We investigate the quark-level effective operators related to the neutrinoless double beta $(0\nu \beta \beta )$ decay process and their ultraviolet completions relevant to chiral enhancement effects at the hadronic level. We have classified several kinds of leptoquark models, matching to different standard model effective operators. Assuming weakly coupled new physics, we find the ongoing $0\nu \beta \beta$ decay experiments are sensitive to new physics scale at around 2–4 TeV, which is in the reach of LHC searches. We discuss the discovery potential of such resonances in the same-sign dilepton channels at the LHC. Therefore, the direct LHC searches and indirect $0\nu \beta \beta$ decay searches are complementary to each other in testing the UV completions of the effective operators for $0\nu \beta \beta$ decay.

The neutrino magnetic moment operator clasps a tiny but nonzero value within the standard model (SM) of particle physics and rather enhanced values in various new physics models. This generation of the magnetic moment (${\mu }_{\nu }$) is through quantum loop corrections which can exhibit spin-flavor oscillations in the presence of an external magnetic field. Also, several studies predict the existence of a primordial magnetic field (PMF) in the early Universe, extending back to the era of Big Bang nucleosynthesis (BBN) and before. The recent North American Nanohertz Observatory for Gravitational Waves measurement can be considered as a strong indication of the presence of these PMFs. In this work, we consider the effect of the PMF on the flux of relic neutrinos. For Dirac neutrinos, we show that half of the active relic neutrinos can become sterile due to spin-flavor oscillations well before becoming nonrelativistic owing to the expansion of the Universe and also before the timeline of the formation of galaxies and hence intergalactic fields, subject to the constraints on the combined value of ${\mu }_{\nu }$ and the cosmic magnetic field at the time of neutrino decoupling. For the upper limit of PMF allowed by the BBN, this can be true even if the experimental bounds on ${\mu }_{\nu }$ approach a few times its SM value.

Inspired by the detection of $T_{cc}$ tetraquark state by LHCb Collaboration, we perform a systemical investigation of the low-lying doubly heavy charm tetraquark states with strangeness in the quark delocalization color screening model in the present work. Two kinds of configurations, the meson-meson configuration and diquark-antidiquark configuration, are considered in the calculation. Our estimations indicate that the coupled channel effects play important role in the multiquark system, and a bound state with $J^P=1^{+}$ and a resonance state with $J^P=0^{+}$ have been predicted. The mass of the bound state is evaluated to be (3971–3975) MeV, while the mass and width of the resonance are determined to be (4113–4114) MeV and (14.3–16.1) MeV, respectively.

The upper limit of the branching ratio of the rare ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma$ decay is obtained as $\mathrm{BR}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma )<1.3\times {10}^{-4}$ by the LHCb. In the present work we study this decay within the light cone QCD sum rules employing the ${\mathrm{\Xi }}_b$ distribution amplitudes. At the first stage, the form factors entering the ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma$ decay are obtained. Next, using the results for the form factors the corresponding branching ratio for this decay is estimated to be $\mathrm{BR}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma )=(4.8\pm 1.3)\times {10}^{-5}$. This value lies below the upper limit established by the LHCb collaboration. Our finding for the branching ratio is also compared with the results of the other theoretical approaches existing in the literature.

A study is presented of the impact of updated simulated inclusive electron ion collider deep inelastic scattering data on the determination of the proton and nuclear parton distribution functions (PDFs) at next-to-next-to-leading and next-to-leading order in QCD, respectively. The influence on the proton PDFs is evaluated relative to the HERAPDF2.0 set, which uses inclusive HERA data only, and also relative to the global fitting approach of the MSHT20 PDFs. The impact on nuclear PDFs is assessed relative to the EPPS21 global fit and is presented in terms of nuclear modification ratios. For all cases studied, significant improvements in the PDF uncertainties are observed for several parton species. The most striking impact occurs for the nuclear PDFs in general and for the region of high Bjorken $x$ in the proton PDFs, particularly for the valence quark distributions.

We apply Bayesian inference to determine the posterior likelihood distribution for the parameters describing the initial condition of the small-$x$ Balitsky-Kovchegov evolution equation at leading logarithmic accuracy. The HERA structure function data is found to constrain most of the model parameters well. In particular, we find that the HERA data prefers an anomalous dimension $\gamma \approx 1$ unlike in previous fits where $\gamma >1$ which led to, e.g., the unintegrated gluon distribution and the quark-target cross sections not being positive definite. The determined posterior distribution can be used to propagate the uncertainties in the nonperturbative initial condition when calculating any other observable in the color glass condensate framework. We demonstrate this explicitly for the inclusive quark production cross section in proton-proton collisions and by calculating predictions for the nuclear modification factor for the $F_2$ structure function in the EIC and LHeC/FCC-he kinematics.

We calculate the matching, at leading order, of the transverse momentum-dependent fragmentation functions (TMDFFs) for light quarks and gluons fragmenting to a $J/\psi$ onto polarized nonrelativistic QCD (NRQCD) TMDFFs. The NRQCD TMDFFs have an operator product expansion in terms of nonperturbative NRQCD production matrix elements. Using the results we obtain, we make predictions for the light quark fragmentation contribution to the production of polarized $J/\psi$ in semi-inclusive deep inelastic scattering (SIDIS) both for unpolarized and longitudinally polarized beams. These results are an important contribution to polarized $J/\psi$ production in SIDIS and thus are needed for comparison with experiments at the future Electron-Ion Collider.

${T_{cc}(cc\overline{u}\overline{d})}^{+}$ has been reported by the LHCb experiment in 2022. The analysis using the Breit-Wigner parametrization found the small binding energy, 0.273 MeV, which is measured from the threshold of $D^{*+}{D}^0$. In this paper, we consider $T_{cc}$ as a $D{D}^{*}$ hadronic molecule as a deuteronlike state. The one-boson exchange model is employed as for the heavy meson interactions, where we determine the cutoff parameter $\mathrm{\Lambda }$ to reproduce the reported binding energy of $T_{cc}$ with $I(J^P)=0(1^{+})$. We discuss the properties of the bound state and also search for $T_{cc}$ with quantum numbers other than $0(1^{+})$. Furthermore, we analyze $T_{bb}$ as a bottom counterpart of $T_{cc}$, which involves two bottom quarks, and obtain several bound states. Finally, we consider the light-cloud basis for wave functions of the doubly heavy tetraquarks in the heavy quark limit. Using the basis, we find the spin multiplets of their bound states, indicating the spin structures of diquarks in $T_{cc}$ and $T_{bb}$ with the finite quark masses.

Quantum properties of the state associated to the gluon Green’s function in the Balitsky-Fadin-Kuraev-Lipatov approach are studied using a discretization in virtuality space. Considering the coupling constant as imaginary, its density matrix corresponds to a pure state for any energy. Nonlinear corrections due to high gluon densities are modeled through a suppression of infrared modes in the Hamiltonian making it no longer Hermitian. This introduces quantum decoherence into the evolution equation. When the coupling is real this leads to unbounded normalization of states which becomes bounded for sufficient saturation of infrared modes. Physical quantum properties, such as a purity smaller than one or a positive von Neumann entropy, hence are recovered when the infrared/ultraviolet original symmetry of the formalism is broken. Similarly to the work of Armesto, Domínguez, Kovner, Lublinsky and Skokov in [J. High Energy Phys. 05 (2019) 025], an evolution equation of Lindblad type for the normalized density matrix describing the open system is obtained.

We study the mass spectrum of light pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\overrightarrow{B}$, considering the effects of the mixing with the axial-vector meson sector. The analysis is performed within a two-flavor NJL-like model which includes isoscalar and isovector couplings together with a flavor mixing ’t Hooft-like term. The effect of the magnetic field on charged particles is taken into account by retaining the Schwinger phases carried by quark propagators, and expanding the corresponding meson fields in proper Ritus-like bases. The spin-isospin and spin-flavor decomposition of meson mass states is also analyzed. For neutral pion masses it is shown that the mixing with axial vector mesons improves previous theoretical results, leading to a monotonic decreasing behavior with $B$ that is in good qualitative agreement with lattice QCD (LQCD) calculations, both for the case of constant or $B$-dependent couplings. Regarding charged pions, it is seen that the mixing softens the enhancement of their mass with $B$. As a consequence, the energy becomes lower than the one corresponding to a pointlike pion, improving the agreement with LQCD results. The agreement is also improved for the magnetic behavior of the lowest ${\rho }^{+}$ energy state, which does not vanish for the considered range of values of $B$—a fact that can be relevant in connection with the occurrence of meson condensation for strong magnetic fields.

The radiative corrections to the ${\tau }^{-}\to (P_1{P}_2{)}^{-}{\nu }_{\tau }$ ($P_{1,2}=\pi$, $K$) decays are calculated for the first time including the structure-dependent real photon corrections, which are obtained using resonance chiral theory. Our results, whose uncertainty is dominated by the model dependence of the resummation of the radiative corrections and the missing virtual structure-dependent contributions, allow for precise tests of Cabibbo-Kobayashi-Maskawa unitarity, lepton flavor universality, and nonstandard interactions.

We calculate the total thrust resulting from the interaction between charged scalar modes and a superradiant Reissner-Nordström black hole, when the modes are deflected by a hemispherical perfect mirror located at a finite distance from the black hole’s horizon.

Two perfectly conducting, infinite parallel plates will restrict the electromagnetic vacuum, producing an attractive force. This phenomenon is known as the Casimir effect. Here we use electromagnetic field correlators to define the local interaction between the plates and the vacuum, which gives rise to a renormalized stress-energy tensor. We then show that a Lorentz boost of the underlying electric and magnetic fields that comprise the correlators will produce the correct stress-energy tensor in the boosted frame. The infinite surface divergences of the field correlators will transform appropriately, such that they cancel out in the boosted frame and produce the desired finite result.

We provide a covariant framework to study singularity-free Lemaître-Tolman-Bondi spacetimes with effective corrections motivated by loop quantum gravity. We show that, as in general relativity, physically reasonable energy distributions lead to a contraction of the dust shells. However, quantum-gravity effects eventually stop the collapse, the dust smoothly bounces back, and no gravitational singularity is generated. This model is constructed by deforming the Hamiltonian constraint of general relativity with the condition that the hypersurface deformation algebra is closed. In addition, under the gauge transformations generated by the deformed constraints, the structure function of the algebra changes adequately, so that it can be interpreted as the inverse spatial metric. Therefore, the model is completely covariant in the sense that gauge transformations in phase space simply correspond to coordinate changes in spacetime. However, in the construction of the metric, we point out a specific freedom of considering a conformal factor, which we use to obtain a family of singularity-free spacetimes associated with the modified model.

Using the self-force approach, we present the premier first-post-adiabatic accuracy formalism for modeling compact binaries in theories with a massless scalar field nonminimally coupled to gravity. We limit the binary secondary to being a non-spinning compact body with no scalar dipole (we will address the spinning and scalar dipole cases in an upcoming paper). By producing an ansatz for the scalar charged point particle action, we derive first- and second-order perturbative field equations and equations of motion for the secondary compact object. Under our assumptions, implementing this formalism will produce sufficiently accurate waveform templates for precision measurements of the scalar charge of the secondary with LISA data on extreme-mass-ratio inspirals. Our formalism is consistent with almost general scalar-tensor theories of gravity. Implementing our formalism builds on self-force models in general relativity; we show the incorporation into the two-timescale formalism is straightforward. Excitingly, implementation poses no significantly more challenging barriers than computing first-post-adiabatic waveforms in general relativity.

This paper defines the photon surface conditions using Cartan scalars within an invariant spin frame, offering a comprehensive description of the local spacetime geometry. By employing this approach, we gain novel insights into the geometry and dynamics of photon surfaces, independent of the global spacetime structure. We first discuss the photon surface conditions in a Petrov type-D spacetime manifold, and then we simplify those conditions assuming the existence of spherical symmetry. Finally, employing the simplified, spherically symmetric photon surface conditions, we explore the dynamics of photon surfaces in static, collapsing Lemaitre-Tolman-Bondi (LTB) spacetimes and Vaidya spacetimes. Notably, we show that photon surfaces can emerge from the central singularity during the collapse of an inhomogeneous dust cloud modeled by a LTB spacetime. This underscores the significance of our findings in comprehending the potential observational implications of the physics near the ultrahigh gravity region.

We consider the effects of Weyl geometry on the propagation of electromagnetic wave packets and on the gravitational spin Hall effect of light. It is usually assumed that in vacuum the electromagnetic waves propagate along null geodesics, a result which follows from the geometrical optics approximation. However, this model is valid only in the limit of infinitely high frequencies. At large but finite frequencies, the ray dynamics is affected by the wave polarization. Therefore, the propagation of the electromagnetic waves can deviate from null geodesics, and this phenomenon is known as the gravitational spin Hall effect of light. On the other hand, Maxwell’s equations have the remarkable property of conformal invariance. This property is a cornerstone of Weyl geometry and the corresponding gravitational theories. As a first step in our study, we obtain the polarization-dependent ray equations in Weyl geometry, describing the gravitational spin Hall effect of localized electromagnetic wave packets in the presence of nonmetricity. As a specific example of the spin Hall effect of light in Weyl geometry, we consider the case of the simplest conformally invariant action, constructed from the square of the Weyl scalar, and the strength of the Weyl vector only. The action is linearized in the Weyl scalar by introducing an auxiliary scalar field. In static spherical symmetry, this theory admits an exact black hole solution, which generalizes the standard Schwarzschild solution through the presence of two new terms in the metric, having a linear and a quadratic dependence on the radial coordinate. We numerically study the polarization-dependent propagation of light rays in this exact Weyl geometric metric, and the effects of the presence of the Weyl vector on the magnitude of the spin Hall effect are estimated.

In the case of unhindered gravitational collapse of a matter cloud governed by the Lemaître-Tolman-Bondi (LTB) spacetime, the end-state singularity is either locally visible, globally visible, or completely hidden. We have a past null singularity in the first two cases while a future spacelike singularity in the last case. Here, we show an example of a gravitational collapse model whose end state is a future null singularity (it has a causal property that is unlike the cases involving LTB spacetime). We depict such a distinct causal structure of the singularity by conformal diagrams.

In this work we present a general method to obtain the junction conditions of modified theories of gravity whose action can be written in the form $f(X_1,\dots ,X_n)$, where $X_1$ to $X_n$ are any combination of scalar dependencies, e.g., the Ricci scalar $R$, the trace of the stress-energy tensor $T$, the Gauss-Bonnet invariant $\mathcal{G}$, among others. We discriminate the junction conditions into three subgroups: the immediate conditions, arising from the imposition of regularity of the relevant quantities in the distribution formalism; the differential conditions, arising from the differential terms in the field equations; and the coupling conditions, arising from the interaction between different scalars $X_i$. Writing the modified field equations in terms of a linear combination of the different contributions of the scalars $X_i$ allows one to analyze the direct and differential junction conditions independently for each of these scalars, whereas the coupling junction conditions can be analyzed separately afterward. We show that the coupling junction conditions induced on a scalar $X_i$ due to a coupling with a scalar $X_j$ are of the same form as the differential junction conditions of the scalar $X_j$ but applied to the analogous quantity in the framework of the scalar $X_i$. We provide a complete analysis of three different types of spacetime matching, namely smooth matching, matching with a thin shell, and matching with double gravitational layers, and we also describe under which conditions the full sets of junction conditions might be simplified. Our results are applicable to several well-known theories of gravity, e.g., $f(R)$, $f(T)$, and $f(\mathcal{G})$, and can be straightforwardly extrapolated to other theories with scalar dependencies and more complicated scenarios where several dependencies are present simultaneously.

We propose that the dark matter of our Universe could be sterile neutrinos which reside within the twin sector of a mirror twin Higgs model. In our scenario, these particles are produced through a version of the Dodelson-Widrow mechanism that takes place entirely within the twin sector, yielding a dark matter candidate that is consistent with x-ray and gamma-ray line constraints. Furthermore, this scenario can naturally avoid the cosmological problems that are typically encountered in mirror twin Higgs models. In particular, if the sterile neutrinos in the Standard Model sector decay out of equilibrium, they can heat the Standard Model bath and reduce the contributions of the twin particles to $N_{\mathrm{eff}}$. Such decays also reduce the effective temperature of the dark matter, thereby relaxing constraints from large-scale structure. The sterile neutrinos included in this model are compatible with the seesaw mechanism for generating Standard Model neutrino masses.