We probe the phase structure of the regular anti–de Sitter (AdS) black holes using the null geodesics. The radius of photon orbit and minimum impact parameter shows a nonmonotonous behavior below the critical values of the temperature and the pressure, corresponding to the phase transition in extended phase space. The respective differences of the radius of unstable circular orbit and the minimum impact parameter can be seen as the order parameter for the small-large black hole phase transition, with a critical exponent $1/2$. Our study shows that there exists a close relationship between the gravity and thermodynamics for the regular AdS black holes.

The evolution of the gravitational-wave phase in the signal produced by inspiralling binaries of compact stars is modified by the nonzero deformability of the two stars. Hence, the measurement of these corrections has the potential of providing important information on the equation of state of nuclear matter. Extensive work has been carried out over the last decade to quantify these corrections, but it has so far been restricted to stars with zero intrinsic magnetic fields. While the corrections introduced by the magnetic tension and magnetic pressure are expected to be subdominant, it is nevertheless useful to determine the precise conditions under which these corrections become important. To address this question, we have carried out a second-order perturbative analysis of the tidal deformability of magnetized compact stars under a variety of magnetic-field strengths and equations of state describing either neutron stars or quark stars. Overall, we find that magnetically induced corrections to the tidal deformability will produce changes in the gravitational-wave phase evolution that are unlikely to be detected for a realistic magnetic field i.e., $B\sim {10}^{10}–{10}^{12}\mathrm{G}$. At the same time, if the magnetic field is unrealistically large, i.e., $B\sim {10}^{16}\mathrm{G}$, these corrections would produce a sizeable contribution to the phase evolution, especially for quark stars. In the latter case, and if the neglected higher-order terms will remain negligible also for very high magnetic fields, the induced phase differences would represent a unique tool to measure the properties of the magnetic fields, providing information that is otherwise hard to quantify.

Null geodesics, quasinormal modes of a massless scalar field perturbation, and the correspondence with shadow radii are investigated in the background spacetime of high-dimensional Einstein-Yang-Mills black holes. Based on the properties of null geodesics, we obtain the connection between the radius of a photon sphere and the radius of a horizon in the five- and six-dimensional Einstein-Yang-Mills spacetimes. Especially in the five-dimensional case, there exist two branches for the radius of a photon sphere, but only the branch outside the event horizon satisfies the condition of circular null geodesics. Moreover, we find no reflecting points of shadow radii and no spiral-like shapes on the complex plane of quasinormal frequencies and verify the correspondence between the quasinormal modes in the eikonal limit and shadow radii in high-dimensional Einstein-Yang-Mills spacetimes.

Massive black hole binaries (MBHBs) of ${10}^5{\mathrm{M}}_{\odot }-3\times {10}^7{\mathrm{M}}_{\odot }$ merging in low redshift galaxies ($z\le 4$) are sufficiently loud to be detected weeks before coalescence with the Laser Interferometer Space Antenna (LISA). This allows us to perform the parameter estimation on the fly, i.e., as a function of the time to coalescence during the inspiral phase, relevant for early warning of the planned LISA protected periods and for searches of electromagnetic signals. In this work, we study the evolution of the sky position, luminosity distance, chirp mass and mass ratio uncertainties as function of time left before merger. Overall, light systems with total intrinsic mass ${\mathrm{M}}_{\mathrm{tot}}=3\times {10}^5{\mathrm{M}}_{\odot }$ are characterized by smaller uncertainties than heavy ones (${\mathrm{M}}_{\mathrm{tot}}={10}^7{\mathrm{M}}_{\odot }$) during the inspiral. Luminosity distance, chirp mass and mass ratio are well constrained at the end of the inspiral. Concerning sky position, at $z=1$, MBHBs with ${\mathrm{M}}_{\mathrm{tot}}=3\times {10}^5{\mathrm{M}}_{\odot }$ can be localized with a median precision of $\simeq {10}^2{\mathrm{deg}}^2(\simeq 1{\mathrm{deg}}^2)$ at 1 month (1 hour) from merger, while the sky position of heavy MBHBs can be determined to $10{\mathrm{deg}}^2$ only 1 hour before merger. However the uncertainty around the median values broadens with time, ranging in between $0.04–20{\mathrm{deg}}^2$ ($0.3–3\times {10}^3{\mathrm{deg}}^2$) for light (heavy) systems at 1 hour before merger. At merger the sky localization improves down to $\simeq {10}^{-1}{\mathrm{deg}}^2$ for all masses. For the benefit of the observer community, we provide the full set of data from our simulations and simple and ready-to-use analytical fits to describe the time evolution of uncertainties in the aforementioned parameters, valid for systems with total mass between ${10}^5–{10}^7{\mathrm{M}}_{\odot }$ and redshift 0.3–3.

We prove under certain assumptions no-hair theorems for noncanonical self-gravitating static multiple scalar fields in spherically symmetric spacetimes. It is shown that the only static, spherically symmetric and asymptotically flat black hole solutions consist of the Schwarzschild metric and a constant multiscalar map. We also prove that there are no static, horizonless, asymptotically flat, spherically symmetric solutions with static scalar fields and a regular center. The last theorem shows that the static, asymptotically flat, spherically symmetric reflecting compact objects with Neumann boundary conditions cannot support a nontrivial self-gravitating noncanonical (and canonical) multiscalar map in their exterior spacetime regions. In order to prove the no-hair theorems we derive a new divergence identity.

We calculate the primordial black hole abundance in the context of a Wess-Zumino type no-scale supergravity model. We modify the Kähler potential, by adding an extra exponential term. Using just one parameter in the context of this model, we are able to satisfy the Planck cosmological constraints for the spectral index $n_s$, the tensor-to-scalar ratio $r$, and to produce up to $\sim 20\%$ of the dark matter of the Universe in the form of primordial black holes.

The precision of Stage IV cosmic shear surveys will enable us to probe smaller physical scales than ever before, however, model uncertainties from baryonic physics and non-linear structure formation will become a significant concern. The $k$-cut method—applying a redshift-dependent $\ell$-cut after making the Bernardeau-Nishimichi-Taruya transform—can reduce sensitivity to baryonic physics; allowing Stage IV surveys to include information from increasingly higher $\ell$-modes. Here we address the question of whether it can also mitigate the impact of making the reduced shear approximation; which is also important in the high-$\kappa$, small-scale regime. The standard procedure for relaxing this approximation requires the repeated evaluation of the convergence bispectrum, and consequently can be prohibitively computationally expensive when included in Monte Carlo analyses. We find that the $k$-cut cosmic shear procedure suppresses the $w_0{w}_a$ CDM cosmological parameter biases expected from the reduced shear approximation for Stage IV experiments, when $\ell$-modes up to 5000 are probed. The maximum cut required for biases from the reduced shear approximation to be below the threshold of significance is at $k=5.37h{\mathrm{Mpc}}^{-1}$. With this cut, the predicted $1\sigma$ constraints increase, relative to the case where the correction is directly computed, by less than 10% for all parameters. This represents a significant improvement in constraints compared to the more conservative case where only $\ell$-modes up to 1500 are probed [A. Blanchard et al., (Euclid Collaboration), arXiv:1910.09273], and no $k$-cut is used. We also repeat this analysis for a hypothetical, comparable kinematic weak lensing survey. The key parts of code used for this analysis are made publicly available.

We propose a two-phase reheating scenario where the initial preheating dynamics is described by an effective dynamics followed by the standard perturbative reheating. Some of the important universal results of lattice simulation during preheating have been considered as crucial inputs in our two-phase dynamics. In this framework, detailed phenomenological constraints have been obtained on the inflaton couplings with reheating fields and dark matter parameters in terms of the cosmic microwave background (CMB) constrained inflationary scalar spectral index. It is observed that the conventional reheating scenario generically predicts the maximum reheating temperature $T_{\mathrm{re}}^{\max }\simeq {10}^{15}\mathrm{GeV}$, corresponding to an almost instantaneous transition from the end of inflation to radiation domination. This fact will naturally lead to the problem of nonperturbative inflaton decay, which is in direct conflict with the perturbative reheating itself. Taking into account this by incorporating effective nonperturbative dynamics as the initial phase, our model of two-phase reheating scenarios also predicts a model-independent maximum reheating temperature, which does not correspond to the instantaneous process. Furthermore, $T_{\mathrm{re}}^{\max }$ is predicted to lie within $({10}^{13},{10}^{10})\mathrm{GeV}$ if CMB constraints on inflaton couplings with a different reheating field are taken into account. We have further studied in detail the dark matter phenomenology in a model-independent manner and show how dark matter parameter space can be constrained through CMB parameters via the inflaton spectral index. Considering dark matter production during reheating via the freeze-in mechanism, its parameter space has been observed to be highly constrained by our two-phase reheating than the constraints predicted by the conventional reheating scenarios, which are believed to theoretically incomplete.

Recently, a high-energy muon neutrino event was detected in association with a tidal disruption event (TDE) AT2019dsg at the time about 150 days after the peak of the optical/UV luminosity. We propose that such an association could be interpreted as arising from hadronic interactions between relativistic protons accelerated in the jet launched from the TDE and the intense radiation field of TDE inside the optical/UV photosphere, if we are observing the jet at a moderate angle (i.e., approximately $10°-30°$) with respect to the jet axis. Such an off-axis viewing angle leads to a high gas column density in the line of sight, which provides a high opacity for the photoionization and the Bethe-Heitler process and allows the existence of an intrinsic long-term x-ray radiation of comparatively high emissivity. As a result, the cascade emission accompanying the neutrino production, which would otherwise overshoot the flux limits in the x-ray and/or GeV band, is significantly obscured or absorbed. Since the jets of TDEs are supposed to be randomly oriented in the sky, the source density rate of TDE with an off-axis jet is significantly higher than that of TDE with an on-axis jet. Therefore, an off-axis jet is naturally expected in a nearby TDE being discovered, supporting the proposed scenario.

We present a generalized piecewise polytropic parametrization for the neutron-star equation of state using an ansatz that imposes continuity in not only pressure and energy density, but also in the speed of sound. The universe of candidate equations of state is shown to admit preferred dividing densities, determined by minimizing an error norm consisting of integral astrophysical observables. Generalized piecewise polytropes accurately reproduce astrophysical observables, such as mass, radius, tidal deformability and mode frequencies, as well as thermodynamic quantities, such as the adiabatic index. This makes the new equations of state useful for parameter estimation from gravitational waveforms. Since they are differentiable, generalized piecewise polytropes can improve pointwise convergence in numerical relativity simulations of neutron stars. Existing implementations of piecewise polytropes can easily accommodate this generalization with the same number of free parameters. Optionally, generalized piecewise polytropes can also accommodate adjustable jumps in sound speed, which allows them to capture phase transitions in neutron star matter.

We present a simple and intuitive description of both, Schwinger effect and false vacuum decay through bubble nucleation, as tunneling problems in one-dimensional relativistic quantum mechanics. Both problems can be described by an effective potential that depends on a single variable of dimension length, which measures the separation of the particles in the Schwinger pair, or the radius of a bubble for the vacuum decay. We show that both problems can be described as tunneling in one-dimensional quantum mechanics if one interprets this variable as the position of a relativistic particle with a suitably defined effective mass. The same bounce solution can be used to obtain reliable order of magnitude estimates for the rates of Schwinger pair production and false vacuum decay.

We study a scalar singlet dark matter (DM) having mass in the sub-TeV regime by extending the minimal scalar singlet DM setup by additional vectorlike fermions. While the minimal scalar singlet DM satisfies the relic and direct detection constraints for mass beyond TeV only, presence of its portal coupling with vectorlike fermions opens up additional coannihilation channels. These vectorlike fermions also help in achieving electroweak vacuum stability all the way up to Planck scale. We find that for one generation of vectorlike quarks consisting of a $SU(2{)}_L$ doublet and a singlet, scalar singlet DM with mass a few hundred GeV can indeed satisfy relic, direct detection and other relevant constraints while also making the electroweak vacuum absolutely stable. The same can be achieved by introducing vectorlike leptons too, but with three generations. While the model with vectorlike quarks is minimal, the three generations of vectorlike lepton doublet and neutral singlet can also give rise to light neutrino mass at one loop level.

Because the Peccei-Quinn (PQ) symmetry has to be anomalous to solve the strong $CP$ puzzle, some colored and chiral fermions have to transform nontrivially under this symmetry. But when the Standard Model (SM) fermions are charged, as in the PQ or Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) models, this symmetry ends up entangled with the SM global symmetries, baryon ($\mathcal{B}$) and lepton ($\mathcal{L}$) numbers. This raises several questions addressed in this paper. First, the compatibility of axion models with some explicit $\mathcal{B}$- and/or $\mathcal{L}$-violating effects is analyzed, including those arising from seesaw mechanisms, electroweak instanton interactions, or explicit $\mathcal{B}$- and $\mathcal{L}$-violating effective operators. Second, how many of these effects can be simultaneously present is quantified, along with the consequences for the axion mass and vacuum alignment if too many of them are introduced. Finally, large classes of $\mathcal{B}$- and/or $\mathcal{L}$-violating interactions without impact on axion phenomenology are identified, like, for example, the various implementations of the type-I and -II seesaw mechanisms in the DFSZ context.

We suggest to probe the pion light-cone distribution amplitude, applying a dispersion relation for the pion electromagnetic form factor. Instead of the standard dispersion relation, we use the equation between the spacelike form factor $F_{\pi }(Q^2)$ and the integrated modulus of the timelike form factor. For $F_{\pi }(Q^2)$, the QCD light-cone sum rule with a dominant twist-2 term is used. Adopting for the pion twist-2 distribution amplitude a certain combination of the first few Gegenbauer polynomials, it is possible to fit their coefficients $a_{2,4,6,..}$. (Gegenbauer moments) from this equation, employing the measured pion timelike form factor. For the exploratory fit we use the data of the BABAR collaboration. The results definitely exclude the asymptotic twist-2 distribution amplitude. Also the model with a single $a_2\ne 0$ is disfavored by the fit. Considering the models with $a_{n>2}\ne 0$, we find that the fitted values of the second and fourth Gegenbauer moments cover the intervals $a_2(1\mathrm{GeV})=(0.22–0.33)$, $a_4(1\mathrm{GeV})=(0.12–0.25)$. The higher moments starting from $a_8$ are consistent with zero, albeit with large uncertainties. The spacelike pion form factor obtained in two different ways, from the dispersion relation and from the light-cone sum rule, agrees, within uncertainties, with the measurement by the Jefferson Lab $F_{\pi }$ collaboration.

In this work we systematically calculate the mass spectra of open charm and bottom tetraquarks $qq\overline{q}\overline{Q}$ within an extended relativized quark model. The four-body relativized Hamiltonians including the Coulomb potential, confining potential, spin-spin interactions, and relativistic corrections are solved by using the variational method. We find that the predicted masses of four $0^{+}ud\overline{s}\overline{c}$ states are 2765, 3065, 3152, and 3396 MeV, which disfavor the assignment of the newly observed $X_0(2900)$ as a compact tetraquark. Moreover, the mass spectra of the open charm and bottom tetraquarks show quite similar patterns, which preserve the light flavor SU(3) symmetry and heavy quark symmetry well. In addition, our results suggest that the flavor-exotic states $nn\overline{s}\overline{c}$, $nn\overline{s}\overline{b}$, $ss\overline{n}\overline{c}$, and $ss\overline{n}\overline{b}$ and their antiparticles can be searched for in the heavy-light meson plus kaon final states by future experiments. More theoretical and experimental efforts are needed to investigate these singly heavy tetraquarks.

We study the $Z_3$ metastable states in the Polyakov loop Nambu-Jona-Lasinio model. These states exist for temperatures above $T_m\sim 194\mathrm{MeV}$ and can decay via bubble nucleation. We numerically solve the bounce equation to compute the nucleation rate. We speculate that, in the context of heavy-ion collisions, the likely scenario for the decay of the metastable states is via spinodal decomposition.

Using $980{\mathrm{fb}}^{-1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, we report a study of the electromagnetic decays of excited charmed baryons ${\mathrm{\Xi }}_c(2790)$ and ${\mathrm{\Xi }}_c(2815)$. A clear signal (8.6 standard deviations) is observed for ${\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c^0\gamma$, and we measure: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c^0\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c(2645{)}^{+}{\pi }^{-}\to {\mathrm{\Xi }}_c^0{\pi }^{+}{\pi }^{-}]}=0.41\pm 0.05\pm 0.03$. We also present evidence (3.8 standard deviations) for the similar decay of the ${\mathrm{\Xi }}_c(2790{)}^0$ and measure: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Xi }}_c^0\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Xi }}_c^{\prime +}{\pi }^{-}\to {\mathrm{\Xi }}_c^{+}\gamma {\pi }^{-}]}=0.13\pm 0.03\pm 0.02$. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the ${\mathrm{\Xi }}_c(2815{)}^{+}$ and ${\mathrm{\Xi }}_c(2790{)}^{+}$ baryons and set upper limits at the 90% confidence level of: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^{+}\to {\mathrm{\Xi }}_c^{+}\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^{+}\to {\mathrm{\Xi }}_c(2645{)}^0{\pi }^{+}\to {\mathrm{\Xi }}_c^{+}{\pi }^{-}{\pi }^{+}]}<0.09$, and $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^{+}\to {\mathrm{\Xi }}_c^{+}\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^{+}\to {\mathrm{\Xi }}_c^{\prime 0}{\pi }^{+}\to {\mathrm{\Xi }}_c^0\gamma {\pi }^{+}]}<0.06$. Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states.

In this paper we approach to Horndeski and beyond Horndeski theories from the effective fluid perspective. We make explicit the formal equivalence between these theories and general relativity with an effective imperfect fluid. It is shown that, for the viable Horndeski theories, in the general case (arbitrary geometry) the nonvanishing contribution from the higher-order derivative terms to the imperfect fluidlike behavior affects only the heat flux vector but not the anisotropic stresses. The only contribution to the anisotropic stress tensor is due to the nonminimal coupling of the scalar field to the curvature as it is in standard scalar-tensor theories. For the viable beyond Horndeski theories the higher-order derivatives contribute both to the heat flux and to the anisotropic stresses. The effective fluid description is applied to several particular cases of interest. It is corroborated that, in Friedmann-Robertson-Walker background space, due to the underlying symmetries, the effective stress-energy tensor of viable Horndeski and beyond Horndeski theories is formally equivalent to that of a perfect fluid. This result might not be true for other less symmetric backgrounds such as the anisotropic Bianchi I space.

The vector and scalar polarization modes of gravitational waves do not exist in general relativity, and their detection would have significant impacts on fundamental physics. In this paper, we explored the detectability of these anomalous polarization modes in a gravitational wave background around 1 mHz with the future LISA-Taiji network. The inherent geometrical symmetry of the network largely simplifies the correlation analysis. By taking a suitable linear combination of the correlated outputs, the contribution of the standard tensor modes can be canceled algebraically, and the anomalous modes can be exclusively examined. We provide concise expressions for the signal-to-noise ratios of the anomalous modes with this cancellation method. We also discuss the possibility of separately estimating the amplitudes of the vector and scalar modes, using the overall frequency dependence of the associated overlap reduction functions.

We consider a spin-$3/2$ particle and show that with a Planck reduced coupling, we can obtain a sufficiently long lifetime making the spin-$3/2$ particle a good dark matter candidate. We show that this dark matter candidate can be produced during inflationary reheating through the scattering of Standard Model particles. The relic abundance as determined by Planck and other experimental measurements is attained for reasonable values of the reheating temperature $T_{\mathrm{RH}}\gtrsim {10}^8\mathrm{GeV}$. We consider two possible gauge invariant couplings to the extended Standard Model. We find a large range of masses are possible which respect the experimental limits on its decay rate. We expect smoking-gun signals in the form of a monochromatic photon with a possible monochromatic neutrino, which can be probed in the near future in IceCube and other indirect detection experiments.