We explore the inflationary dynamics leading to formation of closed domain walls in course of evolution of an axion like particle (ALP) field whose Peccei-Quinn-like phase transition occurred well before inflationary epoch. Evolving after inflation, the domain walls may leave their imprint in stochastic gravitational waves background, in the frequency range accessible for the pulsar timing array measurements. We derive the characteristic strain power spectrum produced by the distribution of the closed domain walls and relate it with the recently reported NANOGrav signal excess. We found that the slope of the frequency dependence of the characteristic strain spectrum generated by the domain walls is very well centered inside the range of the slopes in the signal reported by the NANOGrav. Analyzing the inflationary dynamic of the ALP field, in consistency with the isocurvature constraint, we reveal those combinations of the parameters where the signal from the inflationary induced ALPs domain walls could saturate the amplitude of the NANOGrav excess. The evolution of big enough closed domain walls may end up in wormholes with the walls escaping into baby universes. We study the conditions when closed walls escape into baby universes and could leave a detectable imprint in the stochastic gravitational waves background.

The tidal deformabilities and radii of strange quark stars are studied via the quasiparticle model which includes the nonperturbative features of QCD in the low-density region. The results show that the mass constraint of $M_{\mathrm{TOV}}>2.0M_{\odot }$ rules out the EOSs which are soft at low densities, while the constraint on the tidal deformability of ${\mathrm{\Lambda }}_{1.4}<800$ from GW170817 rules out the EOSs which are too stiff in the low density region. The range for the radius of a $1.4M_{\odot }$ strange quark star is $11.12\mathrm{km}<R_{1.4}<11.98\mathrm{km}$. ${\mathrm{\Lambda }}_{1.4}$ has a strong correlation with $R_{1.4}$, and the empirical correlation function is ${\mathrm{\Lambda }}_{1.4}=2.86\times {10}^{-5}(R/\mathrm{km}{)}^{6.92}$, which is larger than that for neutron stars. The lower bound of ${\mathrm{\Lambda }}_{1.4}>513.66$ is also obtained. $\tilde{\mathrm{\Lambda }}$ is a monotonically increasing function of the mass ratio $\eta$, but the slope is very small. And we conclude that the range of $\tilde{\mathrm{\Lambda }}$ for GW190425 is $184.81<\tilde{\mathrm{\Lambda }}<320.08$.

Fermion-boson stars are starlike systems composed of the ordinary nuclear matter of a neutron star and bosonic dark matter. The bosonic dark matter has typically been taken to be a complex scalar field. A natural extension is for the complex scalar field to be charged. We make the simplest extension and gauge the scalar field under $U(1)$. We therefore study fermion–charged-boson stars. We make a detailed study of the stability of this system by computing critical curves over the whole of parameter space. We then study how the fermion and boson sectors contribute to the total mass of the star. Finally, we present mass-radius diagrams, showing that an increase in charge can lead to more massive and more compact stars.

We study the holographic information quantities, including the holographic entanglement entropy (HEE), the holographic mutual information (HMI) and the minimum cross section of the entanglement wedge (EWCS), over a special black brane geometry, which has a vanishing ground-state entropy. Thanks to the zero entropy density at the ground state, we expect to extract novel, even singular informational properties in the zero-temperature limit. Surprisingly, we do not observe any singular behavior of entanglement-related physical quantities in the zero-temperature limit. Nevertheless, we find a peculiar property from this model that in the low-temperature region, the HEE decreases with the temperature, which is contrary to that in most holographic models. We argue that this novel phenomenon is brought by the singular property of the zero-temperature limit. In addition, we also compare the features of the information quantities in this special black brane geometry with those in Reissner-Nordstrom anti–de Sitter (RN-AdS) black brane geometry. It is shown that the HEE and HMI of this vanishing ground-state entropy model are always larger than those of RN-AdS geometry, while the EWCS behaves oppositely. Our results indicate that the HMI and EWCS could have different abilities in describing mixed state entanglement.

The mechanism of the four-quark production of the light scalar isovector four-quark state $a_0(980)$ in the $D\to \eta \pi e^{+}{\nu }_e$ decays is discussed. It is shown that the characteristic features of the shape of the $\eta \pi$ mass spectra expected in our scheme can serve as the indicator of the production mechanism and internal structure of the $a_0(980)$ resonance.

We present a first calculation of the heavy flavor contribution to the longitudinally polarized deep-inelastic scattering structure function $g_1^Q$, differential in the transverse momentum or the rapidity of the observed heavy quark $Q$ or antiquark $\overline{Q}$. All results are obtained at next-to-leading order accuracy in QCD within the framework of a newly developed parton-level Monte Carlo generator that also allows one to study observables associated with the produced heavy quark pair such as its invariant mass distribution or its correlation in azimuthal angle. First phenomenological studies are carried out for various heavy quark distributions in a kinematic regime relevant for a future Electron-Ion Collider with a particular emphasis on the expected size of the corresponding double-spin asymmetries and their sensitivity to the still poorly constrained helicity gluon distribution. Theoretical uncertainties associated with the choice of the factorization scale are discussed for selected observables.

In this paper, we study the electroproduction of open heavy flavor $D$ and $B$ mesons in the kinematics of future $ep$ colliders, such as the Electron Ion Collider (EIC), the Large Hadron electron Collider (LHeC), and the Future Circular Collider (FCC-he). We study in detail the dependence of the cross sections on multiplicity of coproduced hadrons, in view of its possible sensitivity to contributions from multi-Pomeron contributions, and discuss different observables which might be used for its study. According to our theoretical expectations, in $ep$ collisions the multi-Pomeron contributions are small in the EIC kinematics, although they might be sizable at LHeC and FCC-he. We also provide theoretical predictions for the production cross sections of heavy mesons in the kinematics of all the above-mentioned $ep$ colliders.

In this study, we investigate the spatially nonuniform-temperature effects on the QCD chiral phase transition in the heavy-ion collisions. Since the QCD effective theory and the Ising model belong to the same universality class, we start our discussion by mimicking the QCD effective potential with an Ising-like effective potential. In contrast to the dynamical slowing down effects which delays the phase transition from quark-gluon-plasma to hadron gas, the spatially nonuniform-temperature effects show a possibility to lift the phase transition temperature. Besides, both the fluctuations and the correlation length are enhanced in the phase transition region. Furthermore, the critical phenomena is strongly suppressed like as the critical slowing down effects. The underlying mechanism is the nonzero-momentum mode fluctuations of the order parameter induced by the nonuniform temperature. Our study provides a method to evaluate the nonuniform-temperature effects, and illustrate its potential influence on analyzing the QCD phase transition signals at RHIC.

Nontopological gauged soliton solutions called $Q$-balls arise in many scalar field theories that are invariant under a $U(1)$ gauge symmetry. The related, but qualitatively distinct, $Q$-shell solitons have only been shown to exist for special potentials. We investigate gauged solitons in a generic sixth-order polynomial potential (that contains the leading effects of many effective field theories) and show that this potential generically allows for both $Q$-balls and $Q$-shells. We argue that $Q$-shell solutions occur in many, and perhaps all, potentials that have previously only been shown to contain $Q$-balls. We give simple analytic characterizations of these $Q$-shell solutions, leading to excellent predictions of their physical properties.

We derive Boltzmann equations for massive spin-$1/2$ fermions with local and nonlocal collision terms from the Kadanoff-Baym equation in the Schwinger-Keldysh formalism, properly accounting for the spin degrees of freedom. The Boltzmann equations are expressed in terms of matrix-valued spin distribution functions, which are the building blocks for the quasiclassical parts of the Wigner functions. Nonlocal collision terms appear at next-to-leading order in $\hslash$ and are sources for the polarization part of the matrix-valued spin distribution functions. The Boltzmann equations for the matrix-valued spin distribution functions pave the way for simulating spin-transport processes involving spin-vorticity couplings from first principles.

We discuss the phase structure of the two-flavor quark-meson model including quantum, thermal, density and critical fluctuations with the functional renormalization group. This study combines two technical advances in the literature, that are also chiefly important for the quantitative access of the phase boundary of QCD at large density or baryon-chemical potential. Specifically we allow for the formation and propagation of shocks as well as a fully self-consistent computation of the order parameter potential for chiral symmetry breaking.

Self-interactions within the dark sector could clump dark matter into heavy composite states with low number density, leading to a highly suppressed event rate in existing direct detection experiments. However, the large interaction cross section between such ultraheavy dark matter (UHDM) and standard model matter results in a distinctive and compelling signature; long, straight damage tracks as they pass through and scatter with matter. In this work, we propose using geologically old quartz samples as large-exposure detectors for UHDM. We describe a high-resolution readout method based on electron microscopy, characterize the most favorable geological samples for this approach, and study its reach in a simple model of the dark sector. The advantage of this search strategy is twofold; the age of geological quartz compensates for the low number density of ultraheavy composite dark matter, and the distinct geometry of the damage track serves as a high-fidelity background rejection tool.

We examine the impact of a faster expanding Universe on the phenomenology of scalar dark matter (DM) associated with $SU(2{)}_L$ multiplets. Earlier works with a radiation dominated Universe have reported the presence of desert region for both inert $SU(2{)}_L$ doublet and triplet DM candidates where the DM is underabundant. We find that the existence of a faster expanding component before big bang nucleosynthesis can revive a substantial part of the desert parameter space consistent with relic density requirements and other direct and indirect search bounds. We also review the possible collider search prospects of the newly obtained parameter space and predict that such region might be probed at the future colliders with improved sensitivity via a disappearing/stable charged track.

The ${\mu }^{+}\to e^{+}X$ decay, where $X$ is a dark sector boson, provides one of the strongest available bounds on the scale of dark sector interactions. The $X$ boson can be an axion or a dark photon. We show that the concurrent determination of the antimuon and positron polarizations makes it possible to distinguish with a confidence level of 99% between the two dark sector portals with as few as 6 observed events in the case of the massless dark photon. Instead, the massive spin-1, dimension 4 dark portal cannot be distinguished from the axionlike case. We also discuss the possibility that the $X$ boson be a massive spin-2 particle.

Nonzero neutrino masses imply the existence of degrees of freedom and interactions beyond those in the Standard Model. A powerful indicator of what these might be is the nature of the massive neutrinos: Dirac fermions versus Majorana fermions. While addressing the nature of neutrinos is often associated with searches for lepton-number violation, there are several other features that distinguish Majorana from Dirac fermions. Here, we compute in great detail the kinematics of the daughters of the decays into charged-leptons and neutrinos of hypothetical heavy neutral leptons at rest. We allow for the decay to be mediated by the most general four-fermion interaction Lagrangian. We demonstrate, for example, that when the daughter charged-leptons have the same flavor or the detector is insensitive to their charges, polarized Majorana-fermion decays have zero forward-backward asymmetry in the direction of the outgoing neutrino (relative to the parent spin), whereas Dirac-fermion decays can have large asymmetries. Going beyond studying forward-backward asymmetries, we also explore the fully differential width of the three-body decays. It contains a wealth of information not only about the nature of the new fermions but also the nature of the interactions behind their decays.

A scan of soft supersymmetry (SUSY) breaking parameters within the string theory landscape with the minimal supersymmetric standard model assumed as the low energy effective field theory—using a power-law draw to large soft terms coupled with an anthropic selection of a derived weak scale to be within a factor of 4 of our measured value—predicts a peak probability of $m_h\simeq 125\mathrm{GeV}$ with sparticle masses typically beyond the reach of LHC Run 2. Such multiverse simulations usually assume a fixed value of the SUSY conserving superpotential $\mu$ parameter to be within the assumed anthropic range, $\mu \lesssim 350\mathrm{GeV}$. However, depending on the assumed solution to the SUSY $\mu$ problem, the expected $\mu$ term distribution can actually be derived. In this paper, we examine two solutions to the SUSY $\mu$ problem. The first is the gravity-safe-Peccei-Quinn model based on an assumed ${\mathbb{Z}}_{24}^R$ discrete $R$-symmetry which allows a gravity-safe accidental, approximate Peccei-Quinn global symmetry to emerge which also solves the strong $CP$ problem. The second case is the Giudice-Masiero solution wherein the $\mu$ term effectively acts as a soft term and has a linear draw to large values. For the first case, we also present the expected landscape distribution for the Peccei-Quinn scale $f_a$; in this case, weak scale anthropics limits its range to the cosmological sweet zone of around $f_a\sim {10}^{11}\mathrm{GeV}$.

The tau lepton plays an important role in the correlation between the low-energy neutrino oscillation data and the lepton flavor structure in heavy neutrino decay. We investigate the lepton flavor signatures with tau lepton at a hadron collider through lepton number violating processes. In the type I seesaw with $\mathrm{U}(1{)}_{\mathrm{B}-\mathrm{L}}$ extension, we study the pair production of heavy neutrinos via a $Z^{\prime }$ resonance. We present a detailed assessment of the search sensitivity to the channels with a tau lepton in the subsequent decay of heavy neutrinos. For the benchmark model with $Z^{\prime }$ only coupled to the third generation fermions, we find that the future circular collider can discover the lepton number violating signal with a tau lepton for $M_{Z^{\prime }}$ up to 2.2 (3) TeV with the gauge coupling $g^{\prime }=0.6$ and the integrated luminosity of $3(30){\mathrm{ab}}^{-1}$. The test on the flavor combinations of the Standard Model charged leptons would reveal the specific nature of different heavy neutrinos.

We investigate scenarios with $\mathcal{O}(1\mathrm{TeV})$ scalar leptoquarks that act as portals between the Standard Model and dark matter. We assume that dark matter is a scalar singlet $S$ which couples to a scalar leptoquark $\mathrm{\Delta }$ and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in $B$ meson decays. We consider the $SS$ annihilation cross sections to estimate the dark matter relic abundance and explore the interplay between astrophysical, collider, and flavor physics bounds on such models. In the heavy dark matter window, $m_S>m_{\mathrm{\Delta }}$, the leptoquark portal becomes the dominant mechanism to explain the dark matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavor physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both $\mathrm{\Delta }$ and $S$ masses are lighter than $\mathcal{O}(10\mathrm{TeV})$.

Lepton flavor violating interactions are absent in the standard model but are expected in various beyond-standard models. In this work, the potential of the future circular electron-positron collider to probe the four-fermion lepton flavor couplings via the $e^{+}{e}^{-}\to e^{\pm }{\tau }^{\mp }$ process is revisited by means of an effective field theory approach. We provide constraints at 95% C.L. on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies, $\sqrt{s}=157.5$, 162.5, 240, and 365 GeV, according to their corresponding integrated luminosities. We demonstrate that the statistical combination of the results from four center-of-mass energies improves the sensitivity to the lepton flavor violation couplings significantly. We compare the results with the prospects from the Belle II Collaboration with $50{\mathrm{ab}}^{-1}$ and other studies at electron-positron colliders.

Using a recently introduced tensor network method, we study the density of states of the lattice Schwinger model, a standard testbench for lattice gauge theory numerical techniques, but also the object of recent experimental quantum simulations. We identify regimes of parameters where the spectrum appears to be symmetric and displays the expected continuum properties even for finite lattice spacing and number of sites. However, we find that for moderate system sizes and lattice spacing of $ga\sim O(1)$, the spectral density can exhibit very different properties with a highly asymmetric form. We also explore how the method can be exploited to extract thermodynamic quantities.