We study the classical quantum (CQ) hybrid dynamics of homogeneous cosmology from a Hamiltonian perspective where the classical gravitational phase space variables and matter state evolve self-consistently with full backreaction. We compare numerically the classical and CQ dynamics for isotropic and anisotropic models, including quantum scalar-field induced corrections to the Kasner exponents. Our results indicate that full backreaction effects leave traces at late times in cosmological evolution; in particular, the scalar energy density at late times provides a potential contribution to dark energy. We also show that the CQ equations admit exact static solutions for the isotropic, and the anisotropic Bianchi IX universes with the scalar field in a stationary state.

In this work we analyze the observational properties of relativistic fluid spheres when orbited by isotropically emitting sources, known as hot spots. We consider fluid star configurations in four different regimes of compacticity, from the Buchdahl limit to nonultracompact solutions, thus obtaining fluid stars with qualitatively different geodesic structures and observational properties. We show that the observational properties for fluid stars at the Buchdahl limit are qualitatively similar to the ones for the Schwarzschild black hole, whereas for more dilute configurations one can find observational properties similar to other fundamentally different models, e.g., bosonic star configurations with and without self interactions. For solutions with a radius in the range $2.25M<R<3M$, where $M$ is the total mass of the fluid star, the presence of a light-ring (LR) pair, which becomes degenerate at $R=3M$, leads to the appearance of additional observational signatures e.g. secondary images and LR contributions, which allow one to distinguish these models from their black-hole counterparts. Fluid star configurations supported by thin shells are also analyzed and it is proven that the stability of the inner LR is increased for these solutions, resulting in a nondifferentiable extremum in the effective potential of the photons. Our results suggest that compact fluid star configurations provide a suitable and physically relevant alternative to the black-hole scenario in accordance with the current generation of observational experiments.

We present the geometric foundations and derivations of equations of motion for symmetric teleparallel theories of gravity in the coincident gauge and covariant frameworks. We discuss the theoretical challenges introduced by the auxiliary fields responsible for the covariantization procedure. We elucidate a tetradic structure interpretation behind this covariant formulation. Regarding the effect of covariantization at the level of the equations of motion, we explicitly show that the only physical change, in case of setting an arbitrary energy-momentum tensor to the right-hand side, resides in the requirement of the fulfillment of the covariant conservation laws. Also, we have explicitly introduced the fundamental covariantly conserved teleparallel tetrad for the symmetric teleparallel frameworks.

A very simple nonsingular inflationary model is presented where the unique matter content is a radiation fluid. The model slowly contracts from a very large, almost empty and flat spacetime and realizes a bounce. It is then launched to a quasi-de Sitter inflationary expansion with more than sixty $e$-folds, which smoothly changes to the usual classical, decelerated radiation-dominated expansion before nucleosynthesis. The initial contracting and final expanding phases are classical, but the intermediate bounce and inflationary phases are induced by quantum cosmological effects emerging from a Gaussian wave function quickly moving in configuration space. During this quantum era, a huge number of photons is created. The scale factor describing all this rich evolution is a surprisingly simple analytic function of conformal time. The cosmological scalar perturbations arising from quantum vacuum fluctuations in the far past of the model present an almost scale invariant spectrum with an amplitude compatible with observations for reasonable values of the free parameters of the model.

We study the conditions for stability of electrically charged, nonconductive perfect fluid tori with respect to linear perturbations. To this end, we employ Lagrangian perturbation formalism, and we assume a system where the fluid orbits a central body. Gravitational field of the latter is described in the Newtonian framework. We first formulate the criteria valid for a general, nonaxisymmetric situation, and then we concentrate on the axisymmetric model in more detail. In the latter case, we generalize the Høiland criterion of stability to a nonvanishing electric charge and classify special examples. Toroidal structures with constant angular momentum distribution are found to be linearly stable. Subsequently, like in the uncharged case, rotating charged fluids are found to be unstable with respect to nonaxisymmetric perturbations.

Providing an accurate modeling of neutrino physics in dense astrophysical environments such as binary neutron star mergers presents a challenge for hydrodynamic simulations. Nevertheless, understanding how flavor transformation can occur and affect the dynamics, the mass ejection, and the nucleosynthesis will need to be achieved in the future. Computationally expensive, large-scale simulations frequently evolve the first classical angular moments of the neutrino distributions. By promoting these quantities to matrices in flavor space, we develop a linear stability analysis of fast flavor oscillations using only the first two “quantum” moments, which notably requires generalizing the classical closure relations that appropriately truncate the hierarchy of moment equations in order to treat quantum flavor coherence. After showing the efficiency of this method on a well-understood test situation, we perform a systematic search of the occurrence of fast flavor instabilities in a neutron star merger simulation. We discuss the successes and shortcomings of moment linear stability analysis, as this framework provides a time-efficient way to design and study better closure prescriptions in the future.

We present the new guided moments (GM) formalism for neutrino modeling in astrophysical scenarios like core-collapse supernovae and neutron star mergers. The truncated moments approximation (M1) and Monte-Carlo (MC) schemes have been proven to be robust and accurate in solving the Boltzmann equation for neutrino transport. However, it is well known that each method exhibits specific strengths and weaknesses in various physical scenarios. The GM formalism effectively solves these problems, providing a comprehensive scheme capable of accurately capturing the optically thick limit through the exact M1 closure and the optically thin limit through an MC-based approach. In addition, the GM method also approximates the neutrino distribution function with a reasonable computational cost, which is crucial for the correct estimation of the different neutrino-fluid interactions. Our work provides a comprehensive discussion of the formulation and application of the GM method, concluding with a thorough comparison across several test problems involving the three schemes (M1, MC, GM) under consideration.

This research studies the intricate interplay between dark and baryonic matter within hybrid neutron stars enriched by anisotropic bosonic dark matter halos. Our modeling, guided by the equation of state with a free parameter, reveals diverse mass-radius correlations for these astronomical objects. A pivotal result is the influence of dark matter characteristics—whether condensed or dispersed—on the observable attributes of neutron stars based on their masses. Our investigation into anisotropic models, which offer a notably authentic representation of dark matter anisotropy, reveals a unique low-density core halo profile, distinguishing it from alternative approaches. Insights gleaned from galactic clusters have further refined our understanding of the bosonic dark matter paradigm. Observational constraints derived from the dynamics of galaxy clusters have been fundamental in defining the dark matter particle mass to lie between 0.05 and 0.5 GeV and the scattering length to range from 0.9 to 3 fm. Using terrestrial Bose-Einstein condensate experiments, we have narrowed down the properties of bosonic dark matter, especially in the often overlooked 3 to 30 GeV mass range. Our findings fortify the understanding of dark and baryonic matter synergies in hybrid neutron stars, establishing a robust foundation for future astrophysical pursuits.

We conduct an investigation on the $1P$- and $2P$-wave charmed baryons using the methods of QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. Our results suggest that the ${\mathrm{\Lambda }}_c(2910{)}^{+}$, ${\mathrm{\Lambda }}_c(2940{)}^{+}$, and ${\mathrm{\Xi }}_c(3123{)}^{+}$ can be well interpreted as the $2P$-wave charmed baryons of $J^P=1/2^{-}$ and $3/2^{-}$, belonging to the $SU(3)$ flavor ${\overline{\mathbf{3}}}_F$ representation. Moreover, the ${\mathrm{\Xi }}_c(3123{)}^{+}$ possesses a partner state characterized by $J^P=1/2^{-}$, denoted as ${\mathrm{\Xi }}_c(1/2^{-},2P)$. Our analysis predicts its mass and width to be $m_{{\mathrm{\Xi }}_c(1/2^{-},2P)}-m_{{\mathrm{\Xi }}_c(3123{)}^{+}}=-18\pm 7\mathrm{MeV}$ and ${\mathrm{\Gamma }}_{{\mathrm{\Xi }}_c(2P,1/2^{-})}=31_{-27}^{+170}\mathrm{MeV}$, with $m_{{\mathrm{\Xi }}_c(3123{)}^{+}}=3122.9\pm 1.3\mathrm{MeV}$. We propose to search for it in the ${\mathrm{\Xi }}_c(1/2^{-},2P)\to {\mathrm{\Sigma }}_{c}K$ decay channel.

The well-known model of the triangle diagrams with $D^{*}\overline{D}{D}^{*}$ and ${\overline{D}}^{*}D{\overline{D}}^{*}$ mesons in the loops is compared with the modern data on the amplitude of the $X(3872)\to {\pi }^0{\chi }_{c1}(1P)$ decay. Considering the $X(3872)$ object as a ${\chi }_{c1}(2P)$ charmonium state, we introduce a parameter $\xi$ characterizing the scale of the isotopic symmetry violation in this decay and find a lower limit of $\xi \simeq 0.0916$. The model incorporates the only fitted parameter associated with the form factor. We analyze in detail the influence of the form factor on the amplitude $X(3872)\to {\pi }^0{\chi }_{c1}(1P)$ and on the parameter $\xi$. As the suppression of the amplitude by the form factor increases, $\xi$ increases. Because the $X(3872)$ resonance is located practically at the threshold of the $D^0{\overline{D}}^{*0}$ channel, the amplitude of $X(3872)\to {\pi }^0{\chi }_{c1}(1P)$ turns out to be proportional to $\sqrt{m_d-m_u}$. Using the estimating values for the coupling constants $g_{XD{\overline{D}}^{*}}$, $g_{{\chi }_{c1}D{\overline{D}}^{*}}$, and $g_{D^{*0}{D}^{*0}{\pi }^0}$, we show that the model of the triangle loop diagrams is in reasonable agreement with the available data. Apart from the difference in the masses of neutral and charged charmed mesons, any additional exotic sources of isospin violation in $X(3872)\to {\pi }^0{\chi }_{c1}(1P)$ (such as a significant difference between the coupling constants $g_{X{D}^0{\overline{D}}^{*0}}$ and $g_{X{D}^{+}{D}^{*-}}$) are not required to interpret the data. This indirectly confirms the isotopic neutrality of the $X(3872)$, which is naturally realized for the $c\overline{c}$ state ${\chi }_{c1}(2P)$.

Physics of the up-type flavor offers unique possibilities of testing the standard model (SM) compared to the down-type flavor sector. Here, we discuss SM and new physics (NP) contributions to the rare charm-meson decay $D^0\to {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$. In particular, we discuss the effect of including the lightest scalar isoscalar resonance in the SM picture, namely, the $f_0(500)$, which manifests in a big portion of the allowed phase space. Other than showing in the total branching ratio at an observable level of about 20%, the $f_0(500)$ resonance manifests as interference terms with the vector resonances, such as at high invariant mass of the leptonic pair in distinct angular observables. Recent data from LHCb optimize the sensitivity to $P$-wave contributions that we analyze in view of the inclusion of vector resonances. We propose the measurement of alternative observables that are sensitive to the $S$-wave and are straightforward to implement experimentally. This leads to a new set of null observables that vanish in the SM due to its gauge and flavor structures. Finally, we study observables that depend on the SM interference with generic NP contributions from semileptonic four-fermion operators in the presence of the $S$-wave.

High-electric-charge compact objects (HECOs) appear in several theoretical particle physics models beyond the Standard Model, and are actively searched for in current colliders, such as the Large Hadron Collider at CERN. In such searches, mass bounds of these objects have been placed, using Drell-Yan and photon-fusion processes at tree level so far. However, such mass-bound estimates are not reliable, given that, as a result of the large values of the electric charge of the HECO, perturbative quantum electrodynamics calculations break down. In this work, we perform a Dyson-Schwinger resummation scheme (as opposed to lattice strong-coupling approach), which makes the computation of the pertinent HECO-production cross sections reliable, thus allowing us to extract improved mass bounds for such objects from ATLAS and MoEDAL searches.

Majorana properties of neutrinos have long been a focus in the pursuit of possible new physics beyond the standard model, which has motivated lots of dedicated theoretical and experimental studies. A future same-sign muon collider is an ideal platform to search for Majorana neutrinos through the lepton number violation process: ${\mu }^{+}{\mu }^{+}\to {\mathrm{W}}^{+}{\mathrm{W}}^{+}$. Specifically, this t-channel kind of process is less kinematically suppressed and has a good advantage in probing Majorana neutrinos at high mass regions up to 10 TeV. In this paper, we perform a detailed fast Monte Carlo simulation study by examining three different final states: (1) pure leptonic state with electrons or muons, (2) semileptonic state, and (3) pure hadronic state in the resolved or merged categories. Furthermore, we perform a full simulation study on the pure leptonic final state to validate our fast simulation results.

We introduce a new algorithm for the simulation of Euclidean dynamical triangulations that mimics the Metropolis-Hastings algorithm, but where all proposed moves are accepted. This rejection-free algorithm allows for the factorization of local and global terms in the action, a condition needed for efficient simulation of theories with global terms, while still maintaining detailed balance. We test our algorithm on the $2d$ Ising model, and against results for EDT obtained with standard Metropolis. Our new algorithm allows us to simulate EDT at finer lattice spacings than previously possible, and we find geometries that resemble semiclassical Euclidean de Sitter space in agreement with earlier results at coarser lattices. The agreement between lattice data and the classical de Sitter solution continues to get better as the lattice spacing decreases.

We relate the interactions of the ${\overline{D}}^{(*)}{K}^{*}$ and $D^{(*)}{K}^{*}$ systems to those of $D^{(*)}{D}^{(*)}$ and $D^{(*)}{\overline{D}}^{(*)}$ respectively, considering the residual strong interactions at the near-threshold energy is too weak to excite the strange quarks inside the hadrons. We propose an effective model to describe the low-energy S-wave interactions that are undertaken by the light $u$, $d$ quarks between two separated heavy hadrons. We find that the existence of molecules in the heavy-(anti)heavy sectors will naturally lead to the emergence of molecular states in ${\overline{D}}^{(*)}{K}^{*}$ and $D^{(*)}{K}^{*}$ systems. The recently observed $T_{cs0}(2900)$ and $T_{c\overline{s}0}^a(2900)$ can be well identified as the $0(0^{+})$ and $1(0^{+})$ partners of $T_{cc}(3875)$ and $Z_c(3900)$ in the charmed strange sector, respectively. We also predict their members under the heavy ($c$ and $s$) quark symmetry and SU(2) flavor symmetry. Most of them are very good molecule candidates, for example, (i) the $0(1^{+})$ states in $D^{*}{D}^{*}$, $\overline{D}{K}^{*}$, ${\overline{D}}^{*}{K}^{*}$; (ii) the $0^{(+)}(2^{+(+)})$ states in $D^{*}{\overline{D}}^{*}$, ${\overline{D}}^{*}{K}^{*}$, $D^{*}{K}^{*}$; (iii) the $1^{-}(0^{++})$ state in $D^{*}{\overline{D}}^{*}$ and $1(1^{+})$ state in $D^{*}{K}^{*}$. The $0^{+}(0^{++})$ state in $D\overline{D}$ and the $0(1^{+})$ state in $D{K}^{*}$ might also exist as virtual states, and the $0(1^{+})$ $D{K}^{*}$ can serve as a key to infer the existence of $0^{+}(0^{++})$ $D\overline{D}$. The $D_s\pi$ invariant mass spectrum of $T_{c\overline{s}0}^a(2900)$ is also studied within the coupled-channel approach, and the molecular interpretation of $T_{c\overline{s}0}^a(2900)$ is consistent with the experimental data. Searching for the predicted states in experiments is crucial to discriminate the different pictures for interpreting these near-threshold exotica.

Based on the one-boson-exchange framework that the $\sigma$ meson serves as an effective parametrization for the correlated scalar-isoscalar $\pi \pi$ interaction, we calculate the coupling constants of the $\sigma$ to the ${\frac{1}{2}}^{+}$ ground state light baryon octet $\mathbb{B}$ by matching the amplitude of $\mathbb{B}\overline{\mathbb{B}}\to \pi \pi \to \overline{\mathbb{B}}\mathbb{B}$ to that of $\mathbb{B}\overline{\mathbb{B}}\to \sigma \to \overline{\mathbb{B}}\mathbb{B}$. The former is calculated using a dispersion relation, supplemented with chiral perturbation theory results for the $\mathbb{B}\mathbb{B}\pi \pi$ couplings and the Muskhelishvili-Omnès representation for the $\pi \pi$ rescattering. Explicitly, the coupling constants are obtained as $g_{NN\sigma }={8.7}_{-1.9}^{+1.7}$, $g_{\mathrm{\Sigma }\mathrm{\Sigma }\sigma }={3.5}_{-1.3}^{+1.8}$, $g_{\mathrm{\Xi }\mathrm{\Xi }\sigma }={2.5}_{-1.4}^{+1.5}$, and $g_{\mathrm{\Lambda }\mathrm{\Lambda }\sigma }={6.8}_{-1.7}^{+1.5}$. These coupling constants can be used in the one-boson-exchange model calculations of the interaction of light baryons with other hadrons.

Augmenting the improved chiral effective potential of the on-shell renormalized $2+1$ flavor quark-meson (RQM) model with the Polyakov-loop potential that accounts for the deconfinement transition, we get the quantum chromodynamics (QCD)-like framework of the renormalized Polyakov quark-meson (RPQM) model. When the divergent quark one-loop vacuum term is included in the effective potential of the quark-meson (QM) model, its tree-level parameters, or the parameters fixed by the use of meson curvature masses, become inconsistent as the curvature masses involve the self-energy evaluations at zero momentum. Using the modified minimal subtraction method, the consistent chiral effective potential for the RQM model has been calculated after relating the counterterms in the on-shell scheme to those in the $\overline{\mathrm{MS}}$ scheme and finding the relations between the renormalized parameters of both the schemes where the physical (pole) masses of the $\pi$, $K$, $\eta$, and ${\eta }^{\prime }$ pseudoscalar mesons and the scalar $\sigma$ meson, the pion and kaon decay constants, have been put into the relation of the running couplings and mass parameter. Using the RPQM model and the PQM model with different forms for the Polyakov-loop potentials in the presence or the absence of the quark backreaction, we have computed and compared the effect of the consistent quark one-loop correction and the quark backreaction on the scaled chiral order parameter, the QCD phase diagrams, and the different thermodynamic quantities. The results have been compared with the $2+1$ flavor lattice QCD data from the Wuppertal-Budapest Collaboration [J. High Energy Phys. 09 (2010) 73, Phys. Lett. B 730, 99 (2014)] and the HotQCD Collaboration [Phys. Rev. D 90, 094503 (2014)].

In most lattice field theories, correlators are plagued by a signal-to-noise problem of exponential difficulty in the time separation. We propose a method for improving the signal-to-noise ratio, in which control variates are systematically constructed from lattice Schwinger-Dyson relations. The method is demonstrated on various two-dimensional lattices in scalar field theory, and a strategy for scaling to larger systems is explored.

We present the results of a missing-energy search for light dark matter which has a new interaction with ordinary matter transmitted by a vector boson, called dark photon $A^{\prime }$. For the first time, this search is performed with a positron beam by using the significantly enhanced production of $A^{\prime }$ in the resonant annihilation of positrons with atomic electrons of the target nuclei, followed by the invisible decay of $A^{\prime }$ into dark matter. No events were found in the signal region with $(10.1\pm 0.1)\times {10}^9$ positrons on target with 100 GeV energy. This allowed us to set new exclusion limits that, relative to the collected statistics, prove the power of this experimental technique. This measurement is a crucial first step toward a future exploration program with positron beams, whose estimated sensitivity is here presented.