We propose a new method to constrain neutrino charges at neutrino beam experiments. Uncharged in the Standard Model, evidence for a neutrino electric charge would be a smoking gun for new physics, shedding light on the Dirac or Majorana nature of neutrinos, and giving insight into the origin of charge quantization. We find that using the most sensitive magnetometers available, existing beam experiments could constrain neutrino charges $|q_{\nu }|\lesssim {10}^{-13}$, in units of the electron charge, while future upgrades could strengthen these bounds significantly. We also discuss electromagnetic dipole moments and show that our proposal is highly sensitive to new long-range forces.

In this paper, we investigate the $CP$ asymmetries ${\mathcal{A}}_{CP}^{pm}$ and ${\mathcal{A}}_{CP}^{mp}$ in $B_c^{\pm }\to B^{\pm }{K}^0+B^{\pm }{\overline{K}}^0\to B^{\pm }{\pi }^{\pm }{e}^{\mp }{\nu }_e$ and $B_c^{\pm }\to B^{\pm }{K}^0+B^{\pm }{\overline{K}}^0\to B^{\pm }{\pi }^{\mp }{e}^{\pm }{\nu }_e$ decays; both of them consist of three parts: the indirect $CP$ violations in $K^0-{\overline{K}}^0$ mixing $A_{CP,\mathrm{mix}}^{pm}$ and $A_{CP,\mathrm{mix}}^{mp}$, the direct $CP$ violations in $B_c$ decay $A_{CP,\mathrm{dir}}^{pm}$ and $A_{CP,\mathrm{dir}}^{mp}$, and the new $CP$ violation effects $A_{CP,\mathrm{int}}^{pm}$ and $A_{CP,\mathrm{int}}^{mp}$, which originate from the interference between the amplitude of the $B_c^{-}\to B^{-}{K}^0({\overline{K}}^0)\to B^{-}{\pi }^{-}{e}^{+}{\nu }_e({\pi }^{+}{e}^{-}{\overline{\nu }}_e)$ decay with the difference between the oscillating effect of $K^0\to {\overline{K}}^0$ and that of ${\overline{K}}^0\to K^0$. The strong phase differences of the direct $CP$ asymmetries $A_{CP,\mathrm{dir}}^{pm}$ and $A_{CP,\mathrm{dir}}^{mp}$ arise from $K^0-{\overline{K}}^0$ mixing parameters. ${\mathcal{A}}_{CP}^{pm}$ and ${\mathcal{A}}_{CP}^{mp}$ are of the order of $\mathcal{O}({10}^{-4})$ and $\mathcal{O}({10}^{-3})$, respectively. The new $CP$ violation effect ${\mathcal{A}}_{CP,\mathrm{int}}^{pm}$ plays a dominant role in ${\mathcal{A}}_{CP}^{pm}$; the $CP$ asymmetry ${\mathcal{A}}_{CP}^{mp}$ is dominated by the indirect $CP$ violation ${\mathcal{A}}_{CP,\mathrm{mix}}^{mp}$, so the $CP$ asymmetry ${\mathcal{A}}_{CP}^{pm}$ provides an ideal place to study the new $CP$ violation effect. We derive another two asymmetry observables ${\mathcal{A}}_{CP}^{pp}$ and ${\mathcal{A}}_{CP}^{mm}$, which are dominated by $K^0-{\overline{K}}^0$ mixing. The observables ${\mathcal{A}}_{CP}^{pm}$, ${\mathcal{A}}_{CP}^{mp}$, ${\mathcal{A}}_{CP}^{pp}$, and ${\mathcal{A}}_{CP}^{mm}$ are hopefully to be marginally observed at the LHC experiment and the HL-LHC experiment.

In this work, we study the charged-current (anti)neutrino induced associated particle ($K\mathrm{\Lambda }$) production ($\mathrm{\Delta }S=0$) from free nucleons in the energy region of a few GeV, relevant to the (anti)neutrino oscillation experiments with accelerator and atmospheric neutrinos. We employ a model based on effective Lagrangians to evaluate the contributions from the nonresonant and the resonant diagrams. The nonresonant background terms are calculated using a microscopic model derived from the SU(3) chiral Lagrangians. For the resonant contributions, we consider the low-lying spin-$\frac{1}{2}$ resonances, such as $S_{11}(1650)$, $P_{11}(1710)$, $P_{11}(1880)$, and $S_{11}(1895)$, and spin-$\frac{3}{2}$ resonances, such as $P_{13}(1720)$ and $P_{13}(1900)$, which have finite branching ratios to the $K\mathrm{\Lambda }$ channel. These resonant contributions are modeled using an effective phenomenological Lagrangian approach, with strong couplings determined from the experimental branching ratios and the decay widths to the $K\mathrm{\Lambda }$ channel. To fix the parameters of the vector current interaction, the model is first used to reproduce satisfactorily the MAMI@Mainz experimental data on the real photon induced scattering off the nucleon resulting an eta meson in the final state and with the CLAS@JLab data for the $K\mathrm{\Lambda }$ production in the final state. The partial conservation of the axial vector current hypothesis and the generalized Goldberger-Treiman relation are used to fix the parameters of the axial vector interaction. The model is then applied to study the weak production of $K\mathrm{\Lambda }$ induced by the neutrinos and antineutrinos and predicts the numerical values for the $Q^2$ distribution $(\frac{d\sigma }{d{Q}^2})$, the kinetic energy distribution for the outgoing kaon $(\frac{d\sigma }{d{p}_K})$, and the total scattering cross sections ($\sigma$) with and without a cut on the center of mass energy $W$. The results presented in this work are relevant for the present and future accelerator experiments like MicroBooNE, T2K, NOvA, MINERvA, SBND, ICARUS, T2-HyperK, and DUNE as well as for the atmospheric neutrino experiments.

We report a new measurement of flux-integrated differential cross sections for charged-current (CC) muon neutrino interactions with argon nuclei that produce no final-state pions (${\nu }_{\mu }\mathrm{CC}0\pi$). These interactions are of particular importance as a topologically defined signal dominated by quasielasticlike interactions. This measurement was performed with the MicroBooNE liquid argon time projection chamber detector located at the Fermilab Booster Neutrino Beam and uses an exposure of $1.3\times {10}^{21}$ protons on target collected between 2015 and 2020. The results are presented in terms of single- and double-differential cross sections as a function of the final-state muon momentum and angle. The data are compared with widely used neutrino event generators. We find good agreement with the single-differential measurements, while only a subset of generators are also able to adequately describe the data in double-differential distributions. This work facilitates comparison with Cherenkov detector measurements, including those located at the Booster Neutrino Beam.

A search for exotic decays of the Higgs boson $H$ into new scalar or pseudoscalar particles that subsequently decay into $b$-quarks is presented. The search considers $ZH$ production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, $H\to 2a\to 4b$, second to a pair of scalars with different masses ($m_{a1}<m_{a2}$), either directly, $H\to a_1{a}_2\to 4b$, or via a longer decay chain, $H\to a_1{a}_2\to 3a_1\to 6b$. The analysis uses proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of $140{\mathrm{fb}}^{-1}$. No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into $4b$ or $6b$, between 4% and 25% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to 2a\to 4b)$, between 24% and 38% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to a_1{a}_2\to 4b)$, and between 10% and 20% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to a_1{a}_2\to 3a_1\to 6b)$, depending on the masses of the scalar particles.

We study the measurements of a freely falling Unruh-DeWitt particle detector near the horizon of a semiclassical Schwarzschild black hole. Our results show that the detector’s response increases smoothly as it approaches and crosses the horizon in both the Hartle-Hawking and Unruh vacua. However, these measurements are dominated by the effects of switching the detector on and off, rather than by the detection of Hawking radiation particles. We demonstrate that a freely falling Unruh-DeWitt detector cannot directly measure Hawking radiation near the horizon because the time required for thermalization is longer than the time spent near the horizon. We propose an operational definition of the effective temperature along an infalling trajectory based on measurements by a particle detector. Using this method, we find that the effective temperature measured by a freely falling observer in the Hartle-Hawking vacuum increases smoothly from the Hawking temperature far from the horizon to twice the Hawking temperature at the horizon, and continues to rise into the interior of the black hole. This effective temperature closely matches an analytical prediction derived by embedding Schwarzschild spacetime into a higher-dimensional Minkowski space, suggesting that further exploration of higher-dimensional embeddings could provide new insights into the near-horizon behavior of black holes.

Recent studies on extremal black holes within effective field theories (EFT) of gravity have revealed an intriguing phenomenon: tidal forces near the horizon experience significant enhancement due to EFT corrections, potentially leading to a breakdown of the EFT framework. In this work, we investigate this effect in a two-black-hole Majumdar-Papapetrou spacetime modified by four-derivative EFT correction terms. Our analysis shows that while the scaling exponents, which measure the strength of the tidal forces near the horizon, remain unchanged under EFT corrections in $D=4$, they decrease for higher dimensions, enhancing the near-horizon tidal forces. However, even in the presence of EFT corrections, these scaling exponents stay well behaved and no such cases arise where the two-derivative contributions vanish and only the higher-derivative terms contribute. We find an expression for the EFT corrections to the scaling exponents till $D\le 10$ and demonstrate that the metric corrections can be structured such that only the near-horizon ${\mathrm{AdS}}_2$ throat undergoes angle-dependent modifications, while the transverse $S^{D-2}$ sector remains unaffected.

While teleparallel $f(T)$ gravity has shown considerable potential in addressing cosmological tensions, such as the $H_0$ and $S_8$ discrepancies, we explore previously overlooked solution spaces within this framework that hold further promise. Specifically, we examine the case where the customary assumption of a strictly positive effective dark energy (DE) density—natural in general relativity—may not apply, offering new possibilities. Focusing on the exponential infrared model $f(T)=T{e}^{T_{*}/T}$, where $T_{*}$ is a characteristic torsion scale, we investigate cosmological solutions parametrized by the dimensionless parameter $\beta =T_{*}/T_0$ with $T_0$ the present-day torsion scalar. This parameter uniquely determines the present-day matter density parameter ${\mathrm{\Omega }}_{\mathrm{m}0}$, and its sign plays a crucial role in characterizing deviations from the standard $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) expansion history. We elaborate on the structural asymmetry between the positive- and negative-$\beta$ branches: while the positive branch (${\beta }_{+}$) leads to dynamics with modest departures from $\mathrm{\Lambda }\mathrm{CDM}$, the negative branch (${\beta }_{-}$) yields more pronounced and nontrivial deviations at cosmological scales. We discuss that, despite these deviations, the negative-$\beta$ branch can remain consistent with local gravity constraints through an effective chameleonlike mechanism—wherein high-density environments naturally suppress deviations from the teleparallel equivalent of general relativity. We extend our analysis by examining the model in the context of dynamical DE. Ensuring consistency with cosmic microwave background (CMB) data, we find that the widely studied ${\beta }_{+}$ case exhibits phantom behavior, while the previously overlooked ${\beta }_{-}$ case—sufficient to avoid instabilities or ghosts—features a sign-changing DE density that transitions smoothly from negative to positive values at redshift $z_{†}\sim 1.5$, consistent with recent approaches to alleviating multiple cosmological tensions. Though the sign-changing DE density in the $f(T)$ model leads to a larger-than-expected enhancement, we further extend the analysis by incorporating a cosmological constant, $\mathrm{\Lambda }$. This extension, $f(T)\to f(T)+2\mathrm{\Lambda }$, broadens the solution space consistent with the SH0ES $H_0$ measurement while maintaining consistency with CMB power spectra. Additionally, it introduces richer phenomenological possibilities, including the potential moderation or cessation of cosmic acceleration at very low redshifts, aligning with recent observational analyses, such as those from DESI BAO data. Our findings also suggest that existing $f(T)$ models, as well as background-equivalent $f(Q)$ models, should be revisited in light of the novel theoretical insights presented here.

Inspired by the amplitude bootstrap program, the spirit of this work is to constrain the space of consistent inflationary correlation functions—specifically, the bispectrum of curvature perturbations—using fundamental principles such as unitarity, locality, analyticity, and symmetries. To this end, we assume a setup for inflation in which de Sitter isometries are only mildly broken by the slow roll of the inflaton field, and study the bispectrum imprinted by a generic hidden sector during inflation. Assuming that the hidden sector’s contributions to primordial non-Gaussianity are dominated by the exchange of a scalar operator (which does not preclude high-spin UV completions), we derive nontrivial positivity constraints on the resulting bispectrum $B(k_1,k_2,k_3)$. In particular, we show that $B$ must be negative in a certain region around the equilateral configuration. For instance, for isosceles triangles (with $k_2=k_3$) this region is given by $0.027\lesssim k_3/k_1\le 2$. Furthermore, we demonstrate that unitarity imposes upper and lower bounds on the bispectrum shape, thereby carving out a bispectrum island where consistent shapes in our setup can reside. We complement our analysis by contemplating alternative setups where the coupling to the hidden sector is allowed to strongly break de Sitter boosts. We also identify situations that would push the bispectrum off the island and the profound physical features they would reveal.

A fast-rolling axion can transfer its kinetic energy to a gauge field via the Chern-Simons coupling, leading to copious production of gauge quanta, which can act as a source of gravitational waves (GWs) with potentially observable amplitudes. In this work, we investigate GW production in a spectator axion model when strong backreaction is taken into account. We find that decreasing the decay constant of the axion enhances GW production. Since the initial value of the axion is larger than its quantum fluctuations, such a condition imposes a lower bound on the axion dacay constant, which sets an upper bound on the amplitude of the energy spectrum of GWs. As a result, the amplitude of the predicted GW energy spectrum is lower than ${10}^{-10}$ in the nHz to mHz frequency range.

The quantum gravity scale within the dark dimension scenario ($M_{*}\sim {10}^9\mathrm{GeV}$) roughly coincides with the energy scale of the KM3-230213A neutrino ($E_{\nu }\sim {10}^8\mathrm{GeV}$). We propose an interpretation for this intriguing coincidence in terms of Hawking evaporation of five-dimensional (5D) primordial black holes (PBHs). 5D PBHs are bigger, colder, and longer-lived than 4D PBHs of the same mass. For brane observers, PBHs residing in the higher-dimensional bulk decay essentially invisibly (only through gravitationally and sterile coupled modes). As a consequence, constraints on the density of PBHs relative to that of dark matter from null searches of Hawking evaporation can be avoided. We demonstrate that Hawking evaporation of 5D bulk PBHs can explain the KM3-230213A neutrino, evade constraints from upper limits on the gamma-ray flux, and remain consistent with IceCube upper limits on the partial decay width of superheavy dark matter particles into neutrinos.

Recent observations of cosmic rays increasingly point to the existence of nearby sources $-$ so-called “local tevatrons”, capable of accelerating particles to TeV energies. In this study, we examine the potential of a typical main-sequence star, represented by the Sun, to act as a source of TeV cosmic rays. We focus on identifying plausible mechanisms through which a quiescent star can accelerate charged particles to relativistic energies. We show that shock-drift acceleration processes operating within the chromospheres of the Sun and similar stars can accelerate particles to energies reaching the TeV scale. Additionally, we provide quantitative estimates of both the maximum achievable particle energies, spectral index of energy spectrum and the resulting cosmic-ray fluxes that such stellar environments could realistically produce. Our results indicate that ordinary stars could potentially contribute to the fine structure observed in the cosmic-ray spectrum at TeV energies and may help explain the local excess of TeV-scale electrons and positrons detected by H. E. S. S. and other observatories.

We study and classify $SU(5)$-grand unified theory (GUT) completions of accidental composite dark matter models. These theories postulate new vectorlike confining dark color dynamics and give an accidentally stable baryonic dark matter candidate. In realistic theories, dark fermion $SU(5)$ irreps split into light dark quarks, whose bound states include the dark matter, and their much heavier GUT partners. A simple analysis shows that such a mass hierarchy requires a fine-tuning of parameters and thus implies a naturalness problem. We select theories requiring that all dangerous metastable states decay before the onset of nucleosynthesis through higher-dimensional operators generated at the GUT scale or at the mass scale of dark quark GUT partners. Demanding Standard Model gauge coupling unification puts severe constraints on the landscape of viable theories. Under the assumption of an approximately degenerate spectrum of dark quark GUT partners, we find that only one model gives precision unification.

We report on the computation of amplitudes describing the radiative decay processes $J/\psi \to \gamma \eta$ and $J/\psi \to \gamma {\eta }^{\prime }$ from first principles via lattice quantum chromodynamics (QCD). Using lattices with two heavier than physical degenerate flavors of light quark where $m_{\pi }\sim 391\mathrm{MeV}$, and a strange quark tuned to approximately the physical value, we compute three-point correlation functions using optimized meson operators with a range of momenta. The use of optimized operators allows access to the ${\eta }^{\prime }$, even though it appears as an excited state, lying above the ground-state $\eta$ in the isoscalar pseudoscalar channel. Statistically precise signals are obtained in this disconnected process by averaging over large numbers of kinematically equivalent correlators. We determine transition form factors as a function of photon virtuality across the timelike region, which describe also the Dalitz processes $J/\psi \to e^{+}{e}^{-}{\eta }^{(\prime )}$. Significantly lower magnitudes of transition form factor for both the $\eta$ and ${\eta }^{\prime }$ are found than those extracted from experimental data, and possible explanations for this observation are presented.

In this work, we investigate the scaling behavior of the entropy associated with the charged hadron multiplicity distribution $P(N)$ in proton-proton collisions at the LHC. We show that the growth of this entropic indicator as a function of the Bjorken-$x$ variable exhibits universal behavior, consistent with observations from deep inelastic scattering. This universality suggests that the entropy scaling is a property of the initial state and reflects the diffusive nature of gluon dynamics at small $x$. Furthermore, we demonstrate that high-multiplicity events are not accurately described by traditional Koba-Nielsen-Olesen scaling and require a more precise description based on a diffusion scaling framework. This new scaling emerges naturally from the universal growth of partonic entropy and offers deeper insight into the dynamics of particle production in high-energy hadronic collisions.

We construct an analytic, string-based representation of the nucleon’s axial and helicity-flip conformal moments of generalized parton distributions (GPDs) that holds for any skewness and for both the quark and gluon channels. The starting point is the Mellin-Barnes resummation of the conformal partial-wave expansion, where the moments are parametrized by open- (Reggeon) and closed-string (Pomeron) trajectories with slopes determined by experimental form factors and meson/glueball spectroscopy. The forward limits are fixed by the empirical unpolarized and polarized parton distributions. Polynomiality, crossing symmetry, and support are satisfied by construction. After next-to-leading order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi/Efremov-Radyushkin-Brodsky-Lepage evolution to $\mu =2\mathrm{GeV}$ our analytic framework (i) reproduces some of the currently available lattice moments of $\mathbb{E}$ and $\tilde{\mathbb{H}}$ in the nonsinglet sector, (ii) predicts sea-quark and gluon polarized moments that will be testable by forthcoming simulations and experiments at Jefferson Lab and the future Electron-Ion Collider, and (iii) yields axial and helicity-flip GPDs in $x$-space in reasonable agreement with lattice QCD.

Substantial contribution of the tensor current in semileptonic decays is regarded as a clear signal for new physics. In this work, we propose a model-independent approach to unambiguously test contribution of the tensor current in semileptonic five-body decays ${\overline{D}}_{(s)}/{\overline{B}}_{(s)}\to V\ell {\overline{\nu }}_{\ell }(\ell =e,\mu ,\tau )$ with $V\to {\pi }^0{\pi }^{+}{\pi }^{-}$, where $V$ denotes vector particles. We derive three parameters associated with the angular asymmetry, which are always equal to one in the Standard Model regardless the data of form factor but will deviate if contribution of the tensor current does not vanish. The outcomes have potential applications in precisely testing the Standard Model and searching for new physics. Relevant measurements can be performed using data collected by BESIII, Belle II, and LHCb.

In this paper we discuss and revisit the finite temperature extension of the renormalization group (RG) treatment of $T=0$ field theories, focusing as a case study on the ${\varphi }^4$ model. We first discuss the extension of RG equations of the very same model from $T=0$ to finite $T$ in the usual way by resorting to sums on the Matsubara frequencies and fixing the physical temperature parameter $T$. We show that this approach, although useful for a variety of applications, may lead to the disappearance of the critical points as extracted from the RG flow. Since the identification of fixed points is key in the study of classical and quantum phase transitions, we propose a modification of the usual finite-temperature RG approach by relating the temperature parameter to the running RG scale, $T\equiv k_T=\tau k$, where $k_T$ is the running cutoff for thermal and $k$ is for the quantum fluctuations. Once this dimensionless temperature $\tau$ is introduced, we investigate the consequences on the thermal RG approach for the ${\varphi }^4$ model and construct its phase diagram. Finally, we formulate requirements for the phase diagram of the ${\varphi }^4$ theory based on known properties of the quantum and classical phase diagrams of the Ising model.

Perturbation theory is used to investigate the evolution of the von Neumann entropy of a subsystem of a bipartite quantum system under the action of a unitary matrix, in the limit where that matrix is close to the unit matrix. The physical context for such a process would be scattering with weak short-ranged interactions where the unitary matrix is the $S$ matrix. We find surprisingly simple criteria for the initial state and the $S$ matrix that guarantee that the subsystem entropy increases. The class of initial states that meet these criteria are more correlated than simple product states of the subsystems. They form a subclass of the set of all separable states, and they can therefore be assembled by classical processes alone.