We derive a set of equations describing the linear response of the convergence properties of a geodesic congruence to arbitrary geometry variations. It is a combination of equations describing the deviations from the standard Raychaudhuri-type equations due to the geodesic shifts and an equation describing the geodesic shifts due to the geometry variations. In this framework, the geometry variations, which can be chosen arbitrarily, serve as probes to investigate the gravitational contraction processes from various angles. We apply the obtained framework to the case of conformal geometry variations, characterized by an arbitrary function $f(x)$, and see that the formulas get simplified to a great extent. We investigate the response of the convergence properties of geodesics in the latest phase of gravitational contractions by restricting the class of conformal geometry variations to the one satisfying the strong energy condition. We then find out that in the final stage, $f$ and $\mathit{D}·\mathit{D}f$ control the overall contraction behavior and that the contraction rate gets larger when $f$ is negative and $|f|$ is so large as to overwhelm $|\mathit{D}·\mathit{D}f|$. (Here $\mathit{D}·\mathit{D}$ is the Laplacian operator on the spatial hypersurfaces orthogonal to the geodesic congruence in concern.) To get more concrete insights, we also apply the framework to the time-reversed Friedmann-Robertson-Walker model as the simplest case of the singularity formations.

We propose a new model in the teleparallel framework where we consider a scalar field nonminimally coupled to both the torsion $T$ and a boundary term given by the divergence of the torsion vector $B=\frac{2}{e}{\partial }_{\mu }(e{T}^{\mu })$. This is inspired by the relation $R=-T+B$ between the Ricci scalar of general relativity and the torsion of teleparallel gravity. This theory in suitable limits incorporates both the nonminimal coupling of a scalar field to torsion, and the nonminimal coupling of a scalar field to the Ricci scalar. We analyze the cosmology of such models, and we perform a dynamical systems analysis on the case when we have only a pure coupling to the boundary term. It is found that the system generically evolves to a late time accelerating attractor solution without requiring any fine-tuning of the parameters. A dynamical crossing of the phantom barrier is also shown to be possible.

We reanalyze the behavior of Friedmann-Lemaître-Robertson-Walker cosmologies in the recently proposed quasidilaton massive-gravity model, and discover that the background dynamics present hitherto unreported features that require unexpected fine-tuning of the additional fundamental parameters of the theory for an observationally consistent background cosmology. We also identify new allowed regions in the parameter space and exclude some of the previously considered ones. The evolution of the mass of gravitational waves reveals nontrivial behavior, exhibiting a mass-squared that may be negative in the past, and that presently, while positive, is larger than the square of the Hubble parameter, $H_0^2$. These properties of the gravity-wave mass have the potential to lead to observational tests of the theory. While quasidilaton massive gravity is known to have issues with stability at short distances, the current analysis is a first step toward the investigation of the more stable extended quasidilaton massive-gravity theory, with some expectation that both the fine-tuning of parameters and the interesting behavior of the gravity-wave mass will persist.

We obtain the electric field and scalar field for a static point charge in closed form in the 5D Schwarzschild-Tangherlini black hole spacetime. We then compute the static self-force in each of these cases by assuming that the appropriate singular field is a 4D Hadamard Green’s function on the constant time Riemannian slice. It is well-known that the Hadamard representation of a Green’s function involves an arbitrary regular biscalar $W_0(x,x^{\prime })$, whose coincidence limit $w(x)$ appears in the expression for the self-force. We develop an axiomatic approach to reduce this arbitrary function to a single arbitrary dimensionless coefficient. We show that in the context of this approach to regularization, the self-force does not depend on any undetermined length scale and need not depend on the internal structure of the charge.

Moving particles outside a star will generally experience quantum friction caused by the Unruh radiation reaction. There exist however radial trajectories that lack this effect (in the outgoing radiation sector, and ignoring backscattering). Along these trajectories, observers perceive just stellar emission, without further contribution from the Unruh effect. They turn out to have the property that the variations of the Doppler and the gravitational shifts compensate each other. They are not geodesics, and their proper acceleration obeys an inverse square law, which means that it could in principle be generated by outgoing stellar radiation. In the case of a black hole emitting Hawking radiation, this may lead to a buoyancy scenario. The ingoing radiation sector has little effect and seems to slow down the fall even further.

In this paper, the geometric and dynamic spatial curvature parameters of the Universe are constrained by type Ia supernova, baryon acoustic oscillation, and cosmic microwave background data. Compared with the previous result, a more stringent constraint is obtained, especially for the dynamic spatial curvature in the case of variable dark energy. No evidence is found that the geometric spatial curvature deviates from the dynamic spatial curvature, which is consistent with general relativity. In the case of dark energy with constant equation of state, it is found that $-8.4\times 10^{-3}\le {\mathrm{\Omega }}_K^{\text{geo}}\le 6.6\times 10^{-3}$ (95% C.L.). This supports the hypothesis of a flat Universe in a very general meaning.

We consider the simplest extension to the Starobinsky model, by allowing an extra scalar field to help drive inflation. We perform our analysis in the Einstein frame and calculate the power spectra at the end of inflation to second order in the slow-roll parameters. We find that the model gives predictions in great agreement with the current Planck data without the need for fine-tuning. Our results encourage current efforts to embed the model in a supergravity setting.

A standard nuclear reaction network for big bang nucleosynthesis (BBN) simulations operates with spin-averaged nuclear inputs—unpolarized reaction cross sections. At the same time, the major part of reactions controlling the abundances of light elements is spin dependent, i.e., their cross sections depend on the mutual orientation of reacting particle spins. Primordial magnetic fields in the BBN epoch may to a certain degree polarize particles and thereby affect some reactions between them, introducing uncertainties in standard BBN predictions. To clarify the points, we have examined the effects of induced polarization on key BBN reactions—$p(n,\gamma )d$, $d(d,p)t$, $d(d,n){}^3\mathrm{He}$, $t(d,n)\alpha$, ${}^3\mathrm{He}(n,p)t$, ${}^3\mathrm{He}(d,p)\alpha$, ${}^7\mathrm{Li}(p,\alpha )\alpha$, ${}^7\mathrm{Be}(n,p){}^7\mathrm{Li}$—and the abundances of elements with $A\le 7$. It has been obtained that the magnetic field with the strength $B_0\le {10}^{12}\mathrm{G}$ (at the temperature of ${10}^9\mathrm{K}$) has almost no effect on the reaction cross sections, and the spin polarization mechanism plays a minor role in the element production, changing the abundances at most by 0.01%. However, if the magnetic field $B_0$ reaches ${10}^{15}\mathrm{G}$ its effect on the key reactions appears and becomes appreciable at $B_0\gtrsim {10}^{16}\mathrm{G}$. In particular, it has been found that such a field can increase the $p(n,\gamma )d$ cross section (relevant to the starting point of BBN) by a factor of 2 and at the same time almost block the ${}^3\mathrm{He}(n,p)t$ reaction responsible for the interconversion of $A=3$ nuclei in the early Universe. This suggests that the spin polarization effects may become important in nonstandard scenarios of BBN considering the existence of local magnetic bubbles inside which the field can reach $\sim {10}^{15}\mathrm{G}$.

We study the magnetic field generation in a neutron star within the model based on the magnetic field instability in the nuclear matter owing to the electron-nucleon parity violating interaction. We suggest that the growing magnetic field takes the energy from thermal background fermions in the neutron star matter. The system of kinetic equations for the spectra of the magnetic helicity density and magnetic energy density as well as the chiral imbalance are solved numerically accounting for this energy source. We obtain that, for the initial conditions corresponding to a typical neutron star, the large scale magnetic field $\sim {10}^{15}\mathrm{G}$ is generated during $({10}^4-{10}^5)\mathrm{yr}$. We suggest that the proposed model describes strong magnetic fields observed in magnetars.

The light pseudoscalar mesons play a twofold role: they may or have to be regarded both as low-lying bound states of the fundamental degrees of freedom of quantum chromodynamics and as the (pseudo) Goldstone bosons of the spontaneously broken chiral symmetries of quantum chromodynamics. We interrelate these aspects in a single quantum-field-theoretic approach relying on the Bethe-Salpeter formalism in instantaneous approximation by very simple means: the shape of the pseudoscalar-meson Bethe-Salpeter wave function dictated by chiral symmetry is used in Bethe-Salpeter equations for bound states of vanishing mass, in order to deduce analytically the interactions which govern the bound states under study. In this way, we obtain exact Bethe-Salpeter solutions for pseudoscalar mesons, in the sense of establishing the rigorous relationship between, on the one hand, the relevant interactions and, on the other hand, the Bethe-Salpeter amplitudes that characterize the bound states.

The standard model predicts that the Higgs boson couples to the fermions in the mass eigenstates. We consider the effects of lepton flavor violating (LFV) $Z$ boson couplings in the case where the Higgs boson has flavor nondiagonal Yukawa interactions with the muon and the tau lepton generated from physics beyond the standard model. We list the formulas of the couplings of the effective interactions among the $\tau$ lepton, the muon and the $Z$ boson. Using these formulas, we calculate the branching fractions of various leptonic and hadronic LFV $\tau$ decays, and the LFV $Z$ boson decay: $Z\to \tau \mu$. Although the $Z$-boson contributions to LFV tau decays cannot be ignored in terms of the counting of operator dimensions or chirality flippings, it turns out that they are not very significant for $\tau \to 3\mu$ and $\tau \to \mu \rho$ decays. We also calculate the branching fractions of the processes, $\tau \to \mu \pi$, $\tau \to \mu {\eta }^{(\prime )}$ and $\tau \to \mu a_1$, which are dominated by the $Z$-boson exchanges due to the spin and the parity of the hadrons.

The LHC is actively searching for narrow dijet resonances corresponding to physics beyond the standard model. Among the many resonances that have been postulated (e.g., colored vectors, scalars, and fermions) one that would have a particularly large production rate at the LHC would be a scalar diquark produced in the $s$ channel via fusion of two valence quarks. In previous work, we introduced a color discriminant variable that distinguishes among various dijet resonances, drawing on measurements of the dijet resonance mass, total decay width and production cross section. Here, we show that this model-independent method applies well to color-triplet and color-sextet scalar diquarks, distinguishing them clearly from other candidate resonances. We also introduce a more transparent theoretical formulation of the color discriminant variable that highlights its relationship to the branching ratios of the resonance into incoming and outgoing partons and to the properties of those partons. While the original description of the color discriminant variable remains convenient for phenomenological use upon discovery of a new resonance, the new formulation makes it easier to predict the value of the variable for a given class of resonance.

Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation processes, we study the compatibility of the dark matter interpretation of the Fermi-LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in the dark matter distribution weaken the constraints and leave open dark matter interpretations over a wide range of mass scales.

We consider the light-front holographic QCD with the light-front wave functions for mesons, modified for massive quarks. We evaluate the wave functions, distribution amplitudes, and form factors for $\pi$, $\rho$, $K$, and $J/\psi$ mesons and photon-to-meson transition form factors for $\pi$, $\eta$, and ${\eta }^{\prime }$ mesons. The results are compared with the experimental data, wherever available.

A model-independent expression for the Dalitz plot of semileptonic decays of neutral kaons, $K_{l3}^0$, including radiative corrections to order $(\alpha /\pi )(q/M_1)$, where $q$ is the momentum transfer and $M_1$ is the mass of the kaon, is presented. The model dependence of radiative corrections is kept in a general form within this approximation, which is suitable for model-independent experimental analyses. Expressions for bremsstrahlung radiative corrections are presented in two forms: one with the triple integral over the kinematical variables of the photon ready to be performed numerically and the other one in a fully analytical form. The final result is restricted to the so-called three-body region of the Dalitz plot and it is not compromised to fixing the values of the form factors at predetermined values.

We present a systematical study on the prompt $J/\psi$ production in association with a $c\overline{c}$ pair via the process, $\gamma \gamma \to H(c\overline{c})+c+\overline{c}$, within the framework of nonrelativistic QCD at the future high-energy $e^{+}{e}^{-}$ collider—International Linear Collider (ILC), including both direct and feed-down contributions. For direct $J/\psi$ production, the states with color-octet channels, especially the ${{}^{3}P}_J^{[8]}$ and ${{}^{1}S}_0^{[8]}$ ones, provide a dominant contribution to the production cross section, which are about 52 times over that of the color-singlet one. This is clearly shown by the transverse momentum ($p_t$) and rapidity distributions. The feed-down contribution from ${\psi }^{\prime }$ and ${\chi }_{cJ}$ ($J=0$, 1, 2) is sizable, which is about 20% to the total prompt cross section. Besides the yields, we also calculate the $J/\psi$ polarization parameter $\lambda$. In the small $p_t$ region, the polarization of the prompt $J/\psi$ is longitudinal due to large contributions through the ${{}^{3}P}_J^{[8]}$ channel, and becomes transverse in the high $p_t$ region due to the ${{}^{3}S}_1^{[8]}$ channel. Thus the $J/\psi$ production via photon-photon collisions at the ILC shall provide a useful platform for testing the color-octet mechanism.

We show the existence of a new gapless collective excitation in a rotating fluid system with chiral fermions, named the chiral vortical wave (CVW). The CVW has its microscopic origin at the quantum anomaly and macroscopically arises from interplay between vector and axial charge fluctuations induced by vortical effects. The wave equation is obtained both from hydrodynamic current equations and from chiral kinetic theory, and its solutions show nontrivial CVW-induced charge transport from different initial conditions. Using the rotating quark-gluon plasma in heavy ion collisions as a concrete example, we show the formation of an induced flavor quadrupole in quark-gluon plasma and estimate the elliptic flow splitting effect for $\mathrm{\Lambda }$ baryons that may be experimentally measured.

In this paper, we discuss the signal of composite spin-1 resonances at the LHC. Motivated by the possible observation of a diboson resonance in the 8 TeV LHC data, we demonstrate that vector resonances from composite Higgs models are able to describe the data. We pay particular attention to the role played by fermion partial compositeness, which is a common feature in composite Higgs models. The parameter space that is both able to account for the diboson excess and passes electroweak precision and flavor tests is explored. Finally, we make projections for signals of such resonances at the 13 TeV run of the LHC.

We analyze the parametric space of the constrained minimal supersymmetric standard model with $\mu >0$ supplemented by a generalized asymptotic Yukawa coupling quasiunification condition which yields acceptable masses for the fermions of the third family. We impose constraints from the cold dark matter abundance in the Universe and its direct-detection experiments, the $B$ physics, as well as the masses of the sparticles and the lightest neutral $CP$-even Higgs boson. Fixing the mass of the latter to its central value from the LHC and taking $40\lesssim \tan \beta \lesssim 50$, we find a relatively wide allowed parameter space with $-11\lesssim A_0/M_{1/2}\lesssim 15$ and a mass of the lightest sparticle in the range (0.09–1.1) TeV. This sparticle is possibly detectable by the present cold dark matter direct search experiments. The required fine-tuning for the electroweak symmetry breaking is much milder than the one needed in the neutralino-stau coannihilation region of the same model.

We study the holographic supersymmetric Yang-Mills (SYM) theory, which is living in a hyperbolic space, in terms of the entanglement entropy. The theory contains a parameter $C$ corresponding to the excitation of the SYM theory, and it controls the dynamical properties of the theory. The entanglement temperature, $T_{\mathrm{ent}}$, is obtained by imposing the thermodynamic law for the relative entanglement entropy and the energy density of the excitation. This temperature is available at any value of the parameter $C$ even in the region where the Hawking temperature disappears. With this new temperature, the dynamical properties of the excited SYM theory are examined in terms of the thermodynamic law. We could find the signatures of phase transitions of the theory.