In neutrino physics, a class of models with local or global family symmetries may be invoked, and then a flavon field is needed to realize full neutrino mixing. This flavon may leave hints in lepton $g-2$ and address their possible anomalies. In this work, we explore this idea in the $(B-L{)}_{ij}$ gauge extension to the standard model (SM), in which realistic neutrino mixing requires both a SM singlet flavon $s$ and a vectorlike lepton (VLL) doublet. The dominant coupling between the flavon and leptons is in the manner of lepton-flavor-violation (LFV). Through an analytical analysis of the SM lepton-VLL mixing matrix, we find that the parameter space of the $s\overline{\mu }e$-type flavon to explain $(g-2{)}_{\mu }$ has been completely excluded by the specific LFV process, muonium-antimuonium oscillation. But the $s\overline{\mu }\tau$-type flavon still has the opportunity to account for the excess in $(g-2{)}_{\mu }$ or the deficit in $(g-2{)}_e$; however, it faces the strong constraint from $\tau \to \mu$ conservation and, in particular, the lepton flavor universality (LFU) test of $Z$ boson decay, which arises due to our way to realize the LFV flavon. The surviving flavon is highly predictable, with mass in the narrow window $m_{\tau }\lesssim m_s\lesssim 2m_{\tau }$ and LFV coupling strength $\sim {10}^{-2}$. Besides, it leaves a TeV scale VLL with a multilepton signature at the LHC.

We investigate the possibility of having a vector boson dark matter in a $U(1{)}_X$ extended two-Higgs doublet model (2HDM) setup. The gauge boson gains mass when a Standard Model (SM) singlet complex scalar, which is charged under the dark $U(1{)}_X$ symmetry, acquires a vacuum expectation value. This scalar acts as the connection between the SM sector and DM via the Higgs portal. An additional exact charge conjugation symmetry inhibits the mixing of this gauge boson with the photon, thereby confirming the stability of DM. On the other hand, 2HDM with type-I $Z_2$ restriction can offer a nonstandard Higgs in the lighter mass range. This freedom allows us to accommodate dark matter mass in the (40–60)-GeV regime where the direct detection constraints are strongest. We study the dark matter phenomenology of such a model while taking care of all possible theoretical and experimental constraints.

The evolution of quarkonia in the QGP medium can be described through the formalism of open quantum systems (OQS). In previous works with OQS, the quarkonium evolution was studied by working in either quantum Brownian or optical regime. In this paper, we set up a general non-Markovian master equation to describe the evolution of the quarkonia in the medium. Because of the non-Markovian nature, it cannot be cast in Lindblad form, which makes it challenging to solve. We numerically solve the master equation for $\mathrm{\Upsilon }(1S)$ without considering stochastic jumps for Bjorken and viscous hydrodynamic background at energies relevant to the large hadron collider (LHC) and relativistic heavy ion collider (RHIC). We quantify the effect of the hierarchy between the system timescale, ${\tau }_{\mathrm{S}}\sim 1/E_b$, and the environment timescale, ${\tau }_{\mathrm{E}}$, on quarkonium evolution and show that it significantly affects the nuclear modification factor. A comparison of our results with the existing experimental data from the LHC and RHIC is presented.

The hidden-charm pentaquark states $P_{c\overline{c}}{(4312)}^{+}$, $P_{c\overline{c}}{(4380)}^{+}$, $P_{c\overline{c}}{(4440)}^{+}$, and $P_{c\overline{c}}{(4457)}^{+}$, all with isospin $I=1/2$, were discovered by the LHCb Collaboration in the decay process ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$. Although their quantum numbers remain undetermined, these states have generated significant theoretical interest. We analyze their spectrum and decay patterns—including those of their spin partners—within the Born-Oppenheimer (BO) effective field theory (BOEFT), a framework grounded in QCD. At leading order in BOEFT, we identify these pentaquark states as bound states in BO potentials that exhibit at short distance a repulsive octet behavior and a nonperturbative shift due to the adjoint baryons masses, while asymptotically approaching the ${\mathrm{\Sigma }}_c\overline{D}$ threshold. We further incorporate $\mathcal{O}(1/m_Q)$ spin-dependent corrections to compute pentaquark multiplet spin splittings. Based on the spectrum, semi-inclusive decay widths to $J/\psi$ and ${\eta }_c$, and the decay width ratios to ${\mathrm{\Lambda }}_c\overline{D}$ and ${\mathrm{\Lambda }}_c{\overline{D}}^{*}$, we provide the first theoretical predictions for the adjoint baryon masses, which can be confirmed by future lattice QCD studies. Moreover, our analysis supports the quantum number assignments: $J^P=(1/2{)}^{-}$ for $P_{c\overline{c}}{(4312)}^{+}$, $(3/2{)}^{-}$ for $P_{c\overline{c}}{(4380)}^{+}$, $(1/2{)}^{-}$ for $P_{c\overline{c}}{(4457)}^{+}$, and $(3/2{)}^{-}$ for $P_{c\overline{c}}{(4440)}^{+}$. We also present results for the lowest bottom pentaquarks.

We revisit the recently published analytic results for unpolarized and polarized semi-inclusive deep inelastic scattering (SIDIS) at next-to-next-to-leading order (NNLO) in quantum chromodynamics (QCD). These expressions for the hard scattering coefficients contain case distinctions in the kinematic $(x,z)$-plane, splitting the analytic result into four regions. By reexpressing the coefficient functions in terms of single-valued polylogarithms, we remove these case distinctions and can present a unified result valid across the entire kinematic range of SIDIS. This reduces the length of the overall expressions by 30% to 60%.

We report a flux-integrated cross section measurement of muon neutrino interactions on water and hydrocarbon via charged current reactions without charged pions in the final state with the WAGASCI-BabyMIND detector, which was installed in the T2K near detector hall in 2018. The detector is located 1.5° off-axis and is exposed to a more energetic neutrino flux than ND280, another T2K near detector, which is located at a different off-axis position. The total flux-integrated cross section is measured to be $1.26\pm 0.18(\text{stat}+\text{syst})\times {10}^{-39}{\mathrm{cm}}^2/\mathrm{nucleon}$ on CH and $1.44\pm 0.21(\text{stat}+\text{syst})\times {10}^{-39}{\mathrm{cm}}^2/\mathrm{nucleon}$ on ${\mathrm{H}}_2\mathrm{O}$. These results are compared to model predictions provided by the neut v5.3.2 and genie v2.8.0 Monte Carlo generators and the measurements are compatible with these models. Differential cross sections in muon momentum and cosine of the muon scattering angle are also reported. This is the first such measurement reported with the WAGASCI-BabyMIND detector and utilizes the 2020 and 2021 datasets.

We investigate the combined effects of a uniform magnetic field and boundary conditions on vacuum energy and topological mass generation in a coupled scalar field theory. The system consists of a real scalar field, subject to Dirichlet boundary conditions, interacting via self- and cross-couplings with a gauge-coupled complex scalar field obeying mixed boundary conditions between two perfectly reflecting parallel plates. The magnetic field induces Landau quantization, leading to novel contributions. Employing zeta-function regularization within the effective potential formalism, we derive the renormalized effective potential up to second order in the coupling constants without imposing a vanishing magnetic field in the renormalization scheme. Our renormalization approach preserves magnetic contributions while properly removing divergences, enabling a consistent treatment of finite-size corrections, magnetic effects, and interaction terms. We compute the vacuum energy per unit area of the plates, analyze the emergence of a topological mass from boundary and magnetic contributions, and evaluate the first-order coupling-constant corrections at two-loop order. Detailed asymptotic analyses are presented for both weak- and strong-field regimes, revealing exponential suppression at high magnetic fields and nontrivial polynomial and logarithmic behavior in the weak-field limit.

It is well known that a minimal distance emerges in quantum field theories owing to the need to regularize the UV divergences. The macroscopical limit at large minimal distance, and weak spatial resolution, is investigated for a self-interacting scalar quantum field theory with the help of the renormalization group. The lowering of the cutoff always opens the dynamics, hence the renormalization group has to be implemented for open quantum field theories. A strongly coupled nonrelativistic scaling regime is found, supporting a second-order phase transition between weakly and strongly open theories. The weakly (strongly) open bare theories develop into strongly (weakly) open dynamics during the renormalization group flow. The two known conditions of the classical limit, the strong decoherence and the suppression of the quantum fluctuations, are confirmed for closed bare theories at distances beyond a nonrelativistic correlation length.

When a local quantum system couples to a quantum field in a cosmological spacetime, the time dependence of the coupling strength is conventionally taken to reflect the design of the local quantum system but not to depend on the large-scale structure of the Universe. In this paper, we consider a novel coupling that incorporates additional time dependence that reflects the cosmological expansion, as motivated by structures that appear in quantum cosmology. We focus on a conformal scalar field in a de Sitter Friedmann-Lemaître-Robertson-Walker cosmology with flat but compact spatial sections in $3+1$ dimensions, and a comoving Unruh-DeWitt detector: the novel coupling posits the detector to couple to the scaled scalar field that appears in the conformally related static spacetime. We survey the differences between the conventional and novel coupling, for detectors that couple to the full field and detectors that couple only to specific field modes, and for detectors with proper time internal dynamics and detectors with conformal time internal dynamics. We also briefly discuss noncompact spatial sections and single-mode detectors with discontinuous time dependence. We find that the novel coupling tends to enhance the deexcitation peaks in the detector’s response, particularly for single-mode detectors.

A generalization of the coadjoint orbit action describes the dynamics of an observer (or instrument). We consider how this fits in with the view of observables in field theory being correlations of readouts of instruments and show how one recovers the usual $S$-matrix formulas. A simple resolution of the Fermi paradox is also pointed out.

We model the motion of a small compact object on a nearly circular orbit around a spinning supermassive black hole, which is also interacting with a thin equatorial accretion disk surrounding the latter, through tools from self-force and Hamiltonian perturbation theory. We provide an analytical and relativistically accurate formalism to calculate the rate of energy and angular momentum exchanged at Lindblad resonances. We show that strong relativistic effects can potentially cause a reversal in the direction of the torque on the small compact object if the surface density gradient is not too large. We analytically explore the dependence of the torque reversal location on the spin of the supermassive black hole and demonstrate that the ratio of the reversal location to the innermost stable circular orbit is approximately insensitive to the spin of the supermassive black hole. Our results show that relativistic torques can be one to two orders of magnitude larger than the Newtonian torque routinely used in the literature to model disk/small-compact-object interactions close to the supermassive black hole. Our results highlight the importance of including relativistic effects when modeling environmental effects in extreme mass-ratio inspirals.

In Keplerian dynamics, a test body orbiting a point particle in circular motion has a monotonically increasing frequency, with decreasing radius. If a dissipative channel is introduced, such as gravitational wave (GW) emission, under the quadrupole approximation, the corresponding GW strain has an ever-increasing frequency with time. A similar statement holds for equatorial motion of a test particle on the Kerr manifold, except such inspiral is cut off at the ISCO, wherein stable circular orbits cease to exist and a plunge is expected. We analyze circular timelike orbits in generic spinning spacetimes and study the conditions in which exotic motion can occur, arising from non-Kerr features. In particular, we derive conditions under which an inspiral towards a compact object is naturally followed by an outspiral motion, and give concrete examples as well as the corresponding GW phenomenology. This analysis serves both as a theoretical exploration of non-Kerrness and as an example of a concrete smoking gun of exotic spacetimes.

We analyze gravitational lensing, in particular the shadow and photon rings, in the Ernst spacetime, also known as the Schwarzschild-Melvin spacetime, which describes a Schwarzschild black hole immersed in a homogenous magnetic field. Although the geodesic equation in this spacetime is chaotic, there are some relevant features that can be determined analytically. Among other things, we give analytic formulas for the vertical diameter of the shadow for an observer at arbitrary inclination and for the horizontal diameter of the shadow for an observer in the equatorial plane. Moreover, we use the strong-deflection formalism for analytically calculating the so-called photon rings of order $\ge 2$ and we use the recently introduced gap parameter ${\mathrm{\Delta }}_2$ for distinguishing lensing of an Ernst black hole from that of a Schwarzschild black hole.

High-fidelity gravitational waveform models are essential for realizing the scientific potential of next-generation gravitational-wave observatories. Highly accurate, state-of-the-art models often rely on extensive phenomenological calibrations to numerical relativity (NR) simulations for the late-inspiral and merger phases, which can limit physical insight and extrapolation to regions where NR data is sparse. To address this, we introduce the spinning effective-to-backwards one-body (SEBOB) formalism, a hybrid approach that combines the well-established effective-one-body (EOB) framework with the analytically driven backwards-one-body (BOB) model, which describes the merger-ringdown from first principles as a perturbation of the final remnant black hole. We present two variants building on the state-of-the-art SEOBNRv5HM model: seobnrv5_nrnqc_bob, which retains standard NR-calibrated nonquasicircular (NQC) corrections and attaches a BOB-based merger-ringdown, and a more ambitious variant, seobnrv5_bob, which uses BOB to also inform the NQC corrections, thereby reducing reliance on NR fitting and enabling higher-order (${\mathcal{C}}^2$) continuity by construction. Implemented in the open-source nrpy framework for optimized c-code generation, the SEBOB model is transparent, extensible, and computationally efficient. By comparing our waveforms to a large catalog of NR simulations, we demonstrate that SEBOB yields accuracies comparable to the highly calibrated SEOBNRv5HM model, providing a viable pathway toward more physically motivated and robust waveform models for precision gravitational-wave astronomy.

As the compact binary catalog continues to grow rapidly, developing and refining tests to probe the nature of compact objects is essential for a comprehensive understanding of both the observed data and the underlying astrophysics of the binary population. We investigate the effectiveness of spin-induced multipole moments (SIQM) and tidal deformability measurements in distinguishing lower mass-gap black hole (BH) binaries from non-BH binaries with different mass and spin configurations. We perform model-agnostic tests on binary BH (BBH) simulations using full Bayesian inference, evaluating the independent and joint measurability of SIQM and tidal parameters across the parameter space. We extend the analysis to simulations of self-interacting spinning boson stars, using synthetic signals that exhibit (a) both SIQM and tidal effects and (b) each effect individually. For case (a), recovery is performed using (i) a BBH model, (ii) a model incorporating both SIQM and tidal effects, and (iii) models including either SIQM or tidal effects. For case (b), we employ (i) a BBH model and (ii) models incorporating either SIQM or tidal effects, consistent with the injection. Simulations assume binaries of total mass of $8M_{\odot }$, varying mass ratios and spin magnitudes, using the inspiral-only taylorf2 waveform model. A three-detector network consists of Advanced LIGO and Virgo at design sensitivity is assumed, with results scalable to future detector sensitivities. We find that employing an incorrect model to analyze the signal can lead to severe biases in parameter inference. Notably, when analyzing a simulated binary boson starlike signal with component masses $(4,4)M_{\odot }$ using a BBH model, the system is incorrectly identified as having masses $(8,2)M_{\odot }$. In contrast, using the correct recovery model that includes both SIQM and tidal deformability effects, successfully recovers the true masses, highlighting the significance of waveform model accuracy in performing reliable distinguishability tests for compact objects in the low-mass gap.

Measurement of the eccentricity of low-mass binary systems through gravitational waves is crucial to distinguish between various formation channels. However, detecting eccentricity in these systems has been challenging due to the lack of accurate eccentric waveform models and the high computational cost associated with Bayesian inferences for systems with low-mass objects. In this work, we assess the eccentricities of seven previously observed low-mass gravitational wave events using publicly available data from the O1-O4a observing runs of the LIGO and Virgo observatories. We analyze the events using a new eccentric waveform model, seobnrv5ehm, and compare our results with the existing model, teobresums-dali. We also present the first eccentricity constraints for GW190814. To improve the accuracy of our parameter estimation, we include higher-order modes in both waveform models. We optimize inference by employing efficient marginalization techniques to alleviate the computational costs associated with low-mass systems and parallelization techniques for sampling large parameter spaces. We find that one of the sources, GW200105, exhibits a non-negligible eccentricity, with a measured eccentricity of $e=0.125_{-0.082}^{+0.029}$ at 20 Hz (90% credible level) for seobnrv5ehm and $e=0.135_{-0.088}^{+0.019}$ for teobresums-dali for a uniform eccentricity prior ranging from 0 to 0.2 at a reference frequency of 20 Hz. We find moderate support for the eccentric waveform hypothesis with a Bayes factor of $\sim 6–7$ times more preference for the eccentric model over the noneccentric one. When using a uniform log prior on eccentricity with a minimum bound of ${10}^{-4}$, the support for the eccentric model decreases, with the Bayes factor reduced to 2.35. For the remaining five sources, the results are consistent with low eccentricity, with 90% upper limits ranging from $e\le 0.011$ to $e\le 0.066$. We do not find any support for non-negligible eccentricity in GW190814. Finally, we discuss the challenges of performing Bayesian inference in eccentric, multimodal parameter spaces, including issues related to sampling efficiency and waveform systematics.

In this article, we investigate the phenomenological aspects of a feebly interacting sterile neutrino dark matter candidate within a low-scale seesaw framework. The type-I seesaw model is augmented by a second complex scalar doublet (${\mathrm{\Phi }}_{\nu }$), which couples exclusively to the heavy right-handed neutrinos and the lepton doublet, thereby generating the neutrino Dirac mass term while the first scalar doublet is responsible for giving mass to the remaining Standard Model particles. The lightest sterile neutrino ($N_1$) acts as a feebly interacting massive particle (FIMP), produced via decays of $W^{\pm }$, $Z$ and extra scalars present in the setup. We point out that $W^{\pm }$ and $Z$ contributions were overlooked in the previous studies, which actually dominate the $N_1$ production by a factor of $\sim {10}^{13}$ and solely determines the relic abundance. Incorporating them leads to several novel consequences for the DM phenomenology like a new nonthermal condition which leads to smaller Yukawa couplings. We thoroughly discuss about the enhancement possibilities of $N_1$’s mass which is controlled by the small vacuum expectation value ($v_{\nu }$) of the second Higgs doublet. After incorporating the latest Lyman-$\alpha$ forest observations, this setup can accommodate both warm and cold dark matter scenarios.

The linear seesaw (LSS) model provides a natural framework for generating small neutrino masses at low energy scales, thereby offering promising testability prospects. However, in generic LSS models, the exact mass degeneracy (before the electroweak symmetry breaking) between the two sterile neutrinos that form a Dirac pair precludes the generation of $CP$ asymmetries from their interplay, posing a significant challenge to explaining the observed baryon (or lepton) asymmetry of the Universe via the leptogenesis mechanism. In this work, we explore two well-motivated approaches to generate a suitable mass splitting for the two sterile neutrinos that form a Dirac pair, and consequently naturally realize a resonantly enhanced generation of baryon (and lepton) asymmetry. First, we demonstrate that the renormalization group evolution effects can naturally induce the desired mass splitting for the sterile neutrinos, resulting in a successful generation of the observed baryon asymmetry of the Universe. Second, motivated by the recent result from the EMPRESS Collaboration that indicates the possible existence of a large lepton asymmetry of the Universe, we explore the possibility that a large lepton asymmetry might naturally follow from the electroweak symmetry breaking, which automatically induces the desired mass splitting for the sterile neutrinos.

The first coupled-channel determination of two-body $D$ and $D^{*}$ scattering amplitudes in isospin-1 from lattice quantum chromodynamics (QCD) is presented. Using three lattice volumes at $m_{\pi }\approx 391\mathrm{MeV}$, finite-volume energies relevant for the channels of interest are determined. Through the Lüscher formalism, these energies are used to constrain amplitudes of coupled $J^P=0^{+}DD-D^{*}{D}^{*}$, $J^P=1^{+}D{D}^{*}-D^{*}{D}^{*}$, and $J^P=2^{+}DD-D{D}^{*}-D^{*}{D}^{*}$ scattering. All channels feature weakly repulsive interactions in the $S$-wave, except for a weak $D^{*}{D}^{*}$ attraction in $J^P=0^{+}$. No amplitude singularities corresponding to physical states are found. Some of these amplitudes will be a necessary component of future lattice QCD analyses of $DD\pi$ and $D{D}^{*}$ scattering, taking into account three-body and left-hand cut effects.

We study the decays ${\pi }^{+}\to l^{+}{\nu }_l$ in the presence of a background electromagnetic plane wave with circular polarization. We find that, in the presence of this background, the number of hadronic form factors required to describe the pion-to-vacuum amplitude increases from one to four. Three of these form factors are associated with the axial vector current and one with the vector piece, which is in general different from zero. We obtain analytical expressions for the corresponding contributions to the decay width, considering in particular some range of values of interest for the frequency and amplitude of the external wave. For laser frequencies $\omega$ of the order of the eV, it is seen that the main correction to the result obtained in absence of the external field is proportional to the vector form factor, carrying a suppression factor of order $\sim (\omega /m_{\pi }{)}^{4/3}$. In addition, we show that our expressions can be connected with the Kroll-Watson formula, which provides the differential cross section for the scattering of a charged particle by some potential in the presence of a strong external electromagnetic wave. Our analytical results are also compatible with previous numerical calculations obtained in the limit of low amplitude laser fields, offering new insight on some characteristics of these results.