We revisit the production of axionlike particles (ALPs) coupled to electrons at tree level in a relativistic plasma. We explicitly demonstrate the equivalence between pseudoscalar and derivative couplings, incorporate previously neglected processes for the first time—namely, semi-Compton production ($\gamma e^{-}\to a{e}^{-}$) and pair annihilation ($e^{+}{e}^{-}\to a\gamma$)—and derive analytical expressions for the bremsstrahlung ($e^{-}N\to e^{-}Na$) production rate, enabling a more computationally efficient evaluation of the ALP flux. Additionally, we assess uncertainties in the production rate arising from electron thermal mass corrections, electron-electron Coulomb interactions, and the Landau-Pomeranchuk-Migdal effect. The ALP emissivity is made available in a public repository as a function of the ALP mass, the temperature, and the electron chemical potential of the plasma. Finally, we examine the impact of ALP production and subsequent decays on astrophysical observables, deriving the leading bounds on ALPs coupling to electrons. At small couplings, the dominant constraints come from the previously neglected decay $a\to e^{+}{e}^{-}\gamma$, except for a region of fireball formation where SN 1987A x-ray observations offer the best probe. At large couplings, bounds are dominated by the energy deposition argument, with a recently developed new prescription for the trapping regime.

At third-generation (3G) gravitational-wave detector networks, compact binaries coalescences produce a “confusion noise” due to unresolved sources and to the error in the reconstruction of resolved sources, that can degrade the sensitivity to cosmological backgrounds. We show how to characterize from first-principles this astrophysical confusion noise by reconstructing the resolved sources at a detector network, subtracting them from the data stream of each detector of the network, and then computing the correlation among detector pairs of these “partially cleaned” data streams that, beside instrumental noise, contain the unresolved sources and the error on the resolved sources. In a two-detector correlation, this residual astrophysical background then acts as an effective correlated noise. We point out that its effect, in the search for a cosmological background, must be evaluated by correlating two detectors with the filter function that optimizes the given cosmological search (and not the search for the astrophysical background itself) and therefore depends on the specific cosmological signal that we want to extract from the data. We show how to obtain search-independent upper bounds on the effect of this astrophysical confusion noise, and how to characterize its actual effect on a given cosmological search. We then apply this methodology to an example of a 3G network and, for a realistic population of mergers, we evaluate explicitly the upper bound on the effect of the astrophysical confusion noise, as well as its actual effect in the search of selected examples of power-law cosmological backgrounds and of backgrounds featuring broad peaks, as in phase transitions.

The study of collinear behavior for gauge theories in the spacelike region is of great phenomenological and theoretical importance. We analytically calculate the two-loop spacelike splitting amplitude for the full color $\mathcal{N}=4$ super-Yang-Mills theory. The result is derived by two complementary methods starting from the known amplitude: one is based on a discontinuity analysis, while the other one is based on calculating Feynman integrals analytically in the collinear limit. Our result explicitly shows terms that violate naive factorization. However we show that factorization is restored at the level of color-summed unpolarized squared amplitudes at next-to-next-to-next-to leading order. We conjecture that the two-loop tripole terms in the generalized splitting amplitudes in quantum chromodynamics are identical to what we obtain in $\mathcal{N}=4$ super Yang-Mills theory.

One of the simplest standard model extensions leading to a domain wall network is a real scalar $S$ with a ${\mathcal{Z}}_2$ symmetry spontaneously broken during universe evolution. Motivated by the swampland program, we explore the possibility that quantum gravity effects are responsible for violation of the discrete symmetry, triggering the annihilation of the domain wall network. We explore the resulting cosmological implications in terms of dark radiation, dark matter, gravitational waves, primordial black holes, and wormholes connected to baby universes.

Motivated by recent anomalies in observables associated with flavor-changing neutral current transitions, specifically $b\to s{\ell }^{+}{\ell }^{-}$ processes, we present a comprehensive analysis of lepton flavor-violating (LFV) decay modes mediated by $b\to s{\ell }_1{\ell }_2$ transitions with ${\ell }_1\ne {\ell }_2$. While such LFV processes are forbidden within the standard model, they naturally arise in several of its extensions, including models featuring additional vectorlike fermions and extra $Z^{\prime }$ bosons. Employing the most general effective Hamiltonian for $b\to s{\ell }_1{\ell }_2$ transitions, we derive the angular distributions of the relevant decay modes. Adopting a model-independent framework, we systematically study the LFV decays $B\to K^{*}{\ell }_1{\ell }_2$, $B_s\to \varphi {\ell }_1{\ell }_2$, $B\to K_2^{*}{\ell }_1{\ell }_2$, and ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{\ell }_1{\ell }_2$. Although LFV mesonic decays have been widely explored, the corresponding baryonic decays remain comparatively underinvestigated. We provide bounds on the branching ratio ($\mathcal{B}$), forward-backward asymmetry (${\mathcal{A}}_{FB}$), and longitudinal lepton polarization fraction (${\mathcal{F}}_L$). Furthermore, considering the projected sensitivities of the LHCb upgrade and Belle II experiments, we estimate upper limits for these observables, offering promising avenues for probing new physics in these LFV channels.

We construct a model of quark and lepton compositeness based on an $SU(15)$ gauge interaction that confines chiral preons, which are also charged under the weakly coupled $SU(4{)}_{\mathrm{PS}}\times SU(2{)}_L\times SU(2{)}_R$ gauge group. The breaking of the latter, down to the Standard Model group, is achieved by scalar $SU(15)$ bound states at a scale in the 30–100 TeV range. The embedding of the QCD gauge group in $SU(4{)}_{\mathrm{PS}}$ slows down the running of ${\alpha }_s$ in the UV. We estimate the effects of the strongly coupled $SU(15)$ dynamics on the running of the $SU(4{)}_{\mathrm{PS}}\times SU(2{)}_L\times SU(2{)}_R$ gauge couplings, which likely remain perturbative beyond the compositeness scale of about ${10}^3–{10}^4\mathrm{TeV}$, and even above a unification scale. A composite vectorlike lepton doublet acquires a mass in the TeV range probed at future colliders, and an extended Higgs sector arises from six-preon bound states.

In this work, we systematically investigate the mass spectra of fully heavy pentaquark states $QQQQ\overline{Q}$ within the framework of QCD sum rules. Employing three configurations of interpolating currents, we obtain the following mass predictions: for the $cccc\overline{c}$ states, the masses are determined to be ${7.79}_{-0.17}^{+0.18}\mathrm{GeV}$, ${7.76}_{-0.18}^{+0.23}\mathrm{GeV}$, ${7.81}_{-0.18}^{+0.17}\mathrm{GeV}$, while for the $bbbb\overline{b}$ states, the corresponding masses are calculated as $22.35\pm 0.19\mathrm{GeV}$, $22.27\pm 0.22\mathrm{GeV}$, ${22.37}_{-0.20}^{+0.18}\mathrm{GeV}$, respectively.

Recently, the new structure $G(3900)$ observed by the BESIII Collaboration in the $e^{+}{e}^{-}\to D\overline{D}$ was identified to be the $P$-wave $D{\overline{D}}^{*}/\overline{D}{D}^{*}$ vector molecular resonance using a unified meson exchange model. Apart from the vector $P$-wave state, a possible pseudoscalar $P$-wave molecular state of the $D{\overline{D}}^{*}/\overline{D}{D}^{*}$ [called $G_0(3900)$ for short] was also predicted, which is likely to be observed in future experiments. Within the molecular framework, we calculated the partial decay widths for a series of hadronic decays of the $G_0$, including $G_0\to \omega ({\rho }^0)J/\psi$, ${\pi }^{+}{\pi }^{-}{\eta }_c(1S)$, ${\pi }^{+}{\pi }^{-}{\chi }_{c1}(1P)$, and $D^0{\overline{D}}^0{\pi }^0$. Under present model parameters, the hidden-charm decay modes are dominated by the $G_0\to \omega J/\psi$ and $G_0\to {\pi }^{+}{\pi }^{-}{\eta }_c(1S)$, and the partial widths can reach 1 MeV and 0.1 MeV, respectively. The open-charm channel $G_0\to D^0{\overline{D}}^0{\pi }^0$ exhibits a rather small decay rate ($\sim 0.1\mathrm{keV}$). In terms of our present predictions, we suggest BESIII and Belle II to search for the pseudoscalar $P$-wave $D{\overline{D}}^{*}/\overline{D}{D}^{*}$ molecular state with $J^{PC}=0^{-+}$ in the hidden-charm processes $G_0\to \omega J/\psi$ or $G_0\to {\pi }^{+}{\pi }^{-}{\eta }_c(1S)$.

We present a measurement of the branching fraction of $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ decays using $387\pm 6\times {10}^6$ $\mathrm{\Upsilon }(4S)$ collected between 2019 and 2022 with the Belle II detector at the SuperKEKB $e^{+}{e}^{-}$ collider. We reconstruct the accompanying $B^{-}$ meson using the hadronic tagging method, while $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ candidates are identified in the recoil. We find evidence for $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B^{+}\to {\tau }^{+}{\nu }_{\tau })=[1.24\pm 0.41(\mathrm{stat})\pm 0.19(\mathrm{syst})]\times {10}^{-4}$.

The lattice dynamics following particle interactions remain not fully understood, and effects from nuclear-recoil interactions in conventional solid-state detectors—such as defect formation—can hinder accurate event-energy interpretation. Neutron capture $(n,\gamma )$ can produce detectable, precise-energy nuclear recoils for detector calibration and solid-state physics studies. This paper proposes a first-of-its-kind experiment to measure the twin products of neutron capture—the postcapture deexcitation gamma and postcapture nuclear recoil. Simulations show that with a 1 mCi californium neutron source, a positive measurement with existing detector technologies is possible in 26.1 gram-days of exposure.

Inspired by the Kovtun-Son-Starinet bound, we propose that holography imposes a lower bound on the Casimir effect. For simplicity, we focus on the Casimir effect between parallel planes for three-dimensional conformal field theories and briefly comment on the generalizations to other boundary shapes and higher dimensions. Remarkably, the ghost-free holographic models impose a universal lower bound on the Casimir effect. We verify the holographic bound by free theories, the Ising model, and $O(N)$ models with $N=2$, 3 at critical points and prove it for the two-dimensional case. Remarkably, a general class of quantum field theories without conformal symmetries also obeys the holographic bound.

The quarkonium production in association with a heavy-quark pair of the same flavor was found to play an important role in various production schemes and provide a distinctive signature that could be studied in experiment. Within the nonrelativistic QCD framework, we perform the first complete calculation of the hadroproduction process $gg\to J/\psi +c\overline{c}$ at the next-to-leading order (NLO) in the expansion of strong coupling constant ${\alpha }_s$. The result tells us that the NLO corrections substantially enhance the color-singlet yield and alter the predicted polarization patterns and, hence, lead to a better agreement with experimental data across the $p_T$ spectrum. In contrast to charm-quark fragmentation, the fixed-order $J/\psi$ and $c\overline{c}$ associated production channel displays a markedly different kinematic behavior. While the inclusion of this process greatly reduces the discrepancy between color-singlet theoretical prediction and experimental measurement, a residual gap of approximately 1 order of magnitude still remains.

Spin foams arose as the covariant (path integral) formulation of quantum gravity depicting transition amplitudes between different quantum geometry states. As such, they provide a scheme to study the no-boundary proposal, specifically the nothing to something transition, and compute relevant observables using high-performance computing. Following recent advances, where stochastic algorithms (Markov chain Monte Carlo) were used, we employ “generative flow networks,” a newly developed machine-learning algorithm to compute the expectation value of the dihedral angle for a 4-simplex and compare the results with previous works.

We consider the motion of a particle in the background of a stationary axially symmetric generic black hole. A particle experiences the action of a force of unspecified nature. We require the force to remain finite in a comoving frame. The result is expressed in terms of several integers characterizing the Taylor expansion of the metric coefficients near the horizon. We show that the polar component of the four-velocity remains finite. As a result, the scenarios of high energy particle collisions, found previously in the context of the BSW effect for equatorial motion, do not change qualitatively in the nonequatorial case. The fact that the polar component is finite, also enables us to fill some gaps in the description of the BSW effect in previous works. This includes (i) classification of particle trajectories for nonequatorial motion, (ii) more coherent derivation of kinematics of the BSW effect, and (iii) discussion of bands in which the BSW effect takes place. Our results have a quite general character and can be used not only in description of high energy particle collisions but also in diverse astrophysical problems for which motion is not constrained by the equatorial plane.

We investigate nonphantom tracker scalar field models as a dynamical dark energy scenario. These models can alleviate the cosmic coincidence problem and transition to a cosmological constantlike behavior at late times. Focusing on the inverse axionlike and inverse steep exponential potentials, we study their background evolution and perturbations, finding a mild suppression in the matter power spectrum compared to $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) but no distinguishing features in the bispectrum. Using combined datasets of $\mathrm{CMB}+\mathrm{BAO}$ (DESI DR1 & DR2) + Pantheon $\mathrm{Plus}+\mathrm{Hubble}$ $\mathrm{parameter}+\mathrm{RSD}$, we perform a statistical comparison based on the Akaike Information Criterion and the Bayesian Information Criterion. Our results indicate that, within the framework of nonphantom tracker models, the data show no evidence for dynamical dark energy. The $\mathrm{\Lambda }\mathrm{CDM}$ model continues to provide a better fit to current observations in the nonphantom regime. We emphasize, however, that our analysis does not rule out the possibility of phantom-crossing dark energy models, which have been found in other studies to provide a better fit to some datasets.

Motivated by recent discoveries of X-ray quasiperiodic eruptions, we revisit the collision of a black hole and an accretion disk. Assuming that they are orbiting a supermassive black hole in orthogonal orbits, we perform a general relativistic simulation of the collision, varying the relative velocity $V_0$ from $0.032c$ to $0.2c$ (where $c$ is the speed of light) with a variety of disk thickness and a realistic local density profile for the disk. Our findings indicate that the mass of the outflow matter from the disk, $m_{\mathrm{ej}}$, is slightly less than the expected value. Meanwhile, the typical energy associated with this outflow $E_{\mathrm{ej}}$ is $\sim m_{\mathrm{ej}}{V}_0^2$. Thus, the predicted peak luminosity from disk flares is approximately equal to the Eddington luminosity of the black hole, whereas the peak time and duration of the flares, which are $\propto m_{\mathrm{ej}}^{1/2}$, are shorter than that previously believed. We also demonstrate that the property of the outflow matter induced by the incoming and outgoing stages of the black hole collision is appreciably different. We find that a high mass accretion rate onto the black hole from the disk persists for a timescale of $\sim {10}^6$ Schwarzschild time of the black hole after the collision for $V_0/c\lesssim 0.1$, making this long-term accretion onto the black hole the dominant emission process for black hole-disk collision events. Implications of these results are discussed.

Direct searches for sub-GeV dark matter are limited by the intrinsic quantum properties of the target material. In this proof-of-concept study, we argue that this problem is particularly well suited for machine learning. We demonstrate that a simple neural architecture consisting of a variational autoencoder and a multilayer perceptron can efficiently generate unique molecules with desired properties. In specific, the energy threshold and signal (quantum) efficiency determine the minimum mass and cross section to which a detector can be sensitive. Organic molecules present a particularly interesting class of materials with intrinsically anisotropic electronic responses and $\mathcal{O}(\mathrm{few})\mathrm{eV}$ excitation energies. However, the space of possible organic compounds is intractably large, which makes traditional database screening challenging. We adopt excitation energies and proxy transition matrix elements as target properties learned by our network. Our model is able to generate molecules that are not in even the most expansive quantum chemistry databases and predict their relevant properties for high-throughput and efficient screening. Following a massive generation of novel molecules, we use clustering analysis to identify some of the most promising molecular structures that optimize the desired molecular properties for dark matter detection.

Matched filtering is a common method for detecting gravitational waves. However, the computational costs of searching large template banks limit the efficiency of classical algorithms when searching for massive black hole binary (MBHB) systems. This work explores the application of a quantum matched filtering algorithm based on Grover’s algorithm to MBHB signals. Under certain simplifying assumptions, the quantum approach can reduce the computational complexity from $O(N)$ to $O(\sqrt{N})$ theoretically, where $N$ is the size of the template bank. Simulated results illustrate the potential reduction in computational costs, while also showing that the performance can degrade in some cases due to instability of the algorithm. These findings reveal both the potential and the limitations of quantum search for MBHB signals, pointing to the importance of developing more robust and stable search strategies alongside realistic modeling in future work.

Core collapse, a process associated with self-interacting dark matter (SIDM) models, can increase the central density of halos by orders of magnitude with observable consequences for dwarf galaxy properties and gravitational lensing. Resonances in the self-interaction cross section, features of hidden-sector models with light mediators and attractive potentials, can boost the strength of self-interactions near specific relative velocities, accelerating collapse in halos with central velocity dispersions near the resonance. To explore this phenomenon, we present a suite of idealized $N$-body simulations of isolated halos with masses ${10}^7–{10}^9{M}_{\odot }$ evolved under two resonant cross section (RCS) models with localized enhancements to the cross section on scales $v\sim 5–50\mathrm{km}{\mathrm{s}}^{-1}$. We show that the change in halo internal structure depends on how the velocity distribution of bound particles moves across resonances in the cross section during core formation and collapse. The interplay between the velocity distribution of bound particles and localized features of the cross section causes deviations from self-similar evolution, a characteristic of velocity-independent cross sections, at the level of up to 20%. Depending on the alignment with resonant features, halos of different masses reach different evolutionary stages after a fixed physical time and develop diverse density profiles and rotation curves.