Applying grand unified theories in the context of the early Universe, cosmic strings are an unavoidable partner of the inflaton field. To render such models compatible with the cosmic microwave background temperature anisotropies, the inflationary scale has to be less than ${10}^{15}\mathrm{GeV}$, a value which is inconsistent with the high inflationary scale deduced from the tensor-to-scalar ratio announced from the BICEP2 collaboration. Some questions may be consequently raised about our understanding of the thermal history of the Universe.

We analyze Dirac spectra of two-dimensional QCD-like theories both in the continuum and on the lattice and classify them according to random matrix theories sharing the same global symmetries. The classification is different from QCD in four dimensions because the antiunitary symmetries do not commute with ${\gamma }_5$. Therefore, in a chiral basis, the number of degrees of freedom per matrix element are not given by the Dyson index. Our predictions are confirmed by Dirac spectra from quenched lattice simulations for QCD with two or three colors with quarks in the fundamental representation as well as in the adjoint representation. The universality class of the spectra depends on the parity of the number of lattice points in each direction. Our results show an agreement with random matrix theory that is qualitatively similar to the agreement found for QCD in four dimensions. We discuss the implications for the Mermin-Wagner-Coleman theorem and put our results in the context of two-dimensional disordered systems.

We examine the causal and geometric horizons of dynamical black holes in Lemaitre-Tolman-Bondi collapsing dust spacetimes. Marginally trapped tubes in these spacetimes may be spacelike, timelike or null and may also be sourced from or disappear into shell-crossing singularities which we resolve with (timelike) shock waves. The event horizon kinks when it intersects a shock wave. We calculate the timelike separation between the crossable boundary (marginally trapped tubes plus connecting shock waves) and event horizon. As measured along the crossable boundary this function can have discontinuities not only in its derivative but also in the function itself. These features are closely related to the geometry of the crossable boundary. Finally, we consider the application of this work for future space explorers seeking to make the closest (nonterminal) approach to a black hole horizon.

Gravitational lens models, some of which might act like a concave lens, have been recently investigated by using a static and spherically symmetric modified spacetime metric that depends on the inverse distance to the $n$th power [T. Kitamura et al., Phys. Rev. D 87, 027501 (2013)]. We re-examine the time delay of light in a gravitational concave lens as well as a gravitational convex one. The frequency shift due to the time delay is also investigated. We show that the sign of the time delay in the lens models is the same as that of the deflection angle of light. The size of the time delay decreases with increase in the parameter $n$. We also discuss possible parameter ranges that are relevant to pulsar timing measurements in our Galaxy.

We numerically solve the Teukolsky equation in the time domain to obtain the gravitational-wave emission of a small mass inspiraling and plunging into the equatorial plane of a Kerr black hole. We account for the dissipation of orbital energy using the Teukolsky frequency-domain gravitational-wave fluxes for circular, equatorial orbits, down to the light-ring. We consider Kerr spins $-0.99\le q\le 0.99$, and compute the inspiral-merger-ringdown (2,2), (2,1), (3,3), (3,2), (4,4), and (5,5) modes. We study the large-spin regime, and find a great simplicity in the merger waveforms, thanks to the extremely circular character of the plunging orbits. We also quantitatively examine the mixing of quasinormal modes during the ringdown, which induces complicated amplitude and frequency modulations in the waveforms. Finally, we explain how the study of small mass-ratio black-hole binaries helps extending effective-one-body models for comparable-mass, spinning black-hole binaries to any mass ratio and spin magnitude.

General types of Bose-Einstein condensates are considered. The formation of black-hole analogues is examined for both short- and long-range interactions for arbitrary spatial dimensions greater than 2. The former case includes nonlinear derivative terms plus an inevitable external potential, while the latter one consists solely of gravitylike self-interactions for which intrinsic formation of analogue Schwarzschild-type background space-times is possible. The corresponding geometries are studied, and it is shown how they can be made stable. Their Hawking temperature is estimated, and it is found that in certain setups it can be significantly increased, thus providing better detectability.

We find the excitations and construct the conserved charges (mass and angular momentum) of the recently found minimal massive gravity (MMG) in $2+1$ dimensions in asymptotically anti-de Sitter spacetimes. The field equation of the theory does not come from an action and lacks the required Bianchi identity needed to define conserved charges. But the theory, which also provides a healthy extension of the topologically massive gravity in the bulk and boundary of spacetime, does admit conserved charges for the metric that are solutions. Our construction is based on background Killing vectors and imperative to provide physical meaning to the integration constants in the black hole-type metrics. As an example, we compute the mass and angular momentum of the Bañados-Teitelboim-Zanelli black hole in MMG. We also find the central charges of the boundary field theory and study the chiral gravity limit of MMG.

We explore models for the GeV Galactic Center excess (GCE) observed by the Fermi Telescope, focusing on $\chi \chi \to f\overline{f}$ annihilation processes in the $Z_3$ next-to-minimal supersymmetric standard model (NMSSM). We begin by examining the requirements for a simplified model [parametrized by the couplings and masses of dark matter (DM) and mediator particles] to reproduce the GCE via $\chi \chi \to f\overline{f}$, while simultaneously thermally producing the observed relic abundance. We apply the results of our simplified model to the $Z_3$ NMSSM for singlino/Higgsino (S/H) or bino/Higgsino (B/H) DM. In the case of S/H DM, we find that the DM must be very close to a pseudoscalar resonance to be viable, and large $\tan \beta$ and positive values of $\mu$ are preferred for evading direct detection constraints while simultaneously obtaining the observed Higgs mass. In the case of B/H DM, by contrast, the situation is much less tuned: annihilation generally occurs off resonance, and for large $\tan \beta$, direct detection constraints are easily satisfied by choosing $\mu$ sufficiently large and negative. The B/H model generally has a light, largely MSSM-like pseudoscalar with no accompanying charged Higgs, which could be searched for at the LHC.

We investigate the ratio of the branching fractions of the molecular candidates decaying into the ground and radially excited states within the quark-interchange model. Our numerical results suggest that these molecular candidates are more likely to decay into the radially excited states than into ground states. In particular, the ratio $\mathrm{\Gamma }[Z_c(4430)\to \pi \psi (2S)]/\mathrm{\Gamma }[Z_c(4430)\to \pi J/\psi ]\sim 9.9$ is close to the experimental measurement, which supports the interpretation of $Z_c(4430)$ as the $\overline{D}{D}^{*}(2S)$ molecular state. The ratios of the branching fractions of $Z_b(10610)$ and $Z_b(10650)$ to $\pi \mathrm{\Upsilon }(2S,3S)$ and $\pi \mathrm{\Upsilon }(1S)$ agrees very well with the Belle Collaboration’s measurement. We also predict the similar ratios for $Z_c(3900)$, $Z_c(4020)$, $R_{Z_c(3900)}\approx 1.4$, and $R_{Z_c(4020)}\approx 4.8$. Hopefully, the $\pi \psi (2S)$ mode and the ratios $R_{Z_c(3900)}$ and $R_{Z_c(4020)}$ will be measured by the BESIII and Belle collaborations in the near future, which shall be very helpful for understanding the underlying dynamics of these exotic states.

We update the theoretical framework for the QCD calculation of transition form factors ${\gamma }^{*}\gamma \to \eta$ and ${\gamma }^{*}\gamma \to {\eta }^{\prime }$ at large photon virtualities including full next-to-leading order analysis of perturbative corrections, the charm quark contribution, and taking into account $SU(3)$-flavor breaking effects and the axial anomaly contributions to the power-suppressed twist-four distribution amplitudes. The numerical analysis of the existing experimental data is performed with these improvements.

We extract the Glauber divergences from the spectator amplitudes for two-body hadronic decays $B\to M_1{M}_2$ in the $k_T$ factorization theorem, where $M_2$ denotes the meson emitted at the weak vertex. Employing the eikonal approximation, the divergences are factorized into the corresponding Glauber phase factors associated with the $M_1$ and $M_2$ mesons. It is observed that the latter factor enhances the spectator contribution to the color-suppressed tree amplitude by modifying the interference pattern between the two involved leading-order diagrams. The first factor rotates the enhanced spectator contribution by a phase, and changes its interference with other tree diagrams. The above Glauber effects are compared with the mechanism in elastic rescattering among various $M_1{M}_2$ final states, which has been widely investigated in the literature. We postulate that only the Glauber effect associated with a pion is significant, due to its simultaneous roles as both a $q\overline{q}$ bound state and a pseudo-Nambu-Goldstone boson. Treating the Glauber phases as additional inputs in the perturbative QCD (pQCD) approach, we find a good fit to all the $B\to \pi \pi$, $\pi \rho$, $\pi \omega$, and $\pi K$ data, and resolve the long-standing $\pi \pi$ and $\pi K$ puzzles. The nontrivial success of this modified pQCD formalism is elaborated.

We observe that the linear potential used as a leading approximation for describing color confinement in the instant form of dynamics corresponds to a quadratic confining potential in the front form of dynamics. In particular, the instant-form potentials obtained from lattice gauge theory and string models of hadrons agree with the potentials determined from models using front-form dynamics and light-front holography, not only in their shape, but also in their numerical strength.

We point out that the observed neutrino mixing pattern at low energies is very likely to originate from the $3\times 3$ Pontecorvo-Maki-Nakagawa-Sakata (PMNS) lepton flavor mixing matrix $U$ which possesses the exact $\mu$-$\tau$ permutation symmetry $|U_{\mu i}|=|U_{\tau i}|$ (for $i=1$, 2, 3) at a superhigh energy scale ${\mathrm{\Lambda }}_{\mu \tau }\sim 10^{14}\mathrm{GeV}$. The deviation of ${\theta }_{23}$ from 45° and that of $\delta$ from 270° in the standard parametrization of $U$ are therefore a natural consequence of small PMNS $\mu$-$\tau$ symmetry breaking via the renormalization-group equations (RGEs) running from ${\mathrm{\Lambda }}_{\mu \tau }$ down to the electroweak scale ${\mathrm{\Lambda }}_{\text{EW}}\sim 10^2\mathrm{GeV}$. We find that the RGE-corrected value of ${\theta }_{23}$ is uniquely correlated with the neutrino mass ordering. In the minimal supersymmetric standard model, the best-fit results ${\theta }_{23}\simeq 42.4°$ reported by Capozzi et al. (or ${\theta }_{23}\simeq 48.9°$ reported by Forero et al.) at ${\mathrm{\Lambda }}_{\text{EW}}$ can arise from ${\theta }_{23}=45°$ at ${\mathrm{\Lambda }}_{\mu \tau }$ if the neutrino mass ordering is inverted (or normal). Accordingly, the preliminary best-fit results of $\delta$ at ${\mathrm{\Lambda }}_{\text{EW}}$ can also evolve from $\delta =270°$ at ${\mathrm{\Lambda }}_{\mu \tau }$ no matter whether the massive neutrinos are Dirac or Majorana particles.

In this paper we study the generalized electrodynamics contribution to the electron-positron scattering process $e^{-}{e}^{+}\to e^{-}{e}^{+}$, i.e., Bhabha scattering. Within the framework of the standard model and for energies larger than the electron mass, we calculate the cross section for the scattering process. This quantity is usually calculated in the framework of Maxwell electrodynamics and (for phenomenological reasons) is corrected by a cutoff parameter. On the other hand, by considering generalized electrodynamics instead of Maxwell’s, we show that the Podolsky mass plays the part of a natural cutoff parameter for this scattering process. Furthermore, by using experimental data on Bhabha scattering we estimate its lower bound. Nevertheless, in order to have a mathematically well-defined description of our study we shall present our discussion in the framework of the Epstein-Glaser causal theory.

Recently we suggested a reformulation of general relativity which completely sequesters from gravity all of the vacuum energy from a protected matter sector, assumed to contain the standard model. Here we elaborate further on the mechanism, presenting additional details of how it cancels all loop corrections and renders all contributions from phase transitions automatically small. We also consider cosmological consequences in more detail and show that the mechanism is consistent with a variety of inflationary models that make a universe big and old. We discuss in detail the underlying assumptions behind the dynamics of our proposal, and elaborate on the relationship of the physical interpretation of divergent operators in quantum field theory and the apparent “acausality” which our mechanism seems to entail, which we argue is completely harmless. It is merely a reflection of the fact that any UV sensitive quantity in quantum field theory cannot be calculated from first principles, but is an input whose numerical value must be measured. We also note that since the universe should be compact in spacetime, and so will collapse in the future, the current phase of acceleration with $w_{\mathrm{DE}}\approx -1$ is just a transient. This could be tested by future cosmological observations.

It has been shown in an earlier work [arXiv:1303.1535] that there exists a pair of canonically conjugate variables $(f^{ab},N_{bc}^a)$ in general relativity which also act as thermodynamically conjugate variables on any horizon. In particular their variations $(f^{bc}\delta N_{bc}^a,N_{bc}^a\delta f^{bc})$, which occur in the surface term of the Einstein-Hilbert action, when integrated over a null surface, have direct correspondence with $(S\delta T,T\delta S)$ where $(T,S)$ are the temperature and entropy. We generalize these results to Lanczos-Lovelock models in this paper. We identify two such variables in Lanczos-Lovelock models such that (a) our results reduce to that of general relativity in the appropriate limit and (b) the variation of the surface term in the action, when evaluated on a null surface, has direct thermodynamic interpretation as in the case of general relativity. The variations again correspond to $S\delta T$ and $T\delta S$ where $S$ is now the appropriate Wald entropy for the Lanczos-Lovelock model. The implications are discussed.

Given the extreme accuracy of modern space science, a precise relativistic modeling of observations is required. We use the time transfer function formalism to study light propagation in the field of uniformly moving axisymmetric bodies, which extends the field of application of previous works. We first present a space-time metric adapted to describe the geometry of an ensemble of uniformly moving bodies. Then, we show that the expression of the time transfer functions in the field of a uniformly moving body can be easily derived from its well-known expression in a stationary field by using a change of variables. We also give a general expression of the time transfer function in the case of an ensemble of arbitrarily moving point masses. This result is given in the form of an integral that is easily computable numerically. We also provide the derivatives of the time transfer function in this case, which are mandatory to compute Doppler and astrometric observables. We particularize our results in the case of moving axisymmetric bodies. Finally, we apply our results to study the different relativistic contributions to the range and Doppler tracking for the Juno mission in the Jovian system.

We study the solutions of string fluid equations under the assumption of a local equilibrium which was previously obtained in the context of the kinetic theory. We show that the fluid can be foliated into noninteracting submanifolds whose equations of motion are exactly that of the wiggly strings considered previously by Vilenkin and Carter. In a special case of negligible statistical variance in either the left- or the right-moving directions of microscopic strings, the submanifolds are described by the action of a null-current-carrying chiral string. When both variances vanish the submanifolds are described by the Nambu-Goto action and the string fluid reduces to the string dust introduced by Stachel.

Supermassive black holes and intermediate mass black holes are believed to exist in the Universe. There is no established astrophysical explanation for their origin, and considerations have been made in the literature that those massive black holes (MBHs) may be primordial black holes (PBHs), black holes which are formed in the early universe (well before the matter-radiation equality) due to the direct collapse of primordial overdensities. This paper aims at discussing the possibility of excluding the PBH scenario as the origin of the MBHs. We first revisit the constraints on PBHs obtained from the cosmic microwave background (CMB) distortion that the seed density perturbation causes. By adopting a recent computation of the CMB distortion sourced by the seed density perturbation and the stronger constraint on the CMB distortion set by the COBE/FIRAS experiment used in the literature, we find that PBHs in the mass range $6\times 10^4{M}_{\odot }\text{−}5\times 10^{13}{M}_{\odot }$ are excluded. Since PBHs lighter than $6\times 10^4{M}_{\odot }$ are not excluded from the nonobservation of the CMB distortion, we propose a new method which can potentially exclude smaller PBHs as well. Based on the observation that large density perturbations required to create PBHs also result in the copious production of ultracompact minihalos (UCMHs), compact dark matter halos formed at around the recombination, we show that weakly interacting massive particles (WIMPs) as dark matter annihilate efficiently inside UCMHs to yield cosmic rays far exceeding the observed flux. Our bound gives severe restriction on the compatibility between the particle physics models for WIMPs and the PBH scenario as the explanation of MBHs.