We explore the sensitivity of collider experiments to a broad class of GeV-scale dark vector models of new physics via production in proton and neutron bremsstrahlung and initial state radiation. This is achieved using a new physically motivated model for timelike vector form factors with generic charges for both protons and neutrons, which is fit to a variety of timelike and spacelike data with quantified uncertainties. The production model for both proton and neutron bremsstrahlung is applied to recast and extend the reach of existing FASER data to GeV-mass dark photons, $U(1{)}_B$, $U(1{)}_{B-L}$, and protophobic vectors, as well as forecasts for millicharged particles at FORMOSA.

In this work, we study the potential of analyzing the particular combination of $\kappa$ modifiers given by ${\kappa }_V^2-{\kappa }_{2V}$ to disentangle beyond Standard Model Higgs signals in double Higgs production with two extra light jets at LHC. We use the Higgs effective field theory approach, HEFT, for the gauge invariant description of these two ${\kappa }_V$ and ${\kappa }_{2V}$ parameters representing the BSM interactions of the Higgs particle with the electroweak gauge bosons, $HVV$ and $HHVV$, respectively. We illustrate the bonus of studying this particular combination ${\kappa }_V^2-{\kappa }_{2V}$ focusing in just one process, $HHjj$, instead of studying ${\kappa }_V$ and ${\kappa }_{2V}$ separately using various processes. For the detailed analysis here, we focus on the particular final state $H(\to \gamma \gamma )H(\to b\overline{b})j{j}^{\prime }$, with two photons, two b-jets and two light jets, which we analyze fully including parton showering, fragmentation, hadronization and detector effects, in both signal and main background. We find that the sensitivity to ${\kappa }_V^2-{\kappa }_{2V}$ could be notably improved at the HL-LHC by the proper cuts on the final state $b\overline{b}\gamma \gamma j{j}^{\prime }$ that select optimally the events with VBF-topology and $HH$-topology. In particular, we propose strategies based on a good isolation of $\gamma \gamma$ and b-jet pairs, and focus specially on specific variables like ${\eta }_{\gamma \gamma }$ and $P_{\gamma \gamma }^T$ where the signal events distributions may efficiently discriminate between BSM signal versus SM background. We will show here how the high transversality of these two pairs in the signal (inherited from the high transversality of the $H$’s) is correlated with the nonvanishing value of this $({\kappa }_V^2-{\kappa }_{2V})$ combination.

The transverse polarization of $\mathrm{\Lambda }$ hyperons within unpolarized jets is encoded in the transverse-momentum-dependent fragmentation function $D_{1T}^{\perp }(z,{\mathit{p}}_{\perp },{\mu }^2)$. In the vacuum environment, the QCD evolution of this transverse-momentum-dependent fragmentation function is governed by the Collins-Soper equation. However, in the presence of the quark-gluon plasma medium, the jet-medium interaction induces the transverse-momentum-broadening effect that modifies the QCD evolution. As a result, the transverse spin polarization of $\mathrm{\Lambda }$ hyperons in relativistic heavy-ion collisions differs from that in $pp$ collisions. We demonstrate that this difference serves as a sensitive probe for studying jet-medium interaction, offering a novel perspective through the spin degree of freedom.

Diverse searches for direct dark matter in effective electromagnetic and leptophilic interactions resulting from new physics, as well as weakly interactive massive particles with unconventional electronic recoils, are intensively pursued. Low-energy backgrounds from radioactive $\gamma$ rays via Compton scattering and photon coherent scattering are unavoidable in terrestrial detectors. The interpretation of dark matter experimental data is dependent on a better knowledge of the background in the low-energy region. We provide a 2.3% measurement of atomic Compton scattering in the low-momentum transfer range of $180\mathrm{eV}/c$ to $25\mathrm{keV}/c$, using a 10 g germanium detector bombarded by a ${}^{137}\mathrm{Cs}$ source with a 7.2 m-Ci radioactivity, and the scattered photon collected by a cylindrical NaI[Tl] detector. The ability to detect Compton scattering’s doubly differential cross section gives a special test for clearly identifying the kinematic restraints in atomic many-body systems, notably, the Livermore model. Additionally, a low-energy-background comparison is made between coherent photon scattering and Compton scattering, replacing the scattering function of geant4 software, which uses a completely relativistic impulse approximation together with multiconfiguration Dirac-Fock wave functions. For the purpose of investigating sub-GeV mass and electronic recoil dark matter theories, signatures including low-energy backgrounds via high-energy $\gamma$ rays in germanium targets are discussed.

We uncover a surprising universal soft behavior (USB) of a de Sitter (dS) S-matrix for all exceptional effective field theories (EFTs) in dS space, stemming from the recently proposed generalized energy conservation condition. At leading order in the soft limit, the dS S matrices for all exceptional EFTs in four spacetime dimensions exhibit no scaling with the soft momentum, i.e., ${\lim }_{k\to 0}\mathcal{A}(k)\sim \mathcal{O}(1)$, a feature we term USB. We specifically show that USB fixes the four-point amplitudes in Dirac-Born-Infeld theory and Special Galileon, and six-point amplitude in $SU(N)$ nonlinear sigma model given the minimal derivative count. We then conjecture USB fixes the interactions of all exceptional EFTs to all orders, thereby providing a unification criterion for them. Our result further underpins the idea that $\mathrm{\Delta }\ge 4$ exceptional theories in dS are characterized by the spectrum and stability requirement alone, resonating with the low energy theory of gravity-general relativity.

We extend the concept of Krylov complexity to encompass general unitary evolutions involving multiple generators. This generalization enables us to formulate a framework for generalized Krylov complexity, which serves as a measure of the complexity of states associated with continuous symmetries within a model. Furthermore, we investigate scenarios in which different directions of transformation lead to varying degrees of complexity, in close analogy with geometric approaches to complexity, such as Nielsen’s framework. In this context, we introduce a generalized orthogonalization algorithm and delineate its computational structure, which is organized as a network of orthogonal blocks rather than a simple linear chain. Finally, we present explicit evaluations of several illustrative examples to demonstrate the practical application of this framework.

Recently, “cosmohedra” have been introduced as polytopes underlying the cosmological wave function for conformally coupled $\mathrm{Tr}({\mathrm{\Phi }}^3)$ theory in Friedmann-Lemaître-Robertson-Walker cosmologies, generalizing associahedra for flat space scattering amplitudes. In this paper we show that correlation functions are also directly captured by a new polytope—the Correlatron. The combinatorics of correlation functions is an interesting blend of flat space scattering amplitudes and wave functions. This is reflected in the correlatron geometry, which is a one-higher dimensional polytope sandwiched between cosmohedron and associahedron facets. We provide an explicit embedding for the correlatron, which is a natural extension of the “shaving” picture for cosmohedra to one higher dimension. As a byproduct, we also define “graph correlahedra” as polytopes for the contribution to correlators from any fixed graph. We show how the canonical form of these polytopes directly computes the graph correlator, without the power of two weights seen in previous geometric formulations. Finally, we give a prescription for extracting the full correlator from the canonical form of the correlatron.

The acceleration-induced transparency (AIT) effect has been suggested recently to amplify the transition probability of the two-level detector and offers a potential avenue for the experimental detection of the Unruh effect. In this paper, we explore the influence of the AIT effect on quantum entanglement between two detectors accelerated in a thermal field background, since the thermal background field cannot be avoided completely in any experiments. Interestingly, we find that although the background thermal field generally degrades the entanglement between the detectors, the AIT effect can effectively protect it.

Gravitational waves from compact binary coalescences provide unique opportunities to test general relativity (GR) in the strong-field regime. In particular, the merger phase, during which two compact objects finally coalesce, corresponds to the regime of the strongest gravitational fields accessible by direct observation and thus serves as a probe of the nonlinear nature of gravity. In this work, we test GR in the merger phase by analyzing GW150914 using a modified waveform proposed in Watarai et al. [Phys. Rev. D 109, 084058 (2024).], which parametrizes possible deviations from GR during this stage. Within this framework, the inferred deviation parameters can be translated into model-independent constraints on physically meaningful quantities. For GW150914, we find that the additional energy radiated in the merger phase is constrained to be ${0.26}_{-0.62}^{+0.75}\%$ of the total energy emitted over the entire coalescence predicted by GR, and the peak time shift due to beyond-GR effects is ${2.17}_{-9.90}^{+9.56}\mathrm{ms}$, both within the 90% credible interval. These two constraints serve as observational benchmarks for deviations in the nonlinear gravity regime, offering guidance for theoretical investigations of beyond-GR models.

In k-essence theories within general relativity, where the matter Lagrangian depends on a real scalar field $\varphi$ and its kinetic term $X$, static and spherically symmetric compact objects with a positive-definite energy density cannot exist without introducing ghosts. We show that this no-go theorem can be evaded when the k-essence Lagrangian is extended to include a dependence on the field strength $F$ of a $U(1)$ gauge field, taking the general form $\mathcal{L}(\varphi ,X,F)$. In Einstein-scalar-Maxwell theories with a scalar-vector coupling $\mu (\varphi )F$, we demonstrate the existence of asymptotically flat, charged compact stars whose energy density and pressure vanish at the center. With an appropriate choice of the coupling function $\mu (\varphi )$, we construct both electric and magnetic compact objects and derive their metric functions and scalar- and vector-field profiles analytically. We compute their masses and radii, showing that the compactness lies in the range $\mathcal{O}(0.01)<\mathcal{C}<\mathcal{O}(0.1)$. A linear perturbation analysis reveals that electric compact objects are free of strong-coupling, ghost, and Laplacian instabilities at all radii for $\mu (\varphi )>0$, while magnetic compact objects suffer from strong coupling near the center.

The exact measurement of neutrino mass remains a longstanding issue. So far, there has been much success in providing an upper bound for the neutrino rest mass, both theoretically and experimentally. In this work, by exploring the critical radius of a beam of polarized quantum spin-$\frac{1}{2}$ particle deflecting around a classical Kerr black hole, we attempt to provide an additional testing ground for neutrino mass, as well as the mass of other proposed ultralight particles yet to be determined. Notably, the quantum Dirac equation is used to derive a Mathisson-Papapetrou-Dixon (MPD)-like equation satisfied by the polarized beam of massive spin-$\frac{1}{2}$ particles and identify the effective spin in the spin tensor with the particle’s intrinsic quantum spin, confirming the previous theoretical result that the MPD equation can be in fact applied to particles’ intrinsic spin. The result of this work shows that corrections of relative magnitude $>{10}^{-12}$ can be achieved for spin-$\frac{1}{2}$ particles with rest mass equal to $1\mathrm{eV}/c^2$ deflecting around a solar mass Kerr black hole. Although highly theoretical, a new method of extracting the lower bound for the neutrino mass individually is also proposed due to the behavior of the quantum spin correction.

We present a robust and efficient methodology for parameter estimation of gravitational waves generated during the postmerger phase of binary neutron star mergers. Our approach leverages an analytic waveform model combined with empirical relations to predict prior ranges for the postmerger frequencies based on measurements of the chirp mass and effective tidal deformability in the inspiral phase. This enables robust inference of the main features of the postmerger spectrum, avoiding possible multimodality induced by wide priors. Using waveforms derived from numerical relativity, we systematically validate our model across a broad spectrum of neutron star equations of state and mass configurations, demonstrating high fitting factors. Our method can be applied in future detections of gravitational waves from the postmerger phase with third-generation gravitational wave observatories. Furthermore, by integrating the preconditioned Monte Carlo sampling method within the pocomc framework, we achieve substantial computational acceleration compared to conventional Bayesian techniques.

Black hole spectroscopy is an important pillar when studying gravitational waves from black holes and enables tests of general relativity. Most of the gravitational wave signals observed over the last decade originate from binary black hole systems. Binary neutron star or black hole neutron-star systems are rarer but of particular interest for the next-generation ground-based gravitational wave detectors. These events offer the exciting possibility of studying matter effects on the ringdown of “dirty black holes.” In this work, we ask the question; Does matter matter? Using numerical-relativity, we simulate a wide range of collapsing neutron stars producing matter environments, both in isolated scenarios and in binary mergers. Qualitatively, the resulting ringdown signals can be classified into “clean,” “modified,” and “distorted” cases, depending on the amount of matter that is present. We apply standard strategies for extracting quasinormal modes of clean signals, using both theory-agnostic and theory-specific assumptions. Even in the presence of matter, possible modifications of quasinormal modes seem to be dominated by ringdown modeling systematics. We find that incorporating multiple quasinormal modes allows one to drastically reduce mismatches and errors in estimating the final black hole mass at early times. If not treated carefully, deviations in the fundamental quasinormal mode might artificially be overestimated and falsely attributed to the presence of matter or violations of general relativity.

The spectrum of radial oscillations of neutron stars is systematically studied within two frameworks of viscous relativistic hydrodynamics: the relativistic Navier-Stokes and Israel-Stewart theories. A correspondence is established between the discrete stellar eigenmodes and the continuous dispersion relation of perturbations around a homogeneous fluid, providing a basis for interpreting our numerical results. We analyze the Newtonian limit and assess the impact of relativistic corrections, such as the gravitational redshifting of microscopic relaxation timescales. We show that bulk viscosity can significantly affect the behavior of both hydrodynamic and nonhydrodynamic fundamental modes, and that, depending on the magnitude of the viscous effects, it is the nonhydrodynamic mode that becomes unstable beyond the turning point in a sequence of equilibrium configurations. These results provide a useful step toward systematic studies of neutron star quasinormal modes in the presence of viscosity.

Uniqueness of the four-dimensional static, asymptotically flat, Einstein-Maxwell spacetime with both electric and magnetic charges, containing nonextremal massive particle sphere, being an inner boundary in it, has been proved. It is isometric to Reissner-Nordström spacetime with electric/magnetic charges. In contrast to the previous results concerning the classification of photon spheres, it describes the existence of the entire set of spacetme foliations, a set of massive particle spheres addressed to the various energies of the particles. The conformal positive energy, positive mass theorem, and adequate conformal transformations constitute the main tools in the proof.

Scalar, spherically symmetric, radially excited boson stars were previously shown to be stabilized, against spherical dynamics, by sufficiently strong self-interactions. Here, we further test their stability now in a full $3+1\mathrm{D}$ evolution. We show that the stable stars in the former case become afflicted by a nonspherical instability. Then, we perform head-on collisions of both (stable) fundamental and (sufficiently long-lived) excited boson stars. Depending on the stars chosen, either a black hole or a bosonic remnant are possible. In particular, collisions of excited stars result in a bosonic bound state which resembles a dynamical superposition of chains and rings, akin to the ones found as equilibrium solutions in [1]. These evolutions emphasize a key difference concerning the dynamical robustness of fundamental vs excited spherical boson stars, when generic (beyond spherical) dynamics is considered.

We propose a revised cosmological scenario that extends the $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) framework by incorporating metric $f(R)$ gravity in the Jordan frame. In this model, the dark energy component arises from a nonminimally coupled scalar field, decomposed into a smooth background [set to unity to recover general relativity (GR)] and a rapidly varying, massive fluctuation that decays into the dark matter sector. In the near-GR limit, this setup provides a phenomenological extension of $\mathrm{\Lambda }\mathrm{CDM}$ characterized by two additional parameters: the present-day value of the scalar fluctuation and a normalized decay rate. Using a Markov chain Monte Carlo analysis of low-redshift cosmological data, comprising Type Ia supernovae, baryon acoustic oscillation (BAO), and cosmic chronometer measurements, we find that the proposed model achieves a better overall fit than $\mathrm{\Lambda }\mathrm{CDM}$, while the Bayesian evidence remains statistically inconclusive given the inclusion of two extra parameters. The model predicts a moderate increase in the inferred value of $H_0$ and an improved consistency with Dark Energy Spectroscopic Instrument BAO data when adopting the SH0ES prior. Furthermore, describing dark matter particle creation as a transition phase in the late Universe offers an intriguing physical interpretation, potentially capturing features already present in current data and providing a promising avenue to explore extensions of the standard cosmological model within modified gravity frameworks.

We study the dynamics of Friedmann-Lemaître-Robertson-Walker models where a dark energy component with a quadratic equation of state (EoS) nonlinearly interacts with cold dark matter. Thus, two energy scales naturally come into play: ${\rho }_{*}$ is the scale at which the nonlinearity of the EoS becomes relevant; ${\rho }_i$ is the energy scale around which the interaction starts to play an important role in the dynamics. Our focus is to understand whether there are parameter ranges for this system that can produce nonsingular bouncing and emergent cosmologies for any initial condition. We complete a dynamical systems analysis, and find the parameter range such that trajectories always expand from a high energy nonsingular de Sitter state. For flat and negative curvature models this de Sitter state is represented by a fixed point, the asymptotic past from which the Universe emerges. We find a subset of positive curvature models that during contraction get arbitrarily close to the de Sitter state, thus having a quasi-de Sitter bounce, then emerge from the bounce and expand, evolving toward spatial flatness. We find that the dimensionless parameter $q\equiv {\rho }_{*}/{\rho }_i$, which measures the relative strength of the nonlinear terms in the system, plays a crucial role in the topology of the phase space. When $q<3$, some trajectories expand toward a singularity, while others evolve toward a low energy cosmological constant at late times, with a subset going through a decelerated matter dominate era before the final acceleration. When $q>3$, all trajectories are nonsingular, and evolve toward a late-time cosmological constant. We find a subclass in this case in which all trajectories have at least one decelerated matter dominated phase, and accelerate at late times. Therefore, the nonlinear interacting cosmology presented here allows for a subclass of models that are singularity-free and qualitatively realistic for any initial condition.

The cosmic distance duality relation (CDDR) connects the angular diameter distance ($d_A$) and the luminosity distance ($d_L$) at a given redshift. This fundamental relation holds in any metric theory of gravity, provided that photon number is conserved and light propagates along null geodesics. A deviation from this relation could indicate new physics beyond the standard cosmological model. In this work, we test the validity of the CDDR at very low redshifts ($z<0.04$) by combining $d_A$ from the Megamaser Cosmology Project with $d_L$ from the Pantheon + sample of type Ia supernovae (SNIa). We further incorporate high-redshift baryon acoustic oscillations- (BAO) based $d_A$ measurements from DESI DR2 in combination with SNIa data, highlighting the critical role of the $r_d\text{−}{M}_b$ (early-late) calibration in testing the CDDR using these two probes. Assuming CDDR holds, we perform a Bayesian analysis to derive model-independent constraints on the calibration parameters. Using only BAO and SNIa data, we observe a strong degeneracy between $r_d$ and $M_b$. However, the inclusion of calibration-free megamaser measurements breaks this degeneracy, enabling independent constraints without relying on a specific cosmological model or distance-ladder techniques. Additionally, we present a forecast incorporating the expected precision from future megamaser and SNIa observations, demonstrating their potential to significantly tighten constraints on early-late calibration parameters, under the assumption of validity of CDDR.

Gravitational waves (GWs) are ripples in space-time that propagate deformations caused by compact bodies throughout the Universe. As an elastic body, the Earth responds to passing GWs much like a resonant sphere. This interaction produces a redistribution of mass, which results in perturbations of the Earth’s tensor of inertia. By conservation of angular momentum, such perturbations lead to a displacement of the rotation axis within the mantle (polar motion) and to changes in the spin rate, directly linked to variations in the length of day (LOD). In this work, we compute for the first time the perturbations of the Earth’s rotation induced by GWs emitted by compact white-dwarf binaries, using a normal mode summation approach applied to an elliptical, rotating, radially stratified Earth model. Our results indicate maximal amplitudes of approximately ${10}^{-15}\mathrm{\mu }\mathrm{s}$ in the LOD and ${10}^{-15}$ mas for the polar motion—values that remain far below current instrumental sensitivities. These findings highlight the extreme difficulty of detecting GWs through their rotational effects on the Earth, yet the methodology developed here offers a framework that could be extended to other astrophysical bodies.