Gravitational-wave standard sirens present a novel approach for the determination of the Hubble constant. After the recent spectacular confirmation of the method thanks to GW170817 and its optical counterpart, additional standard siren measurements from future gravitational-wave sources are expected to constrain the Hubble constant to high accuracy. At the same time, improved constraints are expected from observations of cosmic microwave background (CMB) polarization and from baryon acoustic oscillation (BAO) surveys. We explore the role of future standard siren constraints on $H_0$ in light of expected $\mathrm{CMB}+\mathrm{BAO}$ data. Considering a ten-parameter cosmological model, in which curvature, the dark energy equation of state, and the Hubble constant are unbounded by CMB observations, we find that a combination of future $\mathrm{CMB}+\mathrm{BAO}$ data will constrain the Hubble parameter to $\sim 1.5\%$. Further extending the parameter space to a time-varying dark energy equation of state, we find that future $\mathrm{CMB}+\mathrm{BAO}$ constraints on $H_0$ are relaxed to $\sim 3.0\%$. These accuracies are within reach of future standard siren measurements from the Hanford-Livingston-Virgo and the Hanford-Livingston-Virgo-Japan-India networks of interferometers, showing the cosmological relevance of these sources. If future gravitational-wave standard siren measurements reach 1% on $H_0$, as expected, they would significantly improve future $\mathrm{CMB}+\mathrm{BAO}$ constraints on curvature and on the dark energy equation of state by up to a factor of $\sim 3$. We also show that the inclusion of $H_0$ constraints from gravitational-wave standard sirens could result in a reduction of the dark energy figure of merit (i.e., the cosmological parameter volume) by up to a factor of $\sim 400$.

We investigate the possibility of constraining statistical anisotropies of the primordial tensor perturbations by using future observations of the cosmic microwave background (CMB) $B$-mode polarization. By parametrizing a statistically anisotropic tensor power spectrum as $P_h(\mathit{k})=P_h(k)\sum _n{g}_n{\cos }^n{\theta }_{\mathit{k}}$, where ${\theta }_{\mathit{k}}$ is an angle of the direction of $\widehat{k}=\mathit{k}/k$ from a preferred direction, we find that it is possible for future $B$-mode observations such as CMB-S4 to detect the tensor statistical anisotropy at the level of $g_n\sim \mathcal{O}(0.1)$.

We consider inflationary models with the inflaton coupled to the Gauss-Bonnet term assuming a special relation ${\delta }_1=2\lambda {\epsilon }_1$ between the two slow-roll parameters ${\delta }_1$ and ${\epsilon }_1$. For the slow-roll inflation, the assumed relation leads to the reciprocal relation between the Gauss-Bonnet coupling function $\xi (\varphi )$ and the potential $V(\varphi )$, and it leads to the relation $r=16(1-\lambda ){\epsilon }_1$ that reduces the tensor-to-scalar ratio $r$ by a factor of $1-\lambda$. For the constant-roll inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts, and the tensor-to-scalar ratio to the first order of ${\epsilon }_1$ by using the method of Bessel function approximation. The tensor-to-scalar ratio is reduced by a factor of $1-\lambda +\lambda \tilde{\eta }$. Comparing the derived $n_s-r$ with the observations, we obtain the constraints on the model parameters $\tilde{\eta }$ and $\lambda$.

Spin-orbit resonances have important astrophysical implications as the evolution and subsequent coalescence of supermassive black hole binaries in one of these configurations may lead to low recoil velocity of merger remnants. It has also been shown that black hole spins in comparable mass stellar-mass black hole binaries could preferentially lie in a resonant plane when their gravitational waves (GWs) enter the advanced LIGO frequency band [1]. Therefore, it is highly desirable to investigate the possibility of detection and subsequent characterization of such GW sources in the advanced detector era, which can, in turn, improve our perception of their high mass counterparts. The current detection pipelines involve only nonprecessing templates for compact binary searches whereas parameter estimation pipelines can afford to use approximate precessing templates. In this paper, we test the performance of these templates in detection and characterization of spin-orbit resonant binaries. We use fully precessing time-domain SEOBNRv3 waveforms as well as four numerical relativity (NR) waveforms to model GWs from spin-orbit resonant binaries and filter them through IMRPhenomD, SEOBNRv4 and IMRPhenomPv2 approximants. We find that the nonprecessing approximants IMRPhenomD and SEOBNRv4 recover only $\sim 70\%$ of injections with fitting factor (FF) higher than 0.97 (or 90% of injections with $\mathrm{FF}>0.9$). This loss in signal-to-noise ratio is mainly due to the missing physics in these approximants in terms of precession and nonquadrupole modes. However, if we use a new statistic, i.e., maximizing the matched filter output over the sky-location parameters as well, the precessing approximant IMRPhenomPv2 performs magnificently better than their nonprecessing counterparts with recovering 99% of the injections with FFs higher than 0.97. Interestingly, injections with $\mathrm{\Delta }\varphi =180°$ have higher FFs ($\mathrm{\Delta }\varphi$ is the angle between the components of the black hole spins in the plane orthogonal to the orbital angular momentum) as compared to their $\mathrm{\Delta }\varphi =0°$ and generic counterparts. This is because $\mathrm{\Delta }\varphi =180°$ binaries are not as strongly precessing as $\mathrm{\Delta }\varphi =0°$ and generic binaries. This implies that we will have a slight observation bias towards $\mathrm{\Delta }\varphi =180°$ and away from $\mathrm{\Delta }\varphi =0°$ resonant binaries while using nonprecessing templates for searches. Moreover, all template approximants are able to recover most of the injected NR waveforms with FFs $>0.95$. For all the injections including NR, the systematic error in estimating chirp mass remains below $<10\%$ with minimum error for $\mathrm{\Delta }\varphi =180°$ resonant binaries. The symmetric mass-ratio can be estimated with errors below 15%. The effective spin parameter ${\chi }_{\mathrm{eff}}$ is measured with maximum absolute error of 0.13. The in-plane spin parameter ${\chi }_p$ is mostly underestimated indicating that a precessing signal will be recovered as a relatively less precessing signal. Based on our findings, we conclude that we not only need improvements in waveform models towards precession and nonquadrupole modes but also better search strategies for precessing GW signals.

In this paper, we use the recent updated source properties of GW170817 to constrain the hybrid equation of state (EOS) constructed by a three-window modeling between the hadronic EOS and quark EOS. Specifically, the hadronic EOS is described by the $\mathrm{NL}3\omega \rho$ model whose corresponding pure neutron star (NS) is already excluded by the constraint of tidal deformability (TD) from GW170817, and the quark EOS is calculated with the $2+1$ flavors Nambu-Jona-Lasinio (NJL) model. We also consider four other constraints on the hybrid EOS. As a result, we find the parameter set ($B^{\frac{1}{4}},\tilde{\mu },\mathrm{\Gamma }$) can be well constrained, indicating the possible existence of the hybrid star (HS) with a crossover inside. The type of the two stars in the binary system for nine representative hybrid EOSs is shown in this paper too. Furthermore, the HSs restricted by five constraints do not suggest a pure quark core but a mixed phase in the center.

We investigate rotationally supported dwarf irregular (DIRR) galaxies as a new category of targets for indirect dark matter (DM) searches with gamma-ray telescopes. In the framework of pointlike analysis, pressure-supported dwarf spheroidal (DSPH) galaxies are usually considered as one of the best categories of targets for indirect DM searches, due to their close distance and negligible astrophysical background. Nonetheless, as a result of their uncertain kinematics, the DM content and astrophysical J-factors of DSPHs are usually affected by significant errors. In this paper, we study a sample of 36 DIRRs as prospective targets of interest. In the framework of the universal rotation curve, the kinematics of DIRR galaxies provides a good estimation of their DM halo density distribution and, consequently, of their astrophysical J-factors. We calculate the J-factors for these 36 DIRR galaxies, whose kinematics have been studied in a previous work. We find a range of values comparable with the J-factors of DSPH galaxies. However, differently from DSPHs an extra astrophysical gamma-ray background component is expected in DIRR galaxies, that is due to their star-formation activity. In this paper, we show via a theoretical approach that for galaxies in our sample the extra astrophysical background component is negligible. Therefore, we conclude that DIRR galaxies can be potentially considered as additional pointlike targets for DM searches with gamma rays. As a first application of this study, we show the sensitivity limits of the Fermi-LAT telescope to these objects and we calculate constraints on the DM particle mass and annihilation cross section. We conclude that the results of the individual study of several DIRR galaxies are not yet competitive with respect to the analysis of one of the most promising DSPH galaxies, i.e., SEGUE1. However, taking into account SEGUE1’s symmetry-related uncertainties in the J-factor calculation might alter this conclusion. Additionally, we calculate constraints for the combined analysis of the seven most promising DIRR galaxies of our sample.

We obtain the two-loop effective potential for general renormalizable theories, using a generalized gauge-fixing scheme that includes as special cases the background-field $R_{\xi }$ gauges, the Fermi gauges, and the familiar Landau gauge, and using dimensional regularization in the bare and $\overline{\mathrm{MS}}$ renormalization schemes. As examples, the results are then specialized to the Abelian Higgs model and to the Standard Model. In the case of the Standard Model, we study how the vacuum expectation value and the minimum vacuum energy depend numerically on the gauge-fixing parameters. The results at fixed two-loop order exhibit nonconvergent behavior for sufficiently large gauge-fixing parameters; this can presumably be addressed by a resummation of higher-order contributions.

The decay of a heavy neutral scalar particle into fermions and into charged scalars are analyzed when in the presence of an external magnetic field and finite temperature. Working in the one-loop approximation for the study of these decay channels, it is shown that the magnetic field leads in general to a suppression of the decay width whenever the kinematic constrain depends explicitly on the magnetic field. Our results are also compared with common approximations found in the literature, e.g., when the magnitude of the external magnetic field is smaller than the decaying product particle masses, i.e., in the weak field approximation, and in the opposite case, i.e., in the strong field approximation. Possible applications of our results are discussed.

A recent improved determination of the fine structure constant, $\alpha =1/137.035999046(27)$, leads to a $\sim 2.4\sigma$ negative discrepancy between the measured electron anomalous magnetic moment and the standard model prediction. That situation is to be compared with the muon anomalous magnetic moment where a positive $\sim 3.7\sigma$ discrepancy has existed for some time. A single scalar solution to both anomalies is shown to be possible if the two-loop electron Barr-Zee diagrams dominate the scalar one-loop electron anomaly effect and the scalar couplings to the electron and two photons are relatively large. We also briefly discuss the implications of that scenario.

We compute the next-to-leading-order corrections to soft-gluon radiation differentially in the one-emission phase space. We show that their contribution to the evolution of color dipoles can be obtained in a modified subtraction scheme, such that both one- and two-emission terms are amenable to Monte Carlo integration. The two-loop cusp anomalous dimension is recovered naturally upon integration over the full phase space. We present two independent implementations of the new algorithm in the two event generators Pythia and Sherpa, and we compare the resulting fully differential simulation to the Catani–Marchesini–Webber (CMW) scheme.

The proton-proton and proton-antiproton inelasticity profiles in the impact parameter display very interesting and sensitive features which cannot be deduced solely from the current large body of high-energy scattering data. In particular, phenomenological studies exhibit a link between the ratio of the real to imaginary parts of the elastic scattering amplitude at a finite momentum transfer, and the corresponding change of character of the inelastic processes from central to peripheral collisions. We describe how a theoretical model, accommodating the existing data, based on the Regge hypothesis including both the Pomeron and odderon as double poles, and $\omega$ and $f$ mesons as single poles in the complex-$J$ plane, generates a hollow in the inelasticity at low impact parameters. The hollowness effect, which generally may be sensitive to model details, does unequivocally take place both for $pp$ and $p\overline{p}$ collisions within the applied Regge framework, indicating inapplicability of inelasticity-folding geometric approaches.

We consider higher-order, scalar-tensor theories which appear degenerate when restricted to the unitary gauge but are not degenerate in an arbitrary gauge. We dub them U-degenerate theories. We provide a full classification of theories that are either DHOST or U-degenerate and that are quadratic in second derivatives of the scalar field and discuss its extension to cubic and higher-order theories. Working with a simple example of U-degenerate theory, we find that, for configurations in which the scalar field gradient is time-like, the apparent extra mode in such a theory can be understood as a generalized instantaneous, or “shadowy” mode, which does not propagate. Appropriate boundary conditions, required by the elliptic nature of part of the equations of motion, lead to the elimination of the apparent instability associated with this extra mode.

In this article, we investigate the motion of a spinning particle at a constant inclination, different from the equatorial plane, around a Kerr black hole. We mainly explore the possibilities of stable circular orbits for different spin supplementary conditions. The Mathisson-Papapetrou equations are extensively applied and solved within the framework of linear spin approximation. We explicitly show that for a given spin vector of the form $S^a=(0,S^r,S^{\theta },0)$, there exists a unique circular orbit at ($r_c$, ${\theta }_c$) defined by the simultaneous minima of energy, angular momentum, and Carter constant. This corresponds to the innermost stable circular orbit (ISCO) which is located on a nonequatorial plane. We further establish that the location ($r_c$, ${\theta }_c$) of the ISCO for a given spinning particle depends on the radial component of the spin vector ($S^r$) as well as the angular momentum of the black hole ($J$). The implications of using different spin supplementary conditions are investigated.

A spacetime consisting of parallel electric or magnetic fields held together by its own gravity in the presence of a cosmological constant $\mathrm{\Lambda }$ is derived as a limit of the de Sitter or anti–de Sitter C-metric. The limiting procedure is similar to the $\mathrm{\Lambda }=0$ case where the Melvin universe is derived from the C-metric. Under an appropriate coordinate transformation, we show that this solution is equivalent to the solution obtained by Astorino. Some physical and geometrical properties of the solution are studied, as well as its geodesics. For $\mathrm{\Lambda }<0$, the solution is asymptotically locally anti–de Sitter, and can be derived as a double-Wick rotation of a charged anti–de Sitter black hole with a planar horizon.

We compute gravitational self-force (conservative) corrections to tidal invariants for spinning particles moving along circular orbits in a Schwarzschild spacetime. In particular, we consider the square and the cube of the gravitoelectric quadrupolar tidal tensor and the square of the gravitomagnetic quadrupolar tidal tensor. Our results are accurate to first order in spin and through the 9.5 post-Newtonian order. We also compute the associated electric-type and magnetic-type eigenvalues.

Cosmic expansion is expected to influence the size of a black hole shadow observed by a comoving observer. Except for the simplest case of the Schwarzschild black hole in the de Sitter universe, an analytical approach for the calculation of shadow size in an expanding universe is still not developed. In this paper, we present the approximate method based on using the angular size redshift relation. This approach is appropriate for the general case of any multicomponent universe (with matter, radiation, and dark energy). In particular, we show that supermassive black holes at large cosmological distances in the Universe with matter may give a shadow size approaching the shadow size of the black hole in the center of our Galaxy, and present sensitivity limits.

The measurement of the period and period derivative, and the canonical model of dipole radiation have provided a method to estimate the low superficial magnetic fields in the so-called central compact objects (CCOs). In the present work, a scenario is introduced in order to explain the magnetic behavior of such CCOs. Based on magnetohydrodynamic simulations of the post core-collapse supernova phase during the hypercritical accretion episode, we argue that the magnetic field of a newborn neutron star could have been early buried. During this phase, thermal neutrinos are created mainly by the pair annihilation, plasmon decay, photo-neutrino emission and other processes. We study the dynamics of these neutrinos in this environment and also estimate the number expected of the neutrino events with their flavor ratios on Earth. The neutrino burst is the only viable observable that could provide compelling evidence of the hypercritical phase and therefore, the hidden magnetic field mechanism as the most favorable scenario to explain the anomalous low magnetic fields estimated for CCOs.

The scotogenic model can simultaneously account for the presence of dark matter and the origin of neutrino masses. We assume that the flavor neutrino mass matrix has one zero element and Yukawa matrix elements are real in the scotogenic model. It turns out that only one pattern of the flavor neutrino mass matrix in the one-zero-texture scheme within the scotogenic model is viable with the observed neutrino oscillation data, the relic abundance of dark matter, and the upper limit of the branching ratio of the $\mu \to e\gamma$ process.

Intragalaxy signals contain a wealth of information on fundamental physics, both the dark sector and the nature of gravity. While so far largely unexplored, such probes are set to rise dramatically in importance as upcoming surveys provide data of unprecedented quantity and quality on galaxy structure and dynamics. In this paper, we use warping of stellar disks to test the chameleon- or symmetron-screened fifth forces which generically arise when new fields couple to matter. We take $r$-band images of mostly late-type galaxies from the Nasa Sloan Atlas and develop an automated algorithm to quantify the degree of U-shaped warping they exhibit. We then forward model the warp signal as a function of fifth-force strength, $\mathrm{\Delta }G/G_N$, and range, ${\lambda }_C$, and the gravitational environments and internal properties of the galaxies, including full propagation of the non-Gaussian uncertainties. Convolving this fifth-force likelihood function with a Gaussian describing astrophysical and observational noise and then constraining $\mathrm{\Delta }G/G_N$ and ${\lambda }_C$ by Markov chain Monte Carlo, we find the overall likelihood to be significantly increased ($\mathrm{\Delta }\log (\mathcal{L})\simeq 20$) by adding a screened fifth force with ${\lambda }_C\simeq 2\mathrm{Mpc}$ and $\mathrm{\Delta }G/G_N\simeq 0.01$. The variation of $\mathrm{\Delta }\log (\mathcal{L})$ with ${\lambda }_C$ is quantitatively as expected from the correlation of the magnitude of the fifth-force field with the force’s range, and a similar model without screening achieves no increase in likelihood over the General Relativistic case $\mathrm{\Delta }G=0$. Although these results are in good agreement with a previous analysis of the same model using offsets between galaxies’ stellar and gas mass centroids [H. Desmond et al., Phys. Rev. D 98, 064015 (2018).], we caution that the effects of confounding baryonic and dark matter physics must be thoroughly investigated for the results of the inference to be unambiguous.

We investigate the prospect of the LHC for discovering new physics effects via new strategies in the same-sign top pair and same-sign top pair associated with a $W$ boson signatures. Significant enhancement in production of same-sign top quarks (plus a $W$ boson) is a joint property of several models beyond the standard model. We concentrate on the leptonic (electron and muon) decay of the top quarks and study the exclusion reach of the LHC data for a simplified model approach where top quark flavor changing could occur through a $Z^{\prime }$ or a neutral scalar $\varphi$ exchange. Less background contributions and clean signature are the advantages of the leptonic decay mode of the top quarks in the same-sign production processes. A combination is performed on both same-sign top pair and same-sign top pair plus a $W$ boson production modes which enables us to reach a large fraction of the model parameter space. Assuming the couplings of new physics of the order of ${10}^{-2}$, the mass of a flavor changing $Z^{\prime }$ or a neutral scalar above 1 TeV could be excluded. We propose a momentum dependent charge asymmetry and angular observables in the same-sign top process which provide the possibility of separation of new physics signal from the SM backgrounds as well as discrimination of the flavor changing $tuX$ from $tcX$, where $X=Z^{\prime }$, $\varphi$.