The recent Advanced LIGO and Advanced Virgo joint observing runs have not claimed a stochastic gravitational-wave background detection, but one expects this to change as the sensitivity of the detectors improves. The challenge of claiming a true detection will be immediately succeeded by the difficulty of relating the signal to the sources that contribute to it. In this paper, we consider backgrounds that comprise compact binary coalescences and additional cosmological sources, and we set simultaneous upper limits on these backgrounds. We find that the Advanced LIGO/Advanced Virgo network, operating at design sensitivity, will not allow for separation of the sources we consider. Third-generation detectors, sensitive to most individual compact binary mergers, can reduce the astrophysical signal via subtraction of individual sources, and potentially reveal a cosmological background. Our Bayesian analysis shows that, assuming a detector network containing Cosmic Explorer and Einstein Telescope and reasonable levels of individual source subtraction, we can detect cosmological signals ${\mathrm{\Omega }}_{\mathrm{CS}}(25\mathrm{Hz})=4.5\times {10}^{-13}$ for cosmic strings, and ${\mathrm{\Omega }}_{\mathrm{BPL}}(25\mathrm{Hz})=2.2\times {10}^{-13}$ for a broken power-law model of an early Universe phase transition.

Long-term ideal and resistive magnetohydrodynamics (MHD) simulations in full general relativity are performed for a massive neutron star formed as a remnant of binary neutron star mergers. Neutrino radiation transport effects are taken into account as in our previous papers. The simulation is performed in axial symmetry and without considering dynamo effects as a first step. In the ideal MHD, the differential rotation of the remnant neutron star amplifies the magnetic-field strength by the winding in the presence of a seed poloidal field until the electromagnetic energy reaches $\sim 10\%$ of the rotational kinetic energy, $E_{\mathrm{kin}}$, of the neutron star. The timescale until the maximum electromagnetic energy is reached depends on the initial magnetic-field strength and it is $\sim 1\mathrm{s}$ for the case that the initial maximum magnetic-field strength is $\sim {10}^{15}\mathrm{G}$. After a significant amplification of the magnetic-field strength by the winding, the magnetic braking enforces the initially differentially rotating state approximately to a rigidly rotating state. In the presence of the resistivity, the amplification is continued only for the resistive timescale, and if the maximum electromagnetic energy reached is smaller than $\sim 3\%$ of $E_{\mathrm{kin}}$, the initial differential rotation state is approximately preserved. In the present context, the post-merger mass ejection is induced primarily by the neutrino irradiation/heating and the magnetic winding effect plays only a minor role for the mass ejection.

Particle detectors of the European Space Environment Viewing and Analysis Network (SEVAN) network located on mountain peaks in Aragats (Armenia), Lomnicky Stit (Slovakia), and Musala (Bulgaria) are well suited for the detection of thunderstorm ground enhancements (TGEs). The modulation of charged particle flux by the electric field of the thundercloud results in a sizable change in the count rate of detectors, which measure fluxes of electrons, gamma rays, and high-energy muons. The relation between electric-field strength and changes of particle-flux count rates is nonlinear and depends on many unknown parameters of the atmospheric electric field and meteorological conditions. Nonetheless, employing tremendous TGEs as a manifestation of the strongest electric field in the thundercloud and by measuring fluxes of three species of secondary cosmic rays (electrons, gamma rays, and muons) by SEVAN detectors located at altitudes of approximately 3 km, we study the extreme strength of the atmospheric electric field. With the simulation of propagation of charged particles in a uniform electric field using the corsika code, we estimate the maximum potential difference in the thunderous atmosphere, which can reach approximately 500 MV.

We present a technique for translating a black-box machine-learned classifier operating on a high-dimensional input space into a small set of human-interpretable observables that can be combined to make the same classification decisions. We iteratively select these observables from a large space of high-level discriminants by finding those with the highest decision similarity relative to the black box, quantified via a metric we introduce that evaluates the relative ordering of pairs of inputs. Successive iterations focus only on the subset of input pairs that are misordered by the current set of observables. This method enables simplification of the machine-learning strategy, interpretation of the results in terms of well-understood physical concepts, validation of the physical model, and the potential for new insights into the nature of the problem itself. As a demonstration, we apply our approach to the benchmark task of jet classification in collider physics, where a convolutional neural network acting on calorimeter jet images outperforms a set of six well-known jet substructure observables. Our method maps the convolutional neural network into a set of observables called energy flow polynomials, and it closes the performance gap by identifying a class of observables with an interesting physical interpretation that has been previously overlooked in the jet substructure literature.

We modify a kinetic theory of massless fermions to incorporate the effects of the conformal anomaly. Working in a collisionless regime, we emulate the conformal anomaly via a momentum-dependent electric coupling. In this prescription, the conformal anomaly leads to a hedgehoglike structure in the momentum space similar to the Berry phase associated with the axial anomaly. The interplay between the axial and conformal anomalies generates the axial current, proportional to the helicity flow of the electromagnetic background. The corresponding conductivity is determined by the running of the electric coupling between the tip of the Dirac cone and the Fermi surface.

It is customary to apply the so-called narrow width approximation $\mathrm{\Gamma }(B\to R{P}_3\to P_1{P}_2{P}_3)=\mathrm{\Gamma }(B\to R{P}_3)\mathcal{B}(R\to P_1{P}_2)$ to extract the branching fraction of the quasi-two-body decay $B\to R{P}_3$, with $R$ and $P_3$ being an intermediate resonant state and a pseudoscalar meson, respectively. However, the above factorization is valid only in the zero width limit. We consider a correction parameter ${\eta }_R$ from finite-width effects. Our main results are as follows: (i) We present a general framework for computing ${\eta }_R$ and show that it can be expressed in terms of the normalized differential rate and determined by its value at the resonance. (ii) We introduce a form factor $F(s_{12},m_R)$ for the strong coupling involved in the $R(m_{12})\to P_1{P}_2$ decay when $m_{12}$ is away from $m_R$. We find that off-shell effects are small in vector meson productions, but prominent in the $K_2^{*}(1430)$, $\sigma /f_0(500)$, and $K_0^{*}(1430)$ resonances. (iii) We evaluate ${\eta }_R$ in the theoretical framework of QCD factorization (QCDF) and in the experimental parametrization (EXPP) for three-body decay amplitudes. In general, ${\eta }_R^{\mathrm{QCDF}}$ and ${\eta }_R^{\mathrm{EXPP}}$ are similar for vector mesons, but different for tensor and scalar resonances. A study of the differential rates enables us to understand the origin of their differences. (iv) Finite-width corrections to $\mathcal{B}(B^{-}\to RP{)}_{\mathrm{NWA}}$ obtained in the narrow width approximation are generally small, less than 10%, but they are prominent in $B^{-}\to \sigma /f_0(500){\pi }^{-}$ and $B^{-}\to {\overline{K}}_0^{*0}(1430){\pi }^{-}$ decays. The EXPP of the normalized differential rates should be contrasted with the theoretical predictions from QCDF calculation as the latter properly takes into account the energy dependence in weak decay amplitudes. (v) It is common to use the Gounaris-Sakurai model to describe the line shape of the broad $\rho (770)$ resonance. After including finite-width effects, the PDG value of $\mathcal{B}(B^{-}\to \rho {\pi }^{-})=(8.3\pm 1.2)\times {10}^{-6}$ should be corrected to $(7.9\pm 1.1)\times {10}^{-6}$ in EXPP and $(7.7\pm 1.1)\times {10}^{-6}$ in QCDF. (vi) For the very broad $\sigma /f_0(500)$ scalar resonance, we use a simple pole model to describe its line shape and find a very large width effect: ${\eta }_{\sigma }^{\mathrm{QCDF}}\sim 2.15$ and ${\eta }_{\sigma }^{\mathrm{EXPP}}\sim 1.64$. Consequently, $B^{-}\to \sigma {\pi }^{-}$ has a large branching fraction of order ${10}^{-5}$. (vii) We employ the Breit-Wigner line shape to describe the production of $K_0^{*}(1430)$ in three-body $B$ decays and find large off-shell effects. The smallness of ${\eta }_{K_0^{*}}^{\mathrm{QCDF}}$ relative to ${\eta }_{K_0^{*}}^{\mathrm{EXPP}}$ is ascribed to the differences in the normalized differential rates off the resonance. (viii) In the approach of QCDF, the calculated $CP$ asymmetries of $B^{-}\to f_2(1270){\pi }^{-},\sigma /f_0(500){\pi }^{-},K^{-}{\rho }^0$ decays agree with the experimental observations. The nonobservation of $CP$ asymmetry in $B^{-}\to \rho (770){\pi }^{-}$ can also be accommodated in QCDF.

A light boson $U$ from an extra $U(1)$ interpolates between a generalized dark photon coupled to $Q$, $B$, and $L_i$ (or $B-L$), plus possibly dark matter, a dark $Z$ coupled to the $Z$ current, and one axially coupled to quarks and leptons. We identify the corresponding $U(1{)}_F$ symmetries, with $F={\gamma }_{Y}Y+{\gamma }_{B}B+{\gamma }_{L_i}{L}_i+{\gamma }_A{F}_A+{\gamma }_{F^{\prime }}{F}^{\prime }+{\gamma }_d{F}_d$, $F_d$ acting in a dark sector and $F^{\prime }$ on possible semi-inert Brout-Englert-Higgs (BEH) doublets uncoupled to quarks and leptons. The $U$ current is obtained from the $U(1{)}_F$ and $Z$ currents, with a mixing determined by the spin-0 BEH fields. The charge $Q_U$ of chiral quarks and leptons is a combination of $Q$, $B$, $L_i$, and $T_{3L}$ with the axial $F_A$. It involves in general isovector and isoscalar axial terms, in the presence of two BEH doublets. A longitudinal $U$ with axial couplings has enhanced interactions and behaves much as an axionlike particle. Its axial couplings $g_A$, usually restricted to $\lesssim 2\times {10}^{-7}{m}_U(\mathrm{MeV})$, lead to effective pseudoscalar ones $g_P=g_A\times 2m_{q,l}/m_U=2^{1/4}{G}_F^{1/2}{m}_{q,l}{A}_{\pm }$. $A_{\pm }$ is proportional to an invisibility parameter $r=\cos {\theta }_A$ induced by a singlet v.e.v., possibly large and allowing the $U$ to be very weakly interacting. This allows for a very small gauge coupling, expressed with two doublets and a singlet as $g^{\prime \prime }/4\simeq 2\times {10}^{-6}{m}_U(\mathrm{MeV})r/\sin 2\beta$. We discuss phenomenological implications for meson decays, neutrino interactions, atomic-physics parity violation, naturally suppressed ${\pi }^0\to \gamma U$ decays, etc. The $U$ boson fits within the grand unification framework, in symbiosis with a $SU(4{)}_{\mathrm{es}}$ electrostrong symmetry broken at the grand unification scale, with $Q_U$ depending on $Q$, $B-L$, $F_A$, and $T_{3A}$ through three parameters ${\gamma }_Y$, ${\gamma }_A$, and $\eta$.

We investigate supersymmetric hybrid inflation in a realistic model based on the gauge symmetry $SU(4{)}_c\times SU(2{)}_L\times SU(2{)}_R$. The minimal supersymmetric standard model (MSSM) $\mu$ term arises, following Dvali, Lazarides, and Shafi, from the coupling of the MSSM electroweak doublets to a gauge singlet superfield, which plays an essential role in inflation. The primordial monopoles are inflated away by arranging that the $SU(4{)}_c\times SU(2{)}_L\times SU(2{)}_R$ symmetry is broken along the inflationary trajectory. The interplay between the (above) $\mu$ coupling, the gravitino mass, and the reheating following inflation is discussed in detail. We explore regions of the parameter space that yield gravitino dark matter and observable gravity waves with the tensor-to-scalar ratio $r\sim {10}^{-4}–{10}^{-3}$.

Thimble regularization is a possible solution to the sign problem, which is evaded by formulating quantum field theories on manifolds where the imaginary part of the action stays constant (Lefschetz thimbles). A major obstacle is due to the fact that one in general needs to collect contributions coming from more than one thimble. Here we explore the idea of performing Taylor expansions on Lefschetz thimbles. We show that in some cases we can compute expansions in regions where only the dominant thimble contributes to the result in such a way that these (different, disjoint) regions can be bridged. This can most effectively be done via Padé approximants. In this way multi-thimble simulations can be circumvented. The approach can be trusted provided we can show that the analytic continuation we are performing is a legitimate one, which thing we can indeed show. We briefly discuss two prototypal computations, for which we obtained a very good control on the analytical structure (and singularities) of the results. All in all, the main strategy that we adopt is supposed to be valuable not only in the thimble approach, which thing we finally discuss.

We study the phase structure of the two-flavor Nambu–Jona-Lasinio (NJL) model in the chiral limit, extending a previous study of the competition of an inhomogeneous chiral phase and a two-flavor color-superconducting (2SC) phase [M. Sadzikowski, Phys. Lett. B 553, 45 (2003); M. Sadzikowski, Phys. Lett. B 642, 238 (2006)]. There, an analytic expression for the dispersion relations for quasiparticle excitations in the presence of both a particular inhomogeneous chiral condensate, the so-called chiral density wave (CDW), and a homogeneous 2SC condensate was found. In this work we show how to determine the dispersion relations for arbitrary modulations of the chiral condensate in the presence of a homogeneous 2SC condensate, if the dispersion relations in the absence of color superconductivity are known. In our calculations, we employ two different Ansätze for the inhomogeneous chiral condensate, the CDW as well as the real-kink crystal (RKC). Depending on the value of the diquark coupling we find a region of the phase diagram where the inhomogeneous chiral and the 2SC condensates coexist, confirming results of M. Sadzikowski [Phys. Lett. B 553, 45 (2003); 642, 238 (2006)]. Decreasing the diquark coupling favors the inhomogeneous phase over the coexistence phase. On the other hand, increasing the diquark coupling leads to a larger 2SC phase, while the inhomogeneous chiral and the coexistence phases become smaller. In agreement with previous studies the RKC Ansatz is energetically preferred over the CDW Ansatz. Both Ansätze lead to a qualitatively similar phase diagram, however, the coexistence phase is smaller for the RKC Ansatz.

We study the diffusion of charm quarks in the early stage of high energy nuclear collisions at the RHIC and the LHC. The main novelty of the present study is the introduction of the color current carried by the heavy quarks that propagate in the evolving glasma (EG), which is responsible of the energy loss via polarization of the medium. We compute the transverse momentum broadening, ${\sigma }_p$, of charm in the prethermalization stage, and the impact of the diffusion on the nuclear modification factor in nucleus-nucleus collisions. The net effect of energy loss is marginal in the prethermalization stage. The study is completed by the calculation of coordinate spreading, ${\sigma }_x$, and by a comparison with Langevin dynamics. ${\sigma }_p$ in EG overshoots the result of standard Langevin dynamics at the end of the prehydro regime. We interpret this as a result of memory of the color force acting on the charm quarks that implies ${\sigma }_p\propto t^2$. Moreover, ${\sigma }_x\propto t^2$ in the prehydro stage shows that the charm quark in the EG is in the regime of ballistic diffusion.

We combine ALEPH and OPAL results for the spectral distributions measured in $\tau \to {\pi }^{-}{\pi }^0{\nu }_{\tau }$, $\tau \to 2{\pi }^{-}{\pi }^{+}{\pi }^0{\nu }_{\tau }$ and $\tau \to {\pi }^{-}3{\pi }^0{\nu }_{\tau }$ decays with (i) recent BABAR results for the analogous $\tau \to K^{-}{K}^0{\nu }_{\tau }$ distribution and (ii) estimates of the contributions from other hadronic $\tau$-decay modes obtained using CVC and electroproduction data, to obtain a new and more precise nonstrange, inclusive vector, isovector spectral function. The BABAR $K^{-}{K}^0$ and CVC/electroproduction results provide us with alternate, entirely data-based input for the contributions of all exclusive modes for which ALEPH and OPAL employed Monte-Carlo-based estimates. We use the resulting spectral function to determine ${\alpha }_s(m_{\tau })$, the strong coupling at the $\tau$ mass scale, employing finite energy sum rules. Using the fixed-order perturbation theory (FOPT) prescription, we find ${\alpha }_s(m_{\tau })=0.3077\pm 0.0075$, which corresponds to the five-flavor result ${\alpha }_s(M_Z)=0.1171\pm 0.0010$ at the $Z$ mass. While we also provide an estimate using contour-improved perturbation theory (CIPT), we point out that the FOPT prescription is to be preferred for comparison with other ${\alpha }_s$ determinations employing the $\overline{\mathrm{MS}}$ scheme, especially given the inconsistency between CIPT and the standard operator product expansion recently pointed out in the literature. Additional experimental input on the dominant $2\pi$ and $4\pi$ modes would allow for further improvements to the current analysis.

We present a first attempt to design a quantum circuit for the determination of the parton content of the proton through the estimation of parton distribution functions (PDFs), in the context of high energy physics (HEP). The growing interest in quantum computing and the recent developments of new algorithms and quantum hardware devices motivates the study of methodologies applied to HEP. In this work we identify architectures of variational quantum circuits suitable for PDFs representation (qPDFs). We show experiments about the deployment of qPDFs on real quantum devices, taking into consideration current experimental limitations. Finally, we perform a global qPDF determination from collider data using quantum computer simulation on classical hardware and we compare the obtained partons and related phenomenological predictions involving hadronic processes to modern PDFs.

The light-front wave function of a proton composed of three quarks and a perturbative gluon is computed. This is then used to derive expressions for the color charge density correlator $⟨{\rho }^a({\overrightarrow{q}}_1){\rho }^b({\overrightarrow{q}}_2)⟩$ at $\mathcal{O}(g^4)$ due to the emission of a gluon by one of the quarks in the light-cone gauge. The correlator exhibits the soft and collinear singularities. Albeit, we employ exact gluon emission and absorption vertices, and hence the gluon is not required to carry very small light-cone momentum, or to be collinear to the emitting quark. We verify that the correlator satisfies the Ward identity and that it is independent of the renormalization scale, i.e., that ultraviolet divergences cancel. Our expressions provide $x$-dependent initial conditions for Balitsky-Kovchegov evolution of the $C$-even part of the dipole scattering matrix to higher energies. That is, we determine the first nontrivial moment of the color charge fluctuations which act as sources for soft color fields in the proton with wavelengths greater than approximately $1/x\sim 10–100$.

The transverse momentum spectra of hadrons are calculated from the unintegrated gluon distribution (UGD) within the $k_T$-factorization framework at small $x$. Starting from $pp$ collisions, the modification caused by the nuclear medium is incorporated in the UGD at high energies, which is related to the nuclear shadowing phenomenon. Moreover, we consider that particle production from minijet decay is not enough to explain the $p_T$ spectra in $AA$ collisions due to collective phenomena that take place after the hard collision. The Boltzmann-Gibbs blast wave distribution is utilized in order to evaluate the distribution of particle production in equilibrium. Data from the ALICE Collaboration for PbPb collisions at $\sqrt{s}=2.76\mathrm{TeV}$ are analyzed, and the nuclear modification factor for pion production is computed.

The recently discovered fully charmed tetraquark candidate $X(6900)$ is analyzed within the frameworks of effective-range expansion, compositeness relation and width saturation, and a coupled multichannel dynamical study. By taking into account constraints from heavy-quark spin symmetry, the coupled-channel amplitude including the $J/\psi J/\psi$, ${\chi }_{c0}{\chi }_{c0}$, and ${\chi }_{c1}{\chi }_{c1}$ is constructed to fit the experimental di-$J/\psi$ event distributions around the energy region near 6.9 GeV. Another dynamical two-coupled-channel amplitude with the $J/\psi J/\psi$ and $\psi (3770)J/\psi$ is also considered to describe the same datasets. The three different theoretical approaches lead to similar conclusions that the two-meson components do not play dominant roles in the $X(6900)$. Our determinations of the resonance poles in the complex energy plane from the refined coupled-channel study are found to be consistent with the experimental analyses. The coupled-channel amplitudes also have another pole corresponding to a narrow resonance $X(6825)$ that we predict sitting below the ${\chi }_{c0}{\chi }_{c0}$ threshold and of molecular origin. We give predictions to the line shapes of the ${\chi }_{c0}{\chi }_{c0}$ and ${\chi }_{c1}{\chi }_{c1}$ channels, which could provide a useful guide for future experimental measurements.

We discuss the impact of the cosmological measurements on the predictions of the Majorana mass of the neutrinos, the parameter probed by neutrinoless double-beta decay experiments. Using a minimal set of assumptions, we quantify the probabilities of discovering neutrinoless double-beta decay and introduce a new graphical representation that could be of interest for the community

The linearly polarized quasireal photons from the highly Lorentz-contracted Coulomb fields of relativistic heavy ions can fluctuate to quark-antiquark pairs, scatter off a target nucleus, and emerge as vector mesons. In the process, the two colliding nuclei can serve as slits, forming a Young’s double-slit experiment. In addition to the well-known double-slit interference pattern in position space, a similar interference pattern may be expected in polarization space due to the linear polarization of the colliding photons. In this paper, we investigate the interference effect in polarization space as revealed by the asymmetries of the decay angular distribution for vector meson photoprodution in heavy-ion collisions. We find a periodic oscillation pattern with transverse momentum, which can reasonably explain the second-order modulation in azimuth for the ${\rho }^0$ decay observed by the STAR Collaboration.

In 2015, the PHENIX collaboration has measured very forward ($\eta >6.8$) single spin asymmetries of inclusive neutrons in transversely polarized proton-proton and proton-nucleus collisions at a center of mass energy of 200 GeV. A previous publication from this dataset concentrated on the nuclear dependence of such asymmetries. In this measurement the explicit transverse momentum dependence of inclusive neutron single spin asymmetries for proton-proton collisions is extracted using a bootstrapping unfolding technique on the transverse momenta. This explicit transverse momentum dependence will help improve the understanding of the mechanisms that create these asymmetries.

A new approach to the study of nonrelativistic bosonic string in flat spacetime is introduced, based on a holistic Hamiltonian analysis of the minimal action for the string. This leads to a structurally new form of the action which is, however, equivalent to the known results since, under appropriate limits, it interpolates between the minimal action (Nambu-Goto type) where the string metric is taken to be that induced by the embedding and the Polyakov type of action where the world sheet metric components are independent fields. The equivalence among different actions is established by a detailed study of symmetries using constraint analysis. Various vexing issues in the existing literature are clarified. The interpolating action mooted here is shown to reveal the geometry of the string and may be useful in analyzing nonrelativistic string coupled with curved background.