The process of ${\mathrm{\Xi }}_{bc}^{+}\to {\mathrm{\Xi }}_c^{+}J/\psi$ is among the most favored modes for searching for bottom-charm baryons. However, its branching fraction has never been studied in theory. In this work, we investigate the branching fraction of ${\mathrm{\Xi }}_{bc}^{+}\to {\mathrm{\Xi }}_c^{+}J/\psi$ in the final-state-interaction approach, as it is dominated by the color-suppressed nonfactorizable contributions. A similar process, ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}^{0}J/\psi$, is used as a control mode to fix the model parameter. Consequently, the branching fraction of ${\mathrm{\Xi }}_{bc}^{+}\to {\mathrm{\Xi }}_c^{+}J/\psi$ is predicted to be $(1.55_{-0.42}^{+0.50})\times {10}^{-4}$. With the production rate of bottom-charm baryons and the detection efficiencies of the final states, it is expected for considerable signal events to observe ${\mathrm{\Xi }}_{bc}^{+}$ in the near future.

In 2023, KM3NeT observed the highest-energy neutrino seen to date. The most probable estimate places the energy of the neutrino at an extreme value of 220 PeV, and energies up to 2.6 EeV are contained in the 90% probability interval. Even though the source of the signal cannot be ascertained with the available data, this observation already opens unique possibilities to test new physics. Here, we study the implications for the transition magnetic dipole portal connecting active and sterile neutrinos. We remain agnostic regarding the origin of the neutrino and focus on local effects. Concretely, we study the impact of efficient active-sterile transitions on the energy degradation experienced by the neutrino along its path to the detector at Earth. We find that the ultrahigh-energy neutrino event does not add relevant information for sterile neutrinos with masses less than a TeV. However, the observation becomes important at higher masses and can provide the leading constraint in that regime.

We propose a seeded axion-photon conversion scheme to enhance the sensitivity of light-shining-through-a-wall (LSW) experiments for axion detection, where the axions are generated from short-pulse lasers and the usual resonant cavity is not applicable. By injecting a weak, coherent seed electromagnetic (EM) field into the axion-photon conversion region, the axion-induced EM field can constructively interfere with the seed field, amplifying the number of regenerated photons to a level exceeding that of the unseeded scenario. We evaluate the expected signal enhancement, statistical limits from Poisson counting with seed fluctuations and background, and the potential improvement in coupling sensitivity. Compared to a standard LSW setup, the seeded scheme can achieve orders-of-magnitude higher photon yield per axion, potentially surpassing resonance-enhanced experiments in certain parameter regimes. This approach presents a promising pathway to extend the reach of laboratory axion searches, particularly in scenarios where the resonant cavities are impractical.

We study big bang nucleosynthesis (BBN) constraints on heavy QCD axions. BBN offers a powerful probe of new physics that modifies the neutron-to-proton ratio during the process, thanks to the precisely measured primordial Helium-4 abundance. A heavy QCD axion provides an attractive target for this probe, because not only is it a well-motivated hypothetical particle by the strong $CP$ problem, but also it dominantly decays to hadrons if kinematically allowed. A range of its lifetime is thus excluded where the hadronic decays would significantly alter the neutron-to-proton ratio. We compute axion-induced modification of the neutron-to-proton ratio, and obtain robust upper bounds on the axion lifetimes, as low as 0.017 s for the axion mass higher than 300 MeV. Remarkably, this is stronger than projected future cosmic microwave background bounds via $N_{\mathrm{eff}}$. Our bounds are largely insensitive to uncertainties in hadronic cross sections and the axion’s branching fractions into various hadrons, as well as to the precise value of the initial axion abundance. We also incorporate, for the first time, several key improvements, such as scattering processes by energetic $K_L$ and secondary hadrons, that can also be important for studying general hadronic injections during BBN, not limited to those from axion decays.

In the kinetic mixing (KM) portal scenario, the interaction of dark matter (DM) with the particles of the Standard Model (SM) is generated by diagrams connecting the familiar photon with its dark sector analog, the dark photon (DP), via loops of particles carrying both dark and SM quantum numbers, i.e., portal matter (PM). For the case of sub-GeV DM and DP, these PM states may lie in the $\sim 1–10\mathrm{TeV}$ range and be potentially accessible at the HL-LHC as well as at other future lepton and hadron colliders. In perhaps the simplest scenario of this kind, PM consists of just a pair of electrically charged, iso- and color-singlet, vectorlike (VL) fermions having opposite dark charges, with an $O(1)$ mass splitting, yielding a finite value for the strength of the KM, i.e., $\epsilon \sim a\mathrm{few}\times {10}^{-4}$. The dark Higgs induced mixing of PM states with their SM analogs allows for their decay but can also lead to significant distortions in the expected production properties for the PM at future lepton colliders due to $t$-channel dark Higgs exchange, potentially confusing PM identification. We show that the large set of clean observables available at lepton colliders is more that sufficient to resolve any of these ambiguities. The possibility of the production of like-sign PM fields via $t/u$-channel exchange of the same dark Higgs is also briefly explored.

This paper presents a detailed analysis of the three-body final state interactions in the $B^{+}\to D\overline{D}{K}^{+}$ process, whose phase space is sufficient small. To precisely extract the resonance parameters, for instance the ${\chi }_{c0/2}(3930)$ in the $D\overline{D}$ invariant mass distributions, in this process, one has to take into account final state interaction, especially the three-body final state interaction. We employ the dispersive Khuri-Treiman formalism, combined with a parametrization of the $D\overline{D}$ interaction based on heavy quark spin symmetry. By performing a simultaneous fit to the experimental data from LHCb, BABAR, and Belle collaborations, the scheme with three-body interaction successfully describes the invariant mass distributions of the three two-body subsystems. We precisely extract the pole structures of ${\chi }_{c0}(3930)$ and $\psi (3770)$ as $3.913-0.016i\mathrm{GeV}$ and $3.761-0.006i\mathrm{GeV}$ in $B^{+}$ decay. By performing the pole trajectory analysis on a uniformized complex plane, we find that both of them stem from the input bare state.

The tensor form factors of the ${\mathrm{\Delta }}^{+}$ baryon are defined through the matrix element of the tensor current and describe its internal structure and spin distribution. We present the full Lorentz decomposition for the ${\mathrm{\Delta }}^{+}\to {\mathrm{\Delta }}^{+}$ tensor current matrix element, including all independent structures consistent with Lorentz covariance, the Rarita–Schwinger constraints, and the discrete symmetries of Hermiticity, time-reversal, and parity invariance. By investigating the tensor form factors corresponding to both the isovector and isoscalar tensor currents, we observe differences that reflect the distinct contributions of up and down quark components in the ${\mathrm{\Delta }}^{+}$ baryon.

In this work, we adopt the one-boson exchange model to analyze the $D_{(s)}^{(*)}{B}_{(s)}^{(*)}$ interactions from a coupled-channel perspective. For the $I(J^P)=1(1^{+})$ $D{B}^{*}/D^{*}B/D^{*}{B}^{*}$ system, employing the complex scaling method, we obtain a loosely bound state and two resonant states located below the $D{B}^{*}$, $D^{*}B$, and $D^{*}{B}^{*}$ thresholds, respectively. Assuming that the charmoniumlike states $Z_c(3900)$ and $Z_c(4020)$, as well as the bottomoniumlike states $Z_b(10610)$ and $Z_b(10650)$, are molecular states near their respective thresholds, we suggest that the predicted states in the $I(J^P)=1(1^{+})D^{(*)}{B}^{(*)}$ system could be their bottom-charmed analogs. In addition, we extend our analysis to other $D_{(s)}^{(*)}{B}_{(s)}^{(*)}$ combinations with various quantum numbers. Our results indicate that, besides the $I(J^P)=1(1^{+})$ channel, more molecular states with quantum numbers $I(J^P)=0(0^{+}),0(1^{+}),0(2^{+})$, and $1(0^{+})$ may also exist in the bottom-charmed sector. Compared with our earlier study of hidden-bottom systems [Phys. Rev. D 110, 074038 (2024)], where two bound states were obtained in the $I(J^P)=1(1^{+-})$ channel, the present work instead finds resonant states in the $I(J^P)=1(1^{+})$ sector. Moreover, while no molecular state with strangeness was identified in the previous hidden bottom systems, we now obtain molecular states near the $D_s^{(*)}{B}_s^{*}$ threshold. Finally, we provide possible decay channels for future experimental searches, recommending the $B_c/B_c^{*}$ plus light mesons for bound states, and the $D_{(s)}^{(*)}{B}_{(s)}^{(*)}$ channels for resonances.

Independently from the formation mechanism of primordial black holes in the early Universe, their generation is accompanied by a ringdown phase during which they relax to a stationary configuration and gravitational waves under the form of quasinormal modes are emitted. Such gravitational waves generate an irreducible and unavoidable stochastic background, which is testable by current and future experiments. In particular, for primordial black holes with masses exceeding ${10}^{14}{M}_{\odot }$, the associated stochastic background lies within the frequency range accessible to current and upcoming cosmic microwave background experiments, thereby providing a direct observational way to probe the existence of such extremely massive objects.

The stochastic gravitational-wave background (SGWB) generated by the inspiral and merger of binary neutron stars is traditionally modeled assuming that the inspiral is promptly followed by the collapse of the merger remnant to a rotating black hole. While this is reasonable for the most massive binaries, it is not what is expected in general, as the remnant may survive for up to hundreds of milliseconds and radiate an amount of energy that is significantly larger than that lost during the whole inspiral. To account for this additional contribution to the SGWB, we consider a waveform model that includes both the inspiral and the postmerger emission. We show for the first time that for a large set of parametrized equations of state (EOSs) compatible with observational constraints, there is considerable spectral power in the 1–2 kHz range, distinct from that associated with the inspiral and leading to a dimensionless GW energy density ${\mathrm{\Omega }}_{\mathrm{GW}}\simeq {10}^{-10}–{10}^{-9}$. We discuss the enhanced detectability of the SGWB by third-generation detectors such as the Einstein Telescope and Cosmic Explorer, and show how it depends on the signal-to-noise ratio of foreground binaries and on the remnant lifetime. Interestingly, even a nondetection of the high-frequency part of the SGWB could provide valuable constraints on the remnant lifetime, offering novel insights into the postmerger dynamics and the EOS of nuclear matter.

The theory of $f(R)$ gravity with constant curvature (i.e., constant scalar curvature) admits rotating and charged black hole solutions obtained from the Kerr–Newman–(anti) de Sitter metrics of general relativity through appropriate rescalings of the metric parameters. In this paper, we focus on the Kerr–Newman–de Sitter case and present a unified analytic treatment of the horizon structure and its physical properties, allowing for a transparent comparison between general relativity and $f(R)$ gravity with constant curvature. We solve the quartic equation determining the horizon locations and derive closed analytic expressions for the horizon radii. Focusing on extremal configurations, we obtain analytic formulas for the squared rotation parameter $a^2$ and the inverse square of the curvature radius $l^{-2}$ as functions of the horizon location and the electric charge. For generic values of these parameters, the extremality conditions are nonuniversal, reducing to the familiar Kerr-Newman bound only in the limit of vanishing background curvature. We identify an ultraextremal configuration in which $a^2$ attains its maximal value at zero charge and decreases monotonically to zero as the charge approaches its limiting value, while $l^{-2}$ increases correspondingly. As an illustrative example, we show that black holes with charge $q=M/2$ necessarily possess a minimum rotation, which emerges naturally as an intersection point in our analytic description of $a^2$ and $l^{-2}$, when embedded in a universe characterized by a critical value of $l^{-2}$ (equivalently, the scalar curvature or the cosmological constant). Finally, we demonstrate that when the mass satisfies $M^2=(a^2+q^2)(1-a^2/l^2)$, the quartic horizon equation factorizes, leading in the extremal regime to a chiral-like horizon structure that allows only the outer-cosmological horizon merger.

We present realistic eccentricity distributions for extreme mass ratio inspirals (EMRIs) forming via the two-body relaxation channel in nuclear star clusters, tracking their evolution up to the final plunge onto the central Schwarzschild massive black hole (MBH). We find that EMRIs can retain significant eccentricities at plunge, with a distribution peaking at $e_{\mathrm{pl}}\approx 0.2$, and a considerable fraction reaching much higher values. In particular, up to 20% of the forming EMRIs feature $e_{\mathrm{pl}}>0.5$ for central MBH masses $M_{•}$ in the range ${10}^5{M}_{\odot }\le M_{•}\le {10}^6{M}_{\odot }$, partially due to EMRIs forming at large semimajor axes and “cliffhanger EMRI,” usually neglected in literature. This highlights the importance of accounting for eccentricity in waveform modeling and detection strategies for future space-based gravitational wave observatories such as the upcoming Laser Interferometer Space Antenna (LISA). Furthermore, we find that the numerical fluxes in energy and angular momentum currently implemented in the fastemriwaveforms (few) package may not adequately sample the full parameter space relevant to low-mass MBHs ($M_{•}<{10}^6{M}_{\odot }$), potentially limiting its predictive power in that regime. Specifically, for $M_{•}={10}^5{M}_{\odot }$ we find that about 75% (50%) of EMRIs at 2 years (6 months) from plunge fall outside the currently available flux parameter space. Our findings motivate the development of extended flux grids and improved interpolation schemes to enable accurate modeling of EMRIs across a broader range of system parameters.

Direct detection of the cosmic neutrino background ($\mathrm{C}\nu \mathrm{B}$) remains one of the most formidable experimental challenges in modern physics. In this work, we extend recent studies of $\mathrm{C}\nu \mathrm{B}\text{−}\mathrm{induced}$ coherent transitions in polarized nuclear spin ensembles. Adopting an open quantum system framework, we model coherent neutrino effects in large spin ensembles using a Lindblad master equation that also incorporates realistic experimental imperfections such as local dephasing and imperfect polarization. We solve the Lindblad equation numerically by way of a fast and computationally inexpensive method that can be extended to an arbitrarily large number of spins. Using our numerical solutions, we forecast the sensitivities of future experiments such as CASPEr to the local $\mathrm{C}\nu \mathrm{B}$ overdensity parameter ${\delta }_{\nu }$. Our findings indicate that a CASPEr-like experiment, though primarily aimed at axion dark matter search, could also constrain the $\mathrm{C}\nu \mathrm{B}$ overdensity to ${\delta }_{\nu }\sim {10}^{13}$ in configurations achievable by currently planned experimental efforts, and down to ${\delta }_{\nu }\sim {10}^{11}$ in the most optimized scenario. While $\mathrm{C}\nu \mathrm{B}$ detection remains out of reach in the foreseeable future, our results highlight the potential of using quantum sensing to probe fundamental physics.

The fate of the remnant following the merger of two neutron stars initially on quasicircular orbits depends primarily on the mass of the initial neutron stars, the mass ratio, and the still-uncertain dense-matter equation of state (EoS). Previous works studying the threshold mass for prompt collapse to a black hole have primarily focused on the uncertainties in the zero-temperature EoS, which are parametrized by a macroscopic quantity such as the characteristic neutron star radius. However, prompt collapse can take place either with or without a core bounce during the merger. In the bounce-collapse scenario, shocks can produce additional thermal support, potentially altering the threshold for collapse. In this work, we investigate the impact of the uncertainties in the finite-temperature part of the nuclear EoS on the threshold mass for prompt collapse in equal mass mergers. Using two cold EoSs, combined with four parametrizations of the finite-temperature part of the EoS, we find that the threshold mass is insensitive to realistic variations of the thermal prescription, at subpercent accuracy. We report on the thermal properties and ejecta of mergers with masses just above the threshold mass, i.e., which experience a single core-bounce before collapsing. During the bounce, the thermal pressure can reach $\mathcal{O}(1–10)\%$ of the cold pressure at supranuclear densities, depending on the thermal treatment, leading to modest differences in the dynamical ejecta that are launched and in the remnant disk mass as a result.

Ultralight axionlike dark matter (ALDM) is a leading candidate in the dark matter realm, characterized by its prominent wave properties on astronomical scales. Pulsar timing arrays (PTAs) and pulsar polarization arrays (PPAs) aim to detect this dark matter through timing and polarization measurements, respectively, of pulsars. The PTA relies on gravitational effects, as the ALDM halo perturbs the spacetime metric within the Milky Way, while the PPA detects nongravitational effects, namely cosmological birefringence induced by the ALDM Chern-Simons coupling with photons. These two methods complement each other, synergistically enhancing the pulsar array’s capability to identify the ALDM signals in the data. In this article, we provide a foundational development of this synergy. We begin by revisiting previously derived two-point correlation functions for both PTA and PPA, and extend the analysis to include the leading-order correlation between timing and polarization signals, which is encoded as a three-point function. We then explore the constructions of likelihood functions for PTA and combined PTA-PPA analyses within a Bayesian framework, aimed at detecting the characteristic correlations of ALDM signals. We emphasize the non-Gaussianity of the ALDM timing signals, which arises from their nonlinear dependence on the field, in contrast to the Gaussian nature of its polarization signals. To address the complexities introduced, we approach this investigation in two ways: one involves a Gaussian approximation with proper justifications, while the other derives the formalism from the generic Gaussian characteristics of the ALDM field. Particularly, for the combined PTA-PPA case, a clear connection between the three-point correlation function and the likelihood is established. We anticipate that these efforts will lead to further developments in PTA and PTA-PPA analysis methods, better accounting for the influence of non-Gaussianity.

All gravitational-wave signals are inevitably gravitationally lensed by intervening matter as they propagate through the Universe. When a gravitational-wave signal is magnified, it appears to have originated from a closer, more massive system. Thus, high-mass outliers to the gravitational-wave source population are often proposed as natural candidates for strongly lensed events. However, when using a data-driven method for identifying population outliers, we find that high-mass outliers are not necessarily strongly lensed, nor will the majority of strongly lensed signals appear as high-mass outliers. This is both because statistical fluctuations produce a larger effect on observed binary parameters than does lensing magnification, and because lensing-induced outliers must originate from intrinsically high-mass sources, which are rare. Thus, the appearance of a single lensing-induced outlier implies the existence of many other lensed events within the catalog. We additionally show that it is possible to constrain the strong lensing optical depth, which is a fundamental quantity of our Universe, with the detection or absence of high-mass outliers. However, constraints using the latest gravitational-wave catalog are weak—we obtain an upper limit on the optical depth of sources at redshift 1 magnified by a factor of 5 or more of $\tau (\mu \ge 5,z=1)\le 0.035$—and future observing runs will not make an outlier-based method competitive with other probes of the optical depth. However, the full inferred population of compact binaries may be more informative of the distribution of lenses in the Universe, opening a unique opportunity to access the high-redshift Universe and constrain cosmic structures.

We study the circular birefringence experienced by linearly polarized photons colliding with a circularly polarized background creating a vacuum of definite chirality (handedness). For this scenario the standard Heisenberg-Euler approach fails and must be supplemented by derivative corrections which we match to known Hilbert series. Choosing a plane wave background, we find equivalence in the low-energy limit between three approaches: (i) adding derivative corrections to the Heisenberg-Euler Lagrangian, (ii) improving the locally constant field approximation to the one-loop polarization tensor, and (iii) performing a low-energy expansion of the direct $2\to 2$ QED photon-photon scattering amplitude. Going beyond plane-wave backgrounds, we analyze an example of a circularly polarized standing wave sensitive to derivative corrections. We find a parameter regime where these corrections could be probed in experiments.

We investigate the partonic structure of the $\rho$ meson, the lightest spin-1 vector meson, within the light-front quark model (LFQM). To explore the sensitivity to model assumptions, we employ two distinct types of spin wave functions in the LFQM. Using light-front helicity wave functions, we derive explicit expressions for the leading-twist and subleading-twist quark parton distribution functions (PDFs), and evolve the leading-twist PDFs to higher scales with next-to-leading order (NLO) Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution. We have also calculated the Mellin moment from the evolved PDFs using a simple neural network frame and compared with available theoretical predictions. Furthermore, we compute the full set of nine leading-twist transverse-momentum-dependent distributions (TMDs) for the valence quark in the $\rho$ meson, including three tensor TMDs that arise from spin-1 tensor polarization of the hadron. Positivity constraints for the PDFs and TMDs are examined within this framework. Our findings highlight the crucial role of tensor polarization in shaping the three-dimensional partonic structure of vector mesons.

We demonstrate that the weak gravity conjecture (WGC) and the Festina-Lente conjecture (FLC) yield novel bounds on any hypothetical fifth force and millicharged particles (mCPs), as well as on the scale of inflation and on the effective Higgs quartic interaction. In particular, we find that combining the FLC with inflation leads to stronger bounds on mCPs than what the simple application of the FLC provides. Furthermore, we have explored the implications of naturalness on both the FLC and WGC, and have found that these conjectures place a lower limit on the charge of a $U(1)$ gauge group.

In this paper, we propose an approach in high-energy QCD, which allows us to calculate the inclusive quarkonia production at ultrahigh energies. This approach is based on $t$-channel unitarity and on the expressions for dipole densities from the procedure of summing of large Pomeron loops we have developed in our previous papers. In the framework of this approach, we discuss the dependence of quarkonia production on the multiplicity of the accompanying hadrons. In this paper, we used the three gluon- fusion mechanism for quarkonia production, without assuming the multiplicity dependence of the saturation scale. We found the multiplicity distribution of the produced gluon with (${\mathcal{P}}_n^{J/\mathrm{\Psi }}$) and without (${\mathcal{P}}_n^{\text{gluon}}$) the quarkonia production. It turns out that $\frac{{\mathcal{P}}_n^{J/\mathrm{\Psi }}}{{\mathcal{P}}_n^{\text{gluon}}}\propto n^2$, as has been expected and discussed in corresponding publications.