A new theoretical framework, based on the quantum field theory of open systems applied to neutrinos, has been developed. This framework aims to describe the neutrino evolution in external environment, taking into account the effect of neutrino quantum decoherence. We have applied this approach to investigate a novel mechanism for neutrino quantum decoherence, which arises due to the neutrino decay into a lighter neutrino state and a massless particle, as well as the inverse process of absorption of a massless particle by a neutrino. We derived the new generalized Lindblad master equation for the neutrino evolution that accounts for neutrino transitions between states with different momenta. We also demonstrate that studying of neutrino quantum decoherence through this master equation provides a unique possibility to determine or limit the neutrino decay width. On this basis we obtained the constraint on neutrino lifetime $\frac{{\tau }_2}{m_2}>1.83\times {10}^{-10}\frac{\mathrm{s}}{\mathrm{eV}}$ (for the case of the Dirac neutrino scalar decay and neutrino degenerate hierarchy).

Supercooled first-order phase transition (FOPT) can lead to the formation of primordial black holes (PBHs). This scenario imposes stringent requirements on the profile of the effective potential. In this work, we use the singlet extended Standard Model (xSM) as a benchmark model to investigate this possibility at the electroweak scale. The PBHs formed during a supercooled FOPT have a narrow mass distribution around the mass of Earth. This distribution is closely tied to the temperature at which the PBHs form, corresponding to the FOPT at the electroweak scale. This scenario can be probed with microlensing experiments, space-based gravitational wave detectors, and collider experiments. Remarkably, the future space-based gravitational wave detector LISA will hold the potential to either confirm this scenario that leads to PBH formation across the observable Universe in the xSM or completely rule it out. Interestingly, our findings suggest that PBHs within the xSM framework may align with observations of the six ultrashort timescale events reported by the OGLE microlensing experiment.

We discuss the possibility of light scalar dark matter generated by right-handed neutrino in a $L_{\mu }-L_{\tau }$ model, in which the dark matter ${\varphi }_{dm}$ carries $U(1{)}_{L_{\mu }-L_{\tau }}$ charge but it is a singlet in the Standard Model. We discuss the case that dark matter production mainly comes from scattering associated with a pair of right-handed neutrinos non-thermally while other related processes are highly suppressed. A feasible parameter space is considered and we found the correct dark matter relic density can be obtained without influencing the result of leptogenesis result. The heavier right-handed neutrino will induce colder dark matter production and the allowed dark matter mass region is $[{10}^{-5}\mathrm{GeV},0.1\mathrm{GeV}]$.

The nonsinglet part of the chiral symmetry in quantum chromodynamics (QCD) with two light flavors is known to be restored through a crossover transition at a pseudocritical temperature. However, the temperature dependence of the singlet part of the chiral symmetry and whether it is effectively restored at the same temperature is not well understood. Using ($2+1$)-flavor QCD configurations generated using the Möbius domain-wall discretization on an $N_{\tau }=8$ lattice, we construct suitable observables where the singlet and nonsinglet chiral symmetries are disentangled in order to study their temperature dependence across the crossover transition. From the peak of the disconnected part of the chiral susceptibility, we obtain a pseudocritical temperature $T_{pc}={158.7}_{-2.3}^{+2.6}\mathrm{MeV}$ where the nonsinglet part of the chiral symmetry is effectively restored. From a calculation of the topological susceptibility and its temperature dependence we find that the singlet ${\mathrm{U}}_A(1)$ part of the chiral symmetry is not effectively restored at $T\lesssim 186\mathrm{MeV}$.

We explore the application of quantum optimal control (QOC) techniques to state preparation of lattice field theories on quantum computers. As a first example, we focus on the Schwinger model, quantum electrodynamics in $1+1$ dimensions. We demonstrate that QOC can significantly speed up the ground state preparation compared to gate-based methods, even for models with long-range interactions. Using classical simulations, we explore the dependence on the interqubit coupling strength and the device connectivity, and we study the optimization in the presence of noise. While our simulations indicate potential speedups, the results strongly depend on the device specifications. In addition, we perform exploratory studies on the preparation of thermal states. Our results motivate further studies of QOC techniques in the context of quantum simulations for fundamental physics.

We compute the electrical conductivity of the strongly interacting medium in the presence of strong magnetic background fields, $eB=4$, $9{\mathrm{GeV}}^2$, and for different values of the temperature, both in the confined and in the deconfined quark-gluon plasma (QGP) phase. The conductivity is obtained from the Euclidean lattice time correlator of the electrical current, computed on gauge configurations sampled from Monte-Carlo simulations of an improved staggered discretization of $N_f=2+1$ QCD. We perform the inverse Laplace transform of the correlator adopting a recently proposed version of the standard Backus-Gilbert procedure for the inversion. The results obtained in the QGP phase show a sizable enhancement of the conductivity in the direction parallel to the magnetic field, as well as a suppression in the direction orthogonal to it. The enhancement can interpreted through various different mechanisms, typically involving the chiral anomaly, among which the chiral magnetic effect (CME): for this reason we try to interpret our observations based on a CME-inspired Ansatz, we extract the relaxation time of this process, extrapolate it to the continuum limit and compare it to previous results, finding it lower than expected in the explored range of temperatures.

Using a hybrid approach based on a phenomenological heavy-quark potential model and the background field effective theory, we assess the influence of a nontrivial Polyakov loop on the in-medium properties of the heavy quarkonium states. Without resorting to any temperature-dependent parameter, the lattice simulations on the complex heavy-quark potential are well reproduced with the potential model in which the screening masses are determined by the background field effective theory. Because of the reduced screening strength near the deconfining temperature, a nontrivial Polyakov loop leads to a dramatic increase in the binding energies, together with a moderate decrease in the decay widths. In general, a more tightly bounded quarkonium state can be expected, although the increase in the dissociation temperatures is significant only for relatively large-size bounded states. Our results indicate that the background field modification on the binding and decay of the quarkonium states may have a notable impact on the density evolution of quarkonia during the expansion of the fireball, and thus on the final observed quarkonium spectra.

We have investigated the collisional corrections to the spin polarization pseudovector $\delta {\mathcal{P}}^{\mu }$ using quantum kinetic theory in Chapman-Enskog expansion. We derive the spin Boltzmann equation incorporating the Møller scattering process. We further consider two distinct scenarios using hard thermal loop approximations for simplification. In scenario (I), the vector charge distribution function is treated as off equilibrium under the validity domain of gradient expansion. Remarkably, the polarization induced by thermal vorticity and shear viscous tensors are modified, but $\delta {\mathcal{P}}^{\mu }$ in this scenario does not depend on the coupling constant. In scenario (II), the vector charge distribution function is assumed to be in local thermal equilibrium. Then collisional corrections $\delta {\mathcal{P}}^{\mu }$ in this scenario are at $\mathcal{O}({\hslash }^2{\partial }^2)$. Additionally, we evaluate the $\delta {\mathcal{P}}^{\mu }$ using the relaxation time approach for comparative analysis. Our results establish the theoretical framework necessary for future numerical investigations on the interaction corrections to spin polarization.

Chiral effective theory of light diquarks is revisited. We construct an effective Lagrangian based on the linear representation of three-flavor chiral symmetry. Here, we focus on the effect of a chiral and $U(1{)}_A$ symmetric term originated from an eight-point quark interaction. From this model, we obtain the mass formulas of scalar, pseudoscalar, vector, and axial-vector diquarks, which also describe the dependence of diquark masses on the spontaneous chiral symmetry breaking and the $U(1{)}_A$ anomaly. We regard singly heavy baryons as two-body systems composed of one heavy quark and one diquark and then predict the fate of the mass spectrum and the strong decay widths under chiral symmetry restoration.

There exist two distinct ways in realizing the approximate SU(3) flavor symmetry of QCD to describe the two-body nonleptonic decays of charmed baryons: the irreducible SU(3) approach (IRA) and the topological diagram approach (TDA). The TDA has the advantage that it is more intuitive, graphic, and easier to implement model calculations. We perform a global fit to the currently available data of two-body charmed baryon decays within the framework of the TDA and IRA. The number of the minimum set of tensor invariants in the IRA and the topological amplitudes in the TDA is the same, namely, five in the tree-induced amplitudes and four in the penguin amplitudes. Since we employ the new LHCb measurements to fix the sign ambiguity of the decay parameters $\beta$ and $\gamma$, the fit results for the magnitudes of $S$- and $P$-wave amplitudes and their phase shift ${\delta }_P-{\delta }_S$ in both the TDA and IRA are more trustworthy than our previous analyses with uncertainties substantially improved. These results can be tested in the near future. The perspective of having direct $CP$ violation in the charmed baryon sector at the per mille level is briefly discussed.

Cold and dense matter may break rotational symmetry spontaneously and thus form an anisotropic phase in the interior of neutron stars. We consider the concrete example of an anisotropic chiral condensate in the form of a chiral density wave. Employing a nucleon-meson model and taking into account fermionic vacuum fluctuations, we improve and extend previous results by imposing the conditions of electric charge neutrality and electroweak equilibrium, by allowing for a more general form of the vector meson self-interactions, and by including properties of pure neutron matter into the fit of the model parameters. We find that the conditions inside neutron stars postpone the onset of the chiral density wave to larger densities compared to isospin-symmetric nuclear matter. While this still allows for the construction of stars with an anisotropic core, we find that the chiral density wave is energetically preferred only in a corner of the parameter space where matter is too soft to generate stars with realistic masses. Therefore, taking into account constraints from astrophysical data, our calculation predicts an isotropic neutron star core.

In collider experiments, the kinematic reconstruction of heavy, short-lived particles is vital for precision tests of the Standard Model and in searches for physics beyond it. Performing kinematic reconstruction in collider events with many final-state jets, such as the all-hadronic decay of top-antitop quark pairs, is challenging. We present Hypergraph for Particle Event Reconstruction (HyPER), a novel architecture based on graph neural networks that uses hypergraph representation learning to build more powerful and efficient representations of collider events. HyPER is used to reconstruct parent particles from sets of final-state objects. Trained and tested on simulation, the HyPER model is shown to perform favorably when compared to existing state-of-the-art reconstruction techniques, while demonstrating superior parameter efficiency. The novel hypergraph approach allows the method to be applied to particle reconstruction in a multitude of different physics processes.

We investigate the impact of a critical end point (CEP) on the experimentally accessible baryon-number fluctuations of different orders. By now, its potential location has been constrained fairly accurately within first principles functional QCD, together with the location of the chiral crossover line and further thermodynamic observables. This information is incorporated in an advanced QCD-assisted low-energy effective theory which is used for the computation of baryon-number fluctuations at the chemical freeze-out. This computation also takes care of global baryon-number conservation at larger density, where the system changes from grand-canonical to canonical statistics. We observe a prominent peak structure, whose amplitude depends on the location of the CEP, while its position is more sensitive to the location of the freeze-out curve. Our results provide guidance for future low-energy heavy-ion experiments.

We derive a generalization of the Boyd-Grinstein-Lebed (BGL) parametrization. Most form factors (FFs) in $b$-hadron decays exhibit additional branch cuts—namely subthreshold and anomalous branch cuts—beyond the “standard” unitarity cut. These additional cuts cannot be adequately accounted for by the BGL parametrization. For instance, these cuts arise in the FFs for $B\to D^{(*)}$, $B\to K^{(*)}$, and ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }$ processes, which are particularly relevant from a phenomenological standpoint. We demonstrate how to parametrize such FFs and derive unitarity bounds in the presence of subthreshold and/or anomalous branch cuts. Our work paves the way for a wide range of new FF analyses based solely on first principles, thereby minimizing systematic uncertainties.

A mechanism of baryogenesis and dark matter production via $B$ meson oscillations and decays has recently been proposed to explain the observed dark matter abundance and matter-antimatter asymmetry in the universe. This mechanism introduces a low-mass dark sector particle (${\psi }_D$) with a nonzero baryonic charge. We present a search for this new state in $B^{+}\to {\mathrm{\Lambda }}_c^{+}{\psi }_D$ decays using data collected at the $\mathrm{\Upsilon }(4S)$ resonance by the BABAR detector at SLAC, corresponding to an integrated luminosity of $431.0{\mathrm{fb}}^{-1}$. The search leverages the full reconstruction of the $B^{-}$ meson in $\mathrm{\Upsilon }(4S)\to B^{+}{B}^{-}$ decays, accompanied by the reconstruction of a ${\mathrm{\Lambda }}_c^{+}$, to infer the presence of ${\psi }_D$. No significant signal is observed, and limits on the $B^{+}\to {\mathrm{\Lambda }}_c^{+}{\psi }_D$ branching fraction are set at the level of $1.6\times {10}^{-4}$ at 90% confidence level for $0.94<m_{{\psi }_D}<2.99\mathrm{GeV}$. These results set strong constraints on the parameter space allowed by $B$-meson baryogenesis.

We study the conditions for finding an island in an anisotropic universe—Bianchi type I universe filled with radiation. We verify that the existence of islands does not depend on their shape. We then find that islands may form at certain times, near the turnaround point—where the universe turns from contraction to expansion in one of the directions. This is in line with previous analyses regarding cosmological space-times where islands form if one has two energy scales in the problem, such as the typical temperature of the universe and, on top of that, cosmological constant, curvature, anisotropy, or some other mass scale.

In a previous paper [I. Y. Aref’eva et al., Running coupling for holographic QCD with heavy and light quarks: Isotropic case, Phys. Rev. D 110, 126009 (2024)], we investigated the dependence of the running coupling constant on temperature and chemical potential for holographic models of the light and heavy quarks, supported by an Einstein-dilaton-Maxwell action. In this paper, we study the dependence of the corresponding $\beta$-functions on the temperature and the chemical potential. As in the previous paper, we give special attention to the behavior of the $\beta$-functions near the first order phase transitions. We consider different types of boundary conditions for the dilaton. Only one of the possible boundary conditions yields results that agree with lattice calculations at zero chemical potential. The corresponding $\beta$-functions are negative and exhibit jumps at the first order phase transitions. We also show that the renormalization group fluxes are invariant with respect to the choice of the boundary conditions and that our exact solutions for the light and heavy quarks are unstable, as expected, given their negative dilaton potentials.

We present the details for the covariant renormalization of the stress tensor for vacuum tensor perturbations at the level of the effective action, adopting Hadamard regularization techniques to isolate short distance divergences and gauge fixing via the Faddeev-Popov procedure. The subsequently derived renormalized stress tensor can be related to more familiar forms reliant upon an averaging prescription, such as the Isaacson or Misner-Thorne-Wheeler forms. The latter, however, are premised on a prior scale separation (beyond which the averaging is invoked) and therefore unsuited for the purposes of renormalization. This can lead to potentially unphysical conclusions when taken as a starting point for the computation of any observable that needs regularization, such as the energy density associated to a stochastic background. Any averaging prescription, if needed, should only be invoked at the end of the renormalization procedure. The latter necessarily involves the imposition of renormalization conditions via a physical measurement at some fixed scale, which we retrace for primordial gravitational waves sourced from vacuum fluctuations through direct or indirect observation.

We study spherically symmetric spacetime perturbations induced by a neutral scalar in the near-horizon region of extreme Reissner-Nordström black holes. For the unperturbed black hole, the near-horizon region is given by another exact solution of the Einstein-Maxwell equations, namely the Bertotti-Robinson spacetime. Our aim is to extend this connection beyond the background level and identify perturbations of a Bertotti-Robinson spacetime as near-horizon perturbations of an extreme Reissner-Nordström black hole. We explain that explicit identification of the perturbative solutions to the two different backgrounds can only work in appropriate gauges. For this reason, we first solve the two perturbation problems in the most general spherically symmetric gauges and then find the necessary gauge conditions for matching the Reissner-Nordström and Bertotti-Robinson perturbative solutions in the near-horizon limit.