arxt1

[arxt1]

The neutrino pair annihilation ($\nu\bar{\nu}\longrightarrow e^{-}e^{+}$)around a massive source with an $f(R)$ global monopole. (arXiv:2206.00670v1 [gr-qc])

In this work we investigate the neutrino pair annihilation around a gravitational object involving an $f(R)$ global monopole. We derive and calculate the ratio $\frac{\dot{Q}}{\dot{Q_{Newt}}}$ meaning that the energy deposition per unit time is over that in the Newtonian case. It is found that the more deviation from general relativity leads more energy to set free from the annihilation with greater ratio value. It should also be pointed out that the existence of global monopole makes a sharp increase in the ratio $\frac{\dot{Q}}{\dot{Q_{Newt}}}$, causing heavier gamma-ray burst. We also discuss the derivative $\frac{d\dot{Q}}{dr}$ as a function of radius $r$ of star to show the similar characters that the considerable modification of Einstein's gravity and the global monopole with unified theory order will raise the amount of $\frac{d\dot{Q}}{dr}$ greatly. The stellar body with $f(R)$ global monopole can be well qualified as a source of gamma-ray bursts. Moreover, we can select the factor $\psi_{0}$ to be comparable with the accelerating universe while regulate the parameter $\eta$ for the global monopole in order to make the ratio curves to coincide with the results from astronomy. It is possible to probe the monopole from astrophysical observations.

from gr-qc updates on arXiv.org https://ift.tt/BzbtrIu

[arxt1]

Quasinormal modes of Schwarzschild black holes on the real axis. (arXiv:2206.00671v1 [gr-qc])

We study the scattering of gravitational waves by a Schwarzschild black hole and its perturbed siblings to investigate influences of proposed spectral instability of quasinormal modes on the ringdown signal. Our results indicate that information of dominant ringdown signals, which are ascribed to the fundamental (i.e., least damping) quasinormal mode of unperturbed Schwarzschild black holes, is imprinted in the phase shift defined from the transmission amplitude (1/A_{in} in our notation). This approximately parallels the fact that the resonance of quantum systems is imprinted in the phase shift of the S-matrix. The phase shift around the oscillation frequency of the fundamental mode is modified only perturbatively even if the quasinormal-mode spectrum is destabilized by a perturbative bump at a distant location, signifying the stability of the ringdown signal. At the same time, the phase shift at low frequencies is modulated substantially reflecting the late-time excitation of echo signals associated with the quasinormal-mode spectrum after destabilization.

from gr-qc updates on arXiv.org https://ift.tt/LwiXFo4

[arxt1]

The Distribution of Ground State Energies in JT Gravity. (arXiv:2206.00692v1 [hep-th])

It is shown that the distribution of the lowest energy eigenvalue of the quantum completions of Jackiw-Teitelboim gravity is completely described by a non-linear ordinary differential equation (ODE) arising from a non-perturbative treatment of a special random Hermitian matrix model. Its solution matches the result recently obtained by computing a Fredholm determinant using quadrature methods. The new ODE approach allows for analytical expressions for the asymptotic behaviour to be extracted. The results are highly analogous to the well-known Tracy-Widom distribution for the lowest eigenvalue of Gaussian random Hermitian matrices, which appears in a very diverse set of physical and mathematical contexts. Similarly, it is expected that the new distribution characterizes a type of universality that can arise in various gravity settings, including black hole physics in various dimensions, and perhaps beyond. It has an association to a special multicritical generalization of the Gross-Witten-Wadia phase transition.

from gr-qc updates on arXiv.org https://ift.tt/la0iP6f

[arxt1]

Effects of a Geometrically Realized Early Dark Energy Era on the Spectrum of Primordial Gravitational Waves. (arXiv:2206.00721v1 [gr-qc])

In this work we investigate the effects of a geometrically generated early dark energy era on the energy spectrum of the primordial gravitational waves. The early dark energy era, which we choose it to have a constant equation of state parameter $w$, is synergistically generated by an appropriate $f(R)$ gravity in the presence of matter and radiation perfect fluids. As we demonstrate, the predicted signal for the energy spectrum of the $f(R)$ primordial gravitational waves is amplified and can be detectable, for various reheating temperatures, especially for large reheating temperatures. The signal amplitude depends on the duration of the early dark energy era and on the value of the dark energy equation of state parameter, with the most latter affecting more crucially the amplification. Specifically the amplification occurs when the equation of state parameter approaches the de Sitter value $w=-1$. Regarding the duration of the early dark energy era, we find that the largest amplification occurs when the early dark energy era commences at a temperature $T=0.85\,$eV until $T=7.8\,$eV. Moreover we study a similar scenario in which amplification occurs, where the early dark energy era commences at $T=0.29\,$eV and lasts until the temperature is increased by $\Delta T\sim 1.7\,$eV.

from gr-qc updates on arXiv.org https://ift.tt/8AFoiO7

[arxt1]

Probing the rest-frame of the Universe with near-IR cosmic infrared background. (arXiv:2206.00724v1 [astro-ph.CO])

While the cosmic microwave background (CMB) dipole is largely assumed entirely kinematic, there appears evidence that a part of it is primordial. Such possibility arises in models implying a tilt, interpreted as a dark flow, across the observable Universe. The kinematic nature of the entire CMB dipole can be probed using the dipole of cosmic backgrounds from galaxies after the last scattering. The near-IR cosmic infrared background (CIB) spectral energy distribution leads to an amplified dipole compared to the CMB. The CIB dipole is affected by galaxy clustering, decreasing with fainter, more distant galaxies, and by Solar System emissions and Galactic dust, which dominate the net CIB cosmological dipole in the optical/near-IR. We propose a technique that enables an accurate measurement of the kinematic near-IR CIB dipole. The CIB, effectively the integrated galaxy light (IGL), would be reconstructed from resolved galaxies in the forthcoming space-borne wide surveys covering four bands 0.9 to 2.5 micron. The galaxies will be sub-selected from the identified magnitude range where the dipole component from galaxy clustering is below the expected kinematic dipole. Using this technique the dipole can be measured in each of the bands at the statistical signal-to-noise S/N>50--100 with the forthcoming Euclid and Roman surveys, isolating CMB dipole's kinematic nature.

from gr-qc updates on arXiv.org https://ift.tt/IG5pRha

[arxt1]

Remarks on the effects of the quintessence on regular black holes. (arXiv:2206.00753v1 [gr-qc])

We present the generalization of a regular black hole surrounded by quintessence, considering Bardeen-like solutions added with this fluid. We also compare our solution particularized to the Bardeen one with those found in the recent literature, showing that some of them are inconsistent since they add quintessence "by hand", neglecting also the interesting behavior of the complete solution nearby the origin. Then, we present the correct way to implement the quintessential fluid in more general four-dimensional regular black hole geometries and explore some of its consequences, such as removing the black hole regularity at the origin.

from gr-qc updates on arXiv.org https://ift.tt/EHKsnt8

[arxt1]

Unruh quantum Otto engine in the presence of a reflecting boundary. (arXiv:2206.00768v1 [gr-qc])

We introduce a new model of relativistic quantum analogue of the classical Otto engine in the presence of a perfectly reflecting boundary. A single qubit acts as the working substance interacting with a massless quantum scalar field, with the boundary obeying the Dirichlet condition. The quantum vacuum serves as a thermal bath through the Unruh effect. We observe that the response function of the qubit gets significantly modified by the presence of the reflecting boundary. From the structure of the correlation function, we find that three different cases emerge, namely, the near boundary limit, the intermediate boundary limit, and the far boundary limit. As expected, the correlation in the far boundary limit approaches that of the Unruh quantum Otto engine (UQOE) when the reflecting boundary goes to infinity. The effect of the reflecting boundary is manifested through the reduction of the critical excitation probability of the qubit and the work output of the engine. Inspite of the reduced work output, the efficiency of the engine remains unaltered even in the presence of the boundary.

from gr-qc updates on arXiv.org https://ift.tt/KIdRlSc

[arxt1]

The BRST Double Complex for the Coupling of Gravity to Gauge Theories. (arXiv:2206.00780v1 [math-ph])

We consider (effective) Quantum General Relativity coupled to the Standard Model (QGR-SM) and study the corresponding BRST double complex. This double complex is generated by infinitesimal diffeomorphisms and infinitesimal gauge transformations. To this end, we define the respective BRST differentials $P$ and $Q$ and their corresponding anti-BRST differentials $\overline{P}$ and $\overline{Q}$. Then we show that all differentials mutually anticommute, which allows us to introduce the total BRST differential $D := P + Q$ and the total anti-BRST differential $\overline{D} := \overline{P} + \overline{Q}$. Furthermore, we characterize all non-constant Lagrange densities that are essentially closed with respect to the diffeomorphism differentials $P$ and $\overline{P}$ as scalar tensor densities of weight $w = 1$. As a consequence thereof, we obtain that graviton-ghosts decouple from matter if the Yang--Mills theory gauge fixing and ghost Lagrange densities are tensor densities of weight $w = 1$. In particular, we show that every such Lagrange density can be modified uniquely to satisfy said condition. Finally, we introduce a total gauge fixing fermion $\Upsilon$ and show that we can generate the complete gauge fixing and ghost Lagrange densities of QGR-SM via $D \Upsilon$.

from gr-qc updates on arXiv.org https://ift.tt/NVt0ekO

[arxt1]

Revisiting Barrow's Graduated Inflationary Universe: A Warm perspective. (arXiv:2206.00870v1 [gr-qc])

It is presumed that thermal fluctuations present during inflationary epoch can make inflaton scalar field to interact with other fields resulting in the existence of a thermal component during the inflationary period. The presence of this thermal component assists structure formation and reduces reheating dependence as in the contemporary inflationary paradigm. This is known as warm inflation. In 1990 J . D. Barrow \cite{25} considered a scenario of inflation with matter field having a phenomenological equation of state of the type $p+\rho=\gamma\rho^{\lambda},~\gamma\neq 0$ and $\lambda$ constant. He called such inflationary scenarios as "graduated inflation". In this work we reconsider the above equation of state in a scenario of warm inflation. Our aim would be to investigate and understand whether such matter can also act as a viable candidate for warm inflation.

from gr-qc updates on arXiv.org https://ift.tt/y2jHbXK

[arxt1]

Assessing the impact of non-Gaussian noise on convolutional neural networks that search for continuous gravitational waves. (arXiv:2206.00882v1 [gr-qc])

We present a convolutional neural network that is capable of searching for continuous gravitational waves, quasi-monochromatic, persistent signals arising from asymmetrically rotating neutron stars, in $\sim 1$ year of simulated data that is plagued by non-stationary, narrow-band disturbances, i.e., lines. Our network has learned to classify the input strain data into four categories: (1) only Gaussian noise, (2) an astrophysical signal injected into Gaussian noise, (3) a line embedded in Gaussian noise, and (4) an astrophysical signal contaminated by both Gaussian noise and line noise. In our algorithm, different frequencies are treated independently; therefore, our network is robust against sets of evenly-spaced lines, i.e., combs, and we only need to consider perfectly sinusoidal line in this work. We find that our neural network can distinguish between astrophysical signals and lines with high accuracy. In a frequency band without line noise, the sensitivity depth of our network is about $\mathcal{D}^{95\%} \simeq 43.9$ with a false alarm probability of $\sim 0.5\%$, while in the presence of line noise, we can maintain a false alarm probability of $\sim 10\%$ and achieve $\mathcal{D}^\mathrm{95\%} \simeq 3.62$ when the line noise amplitude is $h_0^\mathrm{line}/\sqrt{S_\mathrm{n}(f_k)} = 1.0$. We evaluate the computational cost of our method to be $O(10^{19})$ floating point operations, and compare it to those from standard all-sky searches, putting aside differences between covered parameter spaces. Our results show that our method is more efficient by one or two orders of magnitude than standard searches. Although our neural network takes about $O(10^8)$ sec to employ using our current facilities (a single GPU of GTX1080Ti), we expect that it can be reduced to an acceptable level by utilizing a larger number of improved GPUs.

from gr-qc updates on arXiv.org https://ift.tt/sKdZGvu

[arxt1]

Impact of ultralight bosonic dark matter on the dynamical bar-mode instability of rotating neutron stars. (arXiv:2206.00977v1 [gr-qc])

We investigate the effects ultralight bosonic field dark matter may have on the dynamics of unstable differentially-rotating neutron stars prone to the bar-mode instability. To this aim we perform numerical simulations in general relativity of rotating neutron stars accreting an initial spherically symmetric bosonic field cloud, solving the Einstein-(complex, massive) Klein-Gordon-Euler and the Einstein-(complex) Proca-Euler systems. We find that the presence of the bosonic field can critically modify the development of the bar-mode instability of neutron stars, depending on the total mass of the bosonic field and on the boson particle mass. In some cases, the accreting bosonic field can even quench the dominant $\ell=m=2$ mode of the bar-deformation by dynamically forming a mixed (fermion-boson) star that retains part of the angular momentum of the original neutron star. However, the mixed star undergoes the development of a mixed bar that leads to significant gravitational-wave emission, substantially different to that of the isolated neutron star. Our results indicate that dark-matter accretion in neutron stars could change the frequency of the expected emission of the bar-mode instability, which would have an important impact on ongoing searches for continuous gravitational waves.

from gr-qc updates on arXiv.org https://ift.tt/9ghFwle

[arxt1]

The Integrated Sachs-Wolfe Effect in Interacting Dark Matter-Dark Energy Models. (arXiv:2206.01030v1 [astro-ph.CO])

Interacting dark matter-dark energy (IDMDE) models can be taken to account as one of the present challenges that may affect the cosmic structures. In this work, we study the integrated Sachs-Wolfe (ISW) effect in IDMDE models. To this end, we initially introduce a theoretical framework for IDMDE models. Moreover, we briefly discuss the stability conditions of IDMDE models and by specifying a simple functional form for the energy density transfer rate, we calculate the perturbation equations. In the following, we calculate the amplitude of the matter power spectrum for the IDMDE model and compare it with the corresponding result obtained from the $\Lambda$CDM model. Furthermore, we calculate the amplitude of the ISW auto-power spectrum as a function of multipole order l for the IDMDE model. The results indicate that the amplitude of the ISW auto-power spectrum in the IDMDE model for different phantom dark energy equations of state behaves similar to the one for the $\Lambda$CDM model, whereas, for the quintessence dark energy equations of state, the amplitude of the ISW-auto power spectrum for the IDMDE model should be higher than the one for the $\Lambda$CDM model. Also, it turns out that the corresponding results by different values of the coupling parameter demonstrate that $\xi$ is inversely proportional to the amplitude of the ISW-auto power spectrum in the IDMDE model. Finally, by employing four different surveys, we calculate the amplitude of the ISW-cross power spectrum as a function of multipole order $l$ for the IDMDE model. The results exhibit that the amplitude of the ISW-cross power spectrum for the IDMDE model for all values of $\omega_{\rm x}$ is higher than the one obtained for the $\Lambda$CDM model. Also, it turns out that the amplitude of the ISW-cross power spectrum in the IDMDE model changes inversely with the value of coupling parameter $\xi$.

from gr-qc updates on arXiv.org https://ift.tt/wGyARgV

[arxt1]

Primordial black holes and scalar-induced gravitational waves from scalar-tensor inflation. (arXiv:2206.01039v1 [gr-qc])

The power spectrum of the scalar-tensor inflation with a quadratic form Ricci scalar coupling function $\Omega(\phi)=1- 2\phi/\phi_c+(1+\delta^2)(\phi/\phi_c)^2$ can be enhanced enough to produce primordial black holes and generate scalar-induced gravitational waves. The masses of primordial black holes and the frequencies of scalar-induced gravitational waves are controlled by the parameter $\phi_c$, and their amplitudes are determined by the parameter $\delta$. Primordial black holes with stellar masses, planetary masses, and masses around $10^{-12} M_\odot$ are produced and their abundances are obtained from the peak theory. The frequencies of the corresponding scalar-induced gravitational waves are around $10^{-9}$ Hz, $10^{-6}$ Hz, and $10^{-3}$ Hz, respectively. The primordial black holes with masses around $10^{-12} M_\odot$ can account for almost all of the dark matter, and the scalar-induced gravitational waves with frequencies around $10^{-9}$ Hz can explain the NANOGrav 12.5yrs signal.

from gr-qc updates on arXiv.org https://ift.tt/0C7AhtM

[arxt1]

Looking out for the Galileon in the nanohertz gravitational wave sky. (arXiv:2206.01056v1 [astro-ph.CO])

We study the polarizations induced by the Galileon as a stochastic gravitational wave background in the cross correlated power in a pulsar timing array. Working within Galileon gravity, we first show that the scalar gravitational wave signature of the Galileon is encoded solely in its effective mass, which is controlled by the bare mass, conformal coupling, and a tadpole. Then, we study the phenomenology of the Galileon induced scalar polarizations and place observational constraints on these using the present NANOGrav data set. Our results feature longitudinal spatial correlation, indicative of a $10^{-22}$ eV Galileon, and show the Galileon polarizations as more statistically relevant compared with the tranverse tensor ones expected in general relativity.

from gr-qc updates on arXiv.org https://ift.tt/qhrwSef

[arxt1]

An analogue model for the BTZ black hole. (arXiv:2206.01147v1 [gr-qc])

We present an analogue model for the Ba\~nados, Teitelboim, Zanelli (BTZ) black hole based on a hydrodynamical flow. We numerically solve the fully nonlinear hydrodynamic equations of motion and observe the excitation and decay of the analogue BTZ quasinormal modes in the process. We consider both a small perturbation in the steady state configuration of the fluid and a large perturbation; the latter could be regarded as an example of formation of the analogue (acoustic) BTZ black hole.

from gr-qc updates on arXiv.org https://ift.tt/S8OgDmr

[arxt1]

The energy budget of cosmological first-order phase transitions beyond the bag equation of state. (arXiv:2206.01148v1 [hep-ph])

The stochastic gravitational-wave backgrounds (SGWBs) from the cosmological first-order phase transitions (FOPTs) serve as a promising probe for the new physics beyond the standard model of particle physics. When most of the bubble walls collide with each other long after they had reached the terminal wall velocity, the dominated contribution to the SGWBs comes from the sound waves characterized by the efficiency factor of inserting the released vacuum energy into the bulk fluid motions. However, the previous works of estimating this efficiency factor have only considered the simplified case of the constant sound velocities in both symmetric and broken phases, either for the bag model with equal sound velocities or $\nu$-model with different sound velocities in the symmetric and broken phases, which is not only unrealistic from a viewpoint of particle physics, but also inconsistent since the sound velocity profile should be solved from the fluid equation of motion (EoM). In this paper, we consistently solve the fluid EoM with the iteration method when taking into account the sound-velocity variation across the bubble wall for a general and realistic equation of state (EoS) beyond the simple bag model and $\nu$-model. We have found a universal suppression effect for the efficiency factor of bulk fluid motions, though such a suppression effect could be negligible for the strong FOPT, in which case the previous estimation from a bag EoS on the efficiency factor of bulk fluid motions still works as a good approximation.

from gr-qc updates on arXiv.org https://ift.tt/P4wdVus

[arxt1]

Primordial black hole formation in $F(R)$ bouncing cosmology. (arXiv:2206.01150v1 [gr-qc])

The phenomenology of primordial black holes (PBHs) physics, and the associated PBH abundance constraints, can be used in order to probe the early-universe evolution. In this work, we focus on the bounce realization within $F(R)$ modified gravity and we investigate the corresponding PBH behavior. In particular, we calculate the energy density power spectrum at horizon crossing time as a function of the involved theoretical parameters, and then we extract the PBH abundance in the context of peak theory, considering the non-linear relation between the density contrast and the comoving curvature perturbation, as well as the critical collapse law for the PBH masses. We first calculate the PBH mass function, and then we extract the PBH abundance $\Omega_\mathrm{PBH,f}$ at formation time as a function of the model parameters, namely the involved $F(R)$ parameter $\alpha$ and the Hubble parameter at the transition time from the bounce to the radiation dominated epoch $H_\mathrm{RD}$. Interestingly, we find that in order to have a significant black hole production, namely $10^{-10}<\Omega_\mathrm{PBH,f}<1$, $H_\mathrm{RD}$ and $\alpha$ should lie roughly within the ranges $10^{-7}M_\mathrm{Pl}\leq H_\mathrm{RD}\leq 10^{-6}M_\mathrm{Pl}$, $10^{-9}M_\mathrm{Pl}\leq H_\mathrm{RD}\leq 2\times 10^{-9}M_\mathrm{Pl}$ and $10^{-30}M^2_\mathrm{Pl}\leq \alpha \leq 10^{-12}M^2_\mathrm{Pl}$ respectively. Finally, we show that the excluded region corresponding to PBH overproduction forms a closed ring.

from gr-qc updates on arXiv.org https://ift.tt/yKqsBFD