In this paper we investigate the ${\eta }_c$ production by photon-photon and photon-hadron interactions in $pp$ and $pA$ collisions at the LHC energies. The inclusive and diffractive contributions for the ${\eta }_c$ photoproduction are estimated using the nonrelativistic quantum chromodynamics (NRQCD) formalism. We estimate the rapidity and transverse momentum distributions for the ${\eta }_c$ photoproduction in hadronic collisions at the LHC and present our estimate for the total cross sections at the Run 2 energies. A comparison with the predictions for the exclusive ${\eta }_c$ photoproduction, which is a direct probe of the odderon, is also presented.

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the decay $t(\uparrow )\to X_b+W^{+}$ of a polarized top quark. The spin-momentum correlation in this quasi two-body decay is described by the polar angle distribution $\mathrm{d}\mathrm{\Gamma }/\mathrm{d}\cos {\theta }_P=\frac{\mathrm{\Gamma }}{2}(1+P_t{\alpha }_P\cos {\theta }_P)$, where $P_t$ is the polarization of the top quark and ${\alpha }_P$ denotes the asymmetry parameter of the decay. For the latter we find ${\alpha }_P^{\mathrm{NNLO}}=0.3792\pm 0.0037$.

The decay of accelerated protons has been analyzed both in the laboratory frame (where the proton is accelerated) and in the comoving frame (where the proton is at rest and interacts with the Fulling-Davies-Unruh thermal bath of electrons and neutrinos). The equality between the two rates has been exhibited as an evidence of the necessity of Fulling-Davies-Unruh effect for the consistency of quantum field theory formalism. Recently, it has been argued that neutrino mixing can spoil such a result, potentially opening new scenarios in neutrino physics. In the present paper, we analyze in detail this problem, and we find that, assuming flavor neutrinos to be fundamental and working within a certain approximation, the agreement can be restored.

We study relativistic stars in degenerate higher-order scalar-tensor theories that evade the constraint on the speed of gravitational waves imposed by GW170817. It is shown that the exterior metric is given by the usual Schwarzschild solution if the lower order Horndeski terms are ignored in the Lagrangian and a shift symmetry is assumed. However, this class of theories exhibits partial breaking of Vainshtein screening in the stellar interior and thus modifies the structure of a star. Employing a simple concrete model, we show that for high-density stars the mass-radius relation is altered significantly even if the parameters are chosen so that only a tiny correction is expected in the Newtonian regime. We also find that, depending on the parameters, there is a maximum central density above which solutions cease to exist.

We consider a generalized teleparallel theory of gravitation, where the action contains an arbitrary function of the torsion scalar and a scalar field, $f(T,\varphi )$, thus encompassing the cases of $f(T)$ gravity and a nonminimally coupled scalar field as subclasses. The action is manifestly Lorentz invariant when besides the tetrad one allows for a flat but nontrivial spin connection. We derive the field equations and demonstrate how the antisymmetric part of the tetrad equations is automatically satisfied when the spin connection equation holds. The spin connection equation is a vital part of the covariant formulation, since it determines the spin connection associated with a given tetrad. We discuss how the spin connection equation can be solved in general and provide the cosmological and spherically symmetric examples. Finally, we generalize the theory to an arbitrary number of scalar fields.

We study the anisotropic neutrino emission from the core of neutron stars induced by the star’s magnetic field. We model the core as made out of a magnetized ideal gas of strange quark matter and implement the conditions for stellar equilibrium in this environment. The calculation is performed without resorting to analytical simplifications and for temperature, density, and magnetic field values corresponding to typical conditions for a neutron star’s evolution. The anisotropic neutrino emission produces a rocket effect that contributes to the star’s kick velocity. We find that the computed values for the kick velocity lie within the range of the observed values, reaching velocities of the order of $\sim 1000\mathrm{km}{\mathrm{s}}^{-1}$ for magnetic fields between ${10}^{15}-{10}^{18}\mathrm{G}$ and radii of 20 to 5 km, respectively.

The Milky Way’s Galactic Center harbors a gamma-ray excess that is a candidate signal of annihilating dark matter. Dwarf galaxies remain predominantly dark in their expected commensurate emission. In this work we quantify the degree of consistency between these two observations through a joint likelihood analysis. In doing so we incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center extended gamma-ray excess (GCE) detected by the Fermi Gamma-Ray Space Telescope. The preferred range of annihilation rates and masses expands when including these unknowns. Even so, using two recent determinations of the Milky Way halo’s local density leaves the GCE preferred region of single-channel dark matter annihilation models to be in strong tension with annihilation searches in combined dwarf galaxy analyses. A third, higher Milky Way density determination, alleviates this tension. Our joint likelihood analysis allows us to quantify this inconsistency. We provide a set of tools for testing dark matter annihilation models’ consistency within this combined data set. As an example, we test a representative inverse Compton sourced self-interacting dark matter model, which is consistent with both the GCE and dwarfs.

We investigate the regularization-scheme dependent treatment of ${\gamma }_5$ in the framework of dimensional regularization, mainly focusing on the four-dimensional helicity scheme (fdh). Evaluating distinctive examples, we find that for one-loop calculations, the recently proposed four-dimensional formulation (fdf) of the fdh scheme constitutes a viable and efficient alternative compared to more traditional approaches. In addition, we extend the considerations to the two-loop level and compute the pseudoscalar form factors of quarks and gluons in fdh. We provide the necessary operator renormalization and discuss at a practical level how the complexity of intermediate calculational steps can be reduced in an efficient way.

Vacuum magnetic birefringence is one of the most interesting nonlinear phenomena in quantum electrodynamics because it is a pure photon-photon result of the theory and it directly signalizes the violation of the classical superposition principle of electromagnetic fields in the full quantum theory. We perform analytical and numerical calculations when an electromagnetic wave interacts with an oscillating external magnetic field. We find that in an ideal cavity, when the external field frequency is around the electromagnetic wave frequency, the normal and parallel components of the wave suffer parametric resonance at different rates, producing a vacuum birefringence effect growing in time. We also study the case where there is no cavity and the oscillating magnetic field is spatially localized in a region of length $L$. In both cases we find also a rotation of the elliptical axis.

Recently, the Dark Matter Particle Explorer (DAMPE) experiment released the new measurement of the total cosmic $e^{+}{e}^{-}$ flux between 25 GeV and 4.6 TeV, which indicates a spectral softening at around 0.9 TeV and a tentative peak at around 1.4 TeV. We utilize a scalar dark matter (DM) model to explain the DAMPE peak by $\chi \chi \to Z^{\prime }{Z}^{\prime }\to \ell \overline{\ell }{\ell }^{\prime }\overline{{\ell }^{\prime }}$ with an additional anomaly-free gauged $U(1)$ family symmetry, in which $\chi$, $Z^{\prime }$, and ${\ell }^{(\prime )}$ denote, respectively, the scalar DM, the new gauge boson, and ${\ell }^{(\prime )}=e$, $\mu$, $\tau$ with $m_{\chi }\sim m_{Z^{\prime }}\sim 2\times 1.5(\mathrm{TeV})$. We first illustrate that the minimal framework $G_{\mathrm{SM}}\times U(1{)}_{Y^{\prime }}$ with the above mass choices can explain the DAMPE excess, which, however, be excluded by LHC constraints from the $Z^{\prime }$ searches. Then, we study a nonminimal framework $G_{\mathrm{SM}}\times U(1{)}_{Y^{\prime }}\times U(1{)}_{Y^{\prime \prime }}$ in which $U(1{)}_{Y^{\prime \prime }}$ mixes with $U(1{)}_{Y^{\prime }}$. We show that such a framework can interpret the DAMPE data and at the same time survive all other constraints including the DM relic abundance, DM direct detection, and collider bounds. We also investigate the predicted $e^{+}{e}^{-}$ spectrum in this framework and find that the mass splitting $\mathrm{\Delta }m=m_{\chi }-m_{Z^{\prime \prime }}$ should be less than about 17 GeV to produce the peaklike structure.

We present a detailed study of the applications of two stochastic approaches, stochastic optimization method (SOM) and stochastic analytical inference (SAI), to extract spectral functions from Euclidean correlation functions. SOM has the advantage that it does not require prior information. On the other hand, SAI is a more generalized method based on Bayesian inference. Under mean field approximation SAI reduces to the often-used maximum entropy method (MEM) and for a specific choice of the prior SAI becomes equivalent to SOM. To test the applicability of these two stochastic methods to lattice QCD, firstly, we apply these methods to various reasonably chosen model correlation functions and present detailed comparisons of the reconstructed spectral functions obtained from SOM, SAI and MEM. Next, we present similar studies for charmonia correlation functions obtained from lattice QCD computations using clover-improved Wilson fermions on large, fine, isotropic lattices at 0.75 and $1.5T_c$, $T_c$ being the deconfinement transition temperature of a pure gluon plasma. We find that SAI and SOM give consistent results to MEM at these two temperatures.

We consider $SU(N)$ Yang-Mills theory with massless chiral fermions in a complex representation of the gauge group. The main emphasis is on the so-called hybrid $\psi \chi \eta$ model. The possible patterns of realization of the continuous chiral flavor symmetry are discussed. We argue that the chiral symmetry is broken in conjunction with a dynamical Higgsing of the gauge group (complete or partial) by bifermion condensates. As a result a color-flavor locked symmetry is preserved. The ’t Hooft anomaly matching proceeds via saturation of triangles by massless composite fermions or, in a mixed mode, i.e. also by the “weakly” coupled fermions associated with dynamical Abelianization, supplemented by a number of Nambu-Goldstone mesons. Gauge-singlet condensates are of the multifermion type and, though it cannot be excluded, the chiral symmetry realization via such gauge invariant condensates is more contrived (requires a number of four-fermion condensates simultaneously and, even so, problems remain) and less plausible. We conclude that in the model at hand, chiral flavor symmetry implies dynamical Higgsing by bifermion condensates.

The LHCb Experiment at CERN has observed a doubly-charmed baryon ${\mathrm{\Xi }}_{cc}^{++}=ccu$ with a mass of $3621.40\pm 0.78\mathrm{MeV}$, consistent with many predictions. We use the same methods that led us to predict $M({\mathrm{\Xi }}_{cc},J^P=1/2^{+})=3627\pm 12\mathrm{MeV}$ and $M({\mathrm{\Xi }}_{cc}^{*},J^P=3/2^{+})=3690\pm 12\mathrm{MeV}$ to predict $M({\mathrm{\Omega }}_{cc}^{+},J^P=1/2^{+})=3692\pm 16\mathrm{MeV}$ and $M({\mathrm{\Omega }}_{cc}^{*},J^P=3/2^{+})=3756\pm 16\mathrm{MeV}$. Production and decay are discussed briefly, and predictions for $M({\mathrm{\Omega }}_{bc})$ and $M({\mathrm{\Omega }}_{bb})$ are included.

We perform a detailed study of the grand unified theories $SO(10)$ and $E(6)$ with left-right intermediate gauge symmetries of the form $SU(N{)}_L\otimes SU(N{)}_R\otimes \mathcal{G}$. Proton decay lifetime constrains the unification scale to be $\gtrsim {10}^{16}\mathrm{GeV}$ and, as discussed in this paper, unwanted cosmological relics can be evaded if the intermediate symmetry scale is $\gtrsim {10}^{12}\mathrm{GeV}$. With these conditions, we study the renormalization group evolution of the gauge couplings and do a comparative analysis of all possible left-right models where unification can occur. Both the D-parity conserved and broken scenarios as well as the supersymmetric (SUSY) and nonsupersymmetric (non-SUSY) versions are considered. In addition to the fermion and scalar representations at each stage of the symmetry breaking, contributing to the $\beta$ functions, we list the intermediate left-right groups that successfully meet these requirements. We make use of the dimension-5 kinetic mixing effective operators for achieving unification and large intermediate scale. A significant result in the supersymmetric case is that to achieve successful unification for some breaking patterns, the scale of SUSY breaking needs to be at least a few TeV. In some of these cases, the intermediate scale can be as low as $\sim {10}^{12}\mathrm{GeV}$, for the SUSY scale to be $\sim 30\mathrm{TeV}$. This has important consequences in the collider searches for SUSY particles and phenomenology of the lightest neutralino as dark matter.

Recently, a tetraquark mixing framework has been proposed for light mesons and applied more or less successfully to the isovector resonances, $a_0(980)$, $a_0(1450)$, as well as to the isodoublet resonances, $K_0^{*}(800),K_0^{*}(1430)$. In this work, we present a more extensive view on the mixing framework and apply this framework to the isoscalar resonances, $f_0(500)$, $f_0(980)$, $f_0(1370)$, $f_0(1500)$. Tetraquarks in this framework can have two spin configurations containing either spin-0 diquark or spin-1 diquark and each configuration forms a nonet in flavor space. The two spin configurations are found to mix strongly through the color-spin interactions. Their mixtures, which diagonalize the hyperfine masses, can generate the physical resonances constituting two nonets, which, in fact, coincide roughly with the experimental observation. We identify that $f_0(500)$, $f_0(980)$ are the isoscalar members in the light nonet, and $f_0(1370)$, $f_0(1500)$ are the similar members in the heavy nonet. This means that the spin configuration mixing, as it relates the corresponding members in the two nonets, can generate $f_0(500)$, $f_0(1370)$ among the members in light mass, and $f_0(980)$, $f_0(1500)$ in heavy mass. The complication arises because the isoscalar members of each nonet are subject to an additional flavor mixing known as Okubo-Zweig-Iizuka rule so that $f_0(500)$, $f_0(980)$, and similarly $f_0(1370)$, $f_0(1500)$, are the mixture of two isoscalar members belonging to an octet and a singlet in ${\mathrm{SU}}_f(3)$. The tetraquark mixing framework including the flavor mixing is tested for the isoscalar resonances in terms of the mass splitting and the fall-apart decay modes. The mass splitting among the isoscalar resonances is found to be consistent qualitatively with their hyperfine mass splitting strongly driven by the spin configuration mixing, which suggests that the tetraquark mixing framework works. The fall-apart modes from our tetraquarks also seem to be consistent with the experimental modes. We also discuss possible existence of the spin-1 tetraquarks that can be constructed by the spin-1 diquark.

Sum rules for the low-energy constants of the chiral SU(3) Lagrangian with charmed baryons of spin $J^P=1/2^{+}$ and $J^P=3/2^{+}$ baryons are derived from large-$N_c$ QCD. We consider the large-$N_c$ operator expansion at subleading orders for current-current correlation functions in the charmed baryon-ground states for two scalar and two axial-vector currents.

We propose a model based on Regge theory to describe photoproduction of light vector mesons. We fit the SLAC data and make predictions for the energy and momentum-transfer dependence of the spin-density matrix elements in photoproduction of $\omega$, ${\rho }^0$ and $\varphi$ mesons at $E_{\gamma }\sim 8.5\mathrm{GeV}$, which are soon to be measured at Jefferson Lab.

We study the topological string partition function of a class of toric, double elliptically fibered Calabi-Yau threefolds $X_{N,M}$ at a generic point in the Kähler moduli space. These manifolds engineer little string theories in five dimensions or lower and are dual to stacks of M5-branes probing a transverse orbifold singularity. Using the refined topological vertex formalism, we explicitly calculate a generic building block which allows us to compute the topological string partition function of $X_{N,M}$ as a series expansion in different Kähler parameters. Using this result, we give further explicit proof for a duality found previously in the literature, which relates $X_{N,M}\sim X_{N^{\prime },M^{\prime }}$ for $NM=N^{\prime }{M}^{\prime }$ and $\gcd (N,M)=\gcd (N^{\prime },M^{\prime })$.