We construct exact, regular and topologically nontrivial configurations of the coupled Einstein-nonlinear sigma model in ($3+1$) dimensions. The ansatz for the nonlinear $SU(2)$ field is regular everywhere and circumvents Derrick’s theorem because it depends explicitly on time, but in such a way that its energy-momentum tensor is compatible with a stationary metric. Moreover, the $SU(2)$ configuration cannot be continuously deformed to the trivial Pion vacuum as it possesses a nontrivial winding number. We reduce the full coupled four-dimensional Einstein nonlinear sigma model system to a single second order ordinary differential equation. When the cosmological constant vanishes, such a master equation can be further reduced to an Abel equation. Two interesting regular solutions correspond to a stationary traversable wormhole (whose only “exotic matter” is a negative cosmological constant) and a ($3+1$)-dimensional cylinder whose ($2+1$)-dimensional section is a Lorentzian squashed sphere. The Klein-Gordon equation in these two families of spacetimes can be solved in terms of special functions. The angular equation gives rise to the Jacobi polynomials while the radial equation belongs to the Poschl-Teller family. The solvability of the Poschl-Teller problem implies nontrivial quantization conditions on the parameters of the theory.

We compute the binding energy and angular momentum of a test particle at the last stable circular orbit (LSO) on the equatorial plane around a general relativistic, rotating neutron star (NS). We present simple, analytic, but accurate formulas for these quantities that fit the numerical results and which can be used in several astrophysical applications. We demonstrate the accuracy of these formulas for three different equations of state (EOS) based on nuclear relativistic mean-field theory models and argue that they should remain still valid for any NS EOS that satisfy current astrophysical constraints. We compare and contrast our numerical results with the corresponding ones for the Kerr metric characterized by the same mass and angular momentum.

We consider a particle collision with a high center-of-mass energy near a Bañados-Teitelboim-Zanelli (BTZ) black hole. We obtain the center-of-mass energy of two general colliding geodesic particles in the BTZ black hole spacetime. We show that the center-of-mass energy of two ingoing particles can be arbitrarily large on an event horizon if either of the two particles has a critical angular momentum and the other has a noncritical angular momentum. We also show that the motion of a particle with a subcritical angular momentum is allowed near an extremal rotating BTZ black hole and that a center-of-mass energy for a tail-on collision at a point can be arbitrarily large in a critical angular momentum limit.

We tried to average the Schwarzschild solution for the gravitational point source by analogy with the same problem in Newtonian gravity or electrostatics. We expected to get a similar result, consisting of two parts: the smoothed interior part being a sphere filled with some matter content and an empty exterior part described by the original solution. We considered several variants of generally covariant averaging schemes. The averaging of the connection in the spirit of Zalaletdinov’s macroscopic gravity gave unsatisfactory results. With the transport operators proposed in the literature it did not give the expected Schwarzschild solution in the exterior part of the averaged spacetime. We were able to construct a transport operator that preserves the Newtonian analogy for the outward region but such an operator does not have a clear geometrical meaning. In contrast, using the curvature as the primary averaged object instead of the connection does give the desired result for the exterior part of the problem in a fine way. However for the interior part, this curvature averaging does not work because the Schwarzschild curvature components diverge as $1/r^3$ near the center and therefore are not integrable.

We study the relative contribution of cusps and pseudocusps, on cosmic (super)strings, to the emitted bursts of gravitational waves. The gravitational wave emission in the vicinity of highly relativistic points on the string follows, for a high enough frequency, a logarithmic decrease. The slope has been analytically found to be $-4/3$ for points reaching exactly the speed of light in the limit $c=1$. We investigate the variations of this high-frequency behavior with respect to the velocity of the points considered, for strings formed through a numerical simulation, and we then compute numerically the gravitational waves emitted. We find that for string points moving with velocities as far as ${10}^{-3}$ from the theoretical (relativistic) limit $c=1$, gravitational wave emission follows a behavior consistent with that of cusps, effectively increasing the number of cusps on a string. Indeed, depending on the velocity threshold chosen for such behavior, we show that the emitting part of the string worldsheet is enhanced by a factor $\mathcal{O}(10^3)$ with respect to the emission of cusps only.

The continuous progress toward more precise cosmological surveys and experiments has galvanized recent interest into consistency tests on cosmological parameters and models. At the heart of this effort is quantifying the degree of inconsistency between two or more cosmological data sets. We introduce an intuitive moment-based measure we call the index of inconsistency (IOI) and show that it is sensitive to the separation of the means, the size of the constraint ellipsoids, and their orientations in the parameter space. We find that it tracks accurately the inconsistencies when present. Next, we show that parameter marginalization can cause a loss of information on the inconsistency between two experiments, and we quantify such a loss using the drop in IOI. In order to zoom on a given parameter, we define the relative residual IOI and the relative drop in IOI. While these two quantities can provide insights on the parameters that are most responsible for inconsistencies, we find that the full IOI applied to the whole parameter spaces is what must be used to correctly reflect the degree of inconsistency between two experiments. We discuss various properties of IOI, provide its eigenmode decomposition, and compare it to other measures of discordance. Finally, we apply IOI to current geometry data sets (i.e., an improved Supernovae Type Ia compilation, baryon acoustic oscillations from 6dF, SDSS MGS and Lyman-$\alpha$ forest, and high-$\ell$ cosmic microwave background (CMB) temperature data from Planck-2015) versus growth data sets (i.e., Redshift Space Distortions from WiggleZ and SDSS, Weak Lensing from CFHTLenS, CMB Lensing, Sunyav-Zeldovich effect, and low-$\ell$ CMB temperature and polarization data from Planck-2015). We find that a persistent inconsistency is present between the two data sets. This could reflect the presence of systematics in the data or inconsistencies in the underlying model.

By considering the realization of the emergent universe scenario in Eddington-inspired Born-Infeld (EiBI) theory, we study the stability of the Einstein static universe filled with perfect fluid in EiBI theory against both the homogeneous and inhomogeneous scalar perturbations in this work. We find that in both the spatially flat and closed cases, the emergent universe scenario is no longer viable, since the Einstein static universe cannot be stable against both the homogeneous and inhomogeneous scalar perturbations simultaneously. However, the emergent universe scenario survives in the spatially open case, while the Einstein static universe can be stable under some conditions.

Because of their quantum fluctuations, axion fields had a chance to experience field excursions traversing many minima of their potentials during inflation. We study this situation by analyzing the dynamics of an axion field $\psi$, present during inflation, with a periodic potential given by $v(\psi )={\mathrm{\Lambda }}^4[1-\cos (\psi /f)]$. By assuming that the vacuum expectation value of the field is stabilized at one of its minima, say, $\psi =0$, we compute every $n$-point correlation function of $\psi$ up to first order in ${\mathrm{\Lambda }}^4$ using the in-in formalism. This computation allows us to identify the distribution function describing the probability of measuring $\psi$ at a particular amplitude during inflation. Because $\psi$ is able to tunnel between the barriers of the potential, we find that the probability distribution function consists of a non-Gaussian multimodal distribution such that the probability of measuring $\psi$ at a minimum of $v(\psi )$ different from $\psi =0$ increases with time. As a result, at the end of inflation, different patches of the Universe are characterized by different values of the axion field amplitude, leading to important cosmological phenomenology: (a) Isocurvature fluctuations induced by the axion at the end of inflation could be highly non-Gaussian. (b) If the axion defines the strength of standard model couplings, then one is led to a concrete realization of the multiverse. (c) If the axion corresponds to dark matter, one is led to the possibility that, within our observable Universe, dark matter started with a nontrivial initial condition, implying novel signatures for future surveys.

We will study the cosmological solutions of a class of Galileon models. A special class of the Bianchi type I power-law solutions will be presented in this paper. We will show that these Bianchi type I power-law solutions are stable during the inflationary phase. In addition, we will also show that the presence of a phantom field induces at least an unstable mode for the perturbation equation and destabilizes the power-law solutions.

We study the propagation of ultrahigh-energy cosmic rays in the magnetized cosmic web. We focus on the particular case of highly magnetized voids ($B\sim \mathrm{nG}$), using the upper bounds from the Planck satellite. The cosmic web was obtained from purely magnetohydrodynamical cosmological simulations of structure formation considering different power spectra for the seed magnetic field in order to account for theoretical uncertainties. We investigate the impact of these uncertainties on the propagation of cosmic rays, showing that they can affect the measured spectrum and composition by up to $\simeq 80\%$ and $\simeq 5\%$, respectively. In our scenarios, even if magnetic fields in voids are strong, deflections of 50 EeV protons from sources closer than $\sim 50\mathrm{Mpc}$ are less than 15° in approximately 10–50% of the sky, depending on the distribution of sources and magnetic power spectrum. Therefore, UHECR astronomy might be possible in a significant portion of the sky depending on the primordial magnetic power spectrum, provided that protons constitute a sizeable fraction of the observed UHECR flux.

In the present paper we investigate the production of ultrahigh energy cosmic rays (UHECRs) from Seyferts. We discuss the UHECR luminosities obtained by two possible engine trigger models: pure radiative transfer and the energy extraction from poloidal magnetic flux. The first case is modeled by Kerr slim disk or Bondi accretion mechanisms. Since it is assumed that the broadband spectra of Seyferts indicate that at least the outer portions of their accretion disks are cold and geometrically thin, and since our results point that the consequent radiative energy transfer is inefficient, we build the second approach based on massive Seyferts with sufficient central poloidal magnetic field to trigger an outflow of magnetically driven charged particles capable to explain the observed UHECRs and gamma rays in Earth experiments from a given Seyfert source.

A new frontier in the search for dark matter (DM) is based on the idea of detecting the decoherence caused by DM scattering against a mesoscopic superposition of normal matter. Such superpositions are uniquely sensitive to very small momentum transfers from new particles and forces, especially DM with a mass below 100 MeV. Here we investigate what sorts of dark sectors are inaccessible with existing methods but would induce noticeable decoherence in the next generation of matter interferometers. We show that very soft but medium range ($0.1\mathrm{nm}–1\mu \mathrm{m}$) elastic interactions between nuclei and DM are particularly suitable. We construct toy models for such interactions, discuss existing constraints, and delineate the expected sensitivity of forthcoming experiments. The first hints of DM in these devices would appear as small variations in the anomalous decoherence rate with a period of one sidereal day. This is a generic signature of interstellar sources of decoherence, clearly distinguishing it from terrestrial backgrounds. The OTIMA experiment under development in Vienna will begin to probe Earth-thermalizing DM once sidereal variations in the background decoherence rate are pushed below one part in a hundred for superposed 5-nm gold nanoparticles. The proposals by Bateman et al. and Geraci et al. could be similarly sensitive although they would require at least a month of data taking. DM that is absorbed or elastically reflected by the Earth, and so avoids a greenhouse density enhancement, would not be detectable by those three experiments. On the other hand, the aggressive proposals of the MAQRO collaboration and Pino et al. would immediately open up many orders of magnitude in DM mass, interaction range, and coupling strength, regardless of how DM behaves in bulk matter.

We present the first constraints on the spin-dependent, inelastic scattering cross section of weakly interacting massive particles (WIMPs) on nucleons from XENON100 data with an exposure of $7.64\times {10}^3\mathrm{kg}·\text{days}$. XENON100 is a dual-phase xenon time projection chamber with 62 kg of active mass, operated at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy and designed to search for nuclear recoils from WIMP-nucleus interactions. Here we explore inelastic scattering, where a transition to a low-lying excited nuclear state of ${}^{129}\mathrm{Xe}$ is induced. The experimental signature is a nuclear recoil observed together with the prompt deexcitation photon. We see no evidence for such inelastic WIMP-${}^{129}\mathrm{Xe}$ interactions. A profile likelihood analysis allows us to set a 90% C.L. upper limit on the inelastic, spin-dependent WIMP-nucleon cross section of $3.3\times {10}^{-38}{\mathrm{cm}}^2$ at $100\mathrm{GeV}/c^2$. This is the most constraining result to date, and sets the pathway for an analysis of this interaction channel in upcoming, larger dual-phase xenon detectors.

We present the conformal behavior of the shear viscosity-to-entropy density ratio and the fermion-number diffusion coefficient within the perturbative regime of the conformal window for gauge-fermion theories.

In this paper we continue studying the modification of the axial charge in chiral media by macroscopic helicities. Recently it was shown that magnetic reconnections result in a persistent current of zero mode along flux tubes. Here we argue that in general a change in the helical part of the generalized axial charge results in the same phenomenon. Thus one may say that there is a novel realization of chiral effects requiring no initial chiral asymmetry. The transfer of flow helicity to zero modes is analyzed in a toy model based on a vortex reconnection in a chiral superfluid. Then, we discuss the balance between the two competing processes effect of reconnections and the chiral instability on the example of magnetic helicity. We argue that in the general case there is a possibility for the distribution of the axial charge between the magnetic and fermionic forms at the end of the instability.

The form factors of semileptonic $B_{(s)}\to a_1(K_1){\ell }^{+}{\ell }^{-}$, $\ell =\tau$, $\mu$, $e$ transitions are investigated in the framework of the light-cone sum rules with $B$-meson distribution amplitudes, which play an important role in exclusive $B$ decays. The $B$-meson distribution amplitudes, ${\phi }_{\pm }(\omega )$ are a model-dependent form, so we consider four different parametrizations which can provide a reasonable description of ${\phi }_{\pm }(\omega )$ from QCD corrections. The branching fractions of these transitions are calculated. For a better analysis, a comparison of our results with the prediction of other models is provided.

We formulate the chiral kinetic equation with the longitudinal boost invariance. We particularly focus on the physical interpretation of the particle number conservation. There appear two terms associated with the expansion, which did not exist in the nonchiral kinetic equation. One is a contribution to the transverse current arising from the side-jump effect, and the other is a change in the density whose flow makes the longitudinal current. We point out a characteristic pattern in the transverse current driven by the expansion, which we call the chiral circular displacement.

We review the main results on the generalization of the DGLAP evolution equations within the cut Mellin moments (CMM) approach, which allows one to overcome the problem of kinematic constraints in Bjorken $x$. CMM obtained by multiple integrations as well as multiple differentiations of the original parton distribution also satisfy the DGLAP equations with the simply transformed evolution kernel. The CMM approach provides novel tools to test QCD; here we present one of them. Using appropriate classes of CMM, we construct the generalized Bjorken sum rule that allows us to determine the Bjorken sum rule value from the experimental data in a restricted kinematic range of $x$. We apply our analysis to COMPASS data on the spin structure function $g_1$.

Using the fixed center approximation to Faddeev equations, we investigate the $DKK$ and $DK\overline{K}$ three-body systems, considering that the $DK$ dynamically generates, through its $I=0$ component, the $D_{s0}^{*}(2317)$ molecule. According to our findings, for the $DK\overline{K}$ interaction we find evidence of a state $I(J^P)=1/2(0^{-})$ just above the $D_{s0}^{*}(2317)\overline{K}$ threshold and around the $D{f}_0(980)$ threshold, with mass of about 2833–2858 MeV, made mostly of $D{f}_0(980)$. On the other hand, no evidence related to a state from the $DKK$ interaction is found. The state found could be seen in the $\pi \pi D$ invariant mass.

Heavy vectorlike quarks with electric charge $Q=2/3$ (also called heavy tops) appear naturally in many extensions of the Standard Model. Although these typically predict the existence of further particles below the TeV scale, direct searches for heavy tops have been performed assuming that they decay only into SM particles. The aim of this paper is to overcome this situation. We consider the most constraining experimental LHC searches for vectorlike quarks, including analyses of the $36{\mathrm{fb}}^{-1}$ of data collected in the latest run at 13 TeV of center of mass energy, as well as searches sensitive to heavy tops decaying into a new scalar, $S$. Combining all these, we derive bounds for arbitrary values of the heavy top branching ratios. A simple code that automatizes this process is also provided. At the physics level, we demonstrate that bounds on heavy tops are not inevitably weaker in the presence of new light scalars. We find that heavy tops with masses below $\sim 900\mathrm{GeV}$ are excluded by direct searches, independently of whether they decay into $Zt$, $Ht$, $Wb$ or $St$ (with $S$ giving either missing energy of bottom quarks) or into any combination of them.