The measured orbital period decay of relativistic compact-star binaries, with characteristic orbital periods $\sim 0.1\mathrm{days}$, is explained with very high precision by the gravitational wave (GW) emission of an inspiraling binary in a vacuum predicted by general relativity. However, the binary gravitational binding energy is also affected by an usually neglected phenomenon, namely the dark matter dynamical friction (DMDF) produced by the interaction of the binary components with their respective DM gravitational wakes. Therefore, the inclusion of the DMDF might lead to a binary evolution which is different from a purely GW-driven one. The entity of this effect depends on the orbital period and on the local value of the DM density, hence on the position of the binary in the Galaxy. We evaluate the DMDF produced by three different DM profiles: the Navarro-Frenk-White (NFW) profile, the nonsingular-isothermal-sphere (NSIS) and the Ruffini-Argüelles-Rueda (RAR) DM profile based on self-gravitating keV fermions. We first show that indeed, due to their Galactic position, the GW emission dominates over the DMDF in the Neutron star (NS)-NS, NS-(White Dwarf) WD and WD-WD binaries for which measurements of the orbital decay exist. Then, we evaluate the conditions (i.e. orbital period and Galactic location) under which the effect of DMDF on the binary evolution becomes comparable to, or overcomes, the one of the GW emission. We find that, for instance for $1.3–0.2M_{\odot }$ NS-WD, $1.3–1.3M_{\odot }$ NS-NS, and $0.25–0.50M_{\odot }$ WD-WD, located at 0.1 kpc, this occurs at orbital periods around 20–30 days in a NFW profile while, in a RAR profile, it occurs at about 100 days. For closer distances to the Galactic center, the DMDF effect increases and the above critical orbital periods become interestingly shorter. Finally, we also analyze the system parameters (for all the DM profiles) for which DMDF leads to an orbital widening instead of orbital decay. All the above imply that a direct/indirect observational verification of this effect in compact-star binaries might put strong constraints on the nature of DM and its Galactic distribution.

The effective Lagrangian formalism provides a way to study the new physics effects at the electroweak scale. We study Higgs pair production via vector-boson fusion (VBF) at the Large Hadron Collider within the framework of the effective field theory. The effects from the dimension-six operators involved in VBF Higgs pair production are investigated, particularly ${\mathcal{O}}_{\mathrm{\Phi },2}$ and ${\mathcal{O}}_{\mathrm{\Phi },3}$, which are relevant to the triple Higgs self-coupling, on the integrated cross section and various kinematic distributions. We find that the distributions of Higgs-pair invariant mass, Higgs transverse momentum, and rapidity are significantly altered by the operators ${\mathcal{O}}_{\mathrm{\Phi },2}$ and ${\mathcal{O}}_{\mathrm{\Phi },3}$. These features are helpful in disentangling the contributions from the operators ${\mathcal{O}}_{\mathrm{\Phi },2}$ and ${\mathcal{O}}_{\mathrm{\Phi },3}$ in triple Higgs self-coupling. We also provide the $5\sigma$ discovery and $3\sigma$ exclusion limits for the coefficients of ${\mathcal{O}}_{\mathrm{\Phi },2}$ and ${\mathcal{O}}_{\mathrm{\Phi },3}$ by measuring the VBF Higgs pair-production process, including the sequential $H\to b\overline{b}$ decays at the 14 TeV LHC.

The puzzle of $R(D^{(*)})$ associated with $B\to D^{(*)}\tau \nu$ decay is addressed in the two-Higgs-doublet model. An anomalous coupling of $\tau$ to the charged Higgs is introduced to fit the data from BABAR, Belle, and LHCb. It is shown that all four types of the model yield similar values for the minimum ${\chi }^2$. We also show that the newly normalized $R(D^{(*)})$ with the branching ratio of $B\to \tau \nu$ decay exhibits a much smaller minimum ${\chi }^2$.

We study the naturalness properties of the $B-L$ supersymmetric standard model (BLSSM) with type-I seesaw and compare them to those of the minimal supersymmetric standard model (MSSM) at both low (i.e., Large Hadron Collider) energies and high (i.e., unification) scales. By adopting standard measures of naturalness, we assess that, in the presence of full unification of the additional gauge couplings and scalar/fermionic masses of the BLSSM, such a scenario reveals a somewhat higher degree of fine-tuning (FT) than the MSSM, when the latter is computed at the unification scale and all available theoretical and experimental constraints, but the dark matter (DM) ones, are taken into account. Yet, such a difference, driven primarily by the collider limits requiring a high mass for the gauge boson associated to the breaking of the additional $U(1{)}_{B-L}$ gauge group of the BLSSM in addition to the $SU(3{)}_C\times SU(2{)}_L\times U(1{)}_Y$ of the MSSM, should be regarded as a modest price to pay for the former in relation to the latter, if one notices that the nonminimal scenario offers a significant volume of parameter space where numerous DM solutions of different compositions can be found to the relic density constraints, unlike the case of the minimal structure, wherein only one type of solution is accessible over an ever diminishing parameter space. In fact, this different level of tension within the two SUSY models in complying with current data is well revealed when the FT measure is recomputed in terms of the low-energy spectra of the two models, over their allowed regions of parameter space now in the presence of all DM bounds, as it is shown that the tendency is now opposite, with the BLSSM appearing more natural than the MSSM.

We perform a direct calculation of the gluon momentum fraction of the nucleon, taking into account the mixing with the corresponding quark contribution. We use maximally twisted mass fermion ensembles with $N_f=2+1+1$ flavors at a pion mass of about 370 MeV and a lattice spacing of $a\approx 0.082\mathrm{fm}$ and with $N_f=2$ flavors at the physical pion mass and a lattice spacing of $a\approx 0.093\mathrm{fm}$. We employ stout smearing to obtain a statistically significant result for the bare matrix elements. In addition, we perform a lattice perturbative calculation including two levels of stout smearing to carry out the mixing and the renormalization of the quark and gluon operators. We find, after conversion to the $\overline{\mathrm{MS}}$ scheme at a scale of 2 GeV, $⟨x{⟩}_g^R=0.284(27)(17)(24)$ for pion mass of about 370 MeV and $⟨x{⟩}_g^R=0.267(22)(19)(24)$ for the physical pion mass. In the reported numbers, the first parenthesis indicates statistical uncertainties. The numbers in the second and third parentheses correspond to systematic uncertainties due to excited states contamination and renormalization, respectively.

Numerical stochastic perturbation theory is a powerful tool for estimating high-order perturbative expansions in lattice field theory. The standard algorithms based on the Langevin equation, however, suffer from several limitations which in practice restrict the potential of this technique. In this work we investigate some alternative methods which could in principle improve on the standard approach. In particular, we present a study of the recently proposed instantaneous stochastic perturbation theory, as well as a formulation of numerical stochastic perturbation theory based on generalized hybrid molecular dynamics algorithms. The viability of these methods is investigated in ${\phi }^4$ theory.

The parton model relations in conjunction with quark-hadron duality in deep inelastic scattering suggests an asymptotic dominance of the quark-diquark type of baryonic excited states with a radial Regge uniformly distributed mass-squared spectrum, $M_n^2={\mu }^{2}n+M_0^2$. We argue that this points to a linearly quark-diquark confining potential. We analyze the radial ($n$) and angular-momentum ($J$) Regge trajectories for all light-quark states with baryon number 1 listed in the 2016 edition of the Particle Data Tables. The parameters of the mass-squared trajectories are obtained by linear regression assuming $\mathrm{\Delta }{M}_n^2\sim M_n{\mathrm{\Gamma }}_n$ weighted with the width ${\mathrm{\Gamma }}_n$ of the resonance, and the error analysis is carried out accordingly.

We present a detailed study of nuclear corrections in the deuteron (D) by performing an analysis of data from deep inelastic scattering off proton and D, dilepton pair production in $pp$ and $p\mathrm{D}$ interactions, and $W^{\pm }$ and $Z$ boson production in $pp$ and $p\overline{p}$ collisions. In particular, we discuss the determination of the off-shell function describing the modification of the parton distribution functions in bound nucleons in the context of global QCD fits. Our results are consistent with the ones obtained independently from the study of data on deep inelastic scattering off heavy nuclei with mass number $A\ge 4$, further confirming the universality of the off-shell function of the bound nucleon. We also study the sensitivity to the modeling of the deuteron wave function. As an important application we discuss the impact of nuclear corrections to the deuteron on the determination of the $d$ quark distribution.

We present first evidence for the process $e^{+}{e}^{-}\to \gamma {\eta }_c(1S)$ at six center-of-mass energies between 4.01 and 4.60 GeV using data collected by the BESIII experiment operating at BEPCII. We measure the Born cross section at each energy using a combination of twelve ${\eta }_c(1S)$ decay channels. We also combine all six energies under various assumptions for the energy-dependence of the cross section. If the process is assumed to proceed via the $Y(4260)$, we measure a peak Born cross section ${\sigma }_{\mathrm{peak}}(e^{+}{e}^{-}\to \gamma {\eta }_c(1S))=2.11\pm 0.49(\mathrm{stat}.)\pm 0.36(\mathrm{syst}.)\mathrm{pb}$ with a statistical significance of $4.2\sigma$.

We explore several consequences of the recently discovered intrinsic noncommutativity of the zero-mode sector of closed string theory. In particular, we illuminate the relation between T-duality and this intrinsic noncommutativity and also note that there is a simple closed string product, equivalent to the splitting-joining interaction of the pants diagram, that respects this noncommutativity and is covariant with respect to T-duality. We emphasize the central role played by the symplectic form $\omega$ on the space of zero modes. Furthermore, we begin an exploration of new noncommutative string backgrounds. In particular, we show that a constant nongeometric background field leads to a noncommutative space-time. We also comment on the nonassociativity that consequently arises in the presence of nontrivial flux. In this formulation, the $H$ flux as well as the “nongeometric”$Q$, $R$, and $F$ fluxes are simply the various components of the flux of an almost symplectic form.

We analyzed two-point Green’s functions of operators in six-dimensional (2, 0) theory dual to fermions in maximal gauged supergravity in seven dimensions at finite temperature. We have considered backgrounds with both the charge parameters nonzero as well as only one charge parameter nonzero. In the former case we find all the modes admit Fermi surface(s), while in the latter, some of the modes do not have a Fermi surface. We find backgrounds corresponding to nonzero expectation value of the scalar appearing in the dual operator give rise to Fermi surface(s).

Higher derivative extensions of Einstein gravity are important within the string theory approach to gravity and as alternative and effective theories of gravity. H. Lü, A. Perkins, C. Pope, and K. Stelle [Phys. Rev. Lett. 114, 171601 (2015)] found a numerical solution describing a spherically symmetric non-Schwarzschild asymptotically flat black hole in Einstein gravity with added higher derivative terms. Using the general and quickly convergent parametrization in terms of the continued fractions, we represent this numerical solution in the analytical form, which is accurate not only near the event horizon or far from the black hole, but in the whole space. Thereby, the obtained analytical form of the metric allows one to study easily all the further properties of the black hole, such as thermodynamics, Hawking radiation, particle motion, accretion, perturbations, stability, quasinormal spectrum, etc. Thus, the found analytical approximate representation can serve in the same way as an exact solution.

Density perturbations in the cosmic microwave background within general $f(R,\varphi )$ models of gravity are investigated. The general dynamical equations for the tensor and scalar modes in any $f(R,\varphi )$-gravity model are derived. An application of the equations to the varying-power-law modified gravity toy model is then made. Formulas and numerical values for the tensor-to-scalar ratio, the scalar tilt, and the tensor tilt are all obtained within this specific model. While the model cannot provide a theoretical reason for the value of the energy scale at which inflation should occur, it is found, based on the latest observations of the density perturbations in the sky, that the model requires inflation to occur at an energy scale less than the grand unified theory scale, namely, $\sim {10}^{14}\mathrm{GeV}$. The different energy intervals examined here show that the density perturbations recently obtained from observations are recovered naturally, with very high precision, and without fine tuning the model’s parameters.

Memory effects of gravitational waves from astronomical events or a primordial universe might have the information of new physics. It is intriguing to observe that the memory effect exists in electrodynamics as a net momentum kick, while the memory effect in gravity appears as a net relative displacement. In particular, Winicour has shown that the B-mode memory, which characterizes parity-odd global distribution of memory, does not exist. We study the memory effect in axion electrodynamics and find that the B-mode memory effect can exist, provided the existence of coherently oscillating axion background field. Moreover, we examine the detectability of the axion dark matter using this effect.

We construct an analytical approximation for the numerical black hole metric of P. Kanti et al. [Phys. Rev. D 54, 5049 (1996)] in the four-dimensional Einstein-dilaton-Gauss-Bonnet (EdGB) theory. The continued fraction expansion in terms of a compactified radial coordinate, used here, converges slowly when the dilaton coupling approaches its extremal values, but for a black hole far from the extremal state, the analytical formula has a maximal relative error of a fraction of one percent already within the third order of the continued fraction expansion. The suggested analytical representation of the numerical black hole metric is relatively compact and a good approximation in the whole space outside the black hole event horizon. Therefore, it can serve in the same way as an exact solution when analyzing particles’ motion, perturbations, quasinormal modes, Hawking radiation, accreting disks, and many other problems in the vicinity of a black hole. In addition, we construct the approximate analytical expression for the dilaton field.

We study general properties of static and spherically symmetric bidiagonal black holes in Hassan-Rosen bimetric theory by means of a new method. In particular, we explore the behavior of the black hole solutions both at the common Killing horizon and at the large radii. The former study was never done before and leads to a new classification for black holes within the bidiagonal ansatz. The latter study shows that, among the great variety of the black hole solutions, the only solutions converging to Minkowski, anti–de Sitter, and de Sitter spacetimes at large radii are those of general relativity, i.e., the Schwarzschild, Schwarzschild–anti–de Sitter and Schwarzschild–de Sitter solutions. Moreover, we present a proposition, whose validity is not limited to black hole solutions, which establishes the relation between the curvature singularities of the two metrics and the invertibility of their interaction potential.

We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental $f$ modes. We concentrated on a particular class of alternative theories—the (massive) scalar-tensor theories. The generalization to rapid rotation is important because on one hand the rapid rotation can magnify the deviations from general relativity compared to the static case and on the other hand some of the most efficient emitters of gravitational radiation, such as the binary neutron star merger remnants, are supposed to be rotating close to their Kepler (mass-shedding) limits shortly after their formation. We have constructed several sequences of models starting from the nonrotating case and reaching up to the Kepler limit, with different values of the scalar-tensor theory coupling constant and the scalar field mass. The results show that the deviations from pure Einstein’s theory can be significant, especially in the case of nonzero scalar field mass. An important property of the oscillation modes of rapidly rotating stars is that they can become secularly unstable due to the emission of gravitational radiation, the so-called Chandrasekhar-Friedman-Schutz instability. Such unstable modes are efficient emitters of gravitational radiation. Our studies show that the inclusion of a nonzero scalar field would decrease the threshold value of the normalized angular momentum where this instability starts to operate, but the growth time of the instability seems to be increased compared to pure general relativity.

It is well known that the presence of quantum fields alters many of the classical properties of black holes. In this paper we consider the lowest-order QED corrections to the location and temperature of the event horizons of charged black holes. We conjecture that QED effects protect realistic charged black holes from the phenomenon of mass inflation.

Motivated by cosmological examples, we study quantum field theoretical tunneling from an initial state where the “classical field,” i.e. the vacuum expectation value of the field operator, is spatially homogeneous but performing a time-dependent oscillation about a local minimum. In particular, we estimate both analytically and numerically the exponential contribution to the tunneling probability. We additionally show that after the tunneling event, the classical field solution—the so-called “bubble”—mediati the phase transition can either grow or collapse. We present a simple analytical criterion to distinguish between the two behaviors.