$Z^{\prime }$ gauge bosons arise in many particle physics models as mediators between the dark and visible sectors. We exploit dark matter (DM) complementarity and derive stringent and robust collider, direct and indirect constraints, as well as limits from the muon magnetic moment. We rule out almost the entire region of the parameter space that yields the right dark matter thermal relic abundance, using a generic parametrization of the $Z^{\prime }$-fermion couplings normalized to the standard model Z-fermion couplings for dark matter masses in the 8 GeV–5 TeV range. We conclude that mediators lighter than 2.1 TeV are excluded regardless of the DM mass, and that depending on the $Z^{\prime }$-fermion coupling strength much heavier masses are needed to reproduce the DM thermal relic abundance while avoiding existing limits.

A stationary distribution function that describes the entire process of the propagation of relativistic particles, including the transition between the ballistic and diffusion regimes, is obtained. The spacial component of the constructed function satisfies the first two moments of the Boltzmann equation. The angular part of the distribution provides accurate values for the angular moments derived from the Boltzmann equation, and gives a correct expression in the limit of the small-angle approximation. Using the derived function, we study the gamma-ray images produced through the $pp$ interaction of relativistic particles with gas clouds in the proximity of the accelerator. In general, the morphology and the energy spectra of gamma rays significantly deviate from the “standard” results corresponding to the propagation of relativistic particles strictly in the diffusion regime.

We propose a resonant electromagnetic detector to search for hidden-photon dark matter over an extensive range of masses. Hidden-photon dark matter can be described as a weakly coupled “hidden electric field,” oscillating at a frequency fixed by the mass, and able to penetrate any shielding. At low frequencies (compared to the inverse size of the shielding), we find that the observable effect of the hidden photon inside any shielding is a real, oscillating magnetic field. We outline experimental setups designed to search for hidden-photon dark matter, using a tunable, resonant LC circuit designed to couple to this magnetic field. Our “straw man” setups take into consideration resonator design, readout architecture and noise estimates. At high frequencies, there is an upper limit to the useful size of a single resonator set by $1/\nu$. However, many resonators may be multiplexed within a hidden-photon coherence length to increase the sensitivity in this regime. Hidden-photon dark matter has an enormous range of possible frequencies, but current experiments search only over a few narrow pieces of that range. We find the potential sensitivity of our proposal is many orders of magnitude beyond current limits over an extensive range of frequencies, from 100 Hz up to 700 GHz and potentially higher.

We first give a brief overview of the charmed baryon spectroscopy and discuss their possible structure and spin-parity assignments in the quark model. With the new Belle measurement of the widths of ${\mathrm{\Sigma }}_c(2455)$ and ${\mathrm{\Sigma }}_c(2520)$ and the recent CDF measurement of the strong decays of ${\mathrm{\Lambda }}_c(2595)$ and ${\mathrm{\Lambda }}_c(2625)$, we give updated coupling constants in heavy hadron chiral perturbation theory. We find $g_2=0.565_{-0.024}^{+0.011}$ for $P$-wave transitions between $s$-wave and $s$-wave baryons, and $h_2$, one of the couplings responsible for $S$-wave transitions between $s$-wave and $p$-wave baryons, is extracted from ${\mathrm{\Lambda }}_c(2595{)}^{+}\to {\mathrm{\Lambda }}_c^{+}\pi \pi$ to be $0.63\pm 0.07$. It is substantially enhanced compared to the old value of order 0.437. With the help from the quark model, two of the couplings $h_{10}$ and $h_{11}$ responsible for $D$-wave transitions between $s$-wave and $p$-wave baryons are determined from ${\mathrm{\Sigma }}_c(2880)$ decays. There is a tension for the coupling $h_2$ as its value extracted from ${\mathrm{\Lambda }}_c(2595{)}^{+}\to {\mathrm{\Lambda }}_c^{+}\pi \pi$ will imply ${\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Xi }}_c^{\prime }\pi$ and ${\mathrm{\Xi }}_c(2815{)}^{+}\to {\mathrm{\Xi }}_c^{*}\pi$ rates slightly above the current limits. It is conceivable that SU(3) flavor symmetry breaking can help account for the discrepancy.

The reaction $\gamma p\to {\pi }^{0}p$ is investigated in the energy range above the resonance region. The amplitudes include the leading Regge singularities in the cross channel and correctly describe the differential cross section for beam energies above 4 GeV and for the $s$-channel scattering angle $\cos {\theta }_s\ge 0.6$. The energy dependence of the beam asymmetry and the reaction $\gamma n\to {\pi }^{0}n$ seen is quantitatively consistent with the Regge-pole dominance.

We present a study of the chiral-odd generalized parton distributions (GPDs) for $u$ and $d$ quarks in a proton using the light-front wave functions (LFWFs) of the scalar quark-diquark model for a nucleon constructed from the soft-wall AdS/QCD correspondence. We obtain the GPDs in terms of overlaps of the LFWFs. Numerical results for chiral-odd GPDs in momentum as well as transverse position (impact) spaces considering both zero and nonzero skewness($\zeta$) are presented. For nonzero skewness, the GPDs are also evaluated in longitudinal position space.

The $\mathcal{N}=2^{*}$ theory is obtained by deforming $\mathcal{N}=4$ supersymmetric Yang–Mills theory with two relevant operators of dimensions 2 and 3. We study the holographic entanglement entropy of the $\mathcal{N}=2^{*}$ theory along the whole renormalization group flow. We find that in the UV the holographic entanglement entropy for an arbitrary entangling region receives a universal logarithmic correction, which is related to the relevant operator of dimension 3. This universal behavior can be interpreted on the field theory side by perturbatively evaluating the entanglement entropy of a conformal field theory (CFT) under relevant deformations. In the IR regime, we obtain the large $R$ behavior of the renormalized entanglement entropy for both a strip and a sphere entangling region, where $R$ denotes the size of the entangling region. A term proportional to $1/R$ is found for both cases, which can be attributed to the emergent ${\mathrm{CFT}}_5$ in the IR.

We propose a gravity dual of antiferromagnetic quantum phase transition induced by magnetic field and study the critical behavior around the quantum critical point. It turns out that the boundary critical theory is a strong coupling theory with dynamic exponent $z=2$ and that the hyperscaling law is violated and logarithmic corrections appear near the quantum critical point. Some novel scaling relations are predicated, which can be tested by experiment data in the future. We also make some comparison with experimental data on low-dimensional magnets ${\mathrm{BiCoPO}}_5$ and pyrochlores ${\mathrm{Er}}_{2-2x}{\mathrm{Y}}_{2x}{\mathrm{Ti}}_2{\mathrm{O}}_7$.

Bloch theorem states the impossibility of persistent electric currents in the ground state of nonrelativistic fermion systems. We extend this theorem to generic systems based on the gauged particle number symmetry and study its consequences on the example of chiral transport phenomena. We show that the chiral magnetic effect can be understood as a generalization of the Bloch theorem to a nonequilibrium steady state, similarly to the integer quantum Hall effect. On the other hand, persistent axial currents are not prohibited by the Bloch theorem and they can be regarded as Pauli paramagnetism of relativistic matter. An application of the generalized Bloch theorem to quantum time crystals is also discussed.

Flavor-changing neutral scalar interactions are a standard feature of generic multi-Higgs models. These are constrained by mixing in the neutral meson systems. We consider situations where there are natural cancellations in such contributions. In particular, when the spin-0 particle has both scalar and pseudoscalar couplings, one may have a self-cancellation. We illustrate one such partial cancellation with Branco-Grimus-Lavoura models. We also inquire whether the flavor-changing quark interactions can lead to new production mechanisms for a neutral scalar at LHC.

While the Sauter-Schwinger effect describes nonperturbative electron-positron pair creation from vacuum by a strong and slowly varying electric field $E_{\text{strong}}$ via tunneling, the dynamically assisted Sauter-Schwinger effect corresponds to a strong (exponential) enhancement of the pair-creation probability by an additional weak and fast electric or electromagnetic pulse $E_{\mathrm{weak}}$. Using the WKB and worldline instanton method, we find that this enhancement mechanism strongly depends on the shape of the fast pulse. For the Sauter profile $1/{\cosh }^2(\omega t)$ considered previously, the threshold frequency ${\omega }_{\mathrm{crit}}$ (where the enhancement mechanism sets in) is basically independent of the magnitude $E_{\mathrm{weak}}$ of the weak pulse—whereas for a Gaussian pulse $\exp (-{\omega }^2{t}^2)$, an oscillating profile $\cos (\omega t)$ or a standing wave $\cos (\omega t)\cos (kx)$, the value of ${\omega }_{\mathrm{crit}}$ does depend (logarithmically) on $E_{\mathrm{weak}}/E_{\text{strong}}$.

We provide a systematic treatment of chemical equilibrium in the presence of a specific type of time dependent background. The type of time dependent background we consider appears, for example, in recently proposed axion/Majoron leptogenesis models [A. Kusenko, K. Schmitz, and T. T. Yanagida, Phys. Rev. Lett. 115, 011302 (2015) and M. Ibe and K. Kaneta, Phys. Rev. D 92, 035019 (2015)]. In describing the chemical equilibrium we use quantities which are invariant under redefinition of fermion phases (we refer to this redefinition as a change of basis for short), and therefore it is a basis invariant treatment. The change of the anomaly terms due to the change of the path integral measure [K. Fujikawa, Phys. Rev. Lett. 42, 1195 (1979) and K. Fujikawa, Phys. Rev. D 29, 285 (1984)] under a basis change is taken into account. We find it is useful to go back and forth between different bases, and there are insights which can be more easily obtained in one basis rather than another. A toy model is provided to illustrate the ideas. For the axion leptogenesis model [A. Kusenko, K. Schmitz, and T. T. Yanagida, Phys. Rev. Lett. 115, 011302 (2015)], our result suggests that at $T>{10}^{13}\mathrm{GeV}$, when sphaleron processes decouple and ${\mathrm{\Gamma }}_{B+L}\ll H<{\mathrm{\Gamma }}_L$ (where $H$ is the Hubble parameter at temperature $T$ and ${\mathrm{\Gamma }}_L$ is the $\mathrm{\Delta }L=2$ lepton number violating interaction rate), the amount of $B-L$ created is controlled by the smallness of the sphaleron interaction rate, ${\mathrm{\Gamma }}_{B+L}$. Therefore it is not as efficient as described. In addition, we notice an interesting modification of gauge boson dispersion relations at subleading order.

In this paper, change of basis does not mean change of Lorentz frame. All calculations in this paper are performed in the center-of-momentum frame of the thermal plasma, i.e. the Lorentz frame in which the average momentum of particles is zero.

We study the geodesic motion of massive and massless test particles in the background of a particular class of multiple charge black holes in gauged supergravity theories in $D=4$. We have analyzed the horizon structure along with the nature of the effective potentials for the case of four equal charges. In view of the corresponding effective potentials, we have discussed all the possible orbits in detail for different values of energy and angular momentum of the incoming test particles. The periods for one complete revolution of circular orbits and the advance of perihelion of the planetary orbit have also been investigated in greater detail for massive test particles. We have also discussed the time period of unstable circular motion and cone of avoidance of massless test particles in detail. All the corresponding results obtained for massive and massless test particles are then compared accordingly.

We study a gravity theory where a scalar field with potential, beyond its minimal coupling, is also coupled through a nonminimal derivative coupling with the torsion scalar which is the teleparallel equivalent of Einstein gravity. This theory provides second order equations of motion and we find large-distance, nonperturbative, static, spherically symmetric four-dimensional solutions. Among them a general class of black hole solutions is found for some range of the parameters/integration constants with asymptotics of the form of hyperscaling violating Lifshitz spacetime with spherical horizon topology. Although the scalar field diverges at the horizon, its energy density and pressures are finite there. From the astrophysical point of view, this solution provides extra deflection of light compared to the Newtonian deflection.

We critically examine the gauge and field-parametrization dependence of renormalization group flows in the vicinity of non-Gaußian fixed points in quantum gravity. While physical observables are independent of such calculational specifications, the construction of quantum gravity field theories typically relies on off-shell quantities such as $\beta$ functions and generating functionals and thus face potential stability issues with regard to such generalized parametrizations. We analyze a two-parameter class of covariant gauge conditions, the role of momentum-dependent field rescalings and a class of field parametrizations. Using the product of Newton and cosmological constant as an indicator, the principle of minimum sensitivity identifies stationary points in this parametrization space which show a remarkable insensitivity to the parametrization. In the most insensitive cases, the quantized gravity system exhibits a non-Gaußian UV stable fixed point, lending further support to asymptotically safe quantum gravity. One of the stationary points facilitates an analytical determination of the quantum gravity phase diagram and features ultraviolet and infrared complete RG trajectories with a classical regime.

With a view to developing a formalism that will be applicable at second perturbative order, we devise a new practical scheme for computing the gravitational self-force experienced by a point mass moving in a curved background spacetime. Our method works in the frequency domain and employs the effective-source approach, in which a distributional source for the retarded metric perturbation is replaced with an effective source for a certain regularized self-field. A key ingredient of the calculation is the analytic determination of an appropriate puncture field from which the effective source and regularized residual field can be calculated. In addition to its application in our effective-source method, we also show how this puncture field can be used to derive tensor-harmonic mode-sum regularization parameters that improve the efficiency of the traditional mode-sum procedure. To demonstrate the method, we calculate the first-order-in-the-mass-ratio self-force and redshift invariant for a point mass on a circular orbit in Schwarzschild spacetime.

The basic formulation describing quadratic mode coupling in rotating Newtonian stars is presented, focusing on polar modes. Due to the Chandrasekhar-Friedman-Schutz mechanism, the $f$-mode (fundamental oscillation) is driven unstable by the emission of gravitational waves. If the star falls inside the so-called instability window, the mode’s amplitude grows exponentially, until it is halted by nonlinear effects. Quadratic perturbations form three-mode networks inside the star, which evolve as coupled oscillators, exchanging energy. Coupling of the unstable $f$-mode to other (stable) modes can lead to a parametric resonance and the subsequent saturation of its amplitude, thus suppressing the instability. The saturation point determines the amplitude of the gravitational-wave signal obtained from an individual source, as well as the evolutionary path of the latter inside the instability window.

We discuss the “constant speed of sound” (CSS) parametrization of the equation of state of high-density matter and its application to the field correlator method (FCM) model of quark matter. We show how observational constraints on the maximum mass and typical radius of neutron stars are expressed as constraints on the CSS parameters. We find that the observation of a $2{\mathrm{M}}_{\odot }$ star already severely constrains the CSS parameters, and is particularly difficult to accommodate if the squared speed of sound in the high-density phase is assumed to be around $1/3$ or less. We show that the FCM equation of state can be accurately represented by the CSS parametrization, which assumes a sharp transition to a high-density phase with density-independent speed of sound. We display the mapping between the FCM and CSS parameters, and see that FCM only allows equations of state in a restricted subspace of the CSS parameters.

The Georgi-Machacek model adds two $\mathrm{SU}(2{)}_L$-triplet scalars to the Standard Model in such a way as to preserve custodial SU(2) symmetry. We study the generalizations of the Georgi-Machacek model to $\mathrm{SU}(2{)}_L$ representations larger than triplets. Perturbative unitarity considerations limit the possibilities to models containing only $\mathrm{SU}(2{)}_L$ quartets, quintets, or sextets. These models are phenomenologically interesting because they allow the couplings of the 125 GeV Higgs boson to $WW$ and $ZZ$ to be larger than their values in the Standard Model. We write down the most general custodial SU(2)-preserving scalar potentials for these models and outline their phenomenology. We find that experimental and theoretical constraints on the fermiophobic custodial-fiveplet states present in each of the models lead to absolute upper bounds on the 125 GeV Higgs boson coupling strength to $WW$ and $ZZ$.