In a model of spontaneous scalarization of neutron stars proposed by Damour and Esposito-Farese, a general relativistic branch becomes unstable to trigger tachyonic growth of a scalar field $\varphi$ toward a scalarized branch. Applying this scenario to cosmology, there is fatal tachyonic instability of $\varphi$ during inflation and matter dominance being incompatible with solar-system constraints on today’s field value ${\varphi }_0$. In the presence of a four-point coupling $g^2{\varphi }^2{\chi }^2/2$ between $\varphi$ and an inflaton field $\chi$, it was argued by Anson et al. that a positive mass squared heavier than the square of a Hubble expansion rate leads to the exponential suppression of $\varphi$ during inflation and that ${\varphi }_0$ can remain small even with the growth of $\varphi$ after the radiation-dominated epoch. For several inflaton potentials approximated as $V(\chi )=m^2{\chi }^2/2$ about the potential minimum, we study the dynamics of $\varphi$ during reheating as well as other cosmological epochs in detail. For certain ranges of the coupling $g$, the homogeneous field $\varphi$ can be amplified by parametric resonance during a coherent oscillation of the inflaton. Incorporating the backreaction of created particles under a Hartree approximation, the maximum values of $\varphi$ reached during preheating are significantly smaller than those obtained without the backreaction. We also find that the minimum values of $g$ consistent with solar system bounds on $\varphi$ at the end of reheating are of order ${10}^{-5}$ and hence there is a wide range of acceptable values of $g$. Thus, the scenario proposed by Anson et al. naturally leads to the viable cosmological evolution of $\varphi$ consistent with local gravity constraints, without modifying the property of scalarized neutron stars.

In minisuperspace quantum cosmology, the Lorentzian path integral formulations of the no-boundary and tunneling proposals have recently been analyzed. But it has been pointed out that the wave function of linearized perturbations around a homogeneous and isotropic background is of an inverse Gaussian form and thus that their correlation functions are divergent. In this paper, we revisit this issue and consider the problem of perturbations in Lorentzian quantum cosmology by modifying the dispersion relation based on trans-Planckian physics. We consider two modified dispersion relations, the generalized Corley-Jacobson dispersion relation with higher momentum terms and the Unruh dispersion relation with a trans-Planckian mode cutoff, as examples. We show that the inverse Gaussian problem of perturbations in Lorentzian quantum cosmology is hard to overcome with the trans-Planckian physics modifying the dispersion relation at short distances.

In this paper, we investigate the primordial perturbations of the inflation model induced from the multifield mimetic gravity, where there are two fields during inflation, and both adiabatic and isocurvature perturbation modes are generated. We show that although the original adiabatic perturbation mode indeed loses the kinetic term due to the constraint equation, by applying the curvaton mechanism where one of the fields is viewed as a curvaton field, the adiabatic perturbation can be transferred from the isocurvature one at the end of inflation. Detailed calculations are performed for both inflationary and the consequent radiation-dominant and matter-dominant epochs. Therefore, the so-called “nonpropagating problem” of the adiabatic mode will not harm the multifield mimetic inflation models.

We study the homogeneous and anisotropic dynamics of pseudoscalar inflation coupled to an $\mathrm{SU}(N)$ gauge field. To see how the initially anisotropic universe is isotropized in such an inflation model, we derive the equations to obtain axisymmetric $\mathrm{SU}(N)$ gauge field configurations in Bianchi type-I geometry and discuss a method to identify their isotropic subsets which are the candidates of their late-time attractor. Each isotropic solution is characterized by the corresponding SU(2) subalgebra of the $\mathrm{SU}(N)$ algebra. It is shown numerically that the isotropic universe is a universal late-time attractor in the case of the SU(3) gauge field. Interestingly, we find that a transition between the two distinct gauge-field configurations characterized by different SU(2) subalgebras can occur during inflation. We clarify the conditions for this to occur. This transition could leave an observable imprint on the cosmic microwave background and the primordial gravitational wave background.

The distance-inclination degeneracy limits gravitational-wave parameter estimation of compact binary mergers. Although the degeneracy can be partially broken by including higher-order modes or precession, these effects are suppressed in binary neutron stars. In this work, we implement a new parametrization of the tidal effects in the binary neutron-star waveform, exploiting the binary Love relations, that breaks the distance-inclination degeneracy. The binary Love relations prescribe the tidal deformability of a neutron star as a function of its source-frame mass in an equation-of-state insensitive way and, thus, allows direct measurement of the redshift of the source. If the cosmological parameters are assumed to be known, the redshift can be converted to a luminosity distance, and the distance-inclination degeneracy can thus be broken. We implement this new approach, studying a range of binary neutron-star observing scenarios using Bayesian parameter estimation on synthetic data. In the era of the third-generation detectors, for observations with signal-to-noise ratios ranging from 6 to 167, we forecast up to an $\sim 70\%$ decrease in the 90% credible interval of the distance and inclination and up to an $\sim 50\%$ decrease in that of the source-frame component masses. For edge-on systems, our approach can result in moderate ($\sim 50\%$) improvement in the measurements of distance and inclination for binaries with a signal-to-noise ratio as low as 10. This prescription can be used to better infer the source-frame masses and, hence, refine population properties of neutron stars, such as their maximum mass, impacting nuclear astrophysics. When combined with the search for electromagnetic counterpart observations, the work presented here can be used to put improved bounds on the opening angle of jets from binary neutron-star mergers.

Many gravitational wave (GW) sources in the LISA band are expected to have non-negligible eccentricity. Furthermore, many of them can undergo acceleration because they reside in the presence of a tertiary. Here we develop analytical and numerical methods to quantify how the compact binary’s eccentricity enhances the detection of its peculiar acceleration. We show that the general relativistic precession pattern can disentangle the binary’s acceleration-induced frequency shift from the chirp-mass-induced frequency shift in GW template fitting, thus relaxing the signal-to-noise ratio requirement for distinguishing the acceleration by a factor of $10\sim 100$. Moreover, by adopting the GW templates of the accelerating eccentric compact binaries, we can enhance the acceleration measurement accuracy by a factor of $\sim 100$, compared to the zero-eccentricity case, and detect the source’s acceleration even if it does not change during the observational time. For example, a stellar-mass binary black hole (BBH) with moderate eccentricity in the LISA band yields an error of the acceleration measurement $\sim {10}^{-7}\mathrm{m}·{\mathrm{s}}^{-2}$ for $\mathrm{SNR}=20$ and observational time of 4 yr. In this example, we can measure the BBHs’ peculiar acceleration even when it is $\sim 1\mathrm{pc}$ away from a $4\times {10}^6{\mathrm{M}}_{\odot }$ supermassive black hole. Our results highlight the importance of eccentricity to the LISA-band sources and show the necessity of developing GW templates for accelerating eccentric compact binaries.

We present gravitational wave emission predictions based on three core collapse supernova simulations corresponding to three different progenitor masses. The masses span a large range, between 9.6 and $25M_{\odot }$, are all initially nonrotating, and are of two metallicities: zero and solar. We compute both the temporal evolution of the gravitational wave strains for both the plus and the cross polarizations, as well as their spectral decomposition and characteristic strains. The temporal evolution of our zero metallicity $9.6M_{\odot }$ progenitor model is distinct from the temporal evolution of our solar metallicity $15M_{\odot }$ progenitor model and our zero metallicity $25M_{\odot }$ progenitor model. In the former case, the high-frequency gravitational wave emission is largely confined to a brief time period $\sim 75\mathrm{ms}$ after bounce, whereas in the latter two cases high-frequency emission does not commence until $\sim 125\mathrm{ms}$ after bounce or later. The excitation mechanisms of the high-frequency emission in all three cases correspond to proto-neutron star convection and accretion onto the proto-neutron star from the convective gain layer above it, with the former playing the dominant role for most of the evolution. The low-frequency emission in all three models exhibits very similar behavior. At frequencies below $\sim 250\mathrm{Hz}$, gravitational waves are emitted by neutrino-driven convection and the standing accretion shock instability (SASI). This emission extends throughout the simulations when a gain region is present. In all three models, explosion is observed at $\sim 125$, $\sim 500$, and $\sim 250\mathrm{ms}$ after bounce in the 9.6, 15, and $25M_{\odot }$ progenitor models, respectively. At these times, the low-frequency gravitational wave emission is joined by very low-frequency emission, below $\sim 10\mathrm{Hz}$. These very low-frequency episodes are the result of explosion and begin at the above designated explosion times in each of our models. Our characteristic strains tell us that, in principle, all three gravitational wave signals would be detectable by current-generation detectors for a supernova at a distance of 10 kpc. However, our $9.6M_{\odot }$ progenitor model is a significantly weaker source of gravitational waves, with strain amplitudes approximately 5–10 times less than in our other two models. The characteristic strain for this model tells us that such a supernova would be detectable only within a much more narrow frequency range around the maximum sensitivity of today’s detectors. Finally, in our $9.6M_{\odot }$ progenitor model, we see very high-frequency gravitational radiation, extending up to $\sim 2000\mathrm{Hz}$. This feature results from the interaction of shock- and deleptonization-induced convection with perturbations introduced in the progenitor by nuclear burning during core collapse. While unique to the $9.6M_{\odot }$ progenitor model analyzed here, this very high-frequency emission may, in fact, be a generic feature of the predictions for the gravitational wave emission from all core collapse supernova models when simulations are performed with three-dimensional progenitors.

In this work, we investigate the semileptonic weak decays of spin-$1/2$ doubly heavy baryons ${\mathrm{\Xi }}_{Q{Q}^{\prime }}$ into spin-$3/2$ singly heavy baryons ${\mathrm{\Sigma }}_{Q^{\prime }}^{*}$ within light-cone sum rules. Using the parallel components of the light-cone distribution amplitudes of ${\mathrm{\Sigma }}_{Q^{\prime }}^{*}$, the transition form factors for these decays are calculated both analytically and numerically. The numerical results for these semileptonic weak decays widths and branching ratios are also predicted, which are compared with the same predictions by other theoretical approaches in the literatures. These phenomenology predictions can be tested by the experiments in the future.

Quantum simulations of bosonic field theories require a truncation in field space to map the theory onto finite quantum registers. Ideally, the truncated theory preserves the symmetries of the original model and has a critical point in the same universality class. In this paper, we explore two different truncations that preserve the symmetries of the $1+1$-dimensional $O(3)$ nonlinear $\sigma$ model—one that truncates the Hilbert space for the unit sphere by setting an angular momentum cutoff and a fuzzy sphere truncation inspired by noncommutative geometry. We compare the spectrum of the truncated theories in a finite box with the full theory. We use open boundary conditions, a novel method that improves on the correlation lengths accessible in our calculations. We provide evidence that the angular-momentum truncation fails to reproduce the $\sigma$ model and that the antiferromagnetic fuzzy model agrees with the full theory.

The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyze the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\mathrm{PBH}}\in [{10}^{-16},{10}^{-6}]M_{\odot }$.

In view of various field-theoretic reasons, in the present work, we study the question of if the usual dimensional regularization can be extended to quantum field theories with an ultraviolet cutoff (Poincare-breaking scale) in a way that preserves all the properties of the dimensional regularization. And we find that it can indeed be achieved. The resulting extension gives a framework in which the power-law and logarithmic divergences get detached to involve different scales. This new regularization scheme, the detached regularization as we call it, enables one to treat the power-law and logarithmic divergences differently and independently. We apply the detached regularization to the computation of the vacuum energy and to two well-known quantum field theories, namely the scalar and spinor electrodynamics. As a case study, we consider Fujikawa’s subtractive renormalization in the framework of the detached regularization, and show its effectiveness up to two loops by specializing to scalar self energy. We discuss various application areas of the detached regularization.

Throughout the study of the geodesics of some popular spherically symmetric regular black holes, we hereby prove that the analytically extended Hayward black hole is geodetically incomplete. The simplest extension of the Culetu-Simpson-Visser’s non-analytic smooth black hole is also geodetically incomplete, with the exception of the antipodal continuation of the radial geodesics. However, the huge ambiguity in the extension of nonanalytic spacetimes is tantamount of geodesic incompleteness and such spacetimes do not solve the singularity issue unless at least all the extensions turn out to be complete. Hence, we provide several mere modifications of such spacetimes in order to make them geodetically complete in all possible extensions beyond $r=0$.

Recent advancements in observational techniques have led to new tests of the general relativistic predictions for black-hole spacetimes in the strong-field regime. One of the key ingredients for several tests is a metric that allows for deviations from the Kerr solution but remains free of pathologies outside its event horizon. Existing metrics that have been used in the literature often do not satisfy the null convergence condition that is necessary to apply the strong rigidity theorem and would have allowed us to calculate the location of the event horizon by identifying it with an appropriate Killing horizon. This has led earlier calculations of event horizons of parametrically deformed metrics to either follow numerical techniques or simply search heuristically for coordinate singularities. We show that several of these metrics, almost by construction, are circular. We can, therefore, use the weak rigidity and Carter’s rotosurface theorem and calculate algebraically the locations of their event horizons, without relying on expansions or numerical techniques. We apply this approach to a number of parametrically deformed metrics, calculate the locations of their event horizons, and place constraints on the deviation parameters such that the metrics remain regular outside their horizons. We find that introducing very general parametrizations of potential deviations is typically accompanied by pathological behavior that extends outside the horizons of the black holes. We also show that calculating the angular velocity of the horizon and the effective gravity there offers new insights into the observational signatures of deformed metrics, such as the sizes and shapes of the predicted black-hole shadows.

Resonant excitation of $f$ modes in binary neutron star coalescences influence the gravitational waves (GWs) emission in both quasicircular and highly eccentric mergers and can deliver information on the star interior. Most models of resonant tides are built using approximate, perturbative approaches valid at low frequencies but then often employed up to merger. Thus, these models require to be carefully validated against numerical relativity (NR) simulations in the high-frequency regime. We perform detailed comparisons between a set of high-resolution NR simulations and the state of the art effective-one-body (EOB) model teobresums with various tidal potentials and including a model for resonant tides. For circular mergers, we find that $f$-mode resonances can improve the agreement between EOB and NR, but there is no clear evidence that the tidal enhancement after contact is due to a resonant mechanism. Tidal models with $f$-mode resonances do not consistently reproduce, at the same time, the NR waveforms and the energetics within the errors, and their performance is comparable to resummed tidal models without resonances. For highly eccentric mergers, we show for the first time that our EOB model reproduces the bursty NR waveform to a high degree of accuracy. However, the considered resonant model does not capture the $f$-mode oscillations excited during the encounters and present in the NR waveform. Finally, we analyze GW170817 with both adiabatic and dynamical tide models and find that the data shows no evidence in favor of models including dynamical tides. This is in agreement with the fact that $f$-mode resonances take place near merger frequencies but the latter are not available for GW170817. Measurement with next generation detectors might be possible but will require improved resonant models within EOB waveforms.

The applications of artificial neural networks in the cosmological field have shone successfully during the past decade, this is due to their great ability of modeling large amounts of datasets and complex nonlinear functions. However, in some cases, their use still remains controversial because their ease of producing inaccurate results when the hyperparameters are not carefully selected. In this paper, to find the optimal combination of hyperparameters to artificial neural networks, we propose to take advantage of the genetic algorithms. As a proof of the concept, we analyze three different cosmological cases to test the performance of the architectures achieved with the genetic algorithms and compare them with the standard process, consisting of a grid with all possible configurations. First, we carry out a model-independent reconstruction of the distance modulus using a type Ia supernovae compilation. Second, the neural networks learn to infer the equation of state for the quintessence model, and finally with the data from a combined redshift catalog the neural networks predict the photometric redshift given six photometric bands (urgizy). We found that the genetic algorithms improve considerably the generation of the neural network architectures, which can ensure more confidence in their physical results because of the better performance in the metrics with respect to the grid method.

This paper describes the acceleration of high-energy protons captured by electrostatic waves in the frame of a jet arising in the area of instability of a relativistic jet, where spiral structures are excited. The wave has a spatially heterogeneous structure of $\exp (i{k}_{\parallel }z+i{m}_{\varphi }\varphi )$. Protons can be captured in potential wells created by spiral waves, and thereby experience acceleration via a mechanism known as surfatron acceleration. Expressions for the maximum energy ($E_p\simeq {10}^{19}\mathrm{eV}$) and energy spectrum from jet parameters are obtained.

Axionlike particles (ALPs) are very light, neutral, spin zero bosons predicted by many theories which try to extend and complete the standard model of elementary particles. ALPs interact primarily with two photons and can generate photon-ALP oscillations in the presence of an external magnetic field. They are attracting increasing interest since photon-ALP oscillations produce deep consequences in astrophysics particularly in the very high-energy (VHE) band, where they increase the transparency of the Universe to VHE photons by partially preventing absorption caused by the extragalactic background light. Furthermore, ALPs explain why photons coming from flat spectrum radio quasars (a particular class of active galactic nuclei, AGN) have been observed for energies above 30 GeV—which represents a first hint for the existence of an ALP. In addition, ALPs solve an anomalous redshift dependence of blazar (an AGN class) spectra—which represents a second hint for the existence of an ALP. In this paper, we study another effect of the photon-ALP interaction; the change of the polarization state of photons. In particular, we study the propagation of the photon-ALP beam, starting where photons are produced—we consider photons generated in a galaxy cluster or in the jet of a blazar—crossing several magnetized media (blazar jet, host galaxy, galaxy cluster, extragalactic space, Milky Way) up to its arrival at the Earth, where photons can be detected. In the presence of the photon-ALP interaction, we analyze the final photon survival probability $P_{\gamma \to \gamma }$ and the corresponding photon degree of linear polarization ${\mathrm{\Pi }}_L$ for observed energies in the range $(1-{10}^{15})\mathrm{eV}$ dividing it into three energy bands: (i) UV-x-ray band (${10}^{-3}\mathrm{keV}–{10}^2\mathrm{keV}$), (ii) high-energy (HE) band (${10}^{-1}\mathrm{MeV}–{10}^4\mathrm{MeV}$), and (iii) VHE band (${10}^{-2}\mathrm{TeV}–{10}^3\mathrm{TeV}$). We observe that those photons, which are expected as unpolarized in the absence of ALPs, are made partially polarized by the photon-ALP interaction, which generally modifies the initial photon degree of linear polarization ${\mathrm{\Pi }}_{L,0}$ in a sizable and measurable way. Our findings can be tested by observatories like IXPE (already operative), and by the proposed missions eXTP, XL-Calibur, NGXP and XPP in the x-ray band and by the proposed missions COSI (approved to launch), e-ASTROGAM and AMEGO in the HE range. A possible detection of a departure of the photon polarization from the standard expectations would represent an additional hint for the existence of an ALP. We also discover a peculiar feature in the VHE band, where photons at energies above $\sim (1–10)\mathrm{TeV}$ are fully polarized because of the photon-ALP interaction. A possible detection of this feature would represent a proof for the existence of an ALP, but, unfortunately, current technologies do not yet allow us to detect photon polarization up to such high energies.

We study quantum effects of recently discovered kink solitons which are constructed self-consistently by coupling to a single, excited fermion bound state. Our studies are based on the observation that in a semiclassical expansion the energies of this single level and of the Dirac sea should be treated equally. For these kink solutions we compute the energy of the Dirac sea as the fermion vacuum polarization energy. We find it to be substantial and to typically outweigh the energy gain from binding the single level.