We study a static scalar massless field created by a source located near an electrically charged higher-dimensional spherically symmetric black hole. We demonstrate that there exist biconformal transformations relating static field solutions in the metric with different parameters of the mass $M$ and charge $Q$. Using this symmetry, we obtain the static scalar Green function in the higher-dimensional Reissner-Nordström spacetimes.

We provide an $F(R)$ gravity description of a $\mathrm{\Lambda }\mathrm{CDM}$ bouncing model, without the need for matter fluids or for a cosmological constant. As we explicitly demonstrate, the two cosmological eras that constitute the $\mathrm{\Lambda }\mathrm{CDM}$ bouncing model can be generated by $F(R)$ gravity, which can lead to accelerating cosmologies. The resulting $F(R)$ gravity has the Einstein frame inflationary properties that have concordance with the latest Planck observational data. Both the $F(R)$ gravity stability properties are thoroughly investigated, and also, the gravitational particle production, a feature necessary for the viability of the $\mathrm{\Lambda }\mathrm{CDM}$ bounce scenario, is also addressed. As we will show, the $\mathrm{\Lambda }\mathrm{CDM}$ bounce model can be successfully described by pure $F(R)$ gravity, with appealing phenomenological attributes, which we extensively discuss.

We have recently presented a new approach for numerical relativity simulations in spherical polar coordinates, both for vacuum and for relativistic hydrodynamics. Our approach is based on a reference-metric formulation of the Baumgarte-Shapiro-Shibata-Nakamura equations, a factoring of all tensor components, as well as a partially implicit Runge-Kutta method, and does not rely on a regularization of the equations, nor does it make any assumptions about the symmetry across the origin. In order to demonstrate this feature we present here several off-centered simulations, including simulations of single black holes and neutron stars whose center is placed away from the origin of the coordinate system, as well as the asymmetric head-on collision of two black holes. We also revisit our implementation of relativistic hydrodynamics and demonstrate that a reference-metric formulation of hydrodynamics together with a factoring of all tensor components avoids problems related to the coordinate singularities at the origin and on the axes. As a particularly demanding test we present results for a shock wave propagating through the origin of the spherical polar coordinate system.

We evaluate the Hadamard function and the vacuum expectation value of the current density for a massive complex scalar field in the generalized geometry of a straight cosmic string with a finite core enclosing an arbitrary distributed magnetic flux along the string axis. For the interior geometry, a general cylindrically symmetric static metric tensor is used with finite support. In the region outside the core, both the Hadamard function and the current density are decomposed into the idealized zero-thickness cosmic string and core-induced contributions. The only nonzero component corresponds to the azimuthal current. The zero-thickness part of the latter is a periodic function of the magnetic flux inside the core, with the period equal to the quantum flux. As a consequence of the direct interaction of the quantum field with the magnetic field inside the penetrable core, the core-induced contribution, in general, is not a periodic function of the flux. In addition, the vacuum current, in general, is not a monotonic function of the distance from the string and may change the sign. For a general model of the core interior, we also evaluate the magnetic fields generated by the vacuum current. As applications of the general results, we have considered an impenetrable core modeled by Robin boundary condition, a core with the Minkowski-like interior and a core with a constant positive curvature space. Various exactly solvable distributions of the magnetic flux are discussed.

Descriptions of highly relativistic fermions in a gravitational field in the classical (nonquantum) and quantum approaches are discussed. The results following from the Mathisson-Papapetrou equations for a fast spinning particle in Schwarzschild’s and Kerr’s background are considered. Numerical estimates for electron, proton and neutrino in the gravitational field of black holes are presented. The general relativistic Dirac equation is analyzed from the point of view it is using for the adequate description of highly relativistic fermions in a gravitational field, in the linear and nonlinear spin approximation. It is necessary to have some corrected Dirac equation for a highly relativistic fermion with strong spin-gravity coupling.

We analyze the spectrum of cosmic microwave background (CMB) anisotropies in the timescape cosmology: a potentially viable alternative to homogeneous isotropic cosmologies without dark energy. We exploit the fact that the timescape cosmology is extremely close to the standard cosmology at early epochs to adapt existing numerical codes to produce CMB anisotropy spectra, and to match these as closely as possible to the timescape expansion history. A variety of matching methods are studied and compared. We perform Markov chain Monte Carlo analyses on the parameter space, and fit CMB multipoles $50\le \ell \le 2500$ to the Planck satellite data. Parameter fits include a dressed Hubble constant, $H_0=61.0\mathrm{km}{\sec }^{-1}{\mathrm{Mpc}}^{-1}$ ($\pm 1.3\%$ stat) ($\pm 8\%$ sys), and a present void volume fraction $f_{\mathrm{v}0}=0.627$ ($\pm 2.3\%$ stat) ($\pm 13\%$ sys). We find best fit likelihoods which are comparable to that of the best fit $\mathrm{\Lambda }\mathrm{CDM}$ cosmology in the same multipole range. In contrast to earlier results, the parameter constraints afforded by this analysis no longer admit the possibility of a solution to the primordial lithium abundance anomaly. This issue is related to a strong constraint between the ratio of baryonic to nonbaryonic dark matter and the ratio of heights of the second and third acoustic peaks, which cannot be changed as long as the standard cosmology is assumed up to the surface of last scattering. These conclusions may change if backreaction terms are also included in the radiation-dominated primordial plasma.

The implications of a smaller than unity speed of sound of the scalar perturbations during cosmic inflation is studied in terms of a model independent large-$N$ approach. We show that the $(n_s,r)$ plane is nontrivially degenerated when the effects of a different-than-one speed of sound $c_s$ are taken into account. We also discuss the degeneracies due to $c_s$ in the running of the spectral index, ${\alpha }_s$. We use the bounds on $c_s$ to constrain such degeneracies.

Searches for gravitational waves produced by coalescing black hole binaries with total masses $\gtrsim 25{\mathrm{M}}_{\odot }$ use matched filtering with templates of short duration. Non-Gaussian noise bursts in gravitational wave detector data can mimic short signals and limit the sensitivity of these searches. Previous searches have relied on empirically designed statistics incorporating signal-to-noise ratio and signal-based vetoes to separate gravitational wave candidates from noise candidates. We report on sensitivity improvements achieved using a multivariate candidate ranking statistic derived from a supervised machine learning algorithm. We apply the random forest of bagged decision trees technique to two separate searches in the high mass ($\gtrsim 25{\mathrm{M}}_{\odot }$) parameter space. For a search which is sensitive to gravitational waves from the inspiral, merger, and ringdown of binary black holes with total mass between $25{\mathrm{M}}_{\odot }$ and $100{\mathrm{M}}_{\odot }$, we find sensitive volume improvements as high as ${70}_{\pm 13}\%–{109}_{\pm 11}\%$ when compared to the previously used ranking statistic. For a ringdown-only search which is sensitive to gravitational waves from the resultant perturbed intermediate mass black hole with mass roughly between $10{\mathrm{M}}_{\odot }$ and $600{\mathrm{M}}_{\odot }$, we find sensitive volume improvements as high as ${61}_{\pm 4}\%–{241}_{\pm 12}\%$ when compared to the previously used ranking statistic. We also report how sensitivity improvements can differ depending on mass regime, mass ratio, and available data quality information. Finally, we describe the techniques used to tune and train the random forest classifier that can be generalized to its use in other searches for gravitational waves.

The analysis of physical measurements often copes with highly correlated noises and interruptions caused by outliers, saturation events, or transmission losses. We assess the impact of missing data on the performance of linear regression analysis involving the fit of modeled or measured time series. We show that data gaps can significantly alter the precision of the regression parameter estimation in the presence of colored noise, due to the frequency leakage of the noise power. We present a regression method that cancels this effect and estimates the parameters of interest with a precision comparable to the complete data case, even if the noise power spectral density (PSD) is not known a priori. The method is based on an autoregressive fit of the noise, which allows us to build an approximate generalized least squares estimator approaching the minimal variance bound. The method, which can be applied to any similar data processing, is tested on simulated measurements of the MICROSCOPE space mission, whose goal is to test the weak equivalence principle (WEP) with a precision of $10^{-15}$. In this particular context the signal of interest is the WEP violation signal expected to be found around a well defined frequency. We test our method with different gap patterns and noise of known PSD and find that the results agree with the mission requirements, decreasing the uncertainty by a factor of 60 with respect to ordinary least squares methods. We show that it also provides a test of significance to assess the uncertainty of the measurement.

An SU(2) vectorlike singlet quark with a charge of either $+2/3(t^{\prime })$ or $-1/3(b^{\prime })$ is predicted in many extensions of the Standard Model. The mixing of these quarks with the top or bottom lead to flavor-changing Yukawa interactions and neutral currents. The decay modes of the heavier mass eigenstates are therefore different from the Standard Model-type chiral quarks. The LHC will provide an ideal environment to look for the signals of these exotic quarks. Considering all decays, including those involving $Z$ and Yukawa interactions, we show how one can distinguish between $t^{\prime }$ and $b^{\prime }$ from ratios of event rates with different lepton multiplicities. The ability to reconstruct the Higgs boson with a mass around 125.5 GeV plays an important role in such differentiation.

We survey a few minimal scalar extensions of the standard electroweak model that provide a simple setup for massive neutrinos in connection with an invisible axion. The presence of a chiral $U(1)$ à la Peccei-Quinn drives the pattern of Majorana neutrino masses while providing a dynamical solution to the strong $CP$ problem and an axion as a dark matter candidate. We paradigmatically apply such a renormalizable framework to type-II seesaw and to two viable models for neutrino oscillations where the neutrino masses arise at one and two loops, respectively. We comment on the naturalness of the effective setups as well as on their implications for vacuum stability and electroweak baryogenesis.

We propose a new power counting for the effective field theory describing a near-threshold state with unstable constituents, such as the $X(3872)$ meson. In this counting, the momenta of the heavy particles, the pion mass and the excitation energy of the unstable constituent—the $D^{*}$ in the case of the $X$—are treated as small scales, of order $Q$. The difference $\delta$ between the excitation energy of the $D^{*}$ and the pion mass is smaller than either by a factor $\sim 20$. We therefore assign $\delta$ an order $Q^2$ in our counting. This provides a consistent framework for a double expansion in both $\delta /m_{\pi }$ and the ratio of $m_{\pi }$ to the high-energy scales in this system. It ensures that amplitudes have the correct behavior at the three-body threshold. It allows us to derive, within an effective theory, various results which have previously been obtained using physically motivated approximations.

We present a calculation of Wigner distributions for gluons in a light-front dressed quark model. We calculate the kinetic and canonical gluon orbital angular momentum and spin-orbit correlation of the gluons in this model.

We estimate the susceptibilities of conserved charges for two-flavor strongly interacting matter with varying system sizes, using the Polyakov loop enhanced Nambu–Jona-Lasinio model. The susceptibilities for vanishing baryon densities are found to show a scaling with the system volume in the hadronic as well as partonic phase. This scaling breaks down for a temperature range of about 30–50 MeV around the crossover region. Simultaneous measurements of the various susceptibilities may, thus, indicate how close to the crossover region the freeze-out occurs for the fireball created in heavy-ion collision experiments.

Within the context of holography we study the general class of $d=4$ conformal field theories (CFTs) after applying a universal helical deformation. At finite temperature we construct the associated black hole solutions of Einstein gravity, numerically, by exploiting a Bianchi $VI{I}_0$ ansatz for the bulk $D=5$ metric. At $T=0$ we show that they flow in the IR to exactly the same CFT. The deformation gives rise to a finite, nonzero DC thermal conductivity along the axis of the helix, which we determine analytically in terms of black hole horizon data. We also calculate the AC thermal conductivity along this axis and show that it exhibits Drude-like peaks.

In this paper we propose a novel definition of the bosonic spectral action using zeta function regularization, in order to address the issues of renormalizability and spectral dimensions. We compare the zeta spectral action with the usual (cutoff-based) spectral action and discuss its origin and predictive power, stressing the importance of the issue of the three dimensionful fundamental constants, namely the cosmological constant, the Higgs vacuum expectation value, and the gravitational constant. We emphasize the fundamental role of the neutrino Majorana mass term for the structure of the bosonic action.

New symmetry properties are found for pointlike scalar and Dirac particles (Higgs boson and all leptons) in Riemannian and Riemann-Cartan spacetimes in the presence of electromagnetic interactions. A Hermitian form of the Klein-Gordon equation for a pointlike scalar particle in an arbitrary $n$-dimensional Riemannian (or Riemann-Cartan) spacetime is obtained. New conformal symmetries of initial and Hermitian forms of this equation are ascertained. In the above spacetime, general Hamiltonians in the generalized Feshbach-Villars and Foldy-Wouthuysen representations are derived. The conformal-like transformation conserving these Hamiltonians is found. Corresponding conformal symmetries of a Dirac particle are determined. It is proven that all conformal symmetries remain unchanged by an inclusion of electromagnetic interactions.

For black holes with multiple horizons, the area product of all horizons has been proven to be mass independent in many cases. Counterexamples were also found in some occasions. In this paper, we first prove a theorem derived from the first law of black hole thermodynamics and a mathematical lemma related to the Vandermonde determinant. With these arguments, we develop some general criteria for the mass independence of the entropy product as well as the entropy sum. In particular, if a $d$-dimensional spacetime is spherically symmetric and its radial metric function $f(r)$ is a Laurent series in $r$ with the lowest power $-m$ and the highest power $n$, we find the criterion is extremely simple: The entropy product is mass independent if and only if $m\ge d-2$ and $n\ge 4-d$. The entropy sum is mass independent if and only if $m\ge d-2$ and $n\ge 2$. Compared to previous works, our method does not require an exact expression of the metric. Our arguments turn out to be useful even for rotating black holes. By applying our theorem and lemma to a Myers–Perry black hole with spacetime dimension $d$, we show that the entropy product/sum is mass independent for all $d>4$, while it is mass dependent only for $d=4$, i.e., the Kerr solution.

We revisit alternative mechanisms of gravitational wave production during inflation and argue that they generically emit a non-negligible amount of scalar fluctuations. We find the scalar power is larger than the tensor power by a factor of order $1/{\epsilon }^2$. For an appreciable tensor contribution, the associated scalar emission completely dominates the zero-point fluctuations of the inflaton, resulting in a tensor-to-scalar ratio $r\sim {\epsilon }^2$. A more quantitative result can be obtained if one further assumes that gravitational waves are emitted by localized subhorizon processes, giving $r_{\max }\simeq 0.3{\epsilon }^2$. However, $\epsilon$ is generally time dependent, and this result for $r$ depends on its instantaneous value during the production of the sources, rather than just its average value, somewhat relaxing constraints from the tilt $n_s$. We calculate the scalar 3-point correlation function in the same class of models and show that non-Gaussianity cannot be made arbitrarily small, i.e. $f_{NL}\gtrsim 1$, independently of the value of $r$. Possible exceptions in multifield scenarios are discussed.