We compute the contribution to the conductivity from holographic Fermi surfaces obtained from probe fermions in an AdS charged black hole. This requires calculating a certain part of the one-loop correction to a vector propagator on the charged black hole geometry. We find that the current dissipation is as efficient as possible and the transport lifetime coincides with the single-particle lifetime. In particular, in the case where the spectral density is that of a marginal Fermi liquid, the resistivity is linear in temperature.

Axially symmetric spacetimes are the only vacuum models for isolated systems with continuous symmetries that also include dynamics. For such systems, we review the reduction of the vacuum Einstein field equations to their most concise form by dimensionally reducing to the three-dimensional space of orbits of the Killing vector, followed by a conformal rescaling. The resulting field equations can be written as a problem in three-dimensional gravity with a complex scalar field as source. This scalar field, the Ernst potential, is constructed from the norm and twist of the spacelike Killing field. In the case where the axial Killing vector is twist-free, we discuss the properties of the axis and simplify the field equations using a triad formalism. We study two physically motivated triad choices that further reduce the complexity of the equations and exhibit their hierarchical structure. The first choice is adapted to a harmonic coordinate that asymptotes to a cylindrical radius and leads to a simplification of the three-dimensional Ricci tensor and the boundary conditions on the axis. We illustrate its properties by explicitly solving the field equations in the case of static axisymmetric spacetimes. The other choice of triad is based on geodesic null coordinates adapted to null infinity as in the Bondi formalism. We then explore the solution space of the twist-free axisymmetric vacuum field equations, identifying the known (unphysical) solutions together with the assumptions made in each case. This singles out the necessary conditions for obtaining physical solutions to the equations.

We derive criteria for whether two cosmological events can have a shared causal past or a shared causal future, assuming a Friedmann-Lemaitre-Robertson-Walker (FLRW) universe with best-fit cosmological parameters from the Planck satellite. We further derive criteria for whether either cosmic event could have been in past causal contact with our own worldline since the time of the hot “big bang,” which we take to be the end of early-universe inflation. We find that pairs of objects such as quasars on opposite sides of the sky with redshifts $z\ge 3.65$ have no shared causal past with each other or with our past worldline. More complicated constraints apply if the objects are at different redshifts from each other or appear at some relative angle less than 180°, as seen from Earth. We present examples of observed quasar pairs that satisfy all, some, or none of the criteria for past causal independence. Given dark energy and the recent accelerated expansion, our observable Universe has a finite conformal lifetime, and hence a cosmic event horizon at current redshift $z=1.87$. We thus constrain whether pairs of cosmic events can signal each other’s worldlines before the end of time. Lastly, we generalize the criteria for shared past and future causal domains for FLRW universes with nonzero spatial curvature.

We revisit the gauge-covariant canonical formalism by separating explicitly physical and gauge degrees of freedom. We show in particular that the gauge-invariant linear and angular momentum operators proposed by Chen et al. can consistently be derived from the standard procedure based on Noether’s theorem. Finally, we demonstrate that this approach is essentially equivalent to the gauge-invariant canonical formalism based on the concept of Dirac variables. Because of many similarities with the background field method, the formalism developed here should also be relevant to general relativity and any metric theories.

If the dark matter of our Galaxy is composed of heavy nuggets of quarks or antiquarks in a color superconducting phase there will be a small but nonzero flux of these objects through the Earth’s atmosphere. A nugget of quark matter will deposit only a small fraction of its kinetic energy in the atmosphere and is unlikely to be detectable. If however the impacting object is composed of antiquarks the energy deposited can be quite large and contain a significant charged particle content. These relativistic secondary particles will subsequently be deflected by the Earth’s magnetic field resulting in the emission of synchrotron radiation. This work argues that this radiation, along with a thermal component emitted from the nugget’s surface, should be detectable at radio frequencies and that both present and proposed experiments are likely to prove capable of detecting such a signal.

The IceCube neutrino observatory has detected two cascade events with energies near 1 PeV [A. Ishihara Proceedings of Neutrino 2012 Conference, http://neu2012.kek.jp/index.html; M. Aartsen et al. (IceCube Collaboration) Phys. Rev. Lett. 111, 021103 (2013)]. Without invoking new physics, we analyze the source of these neutrinos. We show that atmospheric conventional neutrinos and cosmogenic neutrinos (those produced in the propagation of ultra-high-energy cosmic rays) are strongly disfavored. For atmospheric prompt neutrinos or a diffuse background of neutrinos produced in astrophysical objects, the situation is less clear. We show that there is tension with observed data, but that the details depend on the least-known aspects of the IceCube analysis. Very likely, prompt neutrinos are disfavored and astrophysical neutrinos are plausible. We demonstrate that the fastest way to reveal the origin of the observed PeV neutrinos is to search for neutrino cascades in the range below 1 PeV, for which dedicated analyses with high sensitivity have yet to appear, and where many more events could be found.

We explore the whole phase space of the so-called Veneziano/QCD ghost dark energy models where the dynamics of the inner trapping horizon is ignored and also the more realistic models where the time dependence of the horizon is taken into consideration. We pay special attention to the choice of phase space variables leading to bounded and compact phase space so that no critical point of physical interest is missing. It is demonstrated that ghost dark energy is not a suitable candidate to explain the presently accepted cosmological paradigm, since no critical point associated with matter dominance is found in the physical phase space of the model. A transient stage of matter dominance—responsible for the observed amount of cosmic structure—is an essential ingredient of the accepted cosmological paradigm. The above drawback is in addition to the well-known problem with classical instability against small perturbations of the background density originated from negativity of the sound speed squared.

The merger of black hole-neutron star binaries can eject substantial material with the mass $\sim 0.01–0.1M_{\odot }$ when the neutron star is disrupted prior to the merger. The ejecta shows significant anisotropy, and travels in a particular direction with the bulk velocity $\sim 0.2c$. This is drastically different from the binary neutron star merger, for which ejecta is nearly isotropic. Anisotropic ejecta brings electromagnetic-counterpart diversity which is unique to black hole-neutron star binaries, such as viewing-angle dependence, polarization, and proper motion. The kick velocity of the black hole, gravitational-wave memory emission, and cosmic-ray acceleration are also discussed.

Polarization characteristics of $\gamma \gamma$ and $\gamma Z$ states in the Higgs boson decays $h\to \gamma \gamma$ and $h\to \gamma Z$ are discussed. Based on effective Lagrangian, describing $h\gamma \gamma$ and $h\gamma Z$ interactions with $CP$-even and $CP$-odd parts, we calculate polarization parameters ${\xi }_1$, ${\xi }_2$, ${\xi }_3$. A nonzero value of the photon circular polarization, defined by parameter ${\xi }_2$, arises due to presence of both parts in effective Lagrangian and its non-Hermiticity. The circular polarization is proportional to the forward-backward asymmetry of fermions in the decay $h\to \gamma Z\to \gamma f\overline{f}$. Measurement of this observable would allow one to search for deviation from the standard model and possible violation of $CPT$ symmetry. We discuss also a possibility to measure parameters ${\xi }_1$, ${\xi }_3$, describing correlation of linear polarizations of photon and $Z$ boson, in the decay $h\to {\gamma }^{*}Z\to {\ell }^{+}{\ell }^{-}Z$ via distribution over the azimuthal angle between the decay planes of ${\gamma }^{*}\to {\ell }^{+}{\ell }^{-}$ and $Z\to \overline{f}f$. Deviation of the measured value of ${\xi }_1$ from zero will indicate $CP$ violation in the Higgs sector.

We explore the Higgs couplings to gauge bosons in the minimal $SO(5)/SO(4)$ 4D composite Higgs model. The pion scatterings put unitary constraints on the couplings and therefore determine the branching ratios of various Higgs decays. Through fine-tuning the parameters, enhancement of Higgs to diphoton rate is possible to be achieved with the existence of vector meson fields.

The tentative gamma-ray line in the Fermi data at $\sim 135\mathrm{GeV}$ motivates a dark matter candidate that couples to photons through loops of charged messengers. It was recently shown that this model can explain the observed line, but achieving the correct phenomenology requires a fairly sizable coupling between the weakly interacting massive particle (WIMP) and the charged messengers. While strong coupling by itself is not a problem, it is natural to wonder whether the phenomenological success is not spoiled by higher order quantum corrections. In this work we compute the dominant two-loop contributions to the electromagnetic form factors of the WIMP and show that over a large portion of the relevant parameter space these corrections are under control, and the phenomenology is not adversely affected. We also discuss more generally the effects of these form factors on signals in direct-detection experiments as well as on the production of the WIMP candidate in colliders. In particular, for low masses of the charged messengers, the production rate at the LHC enjoys an enhancement from the threshold singularity associated with these charged states.

In this paper we present the perturbative computation of the renormalization functions for the quark field and for a complete set of ultralocal fermion bilinears. The computation of the relevant Green’s functions are carried out at one-loop level for the staggered action using massive fermions. The gluon links which appear both in the fermion action and in the definition of the bilinears are improved by applying a stout smearing procedure up to two times, iteratively. In the gluon sector we employ the Symanzik improved gauge action for different sets of values of the Symanzik coefficients. The renormalization functions are presented in (two variants of) the ${\mathrm{RI}}^{\prime }$ and in the $\overline{\mathrm{MS}}$ renormalization scheme; the dependence on all stout parameters, as well as on the fermion mass, the gauge fixing parameter, and the renormalization scale, is shown explicitly. This work is related to our recent paper [Phys. Rev. D 86, 094512 (2012)]. To make our results easily accessible to the reader, we include them in the distribution package of this paper as a Mathematica input file, “Staggered.m.”

To understand the enhanced partial decay width for the decay of ${\chi }_{c1}$ to the vector-meson pair $\varphi \varphi$ recently observed by the BESIII collaboration, we suggest measuring the polarization parameter of the $\varphi$ meson by analyzing the jointed angular distribution in the cascade decay $e^{+}{e}^{-}\to \psi (2S)\to \gamma {\chi }_{cJ}\to \gamma \varphi \varphi \to \gamma 2(K^{+}{K}^{-})$. The formulas to measure polarization parameters are presented, and they are estimated in the framework of perturbative QCD (pQCD) and the quark-pair-creation model. In pQCD we obtain results consistent with the expectation of the helicity selection rule. In the quark-pair-creation model, the parameter associated with the violation of the helicity selection rule is enhanced relative to that estimated in pQCD.

We obtain the first estimates of branching ratios for the weak decays of $B_c$ meson decaying to 2 orbitally excited mesons namely, axial-vector meson ($A$) and tensor meson ($T$) in the final state. We calculate $B_c\to T$ transition form factors using the Isgur-Scora-Grinstein-Wise II framework and, consequently, predict branching ratios of $B_c\to AT$ decays in Cabibbo-Kobayashi-Maskawa favored and suppressed modes.

We show that classical chromomagnetic fields produced coherently in the initial stage of a heavy-ion collision exhibit screening. From the two-point field strength correlator we determine the magnetic mass for SU(2) to be $m_M\simeq 5$ times the saturation scale. Magnetic screening leads to an intuitive understanding of the area law scaling of spatial Wilson loops observed previously. The presence of screening effects in the initial state provides a basis for defining kinetic processes in the early stage of heavy-ion collisions, with electric and magnetic masses of the same order.

We study magnetic geometries with Lifshitz and/or hyperscaling violation exponents (both with a hard wall cutoff in the IR and a smooth black brane horizon) which have a complex scalar field which couples to the magnetic field. The complex scalar is unstable to the production of a vortex lattice in the IR. The lattice is a normalizable mode which is relevant (i.e., grows into the IR.) When one considers linearized backreaction of the lattice on the metric and gauge field, the metric forms a crystalline structure. We analyze the scaling of the free energy, thermodynamic entropy, and entanglement in the lattice phase and find that in the smeared limit, the leading order correction to thermodynamic properties due to the lattice has the scaling behavior of a theory with a hyperscaling violation exponent between 0 and 1, indicating a flow to an effectively lower-dimensional theory in the deep IR.

We study the classical dynamics of the Abelian Higgs model employing an asymptotic multiscale expansion method, which uses the ratio of the Higgs to the gauge field amplitudes as a small parameter. We derive an effective nonlinear Schrödinger equation for the gauge field, and a linear equation for the scalar field containing the gauge field as a nonlinear source. This equation is used to predict the existence of oscillons and oscillating kinks for certain regimes of the ratio of the Higgs to the gauge field masses. Results of direct numerical simulations are found to be in very good agreement with the analytical findings, and show that the oscillons are robust, while kinks are unstable. It is also demonstrated that oscillons emerge spontaneously as a result of the onset of the modulational instability of plane wave solutions of the model. Connections of the results with the phenomenology of superconductors is discussed.

We analytically explore the effect of falling matter on a spherically symmetric wormhole supported by a spherical shell composed of exotic matter located at its throat. The falling matter is assumed to be also a thin spherical shell concentric with the shell supporting the wormhole, and its self-gravity is completely taken into account. We treat these spherical thin shells by Israel’s formalism of metric junction. When the falling spherical shell goes through the wormhole, it necessarily collides with the shell supporting the wormhole. To treat this collision, we assume that the interaction between these shells is only gravity. We show the conditions on the parameters that characterize this model in which the wormhole persists after the spherical shell goes through it.

We show that the higher order gravity model proposed by Meissner and Olechowski has a graviton mode, a massive spin-two excitation, and no scalar mode in a maximally symmetric spacetime; therefore, by choosing the coefficients, we can construct a Lagrangian for “critical gravity” from higher order terms of curvatures in higher dimensions. We also give a comment on construction of the theory with multicriticality in higher order gravities.

We investigate the global structure of a recently discovered simple exact, nonstationary solution of topologically massive and new massive gravity with the asymptotic charges of an undeformed Bañados-Teitelboim-Zanelli black hole. We establish the existence of a timelike singularity in the causal structure of the spacetime even in the absence of angular momentum. The dynamical trapping and event horizons are determined, and we investigate the evolution of the outer horizon showing that it may increase or decrease with time, depending on the value of the mass parameter. Finally, we test two proposals for dynamical entropy on this solution, one of them depending on the Kodama vector. In addition we show that the Kodama vector leads to the correct entropy for all stationary black holes in $2+1$ dimensions.