We consider the construction of generic spherically symmetric thin-shell traversable wormhole spacetimes in standard general relativity. By using the cut-and-paste procedure, we comprehensively analyze the stability of arbitrary spherically symmetric thin-shell wormholes to linearized spherically symmetric perturbations around static solutions. While a number of special cases have previously been dealt with in scattered parts of the literature, herein we take considerable effort to make the analysis as general and unified as practicable. We demonstrate in full generality that stability of the wormhole is equivalent to choosing suitable properties for the exotic material residing on the wormhole throat.

We consider modified theories of gravity with a direct coupling between matter and geometry, denoted by an arbitrary function in terms of the Ricci scalar. Because of such a coupling, the matter stress tensor is no longer conserved and there is an energy transfer between the two components. By solving the conservation equation, we argue that the matter system should gain energy in this interaction, as demanded by the second law of thermodynamics. In a cosmological setting, we show that although this kind of interaction may account for cosmic acceleration, this latter together with the direction of the energy transfer constrain the coupling function.

We study the problem of self-energy of pointlike charges in higher dimensional static spacetimes. Their energy, as a functional of the spacetime metric, is invariant under a specific continuous transformation of the metric. We show that the procedure of regularization of this formally divergent functional breaks this symmetry and results in an anomalous contribution to the finite renormalized self-energy. We propose a method of calculation of this anomaly and present an explicit expression for it in the case of a scalar charge in four- and five-dimensional static spacetimes. This anomalous correction proves to be zero in even dimensions, but it does not vanish in odd-dimensional spacetimes.

The change of the effective dimension of spacetime with the probed scale is a universal phenomenon shared by independent models of quantum gravity. Using tools of probability theory and multifractal geometry, we show how dimensional flow is controlled by a multiscale fractional diffusion equation, and physically interpreted as a composite stochastic process. The simplest example is a fractional telegraph process, describing quantum spacetimes with a spectral dimension equal to 2 in the ultraviolet and monotonically rising to 4 towards the infrared. The general profile of the spectral dimension of the recently introduced multifractional spaces is constructed for the first time.

Recent analyses that include cosmic microwave background (CMB) anisotropy measurements from the Atacama Cosmology Telescope and the South Pole Telescope have hinted at the presence of a dark radiation component at more than two standard deviations. However, this result depends sensitively on the assumption of an Hubble Space Telescope prior on the Hubble constant, where $H_0=73.8\pm 2.4\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ at 68% c.l.. Here we repeat this kind of analysis assuming a prior of $H_0=68\pm 2.8\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ at 68% c.l., derived from a median statistics (MS) analysis of 537 non-CMB $H_0$ measurements from Huchra’s compilation. This prior is fully consistent with the value of $H_0=69.7\pm 2.5\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ at 68% c.l. obtained from CMB measurements under assumption of the standard $\Lambda \mathrm{CDM}$ model. We show that with the MS $H_0$ prior the evidence for dark radiation is weakened to $\sim 1.2$ standard deviations. Parametrizing the dark radiation component through the effective number of relativistic degrees of freedom $N_{\mathrm{eff}}$, we find $N_{\mathrm{eff}}=3.98\pm 0.37$ at 68% c.l. with the Hubble Space Telescope prior and $N_{\mathrm{eff}}=3.52\pm 0.39$ at 68% c.l. with the MS prior. We also discuss the implications for current limits on neutrino masses and on primordial Helium abundances.

The dark matter enclosed in a density perturbation with a large initial amplitude ($\delta \rho /\rho \gtrsim {10}^{-3}$) collapses shortly after recombination and forms an ultracompact minihalo (UCMH). Their high central densities make UCMHs especially suitable for detection via astrometric microlensing: as the UCMH moves, it changes the apparent position of background stars. An UCMH with a mass larger than a few solar masses can produce a distinctive astrometric microlensing signal that is detectable by the space astrometry mission Gaia. If Gaia does not detect gravitational lensing by any UCMHs, then it establishes an upper limit on their abundance and constrains the amplitude of the primordial power spectrum for $k\sim 2700{\mathrm{Mpc}}^{-1}$. These constraints complement the upper bound on the amplitude of the primordial power spectrum derived from limits on gamma-ray emission from UCMHs because the astrometric microlensing signal produced by an UCMH is maximized if the dark matter annihilation rate is too low to affect the UCMH’s density profile. If dark matter annihilation within UCMHs is not detectable, a search for UCMHs by Gaia could constrain the amplitude of the primordial power spectrum to be less than ${10}^{-5}$; this bound is 3 orders of magnitude stronger than the bound derived from the absence of primordial black holes.

Eternal inflation produces pocket universes with all physically allowed vacua and histories. Some of these pocket universes might contain a phase of slow-roll inflation, some might undergo cycles of cosmological evolution, and some might look like the Galilean genesis or other “emergent” universe scenarios. Which one of these types of universe we are most likely to inhabit depends on the measure we choose in order to regulate the infinities inherent in eternal inflation. We show that the current leading measure proposals—namely, the global light-cone cutoff and its local counterpart, the causal diamond measure—as well as closely related proposals, all predict that we should live in a pocket universe that starts out with a small Hubble rate, thus favoring emergent and cyclic models. Pocket universes which undergo cycles are further preferred, because they produce habitable conditions repeatedly inside each pocket.

We generalize the previously proposed running vacuum energy model by including a term proportional to $\dot{H}$, in addition to the existing $H^2$ term. We show that the added degree of freedom is very constrained if both low redshift and high redshift data are taken into account. Best-fit models are undistinguishable from $\Lambda \mathrm{CDM}$ at the present time, but could be distinguished in the future with very accurate data at both low and high redshifts. We stress the formal analogy at the phenomenological level of the running vacuum models with recently proposed dark energy models based on the holographic or entropic point of view, where a combination of $\dot{H}$ and $H^2$ term is also present. However those particular entropic formulations which do not have a constant term in the Friedmann equations are not viable. The presence of this term is necessary in order to allow for a transition from a decelerated to an accelerated expansion. In contrast, the running vacuum models, both the original and the generalized one introduced here contain this constant term in a more natural way. Finally, important conceptual issues common to all these models are emphasized.

We give analytic expressions for image properties of objects seen around point mass lenses embedded in a flat $\Lambda \mathrm{CDM}$ universe. An embedded lens in an otherwise homogeneous universe offers a more realistic representation of the lense’s gravity field and its associated deflection properties than does the conventional linear superposition theory. Embedding reduces the range of the gravitational force acting on passing light beams thus altering all quantities such as deflection angles, amplifications, shears and Einstein ring sizes. Embedding also exhibits the explicit effect of the cosmological constant on these same lensing quantities. In this paper, we present these new results and demonstrate how they can be used. The effects of embedding on image properties, although small, i.e., usually less than a fraction of a percent, have a more pronounced effect on image distortions in weak lensing where the effects can be larger than 10%. Embedding also introduces a negative surface mass density for both weak and strong lensing, a quantity altogether absent in conventional Schwarzschild lensing. In strong lensing, we find only one additional quantity, the potential part of the time delay, which differs from conventional lensing by as much as 4%, in agreement with our previous numerical estimates.

In this paper we study the kinetic theory of many-particle astrophysical systems imposing axial symmetry and extending our previous analysis in Phys. Rev. D 83, 123007 (2011). Starting from a Newtonian model describing a collisionless self-gravitating gas, we develop a framework to include systematically the first general relativistic corrections to the matter distribution and gravitational potentials for general stationary systems. Then, we use our method to obtain particular solutions for the case of the Morgan and Morgan disks. The models obtained are fully analytical and correspond to the post-Newtonian generalizations of classical ones. We explore some properties of the models in order to estimate the importance of post-Newtonian corrections and we find that, contrary to the expectations, the main modifications appear far from the galaxy cores. As a by-product of this investigation we derive the corrected version of the tensor virial theorem. For stationary systems we recover the same result as in the Newtonian theory. However, for time dependent backgrounds we find that there is an extra piece that contributes to the variation of the inertia tensor.

The process of photon splitting is investigated in the presence of strongly magnetized electron-positron plasma. The amplitude of the process is calculated in the general case of plasma with a nonzero chemical potential and temperature. The polarization selection rules and corresponding partial amplitudes for allowed splitting channels are obtained in the case of charge-symmetric plasma. It is found that the new splitting channel forbidden in magnetized vacuum becomes allowed. The absorption rates of the photon splitting are calculated with taking into account the photon dispersion and wave function renormalization. In addition, the comparison of photon splitting and Compton scattering process is made. The influence of the reactions under consideration on the radiation transfer in the framework of the magnetar model of a soft gamma repeater burst is discussed.

Explicit formulae of the equations in the generalized Galileon models are given. We also develop the formulation of the reconstruction. By using the formulation, we can explicitly construct an action that reproduces an arbitrary development of the expansion of the Universe. We show that we can completely and explicitly separate the action to the part relevant for the expansion and the irrelevant part. The irrelevant part is related to the stability of the reconstructed solution, and we can further separate that part to the part relevant for the stability and the part irrelevant for the stability. The conditions showing how the reconstructed solution becomes stable, and therefore become an attractor solution, are also given. Working in the static and spherically symmetric space-time, we investigate how the Vainshtein mechanism works in the generalized Galileon model and how the correction to Newton law becomes small. It is also shown that any spherically symmetric and static geometry can be realized by properly choosing the form of the action, which may show that the solution has a fourth hair corresponding to the scalar field. We again separate the action to the part relevant for the reconstruction for the spherically symmetric and static geometry and the irrelevant part. We show that by choosing the relevant and irrelevant parts appropriately, we can obtain an action that admits both the solution corresponding to an arbitrarily given spherically symmetric and static geometry and the solution corresponding to an arbitrarily given history of the expansion of the Universe.

Oscillations from high-energy photons into light pseudoscalar particles in an external magnetic field are expected to occur in some extensions of the standard model. It is usually assumed that those axionlike particles (ALPs) could produce a drop in the energy spectra of gamma ray sources and possibly decrease the opacity of the Universe for TeV gamma rays. We show here that these assumptions are in fact based on an average behavior that cannot happen in real observations of single sources. We propose a new method to search for photon-ALP oscillations, taking advantage of the fact that a single observation would deviate from the average expectation. Our method is based on the search for irregularities in the energy spectra of gamma ray sources. We predict features that are unlikely to be produced by known astrophysical processes and a new signature of ALPs that is easily falsifiable.

We introduce new observables for the study of the inclusive same-sign dilepton production at the LHC which are built out of ratios of the observed number of same-sign dileptons, both with same $N(\ell ,\ell )$ and different flavor $N(\ell ,{\ell }^{\prime })$. As a case study we apply them to the stau coannihilation region of the constrained minimal supersymmetric standard model. We show that the new variables depend rather mildly on the center of mass energy and how these can be used to constrain the parameter space in the $(m_{1/2},\tan \beta )$ plane.

Using the improved lattice gauge field Hamiltonian and the truncated eigenvalue equation method, we compute the $0^{++}$ glueball wave function of $(2+1)$-dimensional SU(2) gauge field theory. The result shows a good scaling behavior in the weak coupling region $3\le 1/g^2\le 6$.

Theoretical predictions are presented for the production of two $J/\psi$-mesons, of a $J/\psi$-meson in association with an open charm hadron, and of two open charm hadrons from two $c\overline{c}$ pairs in the LHC conditions. Processes in both single- and double-parton scattering mechanisms are taken into consideration. Special attention is paid to the kinematic limits of the LHCb detector, for which comparison with the newest experimental data is carried out.

We investigate inclusive prompt photon and semi-inclusive prompt photon-hadron production in high energy proton-nucleus collisions using the color glass condensate formalism, which incorporates nonlinear dynamics of gluon saturation at small $x$ via the Balitsky-Kovchegov equation with a running coupling. For inclusive prompt photon production, we rewrite the cross section in terms of direct and fragmentation contributions and show that the direct photon (and isolated prompt photon) production is more sensitive to gluon saturation effects. We then analyze azimuthal correlations in photon-hadron production in high energy proton-nucleus collisions and obtain a strong suppression of the away-side peak in photon-hadron correlations at forward rapidities, similar to the observed mono-jet production in deuteron-gold collisions at forward rapidity at the Relativistic Heavy Ion Collider. We make predictions for the nuclear modification factor $R_{p(d)A}$ and photon-hadron azimuthal correlations in proton(deuteron)-nucleus collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider at various rapidities.

Based on Martin-like potential, the masses of quarkonia states and their leptonic decay widths have been reviewed. The hyperfine, spin orbit and tensor interactions are employed to compute the spin splitting of the $nS$ states and the fine splittings of the $P$ and $D$ states. The analysis based on the predicted masses and leptonic decay widths clearly indicates that $\psi (3686)$ is a mixed state with a 50%-50% admixture of $c\overline{c}$ $(2S)$ and the hybrid $c\overline{c}g$ in accordance with the suggestion that resolves the $\rho -\pi$ puzzle related to $\psi (2S)$. And ${\rm Y}(10355)$ as similar admixture of $b\overline{b}$ $(3S)$ with $b\overline{b}g$ in accordance with the resolution of Vogel puzzle related to ${\rm Y}(3S)$ state. Analyses on the level differences of $S$-wave excited states of quantum mechanical bound systems show a systematic behavior as $n$ increases. In view of such systematic behavior expected for quarkonia, we observe that $Y(4260)$ and $Z(4430)$ $1^{--}$ states are closer to the $4S$ and $5S$ states with leptonic decay widths predicted as 0.65 keV and 0.49 keV, respectively. The $c\overline{c}$ $(6S)$ $1^{--}$ state is predicted to be around 4600 MeV and its leptonic decay width 0.39 keV. The present study also favors other charmonialike states, $Y(4360)$ and $Y(4660)$, as admixtures of charmonia $S-D$ states. Similarly we find ${\rm Y}(10865)$ does not fit either the $5S$ state or an admixture of $S-D$ states of a $b\overline{b}$ system. We identify $Y_b(10888)$ observed by Belle as the 6S state of bottonia whose leptonic width is predicted as 0.158 keV. Our predicted leptonic width, 0.242 keV of ${\rm Y}(10575,4S)$, is in good agreement with the experimental value of $0.272\pm 0.029\mathrm{keV}$. We predict the pure ${\rm Y}(5S)$ state at about 100 MeV lower than 10865 MeV and its leptonic width 0.191 keV. The upsilon state ${\rm Y}(11019)$ seems to be the right candidate for the $7S$ state, with 0.134 keV as its predicted leptonic width, which is in very good agreement with the experimental value of $0.13\pm 0.03\mathrm{keV}$.

We revisit the question of whether the ${\mathrm{U}}_A(1)$ symmetry is effectively restored in hot and dense medium. In particular, by generalizing the Witten-Veneziano formula to finite temperature, we investigate whether the mass of ${\eta }^{\prime }$-meson will change in medium due to the restoration of chiral symmetry.