We consider an inhomogeneous model and independently an anisotropic model of primordial power spectrum in order to describe the observed hemispherical anisotropy in cosmic microwave background radiation (CMBR). This anisotropy can be parametrized in terms of the dipole modulation model of the temperature field. Both the models lead to correlations between spherical harmonic coefficients corresponding to multipoles, l and l ± 1. We obtain the model parameters by making a fit to TT correlations in CMBR data. Using these parameters we predict the signature of our models for correlations among different multipoles for the case of the TE and EE modes. These predictions can be used to test whether the observed hemispherical anisotropy can be correctly described in terms of a primordial power spectrum. Furthermore these may also allow us to distinguish between an inhomogeneous and an anisotropic model.
We propose a generalized star product that deviates from the standard one when the fields are considered at different spacetime points by introducing a form factor in the standard star product. We also introduce a recursive definition by which we calculate the explicit form of the generalized star product at any number of spacetime points. We show that our generalized star product is associative and cyclic at linear order. As a special case, we demonstrate that our recursive approach can be used to prove the associativity of standard star products for same or different spacetime points. The introduction of a form factor has no effect on the standard Lagrangian density in a noncommutative spacetime because it reduces to the standard star product when spacetime points become the same. We show that the generalized star product leads to physically consistent results and can fit the observed data on hemispherical anisotropy in the cosmic microwave background radiation.
ABSTRACT In this work, we study the correlation between quasi-periodic oscillation (QPO) frequency and the spectral parameters during various X-ray states in the black hole binary GRS 1915+105 which matches well with the predicted relativistic dynamic frequency (i.e. the inverse of the sound crossing time) at the truncated radii. We have used broad-band data of Large Area X-ray Proportional Counter and Soft X-ray Telescope instruments onboard AstroSat. Spectral fitting shows that the accretion rate varies from ∼0.1 to ∼5.0 × 1018 gm s−1 and the truncated radius changing from the last stable orbit of an almost maximally spinning black hole, ∼1.2 to ∼19 gravitational radii. For this wide range, the frequencies of the C-type QPO (2–6 Hz) follow the trend predicted by the relativistic dynamical frequency model and interestingly, the high-frequency QPO at ∼70 Hz also follows the same trend, suggesting they originate from the innermost stable circular orbit with the same mechanism as the more commonly observed C-type QPO. While the qualitative trend is as predicted, there are quantitative deviations between the data and the theory, and the possible reasons for these deviations are discussed.
We show that the breaking of the conformal invariance of the electromagnetic Lagrangian, which is required for inflationary magnetogenesis, arises naturally in the Poincar\'e gauge theory. We use the minimal coupling prescription to introduce the electromagnetic gauge fields as well as non-Abelian gauge fields in this theory. Due to the addition of non-Abelian gauge fields, we show that the solar constraints on this model can be naturally evaded. We find that in the minimal version of this model the generated magnetic field is too small to explain the observations. We discuss some generalizations of the gravitational action, including the Starobinsky model and a model with conformal invariance. We show that such generalizations naturally generate the kinetic energy terms required for magnetogenesis. We propose a generalization of the minimal model by adding a potential term, which is allowed within the framework of this model, and show that it leads to sufficiently large magnetic fields.
\abstract{The sensitivity with which the $\rm \gamma$ ray sources can be studied is inversely proportional to the angular resolution of an extensive air shower (EAS) array. Therefore it is important to determine the EAS arrival direction as accurately as possible. In this paper, we present the methods that were recently implemented by GRAPES-3 experiment to improve its angular resolution. In the GRAPES-3 experiment, consisting of an array of $\sim$ 400 scintillator detectors, the arrival direction of the shower is determined from the relative arrival times of particles at different detectors. The arrival times measured by each detector is initially corrected for the fixed arrival time caused by the cables connecting the individual detectors to their respective time-to-digital converter channels. A new method was developed based on the random walk technique to measure these fixed arrival times with a smaller uncertainty. A study based on simulations was also performed to verify the efficacy of this method. The arrival times were further corrected for the conical shape of the shower front, the slope of which had exhibited a strong dependence on the shower size and age. The correction for these dependencies led to an improvement in the angular resolution of the array by a factor of $\sim$ 2. The angular resolution of GRAPES-3 array obtained through array division methods is $\rm 0.8^{\circ}$ for energies $\rm E>5\,TeV$, which improves to $\rm0.3^{\circ}$ at $\rm E>100\,TeV$, and finally approaches $\rm0.2^{\circ}$ at $\rm E>500\,TeV$.}
Abstract We study the dipole signal in the slope x of the log N –log S relationship for quasars using the CatWISE2020 catalog of infrared sources. Here N is the number of sources with flux density greater than S . The slope is extracted by using a maximized log-likelihood method as well as Bayesian analysis. We obtain the value x = 1.579 ± 0.001 for a quasar sample of 1355352 sources. We extract the dipole signal in this parameter by employing χ 2 minimization, assuming a sky model of x up to the quadrupole term. We find that the dipole amplitude | D | is 0.005 ± 0.002 and dipole direction ( l, b ) in Galactic coordinate system equal to (201.50° ± 27.87°, -29.37° ± 19.86°). The direction of dipole anisotropy is found to be very close to the hemispherical power asymmetry ( l, b )=(221°,-27°) in the Cosmic Microwave Background (CMB). The dipole signal is also extracted using Bayesian analysis and found to be in good agreement with that obtained using χ 2 minimization. We also obtain a signal of quadrupole anisotropy which is found to be correlated with the ecliptic poles and can be attributed to ecliptic bias.
We explain the large scale correlations in radio polarization in terms of the correlations of galaxy cluster/supercluster magnetic field. Assuming that the polarization correlations closely follow the spatial correlations of the background magnetic field we recover the magnetic field spectral index as -2.74$\pm$0.04.This remarkably agrees with cluster magnetic field spectral index obtained in cosmological magneto-hydrodynamic simulations. We discuss possible physical scenarios in which the observed polarization alignment is plausible.
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