We investigate the emergent factorization of Hilbert space in the low-energy description of matrix models, addressing key aspects of the black hole information paradox. We examine the collective description for the low-energy sector of $SU(N)$ matrix model, characterized by a factorized Hilbert space composed of a finite number of boxes and anti-boxes. This factorization leads us to examine the emergence of thermofield dynamics state in the low energy sector from a fine-tuned state. Our investigation of these matrix models elucidates a concrete mechanism for constructing the truncated algebra of accessible observables, thereby facilitating an understanding of black hole complementarity. In the context of the black hole information paradox, we discuss the origin of the island appearing inside the black hole and provide a reinterpretation of the recent proposal—the holography of information.

The timelike structure of the four-dimensional asymptotically flat Horndeski black holes is studied in detail. Focusing on the motion of massive neutral test particles, we construct the corresponding effective potential and classify the admissible types of orbits. The equations of motion are solved analytically, yielding trajectories expressed in terms of Weierstrass elliptic functions and elementary functions. As an application, we compute the perihelion precession as a classical test of gravity within the Solar System and use it to place observational constraints on the coupling parameter between the scalar field and gravity.

Characterizing eccentricity in gravitational waveforms in a consistent manner is crucial to facilitate parameter estimation, astrophysical population studies, as well as searches for these rare systems. We present a framework to characterize eccentricity directly from gravitational waveforms for nonprecessing eccentric binary black hole mergers using common modulations that eccentricity induces in all spherical harmonic modes of the signals. Our framework is in the spirit of existing methods that use frequency modulations in the waveforms, but we refine the approach by connecting it with state-of-the-art post-Newtonian calculations of the time evolution of the eccentricity. Using 39 numerical relativity (NR) simulations from the SXS and RIT catalogs, as well as waveforms obtained from the post-Newtonian approximation and effective-one-body formalism, we show that our framework provides eccentricity estimates that connect smoothly into the relativistic regime (even up to $\sim 2M$ before merger). We also find that it is necessary to carry existing post-Newtonian calculations to an extra 0.5 post-Newtonian order to adequately characterize existing NR simulations, and provide fits to the extra coefficient for existing simulations. We make the framework publicly available through the python-based gwmodels package.

The search for Galactic binary gravitational waves is a critical challenge for future space-based gravitational wave detectors, such as LISA. We propose an innovative approach to simultaneously explore gravitational waves originating from Galactic binaries by developing a new local maxima particle swarm optimization algorithm. This new approach effectively addresses the inaccuracies often associated with signal subtraction contamination, a challenge for traditional iterative subtraction methods, particularly when dealing with low signal-to-noise ratio (SNR) signals (e.g., $\mathrm{SNR}<15$). We also account for the effects of overlapping signals and degeneracy noise. To demonstrate the effectiveness of our approach, we use residuals from the LISA mock data challenge (LDC1-4), where 10,982 injected sources with $\mathrm{SNR}\ge 15$ have been removed. For the remaining sources with $\mathrm{SNR}<15$, our method successfully identifies 6,508 signals, yielding a false alarm rate of ${\mathrm{FAS}}_{0.8}=36.8\%$. By focusing on a subset of sources—specifically, those with $f>3\mathrm{mHz}$ and those with $f\le 3\mathrm{mHz}$ but $\mathrm{SNR}\ge 13$—we identify 3,406 signals, with a reduced false alarm rate of ${\mathrm{FAS}}_{0.8}=22.5\%$. We further demonstrate that, within the same detection SNR range, our method achieves a comparable or lower FAS than other existing methods.

In this paper, we present two novel analytic anti–de Sitter (AdS) black hole solutions in a two-dimensional dilaton gravity theory with two scalar fields nonminimally coupled to gravity. Our solutions contain two arbitrary integration constants in the blackening factor $f(r)$, allowing for an extremal configuration. Solution I reproduces a previously reported AdS black hole when one of the integration constants in $f(r)$ vanishes. For our black hole configurations, the scalar curvature is constant and negative, corresponding to the ${\mathrm{AdS}}_2$ spacetime. In order to elucidate their black hole nature, we explore the causal structure of these solutions with the aid of suitable Kruskal-like coordinates and Penrose diagrams. By employing the Hamilton-Jacobi method, we construct a boundary counterterm that renders a renormalized action with a vanishing variation. We use this finite action for the partition function in the semiclassical approximation. We establish a consistent thermodynamics, verified by the first law, for our black hole solutions, including the extremal case. Finally, we perform a holographic analysis of the effective theory at the boundary of the black hole solution I. This theory is characterized by a Schwarzian action supplemented by a black hole mass term determined by the two integration constants in $f(r)$. We also examine the holographic implications of the boundary counterterm.

We provide a general algorithm to construct a Hamiltonian, such that its dynamical flow covariantly defines any given spherically symmetric and static metric. This Hamiltonian is defined as a linear combination of the standard (general relativistic) radial diffeomorphism constraint plus a Hamiltonian constraint that is appropriately deformed as compared to its corresponding form in general relativity though it does not include higher-derivative terms. Therefore, given a static model of spherical gravity, it is possible to obtain its Hamiltonian, and, thus, its canonical (second-order) equations of motion. A particularly relevant application of this construction is the study of regular black holes, where proposed geometries often lack an underlying dynamical theory. The present method provides such a theory. In particular, for a wide class of deformations of the Schwarzschild geometry, we explicitly obtain their corresponding Hamiltonian. This construction can be further used to covariantly couple matter. In this way, one can analyze the backreaction of matter fields on the geometry of interest, and, specifically, whether a particular black-hole model may emerge as the end state of a dynamical collapse.

Detecting stochastic gravitational wave background from cosmic strings is crucial for unveiling the evolutionary laws of the early Universe and validating nonstandard cosmological models. In light of extensive existing studies on the detection capabilities of third-generation gravitational wave detectors for cosmic string signals, this work provides a systematic evaluation focused specifically on the performance of next-generation ground-based detector networks. By constructing a hybrid signal model that incorporates multisource astrophysical foregrounds, including compact binary coalescences and compact binary hyperbolic encounters, we develop a parameter estimation methodology based on multicomponent signal separation. Numerical simulations using one-year observational data reveal three key findings: (i) The CE4020ET network, comprising the Einstein Telescope (ET-10 km) and the Cosmic Explorer (CE-40 km and CE-20 km), achieves nearly one order of magnitude improvement in constraining the cosmic string tension $G\mu$ compared to individual detectors, reaching a relative uncertainty $\mathrm{\Delta }G\mu /G\mu <0.5$ for $G\mu >3.5\times {10}^{-15}$ under standard cosmological framework; (ii) the network demonstrates enhanced parameter resolution in nonstandard cosmological scenarios, providing a novel approach to probe pre–big bang nucleosynthesis cosmic evolution; (iii) enhanced detector sensitivity amplifies compact binary hyperbolic encounter foreground interference in parameter estimation, while precise modeling of such signals could further refine $G\mu$ constraints by 1–2 orders of magnitude. This research not only quantifies the detection potential of third-generation detector networks for cosmic string models, but also elucidates the intrinsic connection between foreground modeling precision and cosmological parameter estimation accuracy, offering theoretical foundations for optimizing scientific objectives of next-generation gravitational wave observatories.

One of the key predictions of the standard inflationary paradigm is the quantum mechanical generation of the transverse and traceless tensor fluctuations due to the rapid accelerated expansion of space, which later constitute a stochastic background of primordial gravitational waves (GWs). The amplitude of the (nearly) scale-invariant inflationary tensor power spectrum at large scales provides us with crucial information about the energy scale of inflation in the case of the minimal inflaton coupling to gravity. Furthermore, the spectral energy density, ${\mathrm{\Omega }}_{\mathrm{GW}}(f)$, of the GWs at sufficiently small scales (or, large frequencies $f$) serves as an important observational probe of postinflationary primordial dynamics. In fact, the small-scale spectral tilt, $n_{\mathrm{GW}}=\frac{\mathrm{d}\log {\mathrm{\Omega }}_{\mathrm{GW}}}{\mathrm{d}\log f}$, of the spectral energy density of GWs is sensitive to the (unknown) postinflationary equation of state (EOS), $w$, of the Universe; with a softer EOS ($w<1/3$) leading to a red tilt, $n_{\mathrm{GW}}<0$, while a stiffer EOS ($w>1/3$) resulting in a blue tilt, $n_{\mathrm{GW}}>0$. The postinflationary dynamics, however, is generically expected to be quite complex, potentially involving a number of distinct phases. Hence, in this work, we discuss the possibility of multiple sharp transitions, namely $w_1\to w_2\to w_3\to \dots \to w_n$, in the EOS of the postinflationary Universe and compute the corresponding spectral energy density of the inflationary GWs. We explicitly determine the region of the parameter space $\{w_1,w_2,w_3,\dots ,w_n\}$ which leads to a potentially detectable signal in the upcoming GW detectors, without violating the current constraints.

Assuming a minimal $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) cosmology with three massive neutrinos, the joint analysis of Planck cosmic microwave background data, DESI baryon acoustic oscillations, and distance moduli measurements of type Ia supernovae from the $\mathrm{Pantheon}+\text{sample}$ sets an upper bound on the total neutrino mass, $\sum m_{\nu }\lesssim 0.06–0.07\mathrm{eV}$, that lies barely above the lower limit from oscillation experiments. These constraints are mainly driven by mild differences in the inferred values of the matter density parameter across different probes that can be alleviated by introducing additional background-level degrees of freedom (e.g., by dynamical dark energy models). However, in this work, we explore an alternative possibility. Since both ${\mathrm{\Omega }}_{\mathrm{m}}$ and massive neutrinos critically influence the growth of cosmic structures, we test whether the neutrino mass tension may originate from the way matter clusters, rather than from a breakdown of the $\mathrm{\Lambda }\mathrm{CDM}$ expansion history. To this end, we introduce the growth index $\gamma$, which characterizes the rate at which matter perturbations grow. Deviations from the standard $\mathrm{\Lambda }\mathrm{CDM}$ value ($\gamma \simeq 0.55$) can capture a broad class of models, including nonminimal dark sector physics and modified gravity. We show that allowing $\gamma$ to vary significantly relaxes the neutrino mass bounds to $\sum m_{\nu }\lesssim 0.13–0.2\mathrm{eV}$, removing any tension with terrestrial constraints without altering the inferred value of ${\mathrm{\Omega }}_{\mathrm{m}}$. However, this comes at the cost of departing from standard growth predictions: to have $\sum m_{\nu }\gtrsim 0.06\mathrm{eV}$, one needs $\gamma >0.55$, and we find a consistent preference for $\gamma >0.55$ at the level of $\sim 2\sigma$. This preference increases to $\sim 2.5–3\sigma$ when a physically motivated prior $\sum m_{\nu }\ge 0.06\mathrm{eV}$ from oscillation experiments is imposed.

The dark photon has been postulated as a potential constituent of dark matter, exhibiting notable similarities to the axion. The primary distinction between the two particles lies in the nature of their respective fields: the dark photon field is a vector field with a polarization direction that remains undetermined. This work explores the prospect of utilizing three degenerate modes for scanning the three dimensions of space in order to mitigate the low form factor expected in the detection of the dark photon due to their unknown polarization. The employment of a haloscope with three orthogonal and degenerate modes in conjunction with the coherent sum of signals is demonstrated in this work in order to enhance the dark photon form factor up to the axion form factor, and to determine the direction of the dark photon polarization vector. We show in this manuscript that the maximum form factor is achieved in cavities of cubic, spherical, and cylindrical geometries, considering the introduction of tuning elements. To achieve this adequately, some conditions reviewed in this article must be fulfilled in the resonant cavity, leading to uncertainties in the final measurement. Finally, this technique can allow the simultaneous search for dark matter axions and dark photons, and to the knowledge of the authors, the method shown in this work is the most effective one for detecting dark photons with microwave resonant cavities.

Suspension thermal modes in interferometric gravitational-wave detectors produce narrow, high-$Q$ spectral lines that can contaminate gravitational searches and bias parameter estimation. In KAGRA, cryogenic mirrors are held by thick suspension fibers, designed to sustain such a low-temperature environment, which may further affect inharmonicity modes, fiber dimensions, and mechanical behavior compared to typical interferometers. As these modes remain a prominent source of narrowband contamination, we implement a Kalman filter to model and track violin lines, building on the methodology introduced in [1], and apply subtraction to KAGRA O3GK data. Using gravitational-wave template injections, we validate that the subtraction preserves matched-filter SNR while effectively suppressing line power. Comparisons of power spectral densities and residual analyses confirm that the method removes deterministic line contributions without introducing waveform distortions. This approach provides a cleaner strain channel for searches and parameter estimation and will become increasingly important for future low-temperature detectors with higher-$Q$ suspensions, such as the Einstein Telescope.

Despite decades of research, the existence of asteroid-mass primordial black holes (PBHs) remains almost completely unconstrained and thus could still comprise the totality of dark matter (DM). In this paper, we show that standard searches for continuous gravitational waves–long-lived, quasimonochromatic signals—could detect extreme mass-ratio inspirals of asteroid-mass PBHs in orbit around a stellar-mass companion using future gravitational-wave (GW) data from the Einstein Telescope and the Neutron Star Extreme Matter Observatory. We evaluate the robustness of our projected constraints against the eccentricity of the binary, the choice of the mass of the primary object, and the GW frequency range that we analyze. Furthermore, to determine whether there could be ways to detect asteroid-mass PBHs using current GW data, we quantify the impact of changes in current techniques on the sensitivity toward asteroid-mass PBHs. We show that methods that allow for signals with increased and more complicated frequency drifts over time could obtain much more stringent constraints now than those derived from standard techniques, though at slightly larger computational cost, potentially constraining the fraction of DM that certain asteroid-mass PBHs could compose to be less than 1 with current detectors.

We investigate and compare quantum chromodynamics (QCD) dipole cascade models, the 1D Mueller dipole model, its high energy limit, and its generalization that follows from studies of 1D systems with conformal symmetry. To address the ambiguity stemming from different definitions of the rapidity ranges in experimental measurements, we propose the entropy as the function of the logarithm of the average multiplicity, $S(\ln ⟨n⟩)$, as a universal observable. From the solutions of the models, we calculate both the entropy and the average charged particle multiplicity and compare to data measured in proton-proton collisions. We obtained these quantities directly from the measured multiplicity distributions and determine the model parameters via fits. We find that the generalized dipole model provides a significantly better description of the data than the 1D Mueller model.

In the Higgsino dark matter (DM) scenario of the minimal supersymmetric model (MSSM), the mixing of Gaugino and Higgsino influences the mass splitting between neutralinos predominantly composed of Higgsino and introduces coupling between the DM and Higgs bosons. These effects modify the DM-nucleon scattering cross-section, causing conflicts with the latest direct detection results from LZ experiments for both substantial and minute mixings. Consequently, the experimental measurement of DM relic density necessitates the Higgsino DM mass to be approximately 1.1 TeV. We discovered that in the Higgsino DM scenario of the next-to-minimal supersymmetric model (NMSSM), the mixing of Higgsino and Singlino introduces analogous effects, with a crucial distinction being that the current LZ experiment permits significant mixing between Singlino and Higgsino. This pronounced mixing effect effectively attenuates the interactions between Higgsino-dominated neutralinos and standard model particles, enabling DM masses exceeding roughly 670 GeV to achieve the correct relic abundance. Through analytical formulas and numerical results, we elucidated these characteristics that were not observed before. Our research reveals that in the NMSSM, when comprehensively examining the mixing effects of Higgsino, Gaugino, and Singlino, the properties of Higgsino DM become markedly more intricate compared to the MSSM predictions.

Ultralight dark matter (ULDM) is an attractive candidate for cold dark matter, one of the main mysterious components of the Universe. Recent studies suggest that gravitational wave (GW) laser interferometers can also detect bosonic ULDM fields, which would produce monochromatic signals resembling those from GWs. Distinguishing between these potential origins therefore would be essential. In this work, we develop a method to address this challenge for space-based GW interferometers (such as LISA and Taiji) by utilizing the null-response channel (NRC) in interferometric combinations, a channel constructed to have zero response to a specific type of source from a given direction. We find that while the GW NRC remains blind to GWs from a specific direction, it still responds to ULDM, particularly at frequencies above the interferometer’s critical frequency. The ULDM NRC exhibits similar behavior. Based on these observations, we outline a test procedure to discriminate between signal origins. Our method provides a new diagnostic tool for analyzing monochromatic signals in space-based GW interferometers, potentially expanding the scientific scope of future missions.

We propose a simple and predictive setup that connects neutrino masses, dark matter (DM), and gravitational waves. A minimal lepton parity DM scenario is considered where the residual symmetry $(-1{)}^L$ from the type I seesaw acts as the dark parity $D=(-1{)}^{L+2j}$, ensuring DM stability without imposing any new symmetry. A singlet Majorana fermion $S$ with even lepton parity serves as the DM candidate, interacting via a real scalar $\sigma$ which is also even lepton parity. The scalar potential possesses an accidental ${\mathcal{Z}}_2$ symmetry, whose spontaneous breaking gives rise to unstable domain walls in the presence of explicit ${\mathcal{Z}}_2$-breaking terms allowed by the lepton parity. The subsequent domain wall annihilation generates a stochastic gravitational wave background potentially observable at different gravitational wave experiments.

We consider phenomenological models for nonsingular black holes that satisfy the limiting curvature condition (i.e., that have curvatures that are always sub-Planckian in size) while having a more general dependence on the black hole mass than the most studied examples. These models allow black holes to exist while having regulators that are larger than the horizon scale; it has been shown previously that this can lead to observable consequences in an astrophysical setting, for allowed choices for the regulator scale. Noting that substantial horizon-scale modifications of the metric will affect black hole thermodynamics and Hawking radiation, we study these metrics in the context of primordial black hole dark matter. Considering examples with de Sitter and Minkowski cores, respectively, we study the effect of the regulator in these metrics on the allowed black hole mass ranges (or “bands”), the black hole temperature, specific heat, and lifetime, and the bounds on the primordial black hole fraction of the total dark matter density from the observed extragalactic gamma ray background.

Extremely weak long-range forces may lead to apparent violations of the equivalence principle. The final MICROSCOPE  result, leading at 95% CL to $|\delta |<4.5\times {10}^{-15}$ or $6.5\times {10}^{-15}$ for a positive or negative Eötvös parameter $\delta$, requires taking into account the spin of the mediator, and the sign of $\mathrm{\Delta }(Q/A_r{)}_{\text{Ti}-\text{Pt}}$ ($Q$ denoting the new charge involved). A coupling to $B-L$ or $B$ should verify $|g_{B-L}|<1.1\times {10}^{-25}$ or $|g_B|<8\times {10}^{-25}$, for a spin-1 mediator of mass $m<{10}^{-14}\mathrm{eV}/c^2$, with slightly different limits of $1.3\times {10}^{-25}$ or $6.6\times {10}^{-25}$ in the spin-0 case. The limits increase with $m$, in a way which depends on the density distribution within the Earth. This involves an hyperbolic form factor, expressed through a bilateral Laplace transform as $\mathrm{\Phi }(x=mR)=⟨\sinh mr/mr⟩$, related by analytic continuation to the Earth form factor $\mathrm{\Phi }(ix)=⟨\sin mr/mr⟩$. It may be expressed as $\mathrm{\Phi }(x)=\frac{3}{x^2}(\cosh x-\frac{\sinh x}{x})\times \overline{\rho }(x)/{\rho }_0$, where $\overline{\rho }(x)$ is an effective density, decreasing from the average ${\rho }_0$ at $m=0$ down to the density at the periphery. We give general integral or multishell expressions of $\mathrm{\Phi }(x)$, evaluating it, and $\overline{\rho }(x)$, in a simplified 5-shell model. $\mathrm{\Phi }(x)$ may be expanded as $\sum \frac{x^{2n}}{(2n+1)!}\frac{⟨r^{2n}⟩}{R^{2n}}\simeq 1+.0827x^2+.00271x^4+4.78\times {10}^{-5}{x}^6+5.26\times {10}^{-7}{x}^8+\cdots$, absolutely convergent for all $x$ and potentially useful up to $x\approx 5$. The coupling limits increase at large $x$ like $mR{e}^{mz/2}/\sqrt{1+mr}$ ($z=r-R$ being the satellite altitude), getting multiplied by $\simeq 1.9$, 34, or $1.2\times {10}^9$, for $m={10}^{-13},{10}^{-12}$ or ${10}^{-11}\mathrm{eV}/c^2$, respectively.

We study nonthermal resonant leptogenesis in a general setting, where a heavy Majoron $\varphi$ decays to right-handed neutrinos (RHNs) whose further out-of-equilibrium decay generates the required lepton asymmetry. Domination of the energy budget of the Universe by the $\varphi$ or the RHNs alters the evolution history of the primordial gravitational waves (GWs) of inflationary origin, which re-enter the horizon after inflation, modifying the spectral shape. The decays of $\varphi$ and RHNs release entropy into the early Universe, while nearly degenerate RHNs facilitate low- and intermediate-scale leptogenesis. A characteristic damping of the GW spectrum resulting in kneelike features would provide evidence for low-scale nonthermal leptogenesis. We explore the parameter space for the lightest right-handed neutrino mass $M_1\in [{10}^2,{10}^{14}]\mathrm{GeV}$ and washout parameter $K$ that depends on the light-heavy neutrino Yukawa couplings $\lambda$, in the weak ($K<1$) and strong ($K>1$) washout regimes. The resulting novel features compatible with observed baryon asymmetry are detectable by future experiments, like LISA and Einstein Telescope. By estimating the signal-to-noise ratio for upcoming GW experiments, we investigate the effect of the Majoron mass $M_{\varphi }$ and reheating temperature $T_{\varphi }$, which depends on the $\varphi -N$ Yukawa couplings $y_N$.

Using $\mathcal{N}=1$ supersymmetric QCD (SQCD) as a prototype model, this work presents a formulation of overlap quarks and gluinos on the lattice, with particular emphasis on the construction of chirally symmetric Yukawa terms. By incorporating the Ginsparg-Wilson relation, chiral transformations, and the Majorana condition for gluinos, we construct a consistent framework that preserves a lattice-modified chiral symmetry and reduces the number of required counterterms compared to Wilson-type discretizations. The formulation introduces auxiliary fermionic fields to realize exact chiral symmetry in Yukawa interactions and enables a detailed analysis of the resulting matrix structures. Upon functionally integrating out the auxiliary fields, ultralocal interaction terms emerge as new contributions to the lattice action. This approach provides a robust foundation for nonperturbative lattice studies of supersymmetric gauge theories. Future work will focus on computing all perturbative fine-tunings required in this formulation to enable continuum matching and numerical simulations of SQCD.