A sufficiently rigid relativistic elastic solid can be stable for negative pressure values and thus is capable of driving a stage of accelerated expansion. If a relativistic elastic solid drove an inflationary stage in the early Universe, quantum mechanically excited perturbations would arise in the medium. We quantize the linear scalar and tensor perturbations and investigate the observational consequences of having such an inflationary period. We find that slowly varying sound speeds of the perturbations and a slowing varying equation of state of the solid can produce a slightly red-tilted scalar power spectrum that agrees with current observational data. Even in the absence of nonadiabatic pressures, perturbations evolve on superhorizon scales, due to the shear stresses within the solid. As such, the spectra of perturbations are in general sensitive to the details of the end of inflation and we characterize this dependence. Interestingly, we uncover here accelerating solutions for elastic solids with $1+P/\rho$ significantly greater than 0 that nevertheless have nearly scale-invariant scalar and tensor spectra. Beyond theoretical interest, this may allow for the possibility of viable inflationary phenomenology relatively far from the de Sitter regime.

We present an analytic nonperturbative solution of the Yakubovsky equation for tetraquark states in the case of equal separations and energies, and demonstrate a direct connection between the tetraquark confinement potential and the temporal gluon propagator. To this end we employ a leading-order heavy quark mass expansion of the Coulomb gauge QCD action, and use the dressed two-point functions of the Yang-Mills sector only. As a result, we find a bound state energy that rises linearly with distance and a string tension twice as large as in a $q\overline{q}$-system.

The QCD phase diagram at zero chemical potential and finite temperature subject to an external magnetic field is studied within the three-flavor Nambu–Jona-Lasinio (NJL) model and the NJL model with the Polyakov loop. A scalar coupling parameter dependent on the magnetic field intensity is considered. The scalar coupling has been fitted so that the lattice QCD pseudocritical chiral transition temperatures are reproduced and in the limit of large magnetic field decreases with the inverse of the magnetic field intensity. This dependence of the coupling allows us to reproduce the lattice QCD results with respect to the quark condensates and Polyakov loop: due to the magnetic field the quark condensates are enhanced at low and high temperatures and suppressed for temperatures close to the transition temperatures and the Polyakov loop increases with the magnetic field.

We consider a mixed system of unstable Majorana fermions in a general parity-nonconserving theory and renormalize its propagator matrix to all orders in the pole scheme, in which the squares of the renormalized masses are identified with the complex pole positions and the wave-function renormalization matrices are adjusted in compliance with the Lehmann–Symanzik–Zimmermann reduction formalism. In contrast to the case of unstable Dirac fermions, the wave-function renormalization matrices of the in and out states are uniquely fixed, while they again bifurcate in the sense that they are no longer related by pseudo-Hermitian conjugation. We present closed analytic expressions for the renormalization constants in terms of the scalar, pseudoscalar, vector, and pseudovector parts of the unrenormalized self-energy matrix, which is computable from the one-particle-irreducible Feynman diagrams of the flavor transitions, as well as their expansions through two loops. In the case of stable Majorana fermions, the well-known one-loop results are recovered.

There is strong evidence in favor of the idea that dark matter is self interacting, with the cross section-to-mass ratio $\sigma /m\sim 1{\mathrm{cm}}^2/\mathrm{g}\sim 1\mathrm{barn}/\mathrm{GeV}$. We show that viable models of dark matter with this large cross section are straightforwardly realized with non-Abelian hidden sectors. In the simplest of such models, the hidden sector is a pure gauge theory, and the dark matter is composed of hidden glueballs with a mass around 100 MeV. Alternatively, the hidden sector may be a supersymmetric pure gauge theory with a $\sim 10\mathrm{TeV}$ gluino thermal relic. In this case, the dark matter is largely composed of glueballinos that strongly self interact through the exchange of light glueballs. We present a unified framework that realizes both of these possibilities in anomaly-mediated supersymmetry breaking, where, depending on a few model parameters, the dark matter may be composed of hidden glueballinos, hidden glueballs, or a mixture of the two. These models provide simple examples of multicomponent dark matter, have interesting implications for particle physics and cosmology, and include cases where a subdominant component of dark matter may be extremely strongly self interacting, with interesting astrophysical consequences.

We study the discovery reach of the gluino ($\tilde{g}$) and the lightest stop squark (${\tilde{t}}_1$) with baryonic $R$-parity violation (UDD type) in the context of the minimal supersymmetric standard model (MSSM) at the 14 TeV run of the LHC. We consider the gluino pair production process followed by its decay to a top quark and a real or virtual stop squark. The top quark produced from the decay of the gluino can have sufficient transverse momentum to appear as a single fat jet. We apply the jet substructure technique to tag such a hadronically decaying boosted top quark and find that gluino mass up to 1.65 TeV can be discovered whereas the exclusion limit extends up to 1.9 TeV at the 14 TeV LHC with $300{\mathrm{fb}}^{-1}$ luminosity. We also briefly discuss the discovery prospect of the boosted stop squark, which may be identified as a narrow resonance in the jet mass distribution.

We present analyses on nucleon structure functions at small Bjorken $x$ in the framework of holographic QCD. In this study, we improve the description of the target nucleon in the current setup of the holographic model by introducing a soft-wall AdS/QCD model, in which the anti–de Sitter geometry is smoothly cut off at the infrared boundary. Combining the improved Pomeron-nucleon coupling and the wave function of the five-dimensional U(1) vector field with the Brower-Polchinski-Strassler-Tan Pomeron exchange kernel, we obtain the structure functions. Here we focus on the nonperturbative kinematical region, where ${10}^{-6}\le x\le {10}^{-2}$ and $Q^2\le$ a few (${\mathrm{GeV}}^2$), and show that our calculations for $F_2^p$ and $F_L^p$ are consistent with experimental data of the deep inelastic scattering at HERA. Furthermore, we find that the resulting longitudinal-to-transverse ratio of the structure functions, $F_L^p/F_T^p$, depends on both $x$ and $Q^2$.

Effective contact operators provide the simplest parametrization of dark matter searches at colliders. However, light mediators can significantly change the sensitivity and search strategies. Considering simple models of mediators is an important next step for collider searches. In this paper, we consider the case of a $t$-channel mediator. Its presence opens up new contributions to the $\text{monojet}+{\cancel{\mathrm{E}}}_T$ searches and can change the reach significantly. We also study the complementarity between searches for processes of $\text{monojet}+{\cancel{\mathrm{E}}}_T$ and direct pair production of the mediators. Mediator pair production also gives an important contribution to a CMS-like $\text{monojet}+{\cancel{\mathrm{E}}}_T$ search, where a second hard jet is allowed. There is a large region of parameter space in which the $\text{monojet}+{\cancel{\mathrm{E}}}_T$ search provides the stronger limit. Assuming the relic abundance of the dark matter is thermally produced within the framework of this model, we find that in the Dirac fermion dark matter case, there is no region in the parameter space that satisfies the combined constraint of $\text{monojet}+{\cancel{\mathrm{E}}}_T$ search and direct detection; whereas in the Majorana fermion dark matter case, the mass of dark matter must be larger than about 100 GeV. If the relic abundance requirement is not assumed, the discovery of the $t$-channel mediator predicts additional new physics.

We describe an effective theory of interaction between pairs of dark matter particles (denoted $\chi$) and pairs of $W$ bosons. Such an interaction could accommodate $\chi \overline{\chi }\to WW$ processes, which are a major focus of indirect dark matter experiments, as well as $pp\to W^{*}\to W\chi \overline{\chi }$ processes, which would predict excesses at the LHC in the $W+{\cancel{E}}_T$ final-state. We reinterpret an ATLAS $W+{\cancel{E}}_T$ analysis in the hadronic mode and translate the bounds to the space of indirect detection signals. We also reinterpret the $W+{\cancel{E}}_T$ analysis in terms of Kaluza-Klein graviton emission through the processes $W^{*}\to WG$ and $Z^{*}\to ZG$ in which $G$ is invisible. Finally, the final state is interpreted in terms of a $W^{\prime }$ model where $W^{\prime }\to WZ$, with $W$ decaying hadronically and $Z$ decaying to neutrinos.

The associate $J/\psi +\gamma$ production at the LHC is studied completely at next-to-leading order within the framework of nonrelativistic QCD. By using three sets of color-octet long-distance matrix elements obtained in previous prompt $J/\psi$ studies, we find that only one of them can result in a positive transverse momentum ($p_t$) distribution of $J/\psi$ production rate at the large $p_t$ region. Based on reasonable consideration to cut down background, our estimation is measurable up to $p_t=50\mathrm{GeV}$ with the present data sample collected at 8 TeV LHC. All the color-octet long-distance matrix elements in $J/\psi$ production could be fixed sensitively by including this proposed measurement and our calculation, and then a confident conclusion on the $J/\psi$ polarization puzzle could be achieved.

The empirical observation of near degeneracy of scalar mesons above 1 GeV, namely, the mass of the strange-flavor scalar meson is similar to that of the nonstrange one, is at variance with the naive expectation of the quark model. Qualitatively, the approximate mass degeneracy can be understood as a consequence of self-energy effects due to strong coupled channels which will push down the mass of the heavy scalar meson in the strange sector more than that in the nonstrange partner. However, it works in the conventional model without heavy quark expansion, but not in the approach of heavy meson chiral perturbation theory as mass degeneracy and the physical masses of $D_{s0}^{*}$ and $D_0^{*}$ cannot be accounted for simultaneously. In the heavy quark limit, near mass degeneracy observed in the scalar charm sector will imply the same phenomenon in the $B$ system. We have the prediction $M_{B_0^{*}}\approx M_{B_{s0}^{*}}\approx 5715\mathrm{MeV}+\delta {\mathrm{\Delta }}_S$ based on heavy quark symmetry and the leading-order QCD correction, where $\delta {\mathrm{\Delta }}_S$ arises from $1/m_Q$ corrections. A crude estimate indicates that $\delta {\mathrm{\Delta }}_S$ is of order $-35\mathrm{MeV}$ or less. We stress that the closeness of $B_{s0}^{*}$ and $B_0^{*}$ masses implied by heavy quark symmetry is not spoiled by $1/m_Q$ or QCD corrections. The mass-shift effect on $K_0^{*}(1430)$ is discussed.

We study the processes $\gamma \gamma \to K^{+}{K}^{-}\eta$ and $\gamma \gamma \to K^{+}{K}^{-}{\pi }^0$ using a data sample of $519{\mathrm{fb}}^{-1}$ recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at center-of-mass energies at and near the $\mathit{\Upsilon }(nS)$ ($n=2,3,4$) resonances. We observe ${\eta }_c\to K^{+}{K}^{-}{\pi }^0$ and ${\eta }_c\to K^{+}{K}^{-}\eta$ decays, measure their relative branching fraction, and perform a Dalitz plot analysis for each decay. We observe the $K_0^{*}(1430)\to K\eta$ decay and measure its branching fraction relative to the $K\pi$ decay mode to be $\mathcal{R}(K_0^{*}(1430))=\frac{\mathcal{B}(K_0^{*}(1430)\to K\eta )}{\mathcal{B}(K_0^{*}(1430)\to K\pi )}=0.092\pm 0.025_{-0.025}^{+0.010}$. The ${\eta }_c\to K^{+}{K}^{-}\eta$ and $K_0^{*}(1430)\to K\eta$ results correspond to the first observations of these channels. The data also show evidence for ${\eta }_c(2S)\to K^{+}{K}^{-}{\pi }^0$ and first evidence for ${\eta }_c(2S)\to K^{+}{K}^{-}\eta$.

We develop relativistic wave equations in the framework of the new non-Hermitian $\mathcal{P}\mathcal{T}$ quantum mechanics. The familiar Hermitian Dirac equation emerges as an exact result of imposing the Dirac algebra, the criteria of $\mathcal{P}\mathcal{T}$-symmetric quantum mechanics, and relativistic invariance. However, relaxing the constraint that, in particular, the mass matrix be Hermitian also allows for models that have no counterpart in conventional quantum mechanics. For example it is well known that a quartet of Weyl spinors coupled by a Hermitian mass matrix reduces to two independent Dirac fermions; here, we show that the same quartet of Weyl spinors, when coupled by a non-Hermitian but $\mathcal{P}\mathcal{T}$-symmetric mass matrix, describes a single relativistic particle that can have massless dispersion relation even though the mass matrix is nonzero. The $\mathcal{P}\mathcal{T}$-generalized Dirac equation is also Lorentz invariant, unitary in time, and CPT respecting, even though as a noninteracting theory it violates $\mathcal{P}$ and $\mathcal{T}$ individually. The relativistic wave equations are reformulated as canonical fermionic field theories to facilitate the study of interactions and are shown to maintain many of the canonical structures from Hermitian field theory, but with new and interesting possibilities permitted by the non-Hermiticity parameter $m_2$.

We have recently reported the existence of Kerr black holes with scalar hair in General Relativity minimally coupled to a massive, complex scalar field [C. Herdeiro and E. Radu, Phys. Rev. Lett. 112, 221101 (2014)]. These solutions interpolate between boson stars and Kerr black holes. The latter have a well-known topologically $S^2$ ergosurface (ergosphere) whereas the former develop a $S^1\times S^1$ ergosurface (ergotorus) in a region of parameter space. We show that hairy black holes always have an ergoregion, and that this region is delimited by either an ergosphere or an ergo-Saturn—i.e. a $S^2\oplus (S^1\times S^1)$ ergosurface. In the phase space of solutions, the ergotorus can either appear disconnected from the ergosphere or pinch off from it. We provide a heuristic argument, based on a measure of the size of the ergoregion, that superradiant instabilities—which are likely to be present—are weaker for hairy black holes than for Kerr black holes with the same global charges. We observe that Saturn-like, and even more remarkable, ergosurfaces should also arise for other rotating “hairy” black holes.

We show that in clustering dark energy models the growth index of linear matter perturbations, $\gamma$, can be much lower than in $\mathrm{\Lambda }\mathrm{CDM}$ or smooth quintessence models and presents a strong variation with redshift. We find that the impact of dark energy perturbations on $\gamma$ is enhanced if the dark energy equation of state has a large and rapid decay at low redshift. We study four different models with these features and show that we may have $0.33<\gamma (z)<0.48$ at $0<z<3$. We also show that the constant $\gamma$ parametrization for the growth rate, $f=d\ln {\delta }_m/d\ln a={\mathrm{\Omega }}_m^{\gamma }$, is a few percent inaccurate for such models and that a redshift-dependent parametrization for $\gamma$ can provide about four times more accurate fits for $f$. We discuss the robustness of the growth index to distinguish between general relativity with clustering dark energy and modified gravity models, finding that some $f(R)$ and clustering dark energy models can present similar values for $\gamma$.

We study the effects of modifications of gravity after big bang nucleosynthesis which would manifest themselves mainly before recombination. We consider their effects on the cosmic microwave background (CMB) radiation and on the formation of large scale structure. The models that we introduce here represent all screened modifications of general relativity which evade the local tests of gravity such as the violation of the strong equivalence principle as constrained by the Lunar Ranging experiment. We use the tomographic description of modified gravity which defines models with screening mechanisms of the chameleon or Damour-Polyakov types and allows one to relate the temporal evolution of the mass and the coupling to matter of a scalar field to its Lagrangian and also to cosmological perturbations. The models with early modifications of gravity all involve a coupling to matter which is stronger in the past leading to effects on perturbations before recombination while minimizing deviations from $\mathrm{\Lambda }$CDM structure formation at late times. We find that a new family of early transition models lead to discrepancies in the CMB spectrum which could reach a few percent and appear as both enhancements and reductions of power for different scales.

We develop a method for integrating out the heavy Kaluza-Klein modes of scalar type as well as those of vector and axial-vector types, in a class of hard-wall bottom-up approaches of holographic QCD models, including the Dirac-Born-Infeld and Chern-Simons parts. By keeping only the lowest-lying vector mesons, we first obtain an effective chiral Lagrangian of the vector mesons based on the hidden local symmetry, and all the low-energy constants in the HLS Lagrangian are expressed in terms of holographic integrals and, consequently, are fully determined by the holographic geometry and a few constants of mesons. We find that the Gell-Mann–Oakes–Renner relation is manifestly reproduced at the lowest order of derivative expansion. We also explicitly show that a naive inclusion of the Chern-Simons term cannot reproduce the desired chiral anomaly in QCD, and hence, some counterterms should be provided: This implies that the holographic QCD models of hard-wall type cannot give definite predictions for the intrinsic parity-odd vertices involving vector and axial-vector mesons. After integrating out the vector mesons from the HLS Lagrangian, we further obtain the Lagrangian of chiral perturbation theory for pseudoscalar mesons with all the low-energy constants fully determined.

We present a simple model for a 7 keV scalar dark matter particle which also explains the recently reported anomalous peak in the extragalactic x-ray spectrum at 3.55 keV in terms of its two photon decay. The model is arguably the simplest extension of the Standard Model, with the addition of a real scalar gauge singlet field subject to a reflection symmetry. This symmetry breaks spontaneously at a temperature of order few GeV which triggers the decay of the dark matter particle into two photons. In this framework, the Higgs boson of the Standard Model is also the source of dark matter in the Universe. The model fits the relic dark matter abundance and the partial lifetime for two photon decay, while being consistent with constraints from domain wall formation and dark matter self-interactions. We show that all these features of the model are preserved in its natural embedding into a simple dark $U(1)$ gauge theory with a Higgs mechanism. The properties of the dark photon get determined in such a scenario. High precision cosmological measurements can potentially test these models, as there are residual effects from domain wall formation and non-negligible self-interactions of dark matter.

Local gauge theories are a guiding principle in describing elementary particle interactions. The massive Yang-Mills approach embodies this principle by implementing axial-/vector mesons into the chiral pion Lagrangian, but it has difficulties in describing experimentally measured spectral functions. Here we advance massive Yang-Mills by implementing a dressed $\rho$-meson propagator into the self-energy of the $a_1$ meson while preserving the chiral symmetry of the low-energy strong interaction. This achievement, combined with the concept of a universal high-energy continuum in vector and axial-vector channels, enables us to reconcile the calculated spectral functions with experiment. The thus obtained framework provides a realistic basis for future investigations of the long-standing question of chiral symmetry restoration in the context of dilepton data in heavy-ion collisions.

The geometrical construction of rational maps using a cubic grid has led to many new Skyrmion solutions, with baryon numbers up to 108. Energy spectra of some of the new Skyrmions are calculated here by semiclassical quantization. Quantization of the $B=20$ $T_d$-symmetric Skyrmion, which is one of the newly found Skyrmions, is considered, and this leads to the development of a new approach to solving Finkelstein–Rubinstein constraints. Matrix equations are simplified by introducing a Cartesian version of angular momentum basis states, and the computations are easier. The quantum states of all $T_d$-symmetric Skyrmions, constructed from the cubic grid, are classified into three classes, depending on the contribution of vertex points of the cubic grid to the rational maps. The analysis is extended to the larger symmetry group $O_h$. Quantum states of $O_h$-symmetric Skyrmions, constructed from the cubic grid, form a subset of the $T_d$-symmetric quantum states.