Quasidilaton massive gravity is an extension of massive general relativity to a theory with additional scale invariance and approximate internal Galilean symmetry. The theory has a novel self-accelerated solution with the metric indistinguishable (in the decoupling limit) from the de Sitter space, its curvature set by the graviton mass. The spectra of tensor, vector, and scalar perturbations on this solution contain neither ghosts nor gradient instabilities or superluminal modes, for a range of the parameter space. This represents an example of a self-accelerated solution with viable perturbations, attainable within a low-energy effective field theory.

The energy in the ghost-free massive gravity theory is calculated via explicitly resolving the initial value constraints for spherically symmetric deformations of flat space. It turns out that the energy is positive in some cases, but in other cases it can be negative and even unbounded from below. This could suggest that ghost instability is present. However, it seems that the negative energy states cannot communicate with the positive energy sector since the corresponding solutions of the constraint equations are either not globally defined, not asymptotically flat, or singular. As a result, they cannot describe initial data for the decay of flat space. At the same time, for globally regular and asymptotically flat solutions of the constraints, the energy is always found to be positive. All of this suggests that there is a physical sector of the theory where the energy is positive and the ghost is suppressed, so that the theory is stable. The negative energies show up only in disjoint sectors and thus should be harmless.

One of the methods of study of black holes in astrophysics is based on broadening of the spectrum of radiation of ionized iron atoms. The line $\mathrm{K}\alpha$ associated with iron emission at 6.4 keV is very narrow. If such an ion is revolving around a black hole, this line is effectively broadened as a result of the Doppler and gravitational redshift effects. The profile of the broadened spectrum contains information about the gravitational field of the black hole. In the presence of a regular magnetic field in the vicinity of a black hole, the characteristics of the motion of charged ions are modified. In particular, their innermost stable circular orbits become closer to the horizon. The purpose of this work is to study how this effect modifies the spectrum broadening of lines emitted by such an ion. Our final goal is to analyze whether the change of the spectrum profiles can give us information about the magnetic field in the black hole vicinity.

We present a first exploration of the results of neutron star-black hole mergers using black hole masses in the most likely range of $7M_{\odot }–10M_{\odot }$, a neutrino leakage scheme, and a modeling of the neutron star material through a finite-temperature nuclear-theory based equation of state. In the range of black hole spins in which the neutron star is tidally disrupted (${\chi }_{\mathrm{BH}}\gtrsim 0.7$), we show that the merger consistently produces large amounts of cool ($T\lesssim 1\mathrm{MeV}$), unbound, neutron-rich material ($M_{\mathrm{ej}}\sim 0.05M_{\odot }–0.20M_{\odot }$). A comparable amount of bound matter is initially divided between a hot disk ($T_{\max }\sim 15\mathrm{MeV}$) with typical neutrino luminosity of $L_{\nu }\sim {10}^{53}\mathrm{erg}/\mathrm{s}$, and a cooler tidal tail. After a short period of rapid protonization of the disk lasting $\sim 10\mathrm{ms}$, the accretion disk cools down under the combined effects of the fall-back of cool material from the tail, continued accretion of the hottest material onto the black hole, and neutrino emission. As the temperature decreases, the disk progressively becomes more neutron rich, with dimmer neutrino emission. This cooling process should stop once the viscous heating in the disk (not included in our simulations) balances the cooling. These mergers of neutron star-black hole binaries with black hole masses of $M_{\mathrm{BH}}\sim 7M_{\odot }–10M_{\odot }$, and black hole spins high enough for the neutron star to disrupt provide promising candidates for the production of short gamma-ray bursts, of bright infrared postmerger signals due to the radioactive decay of unbound material, and of large amounts of r-process nuclei.

We construct models of slowly rotating, perfect-fluid neutron stars by extending the classical Hartle—Thorne formalism to generic scalar-tensor theories of gravity. Working at second order in the dimensionless angular momentum, we compute the mass $M$, radius $R$, scalar charge $q$, moment of inertia $I$, and spin-induced quadrupole moment $Q$, as well as the tidal and rotational Love numbers. Our formalism applies to generic scalar-tensor theories, but we focus in particular on theories that allow for spontaneous scalarization. It was recently discovered that the moment of inertia, quadrupole moment, and Love numbers are connected by approximately universal (i.e., equation-of-state independent) “I-Love-Q” relations. We find that similar relations hold also for spontaneously scalarized stars. More interestingly, the I-Love-Q relations in scalar-tensor theories coincide with the general relativistic ones within less than a few percent, even for spontaneously scalarized stars with the largest couplings allowed by current binary-pulsar constraints. This implies that astrophysical measurements of these parameters cannot be used to discriminate between general relativity and scalar-tensor theories, even if spontaneous scalarization occurs in nature. Because of the well-known equivalence between $f(R)$ theories and scalar-tensor theories, the theoretical framework developed in this paper can be used to construct rotating compact stellar models in $f(R)$ gravity. Our slow-rotation expansion can also be used as a benchmark for numerical calculations of rapidly spinning neutron stars in generic scalar-tensor theories.

We investigate large-scale structure formation of collisionless dark matter in the phase space description based on the Vlasov (or collisionless Boltzmann) equation whose nonlinearity is induced solely by gravitational interaction according to the Poisson equation. Determining the time evolution of density and peculiar velocity demands solving the full Vlasov hierarchy for the moments of the phase space distribution function. In the presence of long-range interaction no consistent truncation of the hierarchy is known apart from the pressureless fluid (dust) model, which is incapable of describing virialization due to the occurrence of shell-crossing singularities and the inability to generate vorticity and higher cumulants like velocity dispersion. Our goal is to find a simple ansatz for the phase space distribution function that approximates the full Vlasov distribution function without pathologies in a controlled way and therefore can serve as theoretical $N$-body double and as a replacement for the dust model. We argue that the coarse-grained Wigner probability distribution obtained from a wave function fulfilling the Schrödinger-Poisson equation (SPE) is the sought-after function. We show that its evolution equation approximates the Vlasov equation and therefore also the dust fluid equations before shell crossing, but cures the shell-crossing singularities and is able to describe regions of multistreaming and virialization. This feature was already employed in cosmological simulations of large-scale structure formation by Widrow and Kaiser (1993). The coarse-grained Wigner ansatz allows us to calculate all higher moments from density and velocity analytically, thereby incorporating nonzero higher cumulants in a self-consistent manner. On this basis we are able to show that the Schrödinger method automatically closes the corresponding hierarchy such that it suffices to solve the SPE in order to directly determine density and velocity and all higher cumulants.

The general k-essence Lagrangian for the existence of cosmological scaling solutions is derived in the presence of multiple scalar fields coupled to a barotropic perfect fluid. In addition to the scaling fixed point associated with the dynamics during the radiation and matter eras, we also obtain a scalar-field dominated solution relevant to dark energy and discuss the stability of them in the two-field setup. We apply our general results to a model of two canonical fields with coupled exponential potentials arising in string theory. Depending on model parameters and initial conditions, we show that the scaling matter-dominated epochs followed by an attractor with cosmic acceleration can be realized with/without the couplings to scalar fields. The different types of scaling solutions can be distinguished from each other by the evolution of the dark energy equation of state from high redshifts to today.

We study DBI spinflation models with angular potentials that are derived in string theory. We analyze the background dynamics with different parameter sets and study the impact of changing each parameter on inflationary dynamics. It is known that the conversion of the entropy perturbation into the curvature perturbation gives multifield Dirac-Born-Infeld (DBI) inflation models a possibility of satisfying the observational constraints by relaxing the stringent microphysical constraint that disfavors single-field DBI inflation models. We show that our model is excluded by the Planck satellite observations even with the conversion mechanism regardless of the parameter set.

Cross correlating gamma-ray maps with locations of galaxies in the low-redshift Universe vastly increases sensitivity to signatures of annihilation of dark matter particles. Low-redshift galaxies are ideal targets, as the largest contribution to anisotropy in the gamma-ray sky from annihilation comes from $z\lesssim 0.1$, where we expect minimal contributions from astrophysical sources such as blazars. Cross correlating the five-year data of Fermi-LAT with the redshift catalog of the 2MASS survey can detect gamma rays from annihilation if dark matter has the canonical annihilation cross section and its mass is smaller than $\sim 100\mathrm{GeV}$.

We present the second-order general relativistic description of the observed galaxy number density in a cosmological framework. The observed galaxy number density is affected by the volume and the source effects, both of which arise due to the mismatch between physical and observationally inferred quantities such as the redshift, the angular position, the volume, and the luminosity of the observed galaxies. These effects are computed to the second order in metric perturbations without choosing a gauge condition or adopting any restrictions on vector and tensor perturbations, extending the previous linear-order calculations. Paying particular attention to the second-order gauge transformation, we explicitly isolate unphysical gauge modes and construct second-order gauge-invariant variables. Moreover, by constructing second-order tetrads in the observer’s rest frame, we clarify the relation between the physical and the parametrized photon wave vectors. Our second-order relativistic description will provide an essential tool for going beyond the power spectrum in the era of precision measurements of galaxy clustering. We discuss potential applications and extensions of the second-order relativistic description of galaxy clustering.

In this paper, we investigate a scenario of variable gravity and apply it to the unified description of inflation and late-time cosmic acceleration dubbed quintessential inflation. The scalar field called “cosmon,” which in this model unifies both the concepts, reduces to the inflaton at early epochs. We calculate the slow-roll parameters, the Hubble parameter at the end of inflation, the reheating temperature, and the tensor-to-scalar ratio, and we demonstrate the agreement of the model with observations and the Planck data. As for the postinflationary dynamics, the cosmon tracks the background before it exits the scaling regime at late times. The scenario gives rise to the correct epoch sequence of standard cosmology, namely, radiative regime, matter phase, and dark energy. We show that the long kinetic regime after inflation gives rise to enhancement of the relic gravity wave amplitude, resulting in violation of the nucleosynthesis constraint at the commencement of the radiative regime in the case of an inefficient reheating mechanism, such as gravitational particle production. Instant preheating is implemented to successfully circumvent the problem. As a generic feature, the scenario gives rise to a blue spectrum for gravity waves on scales smaller than the comoving horizon scale at the commencement of the radiative regime.

Neutrino telescopes such as IceCube search for an excess of high energy neutrinos above the steeply falling atmospheric background as one approach to finding extraterrestrial neutrinos. For samples of events selected to start in the detector, the atmospheric background can be reduced to the extent that a neutrino interaction inside the fiducial volume is accompanied by a detectable muon from the same cosmic-ray cascade in which the neutrino was produced. Here we provide an approximate calculation of the veto probability as a function of neutrino energy and zenith angle.

The force exerted by the gravitational field on a Casimir cavity in terms of Archimedes force of vacuum is discussed, the force that can be tested against observation is identified, and it is shown that the present technology makes it possible to perform the first experimental tests. The use of suitable high-$T_c$ superconductors as modulators of Archimedes force is motivated. The possibility is analyzed of using gravitational wave interferometers as detectors of the force, transported through an optical spring from the Archimedes vacuum force apparatus to the gravitational interferometer test masses to maintain the two systems well separated. The use of balances to actuate and detect the force is also analyzed, the different solutions are compared, and the most important experimental issues are discussed.

A Pomeron model applicable to both “soft” and “hard” processes is suggested and tested against the high-energy data from virtual photon-induced reactions. The Pomeron is universal, containing two terms, a soft and a hard one, whose relative weight varies with $\widetilde{Q^2}=Q^2+M_V^2$, where $Q^2$ is the virtuality of the incoming photon and $M_V$ is the mass of the produced vector particle. With a small number of adjustable parameters, the model fits all available data on vector meson production and deeply virtual Compton scattering from HERA. Furthermore, we attempt to apply the model to hadron-induced reactions, by using high-energy data on proton-proton scattering.

The absence of supersymmetry or other new physics at the Large Hadron Collider (LHC) has lead many to question naturalness arguments. With Bayesian statistics, we argue that natural models are most probable and that naturalness is not merely an aesthetic principle. We calculate a probabilistic measure of naturalness, the Bayesian evidence, for the Standard Model (SM) with and without quadratic divergences, confirming that the SM with quadratic divergences is improbable. We calculate the Bayesian evidence for the constrained minimal supersymmetric Standard Model (CMSSM) with naturalness priors in three cases: with only the $M_Z$ measurement; with the $M_Z$ measurement and LHC measurements; and with the $M_Z$ measurement, $m_h$ measurement and a hypothetical null result from a $\sqrt{s}=100\mathrm{TeV}$ Very Large Hadron Collider (VLHC) with $3000/\mathrm{fb}$. The “fine-tuning price” of the VLHC given LHC results would be $\sim 400$, which is slightly less than that of the LHC results given the electroweak scale ($\sim 500$).

We discuss exotic production modes of the Higgs boson and how their phenomenology can be probed in current Higgs analyses. We highlight the importance of differential distributions in disentangling standard production mechanisms from exotic modes. We present two model benchmarks for exotic Higgs production arising from chargino-neutralino production and study their impact on the current Higgs data set. As a corollary, we emphasize that current Higgs coupling fits do not fully explore the space of new physics deviations possible in Higgs data.

A recent numerical lattice calculation of the kaon mixing matrix elements of general $\mathrm{\Delta }S=2$ four-fermion operators using staggered fermions relied on two auxiliary theoretical calculations. Here we describe the methodology and present the results of these two calculations. The first concerns one-loop matching coefficients between staggered lattice operators and the corresponding continuum operators. Previous calculations with staggered fermions have used a nonstandard regularization scheme for the continuum operators, and here we provide the additional matching factors needed to connect to the standard regularization scheme. This is the scheme in which two-loop anomalous dimensions are known. We also observe that all previous calculations of this operator matching using staggered fermions have overlooked one matching step in the continuum. This extra step turns out to have no impact on three of the five operators (including that relevant for $B_K$), but it does affect the other two operators. The second auxiliary calculation concerns the two-loop renormalization group (RG) evolution equations for the $B$ parameters of the $\mathrm{\Delta }S=2$ operators. For one pair of operators, the standard analytic solution to the two-loop RG equations fails due to a spurious singularity introduced by the approximations made in the calculation. We give a nonsingular expression derived using analytic continuation and check the result using a numerical solution to the RG equations. We also describe the RG evolution for “golden” combinations of $B$ parameters and give numerical results for RG evolution matrices needed in the companion lattice calculation.

We present the medium-modified energy collimation in the leading-logarithmic approximation (LLA) and next-to-leading-logarithmic approximation (NLLA) of QCD. As a consequence of more accurate kinematic considerations in the argument of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) fragmentation functions (FFs) we find a new NLLA correction $\mathcal{O}({\alpha }_s)$ which accounts for the scaling violation of DGLAP FFs at small $x$. The jet shape is derived from the energy collimation within the same approximations and we also compare our calculations for the energy collimation with the event generators pythia6 and YaJEM for the first time in this paper. The modification of jets by the medium in both cases is implemented by altering the infrared sector using the Borghini-Wiedemann model. The energy collimation and jet shapes qualitatively describe a clear broadening of showers in the medium, which is further supported by YaJEM in the final comparison of the jet shape with CMS PbPb data at center-of-mass energy 2.76 TeV. The comparison of the biased versus unbiased YaJEM jet shape with the CMS data shows a more accurate agreement for biased showers and illustrates the importance of an accurate simulation of the experimental jet-finding strategy.

We study the charmed baryon production reaction $\overline{p}p\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Lambda }}_c^{+}$ by using the $t$-channel $D^0$ and $D^{*0}$ meson-exchange diagrams within an effective Lagrangian model involving the physical hadron masses and the coupling constants determined from SU(4) flavor symmetry. The initial and final state distortion effects are accounted for by using a simple eikonal approximation-based procedure. The vertex parameters of our model have been checked by employing them to calculate the cross sections for the $\overline{p}p\to \overline{\mathrm{\Lambda }}\mathrm{\Lambda }$ reaction within a similar model. We predict the ${\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Lambda }}_c^{+}$ production cross sections in the range of $1–30\mu \mathrm{b}$ for antiproton beam momenta varying between threshold and $20\mathrm{GeV}/c$. The respective roles of $D^0$ and $D^{*0}$ meson exchanges and also those of the vector and tensor components of the $D^{*0}$ coupling have been investigated.