The rapid progress in gravitational wave astronomy has provided an opportunity for investigating the presence of long-range scalar forces that exclusively manifest around astrophysical black holes. In this paper, we explore a new possibility in this context, particularly in connection to the hypothesis that astrophysical black holes might be horizonless ultracompact objects (UCOs). In the absence of horizons, UCOs could feature unique interiors with extreme environments. This could help generate nontrivial scalar profiles and significant scalar charges. For demonstration, we consider 2-2-holes in quadratic gravity as a concrete example of UCOs. These objects can be formed by ordinary gases and closely resemble black holes externally. However, they have distinct interiors characterized by high curvatures and substantial redshift. In particular, the gases inside could reach extremely high temperatures or densities, making them an ideal object for investigating the generation of scalar profiles by UCOs. Within a minimal model of the scalar field, we find that this unique environment enables the generation of a substantial scalar charge for astrophysical 2-2-holes, which is challenging for other stellar objects. The predicted scalar charge-to-mass ratio of 2-2-holes remains nearly constant across a wide range of masses, offering different predictions for gravitational wave observations compared to other mechanisms.

We investigate a Schwarzschild metric exhibiting a signature change across the event horizon, which gives rise to what we term a Lorentzian-Euclidean black hole. The resulting geometry is regularized by employing the Hadamard partie finie technique, which allows us to prove that the metric represents a solution of vacuum Einstein equations. In this framework, we introduce the concept of atemporality as the dynamical mechanism responsible for the transition from a regime with a real-valued time variable to a new one featuring an imaginary time. We show that this mechanism prevents the occurrence of the singularity and, by means of the regularized Kretschmann invariant, we discuss in which terms atemporality can be considered as the characteristic feature of this black hole.

Recent gravitational wave detections from black hole mergers have underscored the critical role black hole perturbation theory and the Teukolsky equation play in understanding the behavior of black holes. The separable nature of the Teukolsky equation has long been leveraged to study the vacuum linear Teukolsky equation; however, as theory and measurements advance, solving the sourced Teukolsky equation is becoming a frontier of research. In particular, second-order calculations, such as in quasinormal mode and self-force problems, have extended sources. This paper presents a novel method for analytically separating the Teukolsky equation’s source, aimed to improve efficiency. Separating the source is a nontrivial problem due to the angular and radial mixing of generic quantities in Kerr spacetime. We provide a proof-of-concept demonstration of our method and show that it is accurate, separating the Teukolsky source produced by the stress-energy tensor of an ideal gas cloud surrounding a Kerr black hole. The detailed application of our method is provided in an accompanying Mathematica notebook. Our approach opens up a new avenue for accurate black hole perturbation theory calculations with sources in both the time and frequency domain.

The recent advancements in black hole imaging have opened a new era of probing horizon-scale physics with electromagnetic radiation. However, a feature of the observed images, a bright ring encircling a relatively dark region, has not sufficiently proved the existence of event horizons. It thus requires extreme care when studying the possibility of using such image features to examine quantum effects that may change the classical picture of black holes slightly or drastically. In this work, we investigate the image of a horizonless compact object, whose interior metric satisfies the 4D semiclassical Einstein equation nonperturbatively for the Planck constant, and whose entropy agrees with the Bekenstein-Hawking formula. Although the absence of an event horizon allows light rays to pass through the dense interior, the extremely strong redshift significantly darkens the image, making it almost identical to the classical black hole image. In particular, if there is light emission a bit inside the surface of the object, the intensity around the inner shadow is slightly enhanced, which could be a future observable prediction to characterize the object. We also find through a phenomenological parameter that the image is further darkened due to interactions inside. Thus, the image is consistent with current observations, and the object could be a candidate for black holes in quantum theory.

We study the linear stability of spontaneously scalarized black holes (BHs) induced by a scalar field $\varphi$ coupled to a Gauss-Bonnet (GB) invariant $R_{\mathrm{GB}}^2$. For the scalar-GB coupling $\xi (\varphi )=(\eta /8)({\varphi }^2+\alpha {\varphi }^4)$, where $\eta$ and $\alpha$ are constants, we first show that there are no angular Laplacian instabilities of even-parity perturbations far away from the horizon for large multipoles $l\gg 1$. The deviation of angular propagation speeds from the speed of light is largest on the horizon, whose property can be used to put constraints on the model parameters. For $\alpha \gtrsim -1$, the region in which the scalarized BH is subject to angular Laplacian instabilities can emerge. Provided that $\alpha \lesssim -1$ and $-1/2<\alpha {\varphi }_0^2<-0.1155$, where ${\varphi }_0$ is the field value on the horizon with a unit of the reduced Planck mass $M_{\mathrm{Pl}}=1$, there are scalarized BH solutions satisfying all the linear stability conditions throughout the horizon exterior. We also study the stability of spontaneously scalarized BHs in scalar-GB theories with a nonminimal coupling $-\beta {\varphi }^{2}R/16$, where $\beta$ is a positive constant and $R$ is a Ricci scalar. As the amplitude of the field on the horizon approaches an upper limit $|{\varphi }_0|=4/\sqrt{\beta }$, one of the squared angular propagation speeds $c_{\mathrm{\Omega }-}^2$ enters the instability region $c_{\mathrm{\Omega }-}^2<0$. So long as $|{\varphi }_0|$ is smaller than a maximum value determined for each $\beta$ in the range $\beta >5$, however, the scalarized BHs are linearly stable in both angular and radial directions.

Primordial black holes (PBHs) generated in the early Universe are considered as one of the candidates for dark matter. To produce PBHs with sufficient abundance, the primordial scalar power spectrum needs to be enhanced to the order of 0.01. Considering the third-order polynomial potential with polynomial attractors, we show that PBHs with a mass of about ${10}^{17}\mathrm{g}$ can be produced while satisfying the constraints from the cosmic microwave background observations at the $2\sigma$ confidence level. The mass of PBHs produced in the polynomial attractors can be much bigger than that in the exponential $\alpha$ attractors. By adding a negative power-law term to the polynomials, abundant PBHs with different masses and the accompanying scalar-induced gravitational waves (SIGWs) with different peak frequencies are easily generated. The PBHs with masses around ${10}^{-15}–{10}^{-12}{M}_{\odot }$ can account for almost all dark matter. The SIGWs generated in the nanohertz band can explain the recent detection of stochastic gravitational-wave background by the pulsar timing array observations. The non-Gaussianities of the primordial curvature perturbations in the squeezed and equilateral limits are calculated numerically. We find that the non-Gaussianity correction enhances the PBH abundance which makes the production of PBHs much easier, but the effect of non-Gaussianity on the generation of SIGWs is negligible.

In this paper, we introduce two coupling models of early dark energy (EDE) and cold dark matter aimed at alleviating cosmological tensions. We utilize the EDE component in the coupling models to relieve the Hubble tension, while leveraging the interaction between dark matter and dark energy to alleviate the large-scale structure tension. The interaction is implemented in the form of pure momentum coupling and Yukawa coupling. We employed various cosmological datasets, including cosmic microwave background radiation, baryon acoustic oscillations, type Ia supernovae, the local distance-ladder data (SH0ES), and the Dark Energy Survey year-3 data, to analyze our models. We first exclude SH0ES data from the entire dataset to constrain the parameters of novel models. We observe that the values of $H_0$ obtained from two coupling models are $69.47\pm 0.71\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ and $69.65\pm 0.61\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, respectively, at a 68% confidence level, slightly higher than that from the $\mathrm{\Lambda }\mathrm{CDM}$ model, which is $68.21\pm 0.39\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, but they exhibit a significant inconsistency with the SH0ES data, consistent with prior research findings in the EDE model. Subsequently, we incorporate SH0ES data to reconstrain the parameters of various models, our findings reveal that both coupling models yield best-fit values for $H_0$ approximately around $72.23\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, which would alleviate the tension in the Hubble parameter. However, similar to the EDE model, the coupling models yield the $S_8$ values that still surpasses the result of the $\mathrm{\Lambda }\mathrm{CDM}$ model. Nevertheless, the best-fit values for $S_8$ obtained with the two new models are 0.8192 and 0.8177, respectively, which are lower than the 0.8316 achieved by the EDE model. Consequently, although our coupling models fail to fully resolve the large-scale structure tension, they partially mitigate the adverse effect of the original EDE model.

A measurement of a primordial non-Gaussianity (PNG) signal through late- or early-Universe probes has the potential to transform our understanding of the physics of the primordial Universe. While large-scale structure observables in principle contain vital information, interpreting these measurements is challenging due to poorly understood astrophysical effects. Luckily, $N$-body simulations, such as the abacuspng set presented in this study, consisting of 9 boxes, each of size $L_{\mathrm{box}}=2\mathrm{Gpc}/h$ and particle mass of $1.01\times {10}^{10}{M}_{\odot }/h$, provide a viable path forward. As validation, we find good agreement between the simulations and our expectations from one-loop perturbation theory (PT) and the “separate universe” method for the matter bispectrum, matter power spectrum and the halo bias parameter associated with PNG, $b_{\varphi }$. As a science application, we investigate the link between halo assembly bias and $b_{\varphi }$ for halo properties known to play a vital role in accurately predicting galaxy clustering: concentration, shear (environment), and accretion rate. We find a strong response for all three parameters, suggesting that the connection between $b_{\varphi }$ and the assembly history of halos needs to be taken into account by future PNG analyses. We further perform the first study of the $b_{\varphi }$ parameter from fits to early DESI data of the luminous red galaxy (LRG) and quasistellar object (QSO) samples and comment on the effect on $f_{\mathrm{NL}}$ constraints for the allowed galaxy-halo models (note that $\sigma [f_{\mathrm{NL}}]\propto \frac{\sigma [b_{\varphi }]}{b_{\varphi }}$). We find that the error on $f_{\mathrm{NL}}$ is 15, 8, 7 for the LRGs at $z=0.5$ and $z=0.8$ and QSOs at $z=1.4$, respectively, suggesting that a thorough understanding of galaxy assembly bias is warranted so as to perform robust high-precision analysis of local-type PNG with future surveys.

We present the first dynamical model of plasma accretion onto traversable wormholes by performing general relativistic magnetohydrodynamical (GRMHD) simulations of the flow on both sides of the wormhole. We evolve the ideal MHD equations on a wormhole spacetime described by the spherically symmetric Simpson-Visser metric. The disk is initialized on one side of the wormhole and accretes onto the throat driven by the magnetorotational instability (MRI). We show that the inflowing plasma quickly settles in the throat and forms a hot, rotating cloud. The wormhole cloud acts as an engine in which gas coming from one side accumulates at the center, dissipates energy, and powers a mildly relativistic thermal wind toward the other side. Our novel predictions show that accreting wormholes behave very differently from black holes (BHs) in astrophysical environments. In particular, one mouth presents outflows without accretion signatures, contradicting the jet-disk symbiotic relation that holds for black holes.

We present applications of statistical data analysis methods from both bivariate and multivariate statistics to find suitable sets of neutron star features that can be leveraged for accurate and equation of state independent—or universal—relations. To this end, we investigate the ability of various correlation measures such as distance correlation and mutual information in identifying universally related pairs of neutron star features. We also evaluate relations produced by methods of multivariate statistics such as principal component analysis to assess their suitability for producing universal relations with multiple independent variables. As part of our analyses, we also put forward multiple entirely novel relations, including a multivariate relation for the $f$-mode frequency of neutron stars with a reduced average relative error of 0.010, compared to an error of 0.015 of existing, bivariate relations.

We explore the anomaly detection framework based on the normalizing flow (NF) models introduced in Morawski and Bejger [Phys. Rev. C 106, 065802 (2022)] to detect the presence of a large (destabilizing) dense matter phase transition in neutron star (NS) observations of masses and radii, and relate the feasibility of detection with parameters of the underlying mass-radius sequence, which is a functional of the dense matter equation of state. Once trained on simulated data featuring continuous $M(R)$ solutions (i.e., no phase transitions), NF is used to determine the likelihood of a first-order phase transition in a given set of $M(R)$ observations featuring a discontinuity, i.e., to perform the anomaly detection. Different mock test sets, featuring two branch solutions in the $M(R)$ diagram, were parametrized by the NS mass at which the phase transition occurs, $M_c$, and the radius difference between the heaviest hadronic star and lightest hybrid star, $\mathrm{\Delta }R$. We analyze the impact of these parameters on the NF performance in detecting the presence of a first-order phase transition. Among the results, we report that given a set of 15 stars with radius uncertainty of 0.2 km, a detection of a two-branch solution is possible with 95% accuracy if $\mathrm{\Delta }R>0.4\mathrm{km}$.

Top pair production is ideally suited to observe postdecay entanglement, thus providing a novel test of quantum mechanics. We provide top polarized decay amplitudes that can be used to compute semianalytical predictions and, in particular, to better understand why the postdecay entanglement arises. We obtain predictions for the LHC, identifying general phase space regions where experimental measurements of $tW$ entanglement are feasible. We also give predictions for polarized $e^{+}{e}^{-}$ collisions, focusing on the possibility that the postdecay $tW$ entanglement is larger than the $t\overline{t}$ one.

The canonical Gross-Neveu model for $N$ two-component Dirac fermions in $2+1$ dimensions suffers a continuous phase transition at a critical interaction $g_{c1}\sim 1/N$ at large $N$, at which its continuous symmetry $\mathrm{SO}(2N)$ is preserved and a discrete (Ising) symmetry becomes spontaneously broken. A recent mean-field calculation, however, points to an additional transition at a different critical $g_{c2}\sim -N{g}_{c1}$, at which $\mathrm{SO}(2N)\to \mathrm{SO}(N)\times \mathrm{SO}(N)$. To study the latter phase transition we rewrite the Gross-Neveu interaction $g(\overline{\psi }\psi {)}^2$ in terms of three different quartic terms for the single ($L=1$) $4N$-component real (Majorana) fermion, and then extend the theory to $L>1$. This allows us to track the evolution of the fixed points of the renormalization group transformation starting from $L\gg 1$, where one can discern three distinct critical points which correspond to continuous phase transitions into (1) $\mathrm{SO}(2N)$-singlet mass-order-parameter, (2) $\mathrm{SO}(2N)$-symmetric-tensor mass-order-parameters, and (3) $\mathrm{SO}(2N)$-adjoint nematic-order-parameters, down to $L=1$ value that is relevant to the standard Gross-Neveu model. Below the critical value of $L_c(N)\approx 0.35N$ for $N\gg 1$ only the Gross-Neveu critical point (1) still implies a diverging susceptibility for its corresponding ($\mathrm{SO}(2N)$-singlet) order parameter, whereas the two new critical points that existed at large $L$ ultimately become equivalent to the Gaussian fixed point at $L=1$. We interpret this metamorphosis of the $\mathrm{SO}(2N)$-symmetric-tensor fixed point from critical to spurious as an indication that the transition at $g_{c2}$ in the original Gross-Neveu model is turned first-order by fluctuations.

Autoregularization, a new divergence-free framework for calculating scattering amplitudes, uses a Lorentz-invariant scale harvested from the kinematics of a scattering process to regularize the amplitude of the process [N. Prabhu, J. Phys. Commun. 7, 115002 (2023).]. Preliminary validation studies show that autoregularization’s predictions are in good agreement with experimental data—across several scattering processes and a wide range of energy scales. Further, ab initio tree-level calculation of the vacuum energy density of the free fields in the Standard Model, using autoregularization, is shown to yield a value that is smaller than the current estimate of the cosmic critical density. In this paper, we prove that the scattering amplitudes in QED, calculated using autoregularization, are gauge invariant. Our proof, which is valid both for autoregularization and current theory, is stronger in that it shows the amplitude of every Feynman diagram is gauge invariant in contrast to previous proofs, which establish gauge invariance only for sum of amplitudes of Feynman diagrams of a process. Next, we show that—unlike in the standard quantization framework, which requires modification of both the quantization framework itself as well as the Lagrangian in order to quantize gauge fields in covariant gauge—in autoregularization the gauge field in QED can be quantized, in covariant gauge, without modifying the standard quantization procedure or the Lagrangian and without introducing the ghost field. Finally, we illustrate renormalization based on autoregularization up to 1-loop in ${\phi }^4$ theory. Since perturbative corrections are finite in autoregularization, the counterterms are not designed to remove divergences but to implement renormalization prescriptions at every order of perturbation. We also derive the renormalization group equation (RGE). Unlike in some regularization schemes (such as dimensional regularization), in which the physical meaning of the fictitious scale introduced by regularization is unclear, in autoregularization the scale in RGE has a transparent physical meaning—it is the Lorentz-invariant kinematic scale of the scattering process of interest. The increasing simplifications resulting within autoregularization and the agreement between its predictions and experimental data, together with the underlying thermodynamic argument, which shows that the framework is essential for a complete description of quantum fields, all converge to suggest that autoregularization provides the proper framework for the description of quantum fields.

We investigate the sensitivities of the liquid scintillator counter (LSC) at Yemilab and JUNO to solar neutrino oscillation parameters, focusing on ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$. We compare the potential of JUNO with LSC at Yemilab utilizing both reactor and solar data in determining those parameters. We find that the solar neutrino data of LSC at Yemilab is highly sensitive to ${\theta }_{12}$ enabling its determination with a higher precision compared to reactor experiments. Our study also reveals that if $\mathrm{\Delta }{m}_{21}^2$ is larger, with a value close to the best-fit value of KamLAND, JUNO reactor data will have about two times better precision than the reactor LSC at Yemilab. On the other hand, if $\mathrm{\Delta }{m}_{21}^2$ is smaller and closer to the best-fit value of solar neutrino experiments, the precision of the reactor LSC at Yemilab will be better than JUNO.

Assuming axions are potential dark matter (DM) candidate that make up all of the DM abundance, we discuss production of axions via (i) standard misalignment mechanism during the period of reheating and (ii) graviton-mediated 2-to-2 scattering of the inflaton and bath particles, where the inflaton $\varphi$ oscillates in a monomial potential $V(\varphi )\propto {\varphi }^k$ with a general equation of state. Considering reheating takes place purely gravitationally, mediated by massless gravitons, we explore the viable region of the parameter space that agrees with the observed DM relic abundance, satisfying bounds from big bang nucleosynthesis and cosmic microwave background radiation. We also discuss complementarity between dedicated axion search experiments and futuristic gravitational wave search facilities in probing the viable parameter space, thanks to the presence of detectable primordial gravitational waves with an inflationary origin.

One of the difficulties one has to face in the future phenomenological studies of new physics (NP), is the need to deal with increasing amounts of data. It is therefore increasingly important to improve the efficiency in the phenomenological study of NP. Whether it is the use of the Standard Model effective field theory (SMEFT), the use of machine learning (ML) algorithms, or the use of quantum computing, all are means of improving the efficiency. In this paper, we use a ML algorithm, the autoencoder (AE), to study the dimension-8 operators in the SMEFT which contribute to the gluon quartic gauge couplings (gQGCs) at muon colliders. The AE is one of the ML algorithms that has the potential to be accelerated by the quantum computing. It is found that the AE-based anomaly detection algorithm can be used as event selection strategy to study the gQGCs at the muon colliders, and is effective compared with traditional event selection strategies.

In the next decade, the proposed Line Emission Mapper (LEM) telescope concept is poised to revolutionize Galactic and extragalactic x-ray sensitivity. The instruments aboard LEM feature unprecedented eV scale energy resolution and an effective area of $1600{\mathrm{cm}}^2$ at 0.5 keV. Such features are ideally suited to explore decaying dark matter candidates that predict X-ray signals, including axion-like particles and sterile neutrinos. We present the first forecast of LEM sensitivity to dark matter decays and find sensitivity to lifetimes beyond $\sim {10}^{32}\mathrm{s}$ in the keV range, surpassing current limits by several orders of magnitude. Notably, our results show that LEM will be the first ever instrument to probe such long dark matter lifetimes in any mass range for any decay channel.

The large number of $\tau$ leptons available at the Belle II experiment makes it possible to study their properties and the extent of their compositeness. We propose a strategy that relies on three observables defined in terms of elements of the polarization density matrix of the produced $\tau$ pairs, which we obtain via quantum tomography. We find that these observables can explore values of the magnetic dipole moment down to $6.3\times {10}^{-4}$, which is 2 orders of magnitude better than the current experimental limit, constrain the electromagnetic radius below $4.3\times {10}^{-3}\mathrm{fm}$, and exclude an electric dipole moment larger than $1.7\times {10}^{-17}\mathrm{e}\mathrm{cm}$. The quoted limits are at the 95% confidence level (CL) and are obtained for a benchmark integrated luminosity of $1{\mathrm{ab}}^{-1}$ and a Monte Carlo estimate of the statistical sensitivity.