Recent discoveries have highlighted the significance of replica wormholes in resolving the information paradox and establishing the unitarity of black hole evaporation. In this paper, we propose the dissipative Sachdev-Ye-Kitaev (SYK) model as a minimal quantum model that exhibits entanglement dynamics with features qualitatively similar to replica wormholes. As a demonstration, we investigate the entanglement growth of a pair of dissipative SYK models initialized in a thermofield double state. In the regime of large $N$ with weak dissipation, we observe a first-order entanglement transition characterized by a switch of the dominant saddle point: from replica-diagonal solutions for short times to replica wormholelike off-diagonal solutions for long times. Furthermore, we show that the signature of replica wormholes persists even at moderate $N\lesssim 30$ by using the Monte Carlo quantum trajectory method. Our work may pave the way for explorations of replica wormhole physics in quantum simulators.

R7-branes are a class of recently discovered nonsupersymmetric real codimension-two duality defects in type IIB string theory predicted by the swampland cobordism conjecture. For type IIB realizations of 6D SCFTs with $\mathcal{N}=(2,0)$ supersymmetry, wrapping an R7-brane “at infinity” leads to a topological operator associated with a zero-form charge conjugation symmetry that squares to the identity. Similar considerations hold for those theories obtained from further toroidal compactification, but this can be obstructed by bundle curvature effects. Using some minimal data on the topological sector of the R7-branes, we extract the associated fusion rules for these charge conjugation operators. More broadly, we sketch a top down realization of various topological operators/interfaces associated with $\mathsf{C}$, $\mathsf{R}$, and $\mathsf{T}$ transformations. We also use holography to provide strong evidence for the existence of the R7-brane which is complementary to the cobordism conjecture. Similar considerations apply to other string-realized QFTs with symmetry operators constructed via nonsupersymmetric branes which carry a conserved charge.

Gravitational self-force theory is the primary way of modeling extreme-mass-ratio inspirals (EMRIs). One difficulty that appears in second-order self-force calculations is the strong divergence at the worldline of the small object, which causes both numerical and analytical issues. Previous work [Phys. Rev. D 95, 104056 (2017); Phys. Rev. D 103, 124016 (2021)] demonstrated that this could be alleviated within a class of highly regular gauges and presented the metric perturbations in these gauges in a local coordinate form. We build on this previous work by deriving expressions for the highly regular gauge metric perturbations in both fully covariant form and as a generic coordinate expansion. With the metric perturbations in covariant or generic coordinate form, they can easily be expressed in any convenient coordinate system. These results can then be used as input into a puncture scheme in order to solve the field equations describing an EMRI.

We present bhpwave: a new python-based, open-source tool for generating the gravitational waveforms of stellar-mass compact objects undergoing quasicircular inspirals into rotating massive black holes. These binaries, known as extreme-mass-ratio inspirals (EMRIs), are exciting mHz gravitational wave sources for future space-based detectors such as the Laser Interferometer Space Antenna (LISA). Relativistic models of EMRI gravitational wave signals are necessary to unlock the full scientific potential of mHz detectors, yet few open-source EMRI waveform models exist. Thus we built bhpwave, which uses the adiabatic approximation from black hole perturbation theory to rapidly construct gravitational waveforms based on the leading-order inspiral dynamics of the binary. In this work, we present the theoretical and numerical foundations underpinning bhpwave. We also demonstrate how bhpwave can be used to assess the impact of EMRI modeling errors on LISA gravitational wave data analysis. In particular, we find that for retrograde orbits and slowly spinning black holes we can mismodel the gravitational wave phasing by as much as $\sim 10$ radians without significantly biasing EMRI parameter estimation.

This study introduces novel constraints on the free streaming of thermal relic warm dark matter (WDM) from Lyman-$\alpha$ forest flux power spectra. Our analysis utilizes a high resolution, high redshift sample of quasar spectra observed using the HIRES and UVES spectrographs ($z=4.2–5.0$). We employ a Bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization to establish lower limits on the mass of a thermal relic WDM particle of 5.7 keV (at 95% CL). This result surpasses previous limits from the Lyman-$\alpha$ forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales ($k_{\max }=0.2{\mathrm{km}}^{-1}\mathrm{s}$). The approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of Lyman-$\alpha$ forest constraints on WDM models at high redshifts are limited by the availability of high quality quasar spectra. Restricting the analysis to comparable scales and thermal history priors as in prior studies ($k_{\max }<0.1{\mathrm{km}}^{-1}\mathrm{s}$) lowers the bound on the WDM mass to 4.1 keV. As the precision of the measurements increases, it becomes crucial to examine the instrumental and modeling systematics. On the modeling front, we argue that the impact of the thermal history uncertainty on the WDM particle mass constraint has diminished due to improved independent observations. At the smallest scales, the primary source of modeling systematic arises from the structure in the peculiar velocity of the intergalactic medium and inhomogeneous reionization.

This paper investigates the decoherence effect resulting from the interaction of squeezed gravitational waves with a system of massive particles in spatial superposition. This paper investigates the decoherence effect resulting from the interaction of squeezed gravitational waves with a system of massive particles in spatial superposition. We first employ the open quantum system approach to obtain the established decoherence in a spatial superposition of massive objects induced by squeezed gravitational waves. Subsequently, we focus on the spin-$1/2$ particle system, and our analysis reveals that the decoherence rate depends on both the squeezing strength and the squeezing angle of the gravitational waves. Our results demonstrate that squeezed gravitational waves with squeezing strengths of $r_p\ge 1.2$ and a squeezing angle of ${\phi }_p=\pi /2$ can induce a 1% decoherence within 1 s free falling of a cloud of spin-$1/2$ particles. This investigation sheds light on the relationship between squeezed gravitational waves and the coherence of spatial superposition states in systems of massive particles and their spin. The dependence of decoherence on squeezing strength and, in the case of spin-$1/2$ particles, on the squeezing angle paves the way for further exploration and understanding of the quantum-gravity connection. We suggest that such an experimental setup could also be employed to eventually investigate the level of squeezing effect (and hence quantum-related properties) of gravitational waves produced in the early universe from inflation.

Solitons are observed to form in simulations of dark matter (DM) halos consisting of bosonic fields. We use the extended Press-Schechter formalism to compute the mass function of solitons, assuming various forms for the relationship between halo mass and soliton mass. We further provide a new calculation of the rate of soliton major mergers. Solitons composed of axion DM are unstable above a critical mass, and decay to either relativistic axions or photons, depending on the values of the coupling constants. We use the computed soliton major merger rate to predict the enhanced DM decay rate due to soliton instability. For certain values of currently allowed axion parameters, the energy injection into the intergalactic medium from soliton decays to photons is comparable to or larger than the energy injection due to core collapse supernovae at $z>10$. A preceding paper explores the phenomenology of such an energy injection.

If dark matter is composed of axions, then axion stars form in the cores of dark matter halos. These stars are unstable above a critical mass, decaying to radio photons that heat the intergalactic medium, offering a new channel for axion indirect detection. We recently provided the first accurate calculation of the axion decay rate due to axion star mergers. In this work we show how existing data concerning the CMB optical depth leads to strong constraints on the axion photon coupling in the mass range ${10}^{-14}\mathrm{eV}\lesssim m_a\lesssim {10}^{-8}\mathrm{eV}$. Axion star decays lead to efficient reionization of the intergalactic medium during the dark ages. By comparing this nonstandard reionization with Planck legacy measurements of the Thomson optical width, we show that couplings in the range ${10}^{-14}{\mathrm{GeV}}^{-1}\lesssim g_{a\gamma \gamma }\lesssim {10}^{-10}{\mathrm{GeV}}^{-1}$ are excluded for our benchmark model of axion star abundance. Future measurements of the 21 cm emission of neutral hydrogen at high redshift could improve this limit by an order of magnitude or more, providing complementary indirect constraints on axion dark matter in parameter space also targeted by direct detection haloscopes.

The luminosity distance is a key observable of gravitational-wave (GW) observations. We demonstrate how one can correctly retrieve the luminosity distance of compact binary coalescences (CBCs) if the GW signal is strongly lensed. We perform a proof-of-concept parameter estimation for the luminosity distance supposing (i) strong lensing produces two lensed GW signals emitted from a CBC, (ii) the Advanced LIGO-Virgo network detects both lensed signals as independent events, and (iii) the two events are identified as strongly lensed signals originated from the same source. Taking into account the maximum magnification allowed in two lensing scenarios and simulated GW signals emitted from four different binary black holes, we find that the strong lensing can improve the precision of the distance estimation of a CBC by up to a factor of a few compared to that can be expected without lensing.

The Kerr metric that describes the spacetime of a spinning supermassive black hole (SMBH) is axisymmetric, implying that the nearly parabolic geodesics on which stars approach the SMBH depend on the inclination angle $\iota$ of the orbital angular momentum with respect to the SMBH spin. This inclination affects both the geodesic deviation that determines whether a star is tidally disrupted and whether the tidal debris survives direct capture by the event horizon to produce an observable tidal disruption event (TDE). The steady-state TDE rate is the rate at which stars are scattered into the loss cone determined by these spin- and inclination-dependent effects. As the anisotropy of this loss-cone refilling is highly uncertain, we consider the two extreme limits in which stellar inclination is preserved (IP) or isotropized (ISO). We calculate the inclination distribution in these two limits and find a prograde bias in the IP limit because of the strong retrograde bias for direct capture. However, we find a retrograde bias in the ISO limit for intermediate SMBH masses when the empty loss cone suppresses capture and allows the weaker retrograde bias of geodesic deviation to dominate. Partially empty loss cones lead to steeper distributions of the penetration factor $\beta$ than for a full loss cone, with this effect even more pronounced in the ISO limit. We also calculate the total TDE rates and maximum SMBH mass $M_{•,\max }$ for tidal disruption in these two limits. In the IP limit, we find a highly spin-dependent capture cutoff in the TDE rate and $M_{•,\max }\approx {10}^{8.45}{M}_{\odot }$ for maximal SMBH spin. In the ISO limit, we find a strong spin-dependent enhancement in the TDE rate at intermediate SMBH masses, a weakly spin-dependent capture cutoff above $M_{•}\approx {10}^{7.5}{M}_{\odot }$, and $M_{•,\max }\approx {10}^{7.95}{M}_{\odot }$ for maximal SMBH spin.

We provide the first comprehensive study of hyperons in neutron star mergers and quantify their specific impact. We discuss the thermal behavior of hyperonic equations of state (EOSs) as a distinguishing feature from purely nucleonic models in the remnants of binary mergers using a large set of numerical simulations. Finite temperature enhances the production of hyperons, which leads to a reduced pressure as highly degenerate nucleons are depopulated. This results in a characteristic increase of the dominant postmerger gravitational-wave frequency by up to $\sim 150\mathrm{Hz}$ compared to purely nucleonic EOS models. By our comparative approach we can directly link this effect to the occurrence of hyperons. Although this feature is generally weak, it is in principle measurable if the EOS and stellar parameters of cold neutron stars are sufficiently well-determined. Considering that the mass-radius relations of purely nucleonic and hyperonic EOSs may be indistinguishable and the overall challenge to infer the presence of hyperons in neutron stars, these findings are important as a new route to answer the outstanding question about hyperonic degrees of freedom in high-density matter.

Recently it was shown that small deformations of the asymptotically flat black-hole geometry in some region near its horizon which do not alter considerably the fundamental mode, nevertheless, strongly affect the first several (and higher) overtones which deviate at an increasing rate from their nondeformed limits. Here we show that, despite the quasinormal spectrum in anti–de Sitter (AdS) space is totally different from the asymptotically flat one, the outburst of overtones do take place at small near-horizon deformations of Schwarzschild-AdS spacetime as well. Moreover, qualitatively new, nonoscillatory modes appear as a result of such small deformations, representing, thereby, a nonperturbative branch of modes. For this purpose we extend the general parametrization of asymptotically flat black holes to the AdS case. Small near-horizon deformations may originate from various holographically motivated factors, such as quantum corrections or attempts to describe the regime of intermediate coupling via higher curvature terms, while the nonoscillatory modes may be related to the hydrodynamic mode on the gauge theory side. Therefore, the phenomenon of the overtones’ outburst must be taken into consideration when analyzing correlation functions and dispersion relations in the dual field theory. In addition to the ad hoc deformations we consider the case of five-dimensional Einstein-Gauss-Bonnet-AdS black holes as an example of such near horizon deformations and fulfill the detailed study of the overtones.

The detectability of the gravitational-wave signal from $r$-modes depends on the interplay between the amplification of the mode by the Chandrasekhar-Friedman-Schutz (CFS) instability and its damping due to dissipative mechanisms present in the stellar matter. The instability window of $r$-modes describes the region of stellar parameters (angular velocity, $\mathrm{\Omega }$, and redshifted stellar temperature, $T^{\infty }$), for which the mode is unstable. In this study, we reexamine this problem in nonbarotropic neutron stars, taking into account the previously overlooked nonanalytic behavior (in $\mathrm{\Omega }$) of relativistic $r$-modes and enhanced energy dissipation resulting from diffusion in superconducting stellar matter. We demonstrate that at slow rotation rates, relativistic $r$-modes exhibit weaker amplification by the CFS instability compared to Newtonian ones. However, their dissipation through viscosity and diffusion is significantly more efficient. In rapidly rotating neutron stars within the framework of general relativity, the amplification of $r$-modes by the CFS mechanism and their damping due to shear viscosity become comparable to those predicted by Newtonian theory. In contrast, the relativistic damping of the mode by diffusion and bulk viscosity remains significantly stronger than in the nonrelativistic case. Consequently, account for diffusion and general relativity leads to a substantial modification of the $r$-mode instability window compared to the Newtonian prediction. This finding is important for the interpretation of observations of rotating neutron stars, as well as for overall understanding of $r$-mode physics.

Nuclear deexcitation associated with neutrino interactions and nucleon decays has a significant impact on a recent key observable for neutrino detectors: neutron multiplicity. Although several deexcitation simulation studies have been conducted, most are closed-source or have limitations in application. Therefore, we need an open-source deexcitation simulator to be used as a standard deexcitation module in existing neutrino Monte Carlo event generators. To predict the neutron multiplicity comprehensively, the author developed a dedicated nuclear deexcitation simulator based on talys named nucdeex. nucdeex can be used for neutrino interactions and nucleon decays for ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$. The author provides the nucdeex codes and sample codes for applying the nucdeex to widely used neutrino Monte Carlo event generators, NEUT, NuWro, and GENIE.

Positron creation probabilities as well as energy and angular distributions of outgoing positrons in slow collisions of two identical heavy nuclei are obtained within the two-center approach beyond the monopole approximation. The time-dependent Dirac equation for positron wave functions is solved with the help of the generalized pseudospectral method in modified prolate spheroidal coordinates adapted for variable internuclear separation. Depending on the nuclear charge, the results are obtained for both subcritical and supercritical regimes of the positron creation. The signatures of transition to the supercritical regime in the total positron creation probabilities and energy spectra are discussed. The angular distributions of emitted positrons demonstrate a high degree of isotropy.

The three kinds of parameter degeneracy in neutrino oscillation, the intrinsic, sign, and octant degeneracy, form an eight-fold degeneracy. The nature of this eight-fold degeneracy can be visualized on the (${\sin }^{2}2{\theta }_{13}$, $1/{\sin }^2{\theta }_{23}$)-plane, through quadratic curves defined by $P({\nu }_{\mu }\to {\nu }_e)=\mathrm{const}$ and $P({\overline{\nu }}_{\mu }\to {\overline{\nu }}_e)=\mathrm{const}$, along with a straight line $P({\nu }_{\mu }\to {\nu }_{\mu })=\mathrm{const}$. After ${\theta }_{13}$ was determined by reactor neutrino experiments, the intrinsic degeneracy in ${\theta }_{13}$ transforms into an alternative octant degeneracy in ${\theta }_{23}$, which can potentially be resolved by incorporating the value of $P({\nu }_{\mu }\to {\nu }_{\mu })$. In this paper, we analytically discuss whether this octant parameter degeneracy is resolved or persists in the future long baseline accelerator neutrino experiments, such as T2HK, DUNE, T2HKK, and $\mathrm{ESS}\nu \mathrm{SB}$. It is found that the energy spectra near the first oscillation maximum are effective in resolving the octant degeneracy, whereas those near the second oscillation maximum are not.

Dark matter (DM) could be a pseudo-Dirac thermal relic with a small mass splitting that is coupled off diagonally to a kinetically mixed dark photon. This model, particularly in the sub-GeV mass range, is a key benchmark for accelerator searches and direct detection experiments. Typically, the presence of even a tiny fraction of pseudo-Dirac DM in the excited state around the time of recombination would be excluded by DM annihilation bounds from the cosmic microwave background (CMB); thus, viable thermal histories must typically feature an exponential suppression of the excited state. We revisit assumptions about the thermal history in the resonant regime, where the dark photon mass is slightly more than twice the DM mass (to within $\sim 10\%$), leading to an $s$-channel resonance in the annihilation cross section. This resonance substantially reduces the couplings required for achieving the observed relic abundance, implying that in much of the parameter space, the DM kinetically decouples from the Standard Model well before the final DM relic abundance is achieved. We find that the excited state is not thermally depopulated in this regime. In spite of this, we find that the presence of the excited state does not violate CMB bounds, even for arbitrarily small mass splittings. The present-day abundance of the excited state opens up the possibility of signatures that are usually not relevant for pseudo-Dirac DM, including indirect detection, direct detection, and self-interacting DM signatures.

The ATLAS Collaboration has recently reported the results of a low-mass Higgs-boson search in the diphoton final state based on the full Run 2 dataset. The results are based on an improved analysis with respect to the previous analysis, which included a part of the Run 2 data, with a substantially better sensitivity. The “model-dependent” search carried out by ATLAS shows an excess of events at a mass of about 95.4 GeV with a local significance of $1.7\sigma$. The results are compatible with a previously reported excess at the same mass, but with somewhat higher significance of $2.9\sigma$, from the CMS collaboration, also based on the full Run 2 dataset. Combining the two results (neglecting possible correlations), we find a signal strength of ${\mu }_{\gamma \gamma }^{\mathrm{ATLAS}+\mathrm{CMS}}={0.24}_{-0.08}^{+0.09}$, corresponding to an excess of $3.1\sigma$. In this work, we investigate the implications of this result, updating a previous analysis based solely on the CMS Run 2 data. We demonstrate that the ATLAS/CMS combined diphoton excess can be interpreted as the lightest Higgs boson in a Two-Higgs doublet model that is extended by a complex singlet (S2HDM) of Yukawa types II and IV, while being in agreement with all other experimental and theoretical constraints.

An insightful way of presenting the LHC limits on dijet resonances is the coupling-mass plot for a $Z^{\prime }$ boson that has flavor-independent quark interactions. This also illustrates the comparison of low-mass LHC sensitivity with constraints on the flavor-independent $Z^{\prime }$ boson from electroweak and quarkonium measurements. To derive these constraints, we compute the $Z^{\prime }$ mixing with the $Z$, the photon, and the $\mathrm{\Upsilon }$ meson, emphasizing the logarithmic dependence on the masses of the new electroweak-charged fermions (“anomalons”) required to cancel the gauge anomalies. We update the coupling-mass plot, extending it for $Z^{\prime }$ masses from 5 GeV to 5 TeV.