We investigate models involving a vectorlike quark ($X$), which forms a 750 GeV bound state and reproduces the observed diphoton signals at the LHC, in connection with other excesses in the LHC data. An exotic hypercharge of $-4/3$ is required to fit the signal cross section, which indicates that there is an additional particle(s) that mediates the decay of $X$ in the full theory. We find that introducing an SU(2) doublet vectorlike quark of mass around 600 GeV in our UV-complete framework can accommodate not only the diphoton but also the on-$Z$ excess (and potentially a slight excess in the monojet events). Our models also include a dark matter candidate. The most useful way to probe the models at the LHC is via monojet searches. The relic dark matter density is largely determined by coannihilation effects, and indirect detection of dark matter annihilation signals is the alternative and complementary probe of our models.

We propose an experiment for measuring the effective Casimir pressure between two parallel silicon carbide (SiC) plates with aligned nuclear spins. The prospective constraints on an axion-neutron coupling constant for both hadronic and grand unified theory (GUT) axions are calculated using the process of one-axion exchange. For this purpose, a general expression for the additional pressure arising between two polarized plates due to the exchange of one axion between their constituent fermions is derived. We demonstrate that only the polarization component perpendicular to the plates contributes to the pressure. The obtained pressure can be both repulsive and attractive depending on whether the polarizations of both plates are unidirectional or directed in opposite directions. It is shown that although the constraints on an axion-electron coupling obtained in the case of magnetized plates are not competitive, the constraints on an axion-neutron coupling found for plates with polarized nuclear spins are of the same order of magnitude as those obtained previously for the GUT axions alone using the process of two-axion exchange. The proposed experiment allows us also to strengthen the presently known constraints on the axion-neutron coupling constants of GUT axions by using both processes of one- and two-axion exchange.

We investigate the parameter space of a model that extends to the next to minimal supersymmetric standard model with the vectorlike particles [Y.-L. Tang, Phys. Rev. D 90, 075020 (2014)]. We find that the $10+\overline{10}$ model can explain the possible diphoton excess recently revealed by the ATLAS and CMS collaborations, although the predicted signal strength is a little smaller than the observed one.

Revised formulas for the inclusive cross section of a triple parton scattering process in a hadron collision are suggested based on the modified collinear three-parton distributions. The possible phenomenological issues are discussed.

The response of electromagnetic (EM) fields that are produced in noncentral heavy-ion collisions to electromagnetically charged quark gluon plasma can be understood in terms of charge transport and charge diffusion in the hot QCD medium. This article presents a perspective on these processes by investigating the temperature behavior of the related transport coefficients, viz. electrical conductivity and the charge diffusion coefficients along with charge susceptibility. In the process of estimating them, thermal relaxation times for quarks and gluons have been determined first. These transport coefficients have been studied by solving the relativistic transport equation in the Chapman-Enskog method. For the analysis, $2\to 2$, quark-quark, quark-gluon and gluon-gluon scattering processes are taken into account along with an effective description of hot QCD equations of state (EOSs) in terms of temperature dependent effective fugacities of quasiquarks (antiquarks) and quasigluons. Both improved perturbative hot QCD EOSs at high temperature and a lattice QCD EOS are included for the analysis. The hot QCD medium effects entering through the quasiparticle momentum distributions along with an effective coupling, are seen to have significant impact on the temperature behavior of these transport parameters along with the thermal relaxation times for the quasigluons and quasiquarks.

We compute the perturbative corrections to the heavy quark effective theory sum rules for the matrix element of the $\mathrm{\Delta }B=2$ operator that determines the mass difference of $B^0$, ${\overline{B}}^0$ states. Technically, we obtain analytically the nonfactorizable contributions at order ${\alpha }_s$ to the bag parameter that first appear at the three-loop level. Together with the known nonperturbative corrections due to vacuum condensates and $1/m_b$ corrections, the full next-to-leading order result is now available. We present a numerical value for the renormalization group invariant bag parameter that is phenomenologically relevant and compare it with recent lattice determinations.

We propose an action for an unstable Dp-brane with dynamical tension. We show that the equations of motion are equivalent to the equations of motion derived from Dirac-Born-Infeld and Wess-Zumino actions for a non-Bogomol’nyi-Prasad-Sommerfield Dp-brane. We also find the Hamiltonian formulation of this action and analyze the properties of the solutions corresponding to the tachyon vacuum and zero-tension solution.

We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one component superfluid phases, the coexistent superfluid phase has also been found in the anti–de Sitter soliton background for the first time. We construct the complete phase diagram in the $e–\mu$ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of the pole of optical conductivity at $\omega =0$ indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of the pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the nonsmoothness at the critical points as the order parameter of the condensate, which indicates that the phase transitions can also be identified by the behavior of the sound speed. Moreover, as expected from the boundary conformal field theory, the sound speed saturates to $\frac{1}{\sqrt{2}}$ at the large chemical potential limit for our two component holographic superfluid model.

Spectral heat kernel/zeta function regularization procedures are employed in this paper to control the divergences arising from vacuum fluctuations of Bogomolnyi-Prasad-Sommerfield vortices in the Abelian Higgs model. Zero modes of vortex fluctuations are the source of difficulties appearing when the standard Gilkey-de Witt expansion is the tool used in the calculations of one-loop shifts of vortex masses and string tensions. A modified GdW expansion is developed to diminish the impact of the infrared divergences due to the vortex zero modes of fluctuation. With this new technique at our disposal we compute the one-loop vortex mass shifts in the planar AHM and the quantum corrections to the string tension of the magnetic flux tubes living in three dimensions. In both cases it is observed that weak repulsive forces surge between these classically noninteracting topological defects caused by vacuum quantum fluctuations.

We study how the scalar power spectrum of single-scalar inflation depends functionally on models with features which have been proposed to explain anomalies in the data. We exploit a new formalism based on evolving the norm-squared of the scalar mode functions, rather than the mode functions themselves.

The inertial (due to rotation) and gravitational fields of the Earth affect the motion of an elementary particle and its spin dynamics. This influence is not negligible and should be taken into account in high-energy physics experiments. Earth’s influence is manifest in perturbations in the particle motion, in an additional precession of the spin, and in a change of the constitutive tensor of the Maxwell electrodynamics. Bigger corrections are oscillatory, and their contributions average to zero. Other corrections due to the inhomogeneity of the inertial field are not oscillatory but they are very small and may be important only for the storage ring electric dipole moment experiments. Earth’s gravity causes the Newton-like force, the reaction force provided by a focusing system, and additional torques acting on the spin. However, there are no observable indications of the electromagnetic effects due to Earth’s gravity.

In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars. A hadronic chiral SU(3) model is applied to cold neutron stars and proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.

We consider a Weyl-invariant formulation of gravity with a cosmological constant in $d$-dimensional spacetime and show that near two dimensions the classical action reduces to the timelike Liouville action. We show that the renormalized cosmological term leads to a nonlocal quantum momentum tensor which satisfies the Ward identities in a nontrivial way. The resulting evolution equations for an isotropic, homogeneous universe lead to slowly decaying vacuum energy and power-law expansion. We outline the implications for the cosmological constant problem, inflation, and dark energy.

Applying the recently developed dynamical perturbation formalism on cosmological background to scalar-tensor theory, we provide a solid theoretical basis and a rigorous justification for phenomenological models of orbital dynamics that are currently used to interpret experimental measurements of the time-dependent gravitational constant. We derive the field equations for the scalar-tensor perturbations and study their gauge freedom associated with the cosmological expansion. We find a new gauge eliminating a prohibitive number of gauge modes in the field equations and significantly simplifying post-Newtonian equations of motion for localized astronomical systems in the universe with a time-dependent gravitational constant. We identify several new post-Newtonian terms and calculate their effect on secular cosmological evolution of the osculating orbital elements.

The cold dark matter (CDM) model, wherein the dark matter is treated as a pressureless perfect fluid, provides a good fit to galactic and cosmological data. With the advent of precision cosmology, it should be asked whether this simplest model needs to be extended, and whether doing so could improve our understanding of the properties of dark matter. One established parametrization for generalizing the CDM fluid is the generalized dark matter (GDM) model, in which dark matter is an imperfect fluid with pressure and shear viscosity that fulfill certain postulated closure equations. We investigate these closure equations and the three new parametric functions they contain: the background equation of state $w$, the speed of sound $c_s^2$ and the viscosity $c_{\text{vis}}^2$. Taking these functions to be constant parameters, we analyze an exact solution of the perturbed Einstein equations in a flat GDM-dominated universe and discuss the main effects of the three parameters on the cosmic microwave background (CMB). Our analysis suggests that the CMB alone is not able to distinguish between the GDM sound speed and viscosity parameters, but that other observables, such as the matter power spectrum, are required to break this degeneracy. In order to elucidate further the meaning of the GDM closure equations, we also consider other descriptions of imperfect fluids that have a nonperturbative definition and relate these to the GDM model. In particular, we consider scalar fields, an effective field theory (EFT) of fluids, an EFT of large-scale structure, nonequilibrium thermodynamics and tightly coupled fluids. These descriptions could be used to extend the GDM model into the nonlinear regime of structure formation, which is necessary if the wealth of data available on those scales is to be employed in constraining the model. We also derive the initial conditions for adiabatic and isocurvature perturbations in the presence of GDM and standard cosmological fluids and provide the result in a form ready for implementation in Einstein-Boltzmann solvers.

Inspired by the standard model of particle physics, we discuss a mechanism for constructing chiral, anomaly-free gauge theories. The gauge symmetries and particle content of such theories are identified using subgroups and complex representations of simple anomaly-free Lie groups, such as $SO(10)$ or $E_6$. We explore, using mostly $SO(10)$ and the $\mathbf{16}$ representation, several of these “imperfect copies” of the standard model, including $U(1{)}^N$ theories, $SU(5)\otimes U(1)$ theories, $SU(4)\otimes U(1{)}^2$ theories with 4-plets and 6-plets, and chiral $SU(3)\otimes SU(2)\otimes U(1)$. A few general properties of such theories are discussed, as is how they might shed light on nonzero neutrino masses, the dark matter puzzle, and other phenomenologically relevant questions.

The scalar sector of the minimal left-right model at TeV scale is revisited in light of the large quartic coupling needed for a heavy flavor-changing scalar. The stability and perturbativity of the effective potential is discussed and merged with constraints from low-energy processes. Thus, the perturbative level of the left-right scale is sharpened. Lower limits on the triplet scalars are also derived: The left-handed triplet is bounded by oblique parameters, while the doubly charged right-handed component is limited by the $h\to \gamma \gamma$, $Z\gamma$ decays. Current constraints disfavor their detection as long as $W_R$ is within the reach of the LHC.

We revisit the renormalization prescription for the quark-meson model in an extended mean-field approximation, where vacuum quark fluctuations are included. At a given cutoff scale the model parameters are fixed by fitting vacuum quantities, typically including the sigma-meson mass $m_{\sigma }$ and the pion decay constant $f_{\pi }$. In most publications the latter is identified with the expectation value of the sigma field, while for $m_{\sigma }$ the curvature mass is taken. When quark loops are included, this prescription is however inconsistent, and the correct identification involves the renormalized pion decay constant and the sigma pole mass. In the present article we investigate the influence of the parameter-fixing scheme on the phase structure of the model at finite temperature and chemical potential. Despite large differences between the model parameters in the two schemes, we find that in homogeneous matter the effect on the phase diagram is relatively small. For inhomogeneous phases, on the other hand, the choice of the proper renormalization prescription is crucial. In particular, we show that if renormalization effects on the pion decay constant are not considered, the model does not even present a well-defined renormalized limit when the cutoff is sent to infinity.

We study kaon-nucleon systems in the Skyrme model in a method based on the bound state approach of Callan-Klebanov but with the kaon around the physical nucleon of the rotating hedgehog. This corresponds to the variation after projection, reversing the order of semiclassical quantization of $1/N_c$ expansion. The method, however, is considered to be suited to the study of weakly interacting kaon-nucleon systems including loosely $\overline{K}N$ bound states such as $\mathrm{\Lambda }(1405)$. We have found a bound state with binding energy of order 10 MeV, consistent with the observed state. We also discuss the $\overline{K}N$ interaction and find that it consists of an attraction in the middle range and a repulsion in the short range.

With Gaussian expansion method (GEM), realistic wave functions are used to calculate coupled-channel effects for the bottomonium under the framework of ${{}^{3}P}_0$ model. The simplicity and accuracy of GEM are explained. We calculate the mass shifts, probabilities of the $B$ meson continuum, $S-D$ mixing angles, strong and dielectric decay widths. Our calculation shows that both $S-D$ mixing and the $B$ meson continuum can contribute to the suppression of the vector meson’s dielectric decay width. We suggest more precise measurements on the radiative decays of $\mathrm{\Upsilon }(10580)$ and $\mathrm{\Upsilon }(11020)$ to distinguish these two effects. The above quantities are also calculated with simple harmonic oscillator (SHO) wave function approximation for comparison. The deviation between GEM and SHO indicates that it is essential to treat the wave functions accurately for near threshold states.