In this work, we perform Markov Chain Monte Carlo (MCMC) analyses using the Planck 2018 cosmic microwave background datasets, including temperature, polarization, and lensing, in order to compare matter bounce models with observational data. The particular model we consider contains a scalar field with an exponential potential, which behaves as dust in the asymptotic past of the contracting phase; it realizes a quantum bounce, and then behaves as a transient dark energy field at large scales in the expanding phase. The parameter $\lambda$ appearing in the exponential potential is directly related to the model’s scalar spectral index, $n_s$, which is set free in the MCMC analyses, as well as the bounce depth, which controls the amplitude of the power spectrum. We provide constraints on the cosmological parameters and compare the model’s performance against the standard inflationary $\mathrm{\Lambda }\mathrm{CDM}$ scenario. Our results indicate that Planck data alone cannot favor one model with respect to the other, showing that the model we investigate can be a viable alternative to inflation.

We present a discovery-era strategy for intensity frontier experiments based on “didecay” events, in which feebly interacting particles (FIPs) are produced in pairs and then both decay inside the detector. This signature may exist in broad classes of models with FIPs decaying in the same way as minimal “portal” particles. The two displaced vertices may allow reconstruction of the pair invariant mass and hence reveal the production channel, information normally inaccessible at these facilities. This, in turn, lets one discriminate between FIP models that share identical decay signatures. As a case study, we consider the model of Higgs-like scalars and show that SHiP, Belle II, and the Downstream@LHCb can each cover wide domains of viable parameter space using didecays.

We propose discussing the modular flavor model and the stabilization of single modulus field in the Jordan frame supergravity with nonminimal scalar-curvature coupling of the form $\mathrm{\Phi }(\tau ,\overline{\tau })R$. Modular invariance, positivity of the scale factor, and positive definiteness of the Kahler metric constrain stringently the form of the frame function, and consequently the Kahler potential by the relation $\mathrm{\Phi }(\tau ,\overline{\tau })=-3\exp [-K(\tau ,\overline{\tau })/3]$. We discuss some general properties of scalar potentials after the scale transformation from the Jordan frame to the Einstein frame. We find that the shape of the resulting scalar potential in the Einstein frame is quite different from that of ordinary single modulus stabilization mechanism. The scalar potential could be stationary at the $i\infty$ fixed point, leading to a runaway-type vacuum. Such a runaway-type vacuum can be properly stabilized at typical modulus vacuum expectation value with large $\Im \tau$. We also discuss numerically the modulus stabilization for some simplified scenarios.

Metastable cosmic strings are a common prediction of grand unified theories and act as a source of a gravitational-wave background (GWB) that can explain the 2023 pulsar timing array (PTA) signal. In this paper, we revisit the GWB signal from metastable strings, emphasizing the need to carefully distinguish between two different timescales: (i) $t_{\mathrm{LB}}$, the timescale of loop breaking because of spontaneous monopole nucleation on closed string loops, and (ii) $t_{\mathrm{NC}}$, the timescale of network collapse when string segments attached to monopoles begin to enter the Hubble horizon. We discuss under which conditions these two timescales are similar or far apart from each other and illustrate the resulting consequences for the GWB signal. In doing so, we generalize the description of the GWB signal from metastable strings to a three-parameter model in terms of the string tension $G\mu$ and the timescales $t_{\mathrm{LB}}$ and $t_{\mathrm{NC}}$, which allows us to unify the modeling of standard metastable strings with what is known as quasistable strings. In the limit of a large $t_{\mathrm{LB}}/t_{\mathrm{NC}}$ ratio, we, moreover, derive a compact analytical expression for the predicted GWB spectrum in excellent agreement with numerical results in the literature. We thus conclude that our new templates for the GWB spectrum from metastable strings can be readily used in the analysis of future PTA datasets.

The infrared behavior of gauge theories coupled to matter remains an open problem in quantum field theory. For a given gauge group, such theories are expected to flow to an interacting conformal fixed point over a range of fermion or scalar flavors, known as the “conformal window.” Their nature is important for understanding critical phases and phase transitions beyond the Landau paradigm like the deconfined quantum critical point yet remains challenging for conventional nonperturbative approaches. In this work, we study a family of fuzzy-sphere models corresponding to nonlinear sigma models with $\mathrm{Sp}(N)$ global symmetry extended to the strongly coupled region. These theories are expected have an infrared fixed point described by SU(2) quantum chromodynamics in three space-time dimensions with $N$ flavors of fermions. They can be viewed as a generalization of the SO(5) deconfined quantum critical point, corresponding to $N=2$. We investigate them using quantum Monte Carlo for $N$ up to 16. We find evidence that for $N\ge 4$ the phase diagram contains a critical phase that appears to be absent for $N=2$. Within this phase, we measure the two-point correlation function and the excitation spectrum, which exhibit emergent conformal symmetry. We also extract the scaling dimension ${\mathrm{\Delta }}_{\varphi }$ of a leading operator and find consistency with large-$N$ expectations.

Several simple asymptotically free chiral gauge theories are studied. The only “free parameters” of our models are the choice of the gauge group, the matter Weyl fermion representations, and the relative magnitudes of the renormalization-group-invariant scales ${\mathrm{\Lambda }}_i$ associated with each gauge group. None of our models has nontrivial, nonabelian global symmetries (“family-like” fermion representations). We rely on some recent theoretical developments on the dynamics of strongly coupled chiral gauge theories based on the generalized symmetries and associated new types of anomaly matching consideration, but also on the solid knowledge on vector-like gauge theories such as QCD and supersymmetric Yang-Mills theories. The structures of the infrared effective theories, RG flows, and light spectra found in these models are surprisingly rich and intriguing.

Axions that couple to nuclear spins via the axial current interaction can be both produced and detected using nuclear magnetic resonance (NMR) techniques. In this scheme, nuclei driven by a real oscillating magnetic field in one device act as an axion source, which can drive NMR in a nearby spin-polarized sample interrogated with a sensitive magnetometer. We study the prospects for detecting axions through this method and identify two key characteristics that result in compelling detection sensitivity. First, the gradient of the generated axion field can be substantial, set by the inverse distance from the source. Near the source, it reduces to the inverse of the source’s geometric size. Second, because the generated axion field is produced at a known frequency, the detection medium can be tuned precisely to this frequency, enabling long interrogation times. We show that the experimental sensitivity of a pair of centimeter-scale NMR devices operating over a 15-day integration time can already surpass existing astrophysical bounds on the axion-nucleon coupling. A similar sensitivity can be achieved with 10 centimeter-scale NMR devices with only 1 hour of integration time. These dual NMR configurations are capable of probing a wide range of axion masses, up to values comparable to the inverse distance between the source and the sensor.

We derive a closed-form expression for the adjoint polynomials of torus knots and investigate their special properties. The results are presented in the very explicit double sum form and provide a deeper insight into the structure of adjoint invariants essential for the Vogel’s universality of Chern-Simons theory.

We study multipoint Virasoro conformal blocks on the sphere in the comb channel. We arrive at the asymptotic expression for these blocks at large intermediate dimensions, applying the WKB method for the “classical Belavin-Polyakov-Zamolodchikov equation,” which is used to study (classical) Virasoro blocks via the monodromy method. Several applications of this asymptotic are discussed, such as the possibility to generalize Zamolodchikov’s elliptic recursion and numerical evaluation of amplitudes in minimal string theory. Our expressions pass nontrivial checks, such as agreement with known exact expressions for five-point blocks in special cases and the usual series expansion of Virasoro blocks computed using Alday-Gaiotto-Tachikawa correspondence.

Numerical studies of critical phenomena in gravitational collapse have provided key insights into the nonlinear dynamics of Einstein’s field equations in the strong-field regime. However, most prior investigations have been restricted to highly symmetric models, limiting our understanding of the universality of critical behavior. Extending these studies to more general systems poses substantial computational challenges, as resolving the fine-scale structure near the black hole threshold requires extremely high spatial and temporal resolution. In this work, we present the first direct comparison between the discontinuous Galerkin (DG) and finite-difference methods applied to critical phenomena. For the case study, we used the classical example of spherically symmetric gravitational collapse of massless scalar fields. The DG method, which combines the high-order accuracy of spectral techniques with the flexibility and locality of finite-difference schemes, demonstrates significant computational advantages: Near criticality, it achieves comparable accuracy with fewer degrees of freedom, approximately half the number of computational steps, and a third of the run-time required by finite-difference methods. These improvements mitigate the run-time and resolution limitations characteristic of finite-difference simulations in higher dimensions and complex field systems. A detailed extension of the DG framework to the collapse of nonlinear, axisymmetric gravitational waves will be reported in future work.

Superradiant instability of ultralight bosons can produce clouds around rotating black holes, whose continuous gravitational wave (GW) emission is a promising observational target. Precise predictions of the signal frequency and its evolution are essential for detecting such continuous GWs. For axions, self-interactions can populate multiple superradiant modes via nonlinear couplings, and GW emission can occur through various channels. To calculate the frequency shifts of GWs emitted through these channels, we employ relativistic perturbation theory based on a bilinear form. We apply this framework to self-interaction effects for the first time, and also revisit the treatment of the self-gravity contribution. Our results provide a simple and unified framework for calculating frequency shifts, including cases in which multiple modes are excited, and are relevant for next-generation GW observations.

Parameter estimation of gravitational-wave signals is computationally intensive and typically requires millions of likelihood evaluations to construct posterior probability distributions. This computational cost increases significantly in the time domain, which requires nondiagonal covariance matrices to compute the likelihood. Consequently, parameter estimation of long-duration gravitational-wave signals, such as binary neutron star mergers, becomes computationally infeasible in the time domain. In this work, we detail a framework for the heterodyned likelihood that enables rapid inference in the time domain. Our method is applicable to signals with arbitrary mode content, and leverages the smoothness of the ratio of complex-valued waveform modes, approximating the ratio as a linear function within appropriately chosen time bins. This allows downsampling of the waveform modes and a reformulation of the likelihood, such that it depends only on the bin edges. We demonstrate that this likelihood recovers posteriors that are indistinguishable from those obtained using the standard likelihood in the time domain. We also observe dramatic improvement in speed—for a 128 s long gravitational-wave signal, our method is at least $\sim 400$ times faster than the standard time-domain analysis, reducing the wall-clock time to just a few hours. We also demonstrate the reliability and unbiasedness of the likelihood using percentile-percentile tests for binary black hole and binary neutron star injections. We use the Gohberg-Semencul representation of the inverse of a Toeplitz covariance matrix to accelerate matrix-vector products; this has potential applications even in nonheterodyned time-domain inference.

We study a multifield model in loop quantum cosmology for a maximally symmetric spacetime governed by the Einstein-Hilbert action minimally coupled to scalar fields. Using a Legendre transformation, we formulate the Hamiltonian dynamics in canonically equivalent geometrodynamical and Yang-Mills-type representations, incorporating nontrivial couplings through a geometric structure on the multifield configuration space. Implementing the $\overline{\mu }$-scheme polymerization, we obtain the loop-quantum-corrected Friedmann equations. By focusing on the two-field models as an example, we analyze the effective dynamics for specific potentials. The quantum bouncing, transition, and slow-roll inflationary phases are investigated numerically, and viability of the models is assessed by evaluating the number of e-folds during the inflationary phase for certain given initial conditions. The global behavior of the background evolution is further examined through linear stability and dynamical-systems analyses.

Motivated by recent detections of low-mass perturbers in strong gravitational lensing systems, we investigate analogs of these objects in the concerto suite, a set of cosmological $N$-body zoom-in simulations of self-interacting dark matter (SIDM) with high-amplitude, velocity-dependent cross sections. We investigate characteristic halo properties relevant to gravitational imaging measurements, focusing on the projected enclosed mass and the central density slope. In SIDM, these quantities evolve continuously through gravothermal processes, spanning core-expansion and core-collapse phases, in sharp contrast to cold dark matter, where they remain nearly static after halo formation. This SIDM evolution further depends on tidal environment and merger history, which can be probed through strong lensing. We also identify simulated SIDM halos whose properties are consistent with the properties of low-mass perturbers inferred from recent observations, and we demonstrate that the core-collapse mechanism offers a compelling explanation for their observed high densities. Our results highlight the potential of strong gravitational lensing as a powerful probe of dark matter self-interactions.

The Laser Interferometer Space Antenna (LISA) is a space-based gravitational-wave observatory that uses free-falling test masses as inertial references to detect mHz-frequency signals. Interactions between these test masses and galactic or solar energetic particles cause charge buildup and Coulomb forces, a major source of acceleration noise that must be accurately modeled. LISA Pathfinder measurements showed that the Poissonian test-mass charging noise, an important entry in the noise budget, was considerably larger than that in prelaunch simulations, indicating missing physical processes in early models. Emission of low-energy secondary electrons (LEEs) from test-mass and housing surfaces has been proposed as a key mechanism affecting charging and the sensor’s electrostatic response. We report a particle accelerator-based experiment that directly tests the LEE hypothesis by measuring proton-induced test-mass charging in a LISA-like Gravitational Reference Sensor geometry as a function of the test-mass electrostatic potential. A flight-representative test mass and the capacitive sensor electrode housing surrounding it are exposed in vacuum to monoenergetic 70–230 MeV proton beams, while test-mass charging currents are measured with femtoampere sensitivity. By varying the test-mass potential by volts during irradiation, we gain sensitivity to eV-scale charge carriers whose transport and collection depend on these fields. The measurements yield stable, reproducible picoampere-level charging currents and a clear dependence of the net charging rate on test-mass potential. This behavior directly supports the role of low-energy secondary electrons in test-mass charging and is consistent with the LEE-based interpretation of LISA Pathfinder data. These are the first controlled laboratory measurements of low-energy electron effects in test-mass charging for a LISA-like sensor and provide a benchmark for validating charging models and charge-management strategies for LISA and future space-based precision interferometry missions.

In this work, we explore how astronomical observations (specifically measurements of masses and radii) can constrain the presence of quark matter inside neutron stars, namely the phase transition from nuclear matter to deconfined quark matter. Our approach employs Bayesian analysis to study this constraint. In this sense to model Hadronic matter we used the relativistic mean-field approximation, for which we have selected two parameter sets: $NL{3}^{*}\omega \rho$, representing hadronic matter with nucleons only, and $EL3\omega \rho$ with nucleons only and $EL3\omega \rho Y$, which includes hyperons. On the other hand deconfined quark matter is modeled using the vector-MIT bag model. Also, for our purpose, the first order phase transition is implemented using the Maxwell construction. Bayesian inference is performed by optimizing three parameters: the bag constant (i.e. $B^{1/4}$), the vector coupling constant $(G_v)$, and the Dirac sea contribution ($b_4$). We found that a phase transition could exist at densities below $2.0n_0$ for both the $EL3\omega \rho$ and $NL{3}^{*}\omega \rho$ parametrizations. As a consequence, the inferred parameters of the vector MIT bag model, based on our likelihood function, imply hybrid stars with large quark cores.

In this work we study the possibility of modeling the dark matter content in galaxies as a core-halo model consisting of self-gravitating, self-interacting fermions by means of an effective polytropic equation of state. For the core of the halo, the dark matter fermions are degenerate, while for the halo we have considered two possibilities: the fermions have thermalized as a perfect fluid, or they will follow a standard cold dark matter Navarro-Frenk-White profile. The core density profile is obtained by solving the Tolman-Oppenheimer-Volkoff equations, and their properties are determined by the fermion mass, the central density, and the interaction strength. The mass of the fermion and the strength of the fermion self-interaction are fixed by doing a ${\chi }^2$ analysis to fit the rotational curves of low surface brightness galaxies. It was found that the fermion mass should be in the range $155.10\mathrm{eV}<m_f<313.26\mathrm{eV}$ and the interparticle strength in the range $1465.31<y<6002.04$ at 68 C.L. in order to reproduce the rotational curves adequately, in the case when the halo is modeled as a thermalized ideal gas. Similar values are obtained if the halo is modeled following a Navarro-Frenk-White case, namely $42.31\mathrm{eV}<m_f<49.23\mathrm{eV}$ and $71.43<y<132.65$. Once we fixed the values of the mass of the fermion $m_f$ and the interaction strength $y$, we tested the core-halo model with data from the Milky Way, local dwarf spheroidal galaxies, and the SPARC database. We have found good agreement between the data and the core-halo models, varying only one free parameter: the central density. Thus a single fermion can fit hundreds of galaxies. Nevertheless, the dark matter halo surface density relation or the halo total mass and radius depend strongly on the model for the halo.

We study inelastic dark matter (iDM) in a minimal and ultraviolet-complete framework in which the dark photon mass arises from a dark Higgs mechanism. The spontaneous breaking of a $U(1{)}_D$ symmetry splits the Dirac fermion into two Majorana states, thus opening new annihilation channels mediated by the dark Higgs. Focusing on sub-GeV dark matter, we assess the sensitivity of DUNE’s liquid argon cube at the near detector (ND-LAr) to this scenario. We find that the ND-LAr can probe regions of parameter space consistent with the observed relic abundance due to these new annihilation channels, particularly for large dark photon-to-DM mass ratios where decay-based searches lose sensitivity. Our results highlight the complementarity between cosmological constraints and fixed-target experiments and demonstrate the potential of DUNE’s ND-LAr to explore iDM scenarios with extended dark sectors.

Indirect searches for particle dark matter with gamma-ray experiments have produced a large number of constraints on the annihilation cross section (or decay lifetime) over a wide range of dark matter masses. These constraints depend critically on the assumed astrophysical $J$ factor and its uncertainty, which encodes the dark matter distribution in the target and represents the dominant source of systematic uncertainty. As improved observational data and dynamical modeling are expected to revise current $J$-factor determinations, many published limits risk becoming obsolete unless the full experimental analyses are repeated. In this work, we present a general and statistically consistent framework for updating published dark matter limits when revised $J$-factor estimates become available, without requiring access to the full experimental likelihood. We derive an analytical expression that quantifies the impact of astrophysical uncertainties on dark matter limits, treating both Gaussian and log-normal priors on the $J$ factor. The formalism is validated through toy Monte Carlo simulations, including dedicated studies of its numerical stability under successive reinterpretations, and demonstrate their accuracy by reproducing published limits. Lastly, we further show that the formalism naturally extends to the combination of multiple targets through a simple numerical procedure, allowing limits to be combined and updated using only publicly available information. The proposed method is intended as a complementary reinterpretation tool for situations in which a complete experimental reanalysis is impractical, offering a practical means to preserve and extend the scientific relevance of published dark matter constraints across present and future experiments.

It is shown in this paper that the QCD equations for dipole density have the natural solution: the “fan” diagrams of the Pomeron calculus. We found the dipole densities comparing the analytic solution to the Balitsky-Kovchegov (BK) equation for the simplified leading twist kernel with the $t$ channel unitarity. Using these densities we calculate the contributions of large Pomeron loops to dipole-dipole scattering at high energies. Applying the Abramovsky, Gribov and Kancheli cutting rules we found that the produced gluons are distributed accordingly the Koba, Nielsen and Olesen (KNO) law which leads to the entropy $S_E=\ln (xG(x,Q^2))$ in an agreement with Kharzeev-Levin predictions.