We compute the dynamics of particles and strings falling into smooth horizonless spacetimes that match the Schwarzschild black hole but replace its horizon with a smooth cap in supergravity. The cap consists of a regular topological structure formed by the deformations of extra compact dimensions. We show that infalling particles follow Schwarzschild-like trajectories down to the cap, but experience rapidly growing tidal forces that reach extreme values. In addition, infalling strings encounter a region of tidal instability localized at the cap, where transverse modes are excited. This stringy excitation drains their kinetic energy, resulting in tidal trapping. We demonstrate that the onset and strength of this instability depend sensitively on the Kaluza-Klein scale, the string scale, and the mass of the spacetime, ensuring that strings cannot escape the cap region. These results show that horizonless geometries can reproduce key features of black hole absorption while maintaining regularity at the horizon scale, offering compelling evidence for the emergence of effective horizonlike behavior from topological spacetime structures.

The physics of gravitational waves and other classical fields on specifically four-dimensional backgrounds of black holes exhibits electric-magnetic-like dualities. In this paper, we discuss the structure of such dualities in terms of geometrical quantities with a physically intuitive interpretation. In turn, we explain the interplay between the algebraic structure of black hole spacetimes and their associated dualities. For large classes of black hole geometries, explicit constructions are presented. We then use these results and apply them to the holographic study of three-dimensional conformal field theories (CFTs), discussing how such dualities place stringent constraints on the thermal spectra of correlators. In particular, the dualities enforce the recently developed spectral duality relation along with a multitude of implications for the physics of thermal CFTs. A number of numerical results supporting our conclusions is also presented, including a demonstration of how the longitudinal spectrum of quasinormal modes determines the transverse spectrum, and vice versa.

Many quantum-gravity scenarios predict a minute modification of the canonical commutator, known as the generalized uncertainty principle (GUP), whose low-energy signatures are, in principle, accessible to state-of-the-art laboratory tests. We compute first-order minimal-length corrections to the quantum speed limit (QSL) for three cases: uniform superpositions in an infinite square well, coherent harmonic-oscillator states, and squeezed-oscillator states. We identify a universal amplification law: for any pure state, the fractional shift of either speed limit scales linearly with $\beta$ and algebraically with the state’s effective Hilbert-space size. As the effective Hilbert-space dimension can be exceedingly large, the associated minimal-length signatures are amplified by several orders of magnitude. Using high-precision matter-wave timing data, we set a direct bound on the GUP parameter $\beta$, which quantifies minimal-length quantum-gravity effects. Our analysis indicates that phase-locked, short-time overlap fits on kilogram-scale optical-spring modes can tighten this bound by orders of magnitude. We outline two implementable measurement pipelines—continuous back-action-evading single-quadrature readout and stroboscopic, phase-locked pulsed tomography—that exploit this leverage, making QSL-based timing a practical, near-term probe of minimal-length physics on quantum-optical and optomechanical platforms.

The intrinsic nonperturbative features of string-theoretic corrections, particularly those arising from T-duality, have been shown to naturally introduce an effective UV cutoff into the gravitational framework. This cutoff, often referred to as the zero-point length in the context of path integral duality, acts as a fundamental minimal length scale that regulates short-distance divergences. Using the established correspondence between T-duality and path integral duality, it has been shown that the static Newtonian potential becomes regularized at small distances. Building upon this regular behavior, we proceed to construct self-consistent, spherically symmetric, and electrically neutral wormhole solutions, which remain free of curvature singularities and embodies the effects of this duality-induced UV completion. We explore wormhole configurations with the aim of minimizing violations of the null energy condition (NEC). In fact, solutions with a constant redshift function or specific shape functions generally exhibit NEC violations throughout the entire spacetime. To address this, we explore two distinct thin shell constructions: (i) wormholes formed by matching an interior wormhole geometry to an exterior Schwarzschild vacuum spacetime, thereby confining exotic matter to a localized region; and (ii) standard thin-shell wormholes generated by gluing two identical black hole spacetimes across a timelike hypersurface situated outside their event horizons. In both cases, the NEC violations are minimized and restricted to a finite region, improving the physical plausibility and traversability of the resulting configurations.

Cosmic strings play a crucial role in enhancing our understanding of the fundamental structure and evolution of the Universe, unifying our knowledge of cosmology, and potentially unveiling new physical laws and phenomena. The advent and operation of space-based detectors provide an important opportunity for detecting stochastic gravitational wave backgrounds (SGWBs) generated by cosmic strings. However, the intricate nature of an SGWB poses a formidable challenge in distinguishing its signal from the complex noise and other SGWB sources by some traditional methods. Therefore, we attempt to identify SGWBs based on machine learning. Our findings show that the joint detection of Linear Symbols to Attention and Taiji significantly outperforms individual detectors, and even in the presence of numerous low SNR signals. The true positive rate remains exceptionally high with 95%. Our study demonstrates that the multiband joint analysis method significantly enhances the discernment capability for SGWBs from different origins, providing a novel technical approach to disentangle the components in composite SGWB signals. Although our discussion is based solely on simulated data, the relevant methods can provide data-driven analytical capabilities for future observations of SGWBs.

In warm inflation (WI), the persistent thermal bath that is sustained by dissipative interactions with the inflaton field produces a stochastic background of gravitational waves (GWs). In this paper we study the production and evolution of these GWs. Specifically, we investigate the emission of thermal gravitons (gravitons emitted by a thermal bath) from scattering with particles in the bath and then the evolution of the corresponding high-frequency GWs. We find that the bulk of thermal graviton production in WI occurs during the transition to radiation domination after inflation. Further, the energy density of thermal gravitons is enhanced by roughly 1 to 2 orders of magnitude compared to that in a radiation-dominated scenario with the same reheating temperature. We also calculate the spectrum of the resulting stochastic GW background and find that it has a distinctive shape, consisting of a peak at high frequencies ($\sim 100\mathrm{GHz}$) and an almost flat spectrum extending to low frequencies. The peak arises from emission of subhorizon modes that follow the temperature of the bath. The flat part of the spectrum corresponds to the modes that exit the horizon during WI and reenter during radiation domination and reflects the approximately constant temperature of the thermal bath during WI. We show that the detection prospects for the high-frequency peak of the GW spectrum, while improved slightly compared to the radiation-dominated case, still remain challenging. The thermal spectrum’s low-frequency plateau is typically subdominant to the amplitude of the standard vacuum tensor modes from inflation, although WI models can exist where the thermal graviton plateau surpasses the vacuum contribution without exceeding current observational limits on the tensor-to-scalar ratio. Furthermore, we calculate the thermal graviton contribution from WI to dark radiation and show that WI models are generally expected to satisfy current observational bounds including those from the cosmic microwave background.

Cosmological neutrino mass and abundance measurements are reaching unprecedented precision. Testing their stability versus redshift and scale is a crucial issue, as it can serve as a guide for optimizing ongoing and future searches. Here, we perform such analyses, considering a number of redshift, scale, and redshift-and-scale nodes. Concerning the $k$-space analysis of $\sum m_{\nu }$, cosmic microwave background (CMB) observations are crucial, as they lead the neutrino mass constraints. Interestingly, some data combinations suggest a nonzero value for the neutrino mass with $2\sigma$ significance. The most constraining bound we find is $\sum m_{\nu }<0.54\mathrm{eV}$ at 95% confidence level (CL) in the $[{10}^{-3},{10}^{-2}]h/\mathrm{Mpc}$ $k$-bin, a limit that barely depends on the data combination. Regarding the redshift- and scale-dependent neutrino mass constraints, high redshifts ($z>100$) and scales in the range $[{10}^{-3},{10}^{-1}]h/\mathrm{Mpc}$ provide the best constraints. The least constraining bounds are obtained at very low redshifts [0, 0.5] and also at very small scales ($k>0.1h/\mathrm{Mpc}$) due to the absence of observations. Highly relevant is the case of the [100, 1100], $[{10}^{-2},{10}^{-1}]h/\mathrm{Mpc}$ redshift-scale bin, where a $2-3\sigma$ evidence for a nonzero neutrino mass is obtained for all data combinations. The bound from CMB alone at 68% CL is ${0.63}_{-0.24}^{+0.20}\mathrm{eV}$, and the one for the full dataset is ${0.56}_{-0.23}^{+0.20}\mathrm{eV}$, clearly suggesting a nonzero neutrino mass at these scales, possibly related to a deviation of the integrated Sachs-Wolfe amplitude in this redshift range. Concerning the analysis of $N_{\mathrm{eff}}$ in the $k$-space, at intermediate scales ranging from $k={10}^{-3}h/\mathrm{Mpc}$ to $k={10}^{-1}h/\mathrm{Mpc}$, accurate CMB data provide very strong bounds, the most robust one being $N_{\mathrm{eff}}=3.09\pm 0.14$, comparable to the standard expected value without a $k$-bin analysis. If a nonzero neutrino mass is considered, the bounds on the $N_{\mathrm{eff}}$ values at the different $k$-bins are largely unaffected, and the 95% CL tightest limit we find for the neutrino mass in this case is $\sum m_{\nu }<0.205\mathrm{eV}$ from the full dataset. Finally, the $z$ and $k$ analyses of $N_{\mathrm{eff}}$ indicate a high constraining power of cosmological observations at high redshifts and intermediate scales $[{10}^{-2},{10}^{-1}]h/\mathrm{Mpc}$ when extracting the binned values of this parameter.

Extracting the faint gravitational-wave background (GWB) signal from dominant detector noise and disentangling its astrophysical and cosmological components remain significant challenges for traditional methods like cross-correlation analysis. We propose a novel hybrid approach that combines deep learning with Bayesian inference to identify and characterize the GWB more rapidly than current techniques. Our method utilizes a custom-designed multiscale multiheaded autoencoder (MSMHAutoencoder) architecture to separate GWB signals from detector noise and, subsequently, Markov chain Monte Carlo parameter estimation to disentangle the GWB components. Using simulated data representative of the LIGO-Virgo-KAGRA network at design sensitivity, we show that our MSMHAutoencoder can detect with high confidence (log noise Bayes factor of 3) a GWB from compact binary mergers with fractional energy density ${\mathrm{\Omega }}_{\mathrm{CBC}}\approx {10}^{-9}$ at 25 Hz. In the presence of such an astrophysical GWB, we can simultaneously measure a flat cosmological component as faint as ${\mathrm{\Omega }}_{\text{cosmo}}\approx 1.3\times {10}^{-10}$ using 47.4 days of training data.

The fundamental nature of dark matter (DM) remains unknown, with significant uncertainties in its density profile. DM environments surrounding massive binary black holes (BBHs) modify their orbital dynamics, thereby altering gravitational wave (GW) emissions. For BBH systems at the Galactic Center, dynamical friction induced by DM spikes could produce detectable deviations in GW spectra, potentially observable by future space-based detectors. To address the uncertainties in the Galactic Center’s DM profile, we systematically examine two scenarios: the generalized Navarro-Frenk-White (gNFW) profile and its postspike modification. We investigate the evolutionary effects of DM dynamical friction and accretion on the eccentricity and semilatus rectum of secondary black holes (BHs) in elliptical orbits. By constructing orbital models with varying initial eccentricities across the mass-semilatus rectum parameter space and utilizing 30 years of simulated pulsar timing array data from the Square Kilometer Array, we identify detectable parameter regimes of DM effects and employ these GW observational signatures to constrain different DM density profiles. Our analysis reveals that among gNFW profiles ($\gamma =2$, 1.5, 1, 0.5), only $\gamma =2$ produces significant detectable signatures. The formation of DM spikes further enhances these observable waveform deviations for all gNFW slopes.

Bosonic stars—hypothetical astrophysical entities—are generally categorized into two primary classes based on the nature of their constituent particles: Einstein-Klein-Gordon stars, made up of massive scalar bosons, and Proca stars, their vector “cousins.” Depending on the boson masses and field frequencies, these objects may exhibit properties of diffuse, massive structures, with sizes comparable to or even exceeding those of galaxies. This concept has inspired the bosonic dark matter halo hypothesis, providing a theoretical framework to effectively model the dark matter content of galactic halos. In this paper we build on our previous work to explore the possibility of using vector and scalar bosons to model the components of galactic dark matter halos and subhalos in order to reproduce the observed rotation curves of galaxies. By employing diverse combinations of those bosonic dark matter models in conjunction with observable data for a sample of galaxies, we show that our two-component dark matter approach notably improves the agreement between observations and theoretical predictions with respect to our previous investigation. Our framework may shed new light on the enduring mystery surrounding the apparent matter deficit observed in dwarf and spiral galaxies.

Using high-resolution simulations of black hole formation from the direct collapse of massive stars undergoing pulsational pair-instability supernovae (PPISN), we find a new phenomenon which significantly affects the explosion and leads to two peaks in the resulting black hole mass function (BHMF). Lighter stars experiencing the pair-instability can form a narrow shell in which alpha ladder reactions take place, exacerbating the effect of the PPISN. The shell temperature in higher mass stars ($>62M_{\odot }$ at the onset of helium burning for population-III stars with metallicity $Z={10}^{-5}$) is too low for this to occur. As a result, the spectrum of black holes as a function of the initial stellar mass $M_{\mathrm{BH}}(M_i)$ exhibits a shoulder feature whereby a large range of initial masses result in near-identical black hole masses. PPISN therefore predict two peaks in the mass function of astrophysical black holes—one corresponding to the location of the upper black hole mass gap at $57M_{\odot }$ and a second corresponding to the location of the shoulder at $49M_{\odot }$. This shoulder effect may explain the peak at ${35}_{-2.9}^{+1.7}{M}_{\odot }$ in the LIGO/Virgo/KAGRA GWTC-3 catalog of merging binary black holes for variations in the stellar parameters, for example if the ${}^{12}\mathrm{C}(\alpha ,\gamma {)}^{16}\mathrm{O}$ rate is increased by $3\sigma$.

Matter-wave interferometry is highly susceptible to inertial acceleration noises arising from the vibration of the experimental apparatus. There are various methods for noise suppression. In this paper, we propose leveraging the cross-correlation of multidirectional vibration noises to mitigate their dephasing effect in matter-wave interferometers. Specifically, we analyze an interferometer driven by its internal state under an external field and examine the dephasing caused by a two-dimensional random inertial force. As we will demonstrate, the coupling between the two-dimensional inertial force noise components will shift the resonance peak but not change the shape of the power spectral density. Moreover, when the noise approximately resonates with the intrinsic frequency of the test mass, we find that the standard deviation of the phase can be suppressed by a factor roughly equal to the Q factor of the noise. This technique holds significant potential for future gravity experiments utilizing quantum sensors, such as measuring gravitational acceleration and exploring quantum entanglement induced by gravity.

We investigate the phase interference effects in the nonlinear Compton scattering via the collision between a high-energy electron and the laser in the intermediate intensity region, and reveal that the importance of interference effects on the scattered photons depends sensitively on the relative polarization of the scattered photons and laser pulse. For scattered photons polarized parallel to the laser field, the effective distance between two interfered phase points is much larger than that for perpendicularly polarized photons. To signalize the phase interference effect in potential experiments, we introduce the double-pulse scenario for the scattering process, and show that the interference between two phase-separated pulses could significantly modulate the energy-momentum distribution of the scattered photons, leading to the reshaping of the scattered photons’ energy spectrum. By narrowing the angular acceptance of the scattered photons, the spectral modulation can be amplified and sustained for an experiment-realizable phase separation between two pulses.

We investigate the spin correlations between electron-positron pairs created from a photon when it scatters in a high-intensity laser pulse via the nonlinear Breit-Wheeler process. We find that the spin states of the generated electron-positron pair can exhibit strong entanglement, with the degree being sensitive to the photon energy, laser intensity, and the relative polarization of the photon and laser pulse. Photons with a high degree of polarization can create strongly entangled pairs even in the intermediate intensity (nonperturbative) regime. We find that if the photons are provided by a Compton source, strongly spin-entangled electron-positron pairs can be generated with technology available today.

A theoretical framework based on a spontaneously broken $Z_4$ symmetry is proposed to simultaneously explain neutrino mass generation via the inverse seesaw mechanism and dark matter (DM) production through a freeze-in scenario. This work extends the standard model with right-handed neutrinos $N_i$, additional fermions ${\chi }_i$, and a complex scalar $S$. An unbroken $Z_2$ subgroup ensures the stability of the DM candidate, whose relic abundance is dominantly produced via decay and scattering processes involving heavy singlet fermions. Phenomenological analyses show that this relatively minimal construction accommodates the observed neutrino oscillation parameters, consistent with the latest global fit data. Furthermore, the model successfully reproduces the observed DM relic density within the parameter space relevant to neutrino phenomenology, establishing a connection between neutrino properties and DM production.

We introduce a new topology for weakly supervised anomaly detection searches, diobject plus X. In this topology, one looks for a resonance decaying to two standard model particles produced in association with other anomalous event activity (X). This additional activity is used for classification. We demonstrate how anomaly detection techniques which have been developed for dijet searches focusing on jet substructure anomalies can be applied to event-level anomaly detection in this topology. To robustly capture event-level features of multiparticle kinematics, we employ new physically motivated variables derived from the geometric structure of a collision’s phase space manifold. As a proof of concept, we explore the application of this approach to several benchmark signals in the di-$\tau$ and di-$\mu$ plus X final states. We demonstrate that our anomaly detection approach can reach discovery-level significances for signals that would be missed in a conventional bump-hunt approach.

We explore the spontaneous breaking of global baryon number for baryogenesis. We introduce a model with three majorana fermions and a complex scalar carrying baryon number charge. After symmetry breaking, the baryon asymmetry is generated below the electroweak scale via the decays of one of the majorana fermions. The main focus of the paper is the phenomenology of the Nambu-Goldstone boson of $U(1{)}_B$, which we call the bajoron. With small sources of explicit baryon number violation, the bajoron acquires a small mass and is generally very long-lived. The model avoids proton decay, satisfies cosmological constraints, and offers interesting collider phenomenology for the Large Hadron Collider. These long-lived particles tied to baryogenesis strongly support the development of far-detector experiments such as MATHUSLA, FASER, SHiP, and others.

In this work, we provide a comprehensive study of fermion-portal dark matter models in the freeze-in regime at a future muon collider. For different possible nonsinglet fermion portals, we calculate the upper bound on the mediator’s mass arising from the relic abundance calculation and discuss the reach of a future muon collider in probing their viable parameter space in prompt and long-lived particle search strategies. In particular, we develop rudimentary search strategies in the prompt region and show that cuts on the invariant dilepton or dijet masses, the missing transverse mass $M_{T2}$, pseudorapidity and energy of leptons or jets, and the opening angle between the lepton or the jet pair can be employed to subtract the Standard Model background. In the long-lived particle regime, we discuss the signals of each model and calculate their event counts. In this region, the lepton-(quark-)portal model signal consists of charged tracks ($R$-hadrons) that either decay in the detector to give rise to a displaced lepton (jet) signature, or are detector stable and give rise to heavy stable charged track signals. As a byproduct, a pipeline is developed for including the nontrivial parton distribution function of a muon component inside a muon beam; it is shown that this leads to nontrivial effects on the kinematic distributions and attainable significances. We also highlight phenomenological features of all models unique to a muon collider and hope our results, for this motivated and broad class of dark matter models, inform the design of a future muon collider detector. We also speculate on suggestions for improving the sensitivity of a muon collider detector to long-lived particle signals in fermion-portal models.

Worldwide efforts are underway to detect neutrinoless double beta ($0\nu \beta \beta$) decay using experiments based on various technologies and target isotopes. Future experiments in this regard aim to exclude the inverted order (IO) condition or explore the normal order (NO) band. Consequently, comparing the sensitivities of proposed $0\nu \beta \beta$ decay experiments with promising prospects is essential. The current study adopts sensitivity metrics, including exclusion and discovery sensitivities, half-life sensitivities, and $m_{\beta \beta }$ sensitivities, to provide a comprehensive evaluation of ten typical promising experiments: LEGEND, CDEX, nEXO, XLZD, PandaX, NEXT, KamLAND-Zen, JUNO, $\mathrm{SNO}+$, and CUPID, and highlight their unique features. Based on reported experimental parameters, the concept of a “technical line” is introduced to determine the location that each experiment may realize in the $\xi$ and ${\lambda }_b$ space, where $\xi$ represents the sensitive exposure per year, and ${\lambda }_b$ denotes the expected annual rate of background events. Half-life sensitivities for the selected experiments are calculated, some of them in multiple phases and others in conservative or aggressive condition. The results indicate that increasing the operation time is more beneficial for zero-background experiments, which also demonstrate greater competitiveness in discovery sensitivity. $m_{\beta \beta }$ sensitivities are presented as uncertainty bands arising from the nuclear matrix element uncertainties. Additionally, half-life and $m_{\beta \beta }$ sensitivities are estimated under ideal conditions also in the form of uncertainty bands, where only irreducible $2\nu \beta \beta$ and solar B-8 neutrino induced background remain.

In light of current constraints from supersymmetry (SUSY) searches within the LHC as well as findings from direct dark matter detection experiments such as LUX-ZEPLIN (LZ), we revisit the three-family Pati-Salam model derived from intersecting D6-branes in type IIA string theory compactified on the $T^6/({\mathbb{Z}}_2\times {\mathbb{Z}}_2)$ orientifold, known for its realistic low-energy phenomenology. Because the muon anomalous magnetic moment might be in accordance with the Standard Model prediction, we conduct a comprehensive scan over the model’s parameter space for each sign of the Higgsino mass parameter, $\mu <0$ and $\mu >0$. We found that a gravitino mass is typically greater than 1.5 TeV in both scenarios while simultaneously satisfying the LHC SUSY bounds, B-physics observables, along with the Higgs mass constraint. Within the experimentally viable region of the parameter space, the mass spectra of sparticles are found to fall within the following ranges: Gluinos lie in the range of 2–18 TeV, the first- and second-generation squarks and sleptons span 3–16 TeV and 1–6 TeV, respectively. For third-generation sfermions, the lightest stop, which can satisfy the dark matter relic density through neutralino-stop coannihilation consistent with the Planck $5\sigma$ bounds, has a mass in the range of 0.5–1.2 TeV. Note that the lightest neutralino will be as heavy as 2.9 TeV. Additionally, the lightest stau could be as light as 200 GeV, as well as heavy up to 5.2 TeV. We further identify several viable mechanisms, including multiple coannihilation channels and resonance mechanisms, and the observed dark matter relic abundance is successfully realized.