These results can help us know more about holographic superconductors in the asymptotic AdS black holes.
119299977
Dynamical evolution of a scalar field coupling to Einstein’s tensor in the Reissner-Nordström black hole spacetime
We study the dynamical evolution of a scalar field coupling to Einstein's tensor in the background of a Reissner-Nordstrom black hole. Our results show that the coupling constant η imprints in the wave dynamics of a scalar perturbation. In the weak coupling, we find that with the increase of the coupling constant η the real parts of the fundamental quasinormal frequencies decrease and the absolute values of imaginary parts increase for fixed charge q and multipole number l. In the strong coupling, we find that for l ≠ 0 the instability occurs when η is larger than a certain threshold value η c which deceases with the multipole number l and charge q. However, for the lowest l = 0, we find that there does not exist such a threshold value and the scalar field always decays for arbitrary coupling constant.
11090952
Cosmic ray threshold anomaly and kinematics in the dS spacetime
We present a covariant framework of kinematics in the dS spacetime, which is a natural postulate of recent astronomical observations ($\Lambda>0)$. One-particle states are presented explicitly. It is noticed that the dispersion relation of free particles is dependent on the degrees of freedom of angular momentum and spin. This fact can be referred to as the effects of the cosmological constant on kinematics of particles. The kinematics in dS spacetime is used to investigate the phenomenon of ultra high energy cosmic rays. We emphasize the possibility of solving the threshold anomalies of the interactions between ultra high energy cosmic rays and soft photons in the covariant framework of kinematics in the dS spacetime.
118839273
Cosmological perturbations in f(T) gravity
We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.