We derive a kinetic equation for chiral matter at nonzero chemical potential that governs the response of the parity-odd part of the distribution function to perturbations of the Robertson-Walker metric. The derivation is based on a recent evaluation of the gravitational polarization tensor at nonzero chemical potential. We also provide the equations for gravity waves that follow from the anisotropic stress tensor describing the lepton asymmetry. These equations can be used to assess the effects that a nonzero neutrino chemical potential would have on the evolution of cosmological perturbations.

In our previous paper [N. Maru and N. Okada, Phys. Rev. D 87, 095019 (2013)], we have investigated effects of a simple gauge-Higgs unification model on the diphoton signal events from the Higgs boson production at the Large Hadron Collider. We have found that in this model the effective Higgs-to-diphoton coupling can be enhanced by 1-loop corrections with Kaluza-Klein (KK) modes of bulk fields. This result can be an explanation for the observed excess of the signal strength in the Higgs-to-diphoton decay channel. In this paper, we investigate KK-mode effects on another Higgs boson decay mode, $H\to Z\gamma$. One naturally expects that the KK modes also contribute to the effective $H\mathrm{\text{−}}Z\mathrm{\text{−}}\gamma$ coupling and can cause some deviation for the $H\to Z\gamma$ decay mode from the Standard Model prediction. Revealing a correlation between the KK-mode effects on the Higgs-to-diphoton and $H\mathrm{\text{−}}Z\mathrm{\text{−}}\gamma$ couplings is an interesting topic in terms of a possibility to discriminate a variety of models for physics beyond the Standard Model. We show a very striking result for the gauge-Higgs unification model, namely, the absence of KK-mode contributions to the $H\mathrm{\text{−}}Z\mathrm{\text{−}}\gamma$ coupling at the 1-loop level. This is a very specific and general prediction of the gauge-Higgs unification scenario.

Within the Nambu–Jona-Lasinio model the temperature dependence of the shear viscosity is calculated to the first nontrivial order in the $1/N_c$ expansion with $\Phi$-derivable approximations. The two-particle irreducible effective action is computed to next-to-leading order, from which the integral equations for the 3- and 4-point vertices are obtained. These sum infinite sets of diagrams contributing to the shear viscosity at the same order in the $1/N_c$ expansion. We find that the shear viscosity decreases rapidly when the chiral crossover is approached. Comparing with the hadron phase, the quark-gluon plasma phase has a low shear viscosity, which is consistent with the measurements. The ratio of the shear viscosity to entropy density is also calculated.

We study pure weak eigenstate Dirac fermionic dark matter (DM). We consider WIMP with renormalizable interaction. According to results of direct searches and the nature of DM (electrical neutral and being a pure weak eigenstate), the quantum number of DM is determined to be $I_3=Y=0$. There are only two possible cases: either DM has nonvanishing weak isospin ($I\ne 0$) or it is an isosinglet ($I=0$). In the first case, the Sommerfeld enhancement is sizable for large $I$, producing large ${\chi }^0\overline{{\chi }^0}\to VV$ rates. In particular, we obtain large $\chi \overline{\chi }\to W^{+}{W}^{-}$ cross section, which is comparable to the latest bounds from indirect searches and $m_{\chi }$ is constrained to be larger than a few hundred GeV to a few TeV. It is possible to give correct relic density with $m_{\chi }$ higher than these lower bounds. In the second case, to couple DM to standard model (SM) particles, a SM-singlet vector mediator $X$ is required from renormalizability and the SM gauge quantum numbers. To satisfy the latest bounds of direct searches and to reproduce the DM relic density at the same time, resonant enhancement in DM annihilation diagram is needed. Thus, the masses of DM and the mediator are related. Furthermore, this model is not sufficient to explain the deviation in muon $g-2$.

We show that at higher frequencies, and thus higher axion masses, single-photon detectors become competitive and ultimately favored, when compared to quantum-limited linear amplifiers, as the detector technology in microwave cavity experimental searches for galactic halo dark matter axions. The crossover point in this comparison is of order 10 GHz ($\sim 40\mu \mathrm{eV}$), not far above the frequencies of current searches.

A set of kinetic equations is used to study equilibration of the anisotropic quark-gluon plasma produced by decays of color flux tubes possibly created at the very early stages of ultrarelativistic heavy-ion collisions. The decay rates of the initial color fields are given by the Schwinger formula, and the collision terms are treated in the relaxation-time approximation. By connecting the relaxation time with viscosity we are able to study production and thermalization processes in the plasma characterized by different values of the ratio of the shear viscosity to entropy density, $\overline{\eta }$. For the lowest (Kovtun-Son-Starinets) value of this ratio, $4\pi \overline{\eta }=1$, and realistic initial conditions for the fields, the system approaches the viscous-hydrodynamics regime within $1–2\mathrm{fm}/\mathrm{c}$. On the other hand, for larger values of the viscosity, $4\pi \overline{\eta }\ge 3$, the collisions in the plasma become inefficient to destroy collective phenomena which manifest themselves as oscillations of different plasma parameters. The presence of such oscillations brings in differences between the kinetic and hydrodynamic descriptions, which suggest that the viscous-hydrodynamics approach after $1–2\mathrm{fm}/\mathrm{c}$ is not complete if $4\pi \overline{\eta }\ge 3$ and should be extended to include dissipative phenomena connected with color conductivity.

The boundary of a manifold can alter the phase of a theory in the bulk. We explore the possibility of a boundary-induced phase transition for the chiral symmetry of QCD. In particular, we investigate the consequences of imposing homogeneous Dirichlet boundary conditions on the quark fields. Such boundary conditions are sometimes employed in lattice gauge theory computations, for example, when including external electromagnetic fields, or when computing quark propagators with a reduced temporal extent. Homogeneous Dirichlet boundary conditions force the chiral condensate to vanish at the boundary, and thereby obstruct the spontaneous breaking of chiral symmetry in the bulk. We show the restoration of chiral symmetry due to a boundary is a nonperturbative phenomenon depending upon the mechanism of spontaneous symmetry breaking, and utilize the sigma model to exemplify the issues. Within this model, we find that chiral symmetry is completely restored if the length of the compact direction is less than 2.0 fm. For lengths greater than about 4 fm, an approximately uniform chiral condensate forms centered about the midpoint of the compact direction. While the volume-averaged condensate approaches the infinite volume value as the compact direction becomes very long, the finite-size corrections are shown to be power law rather than exponential.

We show that in TeV scale left-right (L-R) symmetric seesaw models, there are new dominant contributions to the collider signals of heavy Majorana neutrinos arising from the heavy-light neutrino mixing, which directly probe the seesaw matrix in a certain class of models. We propose a way to distinguish this contribution from the widely discussed one that only probes the Majorana nature of the heavy right-handed neutrinos, by analyzing some simple kinematical variables. We find that in this class of L-R seesaw models the existing LHC data already yield slightly stronger constraints on the heavy-light neutrino mixing than those derived for standard seesaw models, and the improvement will be significant as more data are collected.

Large, high-energy ($E>100\mathrm{GeV}$) cosmic neutrino telescopes are now quite mature. IceCube, for example, observes about 50 000 well-reconstructed single atmospheric neutrino events/year, with energies above 100 GeV. Although the neutrino detection probability is small, current detectors are large enough so that it is possible to detect two neutrinos from the same cosmic-ray interaction. In this paper, we calculate the expected rate of double-neutrino interactions from a single cosmic-ray air shower. The rate is small, about $0.07\mathrm{events}/\mathrm{year}$ for a $1{\mathrm{km}}^3$ detector like IceCube, with only a small dependence on the assumed cosmic-ray composition and hadronic interaction model. For a larger detector, like the proposed KM3Net, the rate is about $0.8\mathrm{events}/\mathrm{year}$, high enough to be easily observable. These double neutrino interactions are the major irreducible background to searches for pairs of supersymmetric particles produced in neutrino or cosmic-ray air-shower interactions. Other standard model backgrounds are considered, and found to be small.

We derive closed expressions and useful expansions for the contributions of the tree-level $W$-boson propagator to the muon and $\tau$ leptonic decay rates. Calling $M$ and $m$ the masses of the initial and final charged leptons, our results in the limit $m=0$ are valid to all orders in $M^2/M_W^2$. In the terms of $\mathcal{O}(m_j^2/M_W^2)$ ($m_j=M$, $m$), our leading corrections, of $\mathcal{O}(M^2/M_W^2)$, agree with the canonical value $(3/5)M^2/M_W^2$, while the coefficient of our subleading contributions, of $\mathcal{O}(m^2/M_W^2)$, differs from that reported in the recent literature. A possible explanation of the discrepancy is presented. The numerical effect of the $\mathcal{O}(m_j^2/M_W^2)$ corrections is briefly discussed. A general expression, valid for arbitrary values of $M_W$, $M$, and $m$ in the range $M_W>M>m$, is given in the Appendix. The paper also contains a review of the traditional definition and evaluation of the Fermi constant.

We present the first signature-based search for delayed photons using an exclusive photon plus missing transverse energy final state. Events are reconstructed in a data sample from the CDF II detector corresponding to $6.3{\mathrm{fb}}^{-1}$ of integrated luminosity from $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collisions. Candidate events are selected if they contain a photon with an arrival time in the detector larger than expected from a promptly produced photon. The mean number of events from standard model sources predicted by the data-driven background model based on the photon timing distribution is $286\pm 24$. A total of 322 events are observed. A $p$ value of 12% is obtained, showing consistency of the data with standard model predictions.

Hyperscaling violating “strange metal” phase of heavy fermion compounds can be described holographically by probe D-branes in the background of a Lifshitz space-time (dynamical exponent $z$ and spatial dimensions $d$) with hyperscaling violation (corresponding exponent $\theta$). Without the hyperscaling violation, strange metals are known to exhibit zero sound mode for $z<2$ analogous to the Fermi liquids. In this paper, we study its fate in the presence of hyperscaling violation and find that in this case, the zero sound mode exists for $z<2(1+|\theta |/d)$, where the positivity of the specific heat and the null energy condition of the background dictate that $\theta <0$ and $z\ge 1$. However, for $z\ge 2(1+|\theta |/d)$, there is no well-defined quasiparticle for the zero sound. The systems behave like Fermi liquid for $2|\theta |=dz$ and like Bose liquid for $2|\theta |=qdz$ (where $q$ is the number of spatial dimensions along which D-branes are extended in the background space), but in general they behave as a new kind of quantum liquid. We also compute the ac conductivity of the systems and briefly comment on the results.

We reexamine a recently proposed scenario where the deformed dispersion relations associated with a flow of the spectral dimension to a UV value of 2 leads to a scale-invariant spectrum of cosmological fluctuations, without the need for inflation. In that scenario Einstein gravity was assumed. The theory displays a wavelength-dependent speed of light but by transforming to a suitable “rainbow frame” this feature can be removed, at the expense of modifying gravity. We find that the ensuing rainbow gravity theory is such that gravity switches off at high energy (or at least leads to a universal conformal coupling). This explains why the fluctuations are scale invariant on all scales: there is no horizon scale as such. For dispersion relations that do not lead to exact scale invariance we find instead esoteric inflation in the rainbow frame. We argue that these results shed light on the behavior of gravity under the phenomenon of dimensional reduction.

We investigate the nature of the phase transition for charged scalars in the presence of a magnetic background for a theory with spontaneous symmetry breaking. We perform a careful treatment of the negative mass squared as a function of the order parameter and present a suitable method to obtain magnetic and thermal corrections up to ring order for the high temperature limit and the case where the magnetic field strength is larger than the absolute value of the square of the mass parameter. We show that for a given value of the self-coupling, the phase transition is first order for a small magnetic field strength and becomes second order when the magnetic field strength grows. We also show that the critical temperature in the presence of the magnetic field is always below the critical temperature for the case where the field is absent.

An improved analysis of the diphoton decay rate of the Higgs boson in the inert doublet model is presented together with a critical discussion of the results existing in the literature. For a Higgs boson mass $M_h$ of 125 GeV and taking into account various constraints—vacuum stability, existence of the inert vacuum, perturbative unitarity, electroweak precision tests, and the LEP bounds—we find regions in the parameter space where the diphoton rate is enhanced. The resulting regions are confronted with the allowed values of the dark matter mass. We find that a significant enhancement in the two-photon decay of the Higgs boson is only possible for constrained values of the scalar couplings ${\lambda }_3\sim h{H}^{+}{H}^{-}$, ${\lambda }_{345}\sim hHH$ and the masses of the charged scalar and the dark matter particle. The enhancement above 1.3 demands that the masses of $H^{\pm }$ and $H$ be less than 135 GeV (and above 62.5 GeV) and $-1.46<{\lambda }_3$, ${\lambda }_{345}<-0.24$. In addition, we analyze the correlation of the diphoton and $Z\gamma$ rates.

The moments of the hadronic spectral functions are of interest for the extraction of the strong coupling ${\alpha }_s$ and other QCD parameters from the hadronic decays of the $\tau$ lepton. Motivated by the recent analyses of a large class of moments in the standard fixed-order and contour-improved perturbation theories, we consider the perturbative behavior of these moments in the framework of a QCD nonpower perturbation theory, defined by the technique of series acceleration by conformal mappings, which simultaneously implements renormalization-group summation and has a tame large-order behavior. Two recently proposed models of the Adler function are employed to generate the higher-order coefficients of the perturbation series and to predict the exact values of the moments, required for testing the properties of the perturbative expansions. We show that the contour-improved nonpower perturbation theories and the renormalization-group-summed nonpower perturbation theories have very good convergence properties for a large class of moments of the so-called “reference model,” including moments that are poorly described by the standard expansions. The results provide additional support for the plausibility of the description of the Adler function in terms of a small number of dominant renormalons.

In view of the recent measurement of nonzero ${\theta }_{13}$, we carry out a systematic study of a simple class of neutrino models that has one diagonal texture or cofactor zero in the mass matrix. There are seven free parameters in the model, and five of them are already measured by neutrino oscillation experiments; some cases for the normal or inverted hierarchy are excluded, and for the rest we obtain the preferred values for the lightest neutrino mass and Dirac $CP$ phase. We find that there are strong similarities between one diagonal texture zero models with one mass hierarchy and one diagonal cofactor zero models with the opposite mass hierarchy. We also make predictions for neutrinoless double beta decay for these models. For the one cofactor zero models, we present a simple realization based on a new $U(1)$ gauge symmetry.

We classify explicitly all the possible generalized $CP$ symmetries that are definable in $\Delta (27)$ flavor models. In total, only 12 transformations are possible. We also show interesting consequences of considering some of them as residual symmetries of the neutrino sector.

Some gauge theories with Coulomb branches exhibit singularities in perturbation theory, which are usually resolved by nonperturbative physics. In string theory this corresponds to the resolution of timelike singularities near the core of orientifold planes by effects from F or M theory. We propose a new mechanism for resolving Coulomb branch singularities in three-dimensional gauge theories, based on Chern-Simons interactions. This is illustrated in a supersymmetric $SU(2)$ Yang-Mills-Chern-Simons theory. We calculate the one-loop corrections to the Coulomb branch of this theory and find a result that interpolates smoothly between the high-energy metric (that would exhibit the singularity) and a regular singularity-free low-energy result. We suggest possible applications to singularity resolution in string theory and speculate a relationship to a similar phenomenon for the orientifold six-plane in massive IIA supergravity.

Solutions of a kinetic equation are investigated which describe, on a nonperturbative basis, the vacuum creation of quasiparticle electron-positron pairs due to a strong laser field. The dependence of the quasiparticle electron (positron) distribution function and the particle number density is explored in a wide range of the laser radiation parameters, i.e., the wavelength $\lambda$ and amplitude of electric field strength $E_0$. Three domains are found: the domain of vacuum polarization effects where the density of the $e^{-}{e}^{+}$ pairs is small (the “calm valley”) and two accumulation domains in which the production rate of the $e^{-}{e}^{+}$ pairs is strongly increased and the $e^{-}{e}^{+}$ pair density can reach a significant value (the short wavelength domain and the strong field one). In particular, the obtained results point to a complicated short-distance electromagnetic structure of the physical vacuum in the domain of short wavelengths $\lambda \lesssim {\lambda }_{\mathrm{acc}}=\pi /m$. For moderately strong fields $E_0\lesssim E_c=m^2/e$, the accumulation regime can be realized where a plasma with a high density of $e^{-}{e}^{+}$ quasiparticles can be achieved. In this domain of the field strengths and in the whole investigated range of wavelengths, an observation of the dynamical Schwinger effect can be facilitated.