We explore the potential of pulsar timing arrays (PTAs) such as NANOGrav, EPTA, and PPTA to detect the stochastic gravitational wave background in theories of massive gravity. In general relativity, the function describing the dependence of the correlation between the arrival times of signals from two pulsars on the angle between them is known as the Hellings-Downs curve. We compute the analogous overlap reduction function for massive gravity, including the additional polarization states and the correction due to the mass of the graviton, and compare the result with the Hellings-Downs curve. The primary result is a complete analytical form for the analog Hellings-Downs curve, providing a starting point for future numerical studies aimed at a detailed comparison between PTA data and the predictions of massive gravity. We study both the massless limit and the stationary limit as checks on our calculation, and discuss how our formalism also allows us to study the impact of massive spin-2 dark matter candidates on data from PTAs.

We conduct an analysis of the quasinormal modes for generic spin perturbations of the Kerr black hole using the isomonodromic method. The strategy consists of solving the Riemann-Hilbert map relating the accessory parameters of the differential equations involved to monodromy properties of the solutions, using the $\tau$-function for the Painlevé V transcendent. We show excellent accordance of the method with the literature for generic rotation parameter $a<M$. In the extremal limit, we determined the dependence of the modes with the black hole temperature and establish that the extremal values of the modes are obtainable from the Painlevé V and III transcendents.

In this work we revisit constraints on $k$-inflation with a Dirac-Born-Infeld (DBI) kinetic term and a power-law kinetic term from reheating. For the DBI kinetic term we choose monomial potentials, $V\propto {\varphi }^n$ with $n=2/3$, 1, 2, and 4, and natural inflaton potential, and for the power-law kinetic term we choose quadratic, quartic, and exponential potentials. The phase of reheating can be parametrized in terms of the reheating temperature, $T_{re}$, the number of $e$-folds during reheating $N_{re}$, and the effective equation of state during reheating $w_{re}$. These parameters can be related to the spectral index $n_s$ and other inflationary parameters depending on the choice of inflaton kinetic term and potential. By demanding that $w_{re}$ should have a finite range and $T_{re}$ should be above the electroweak scale, one can obtain bounds on $n_s$ that can provide bounds on the tensor-to-scalar ratio, $r$. We find, for $k$-inflation with a DBI kinetic term, and quadratic and quartic potentials, that the upper bound on $r$ for the physically plausible value of $0\le w_{re}\le 0.25$ is slightly larger than the Planck 2018 and BICEP2/Keck array bound, and for $n=2/3$ and 1, the reheating equation of state should be less than 0 to satisfy Planck 2018 joint constraints on $n_s$ and $r$. However, natural inflation with the DBI kinetic term is compatible with Planck 2018 bounds on $r$ and joint constraints on $n_s$ and $r$ for the physically plausible range $0\le w_{re}\le 0.25$. The quadratic and quartic potential with a power-law kinetic term are also compatible with Planck 2018 joint constraints on $n_s$ and $r$ for $0\le w_{re}\le 1$. However, for an exponential potential with a power-law kinetic term, the equation of state during reheating, $w_{re}$, should be greater than 1 for $r-n_s$ predictions to lie within 68% C.L. of joint constraints on $n_s$ and $r$ from Planck 2018 observations.

Models of inflationary cosmology admit a choice of the metric for which the geometry of homogeneous isotropic solutions becomes flat Minkowski space in the infinite past. In this primordial flat frame all mass scales vanish in the infinite past and quantum scale symmetry is realized. The cosmological evolution is dominantly described by the slow increase of a scalar field which sets the scale of all masses. We construct the primordial flat frame for standard models of inflation as Starobinsky inflation or chaotic inflation. In particular, we discuss the evolution of inhomogeneous solutions in the neighborhood of the homogeneous isotropic background solution and their relation to the observable primordial fluctuation spectrum. If the propagators for the graviton and scalar field remain regular, our observed inhomogeneous universe can be extrapolated back to the infinite past in physical time. In this case there is no physical big-bang singularity—the latter reflects only a singular choice of “field coordinates.” Independently of the issue of singularity the primordial flat frame offers a new view on the physical properties of the inflationary universe, which can be characterized as a very slowly evolving almost empty “vacuum” state with approximate scale symmetry.

We have refined our previously suggested scenario of generation of the cosmological baryon asymmetry through an asymmetric capture of baryons and antibaryons by a primordial black hole [A. D. Dolgov and N. A. Pozdnyakov, arXiv:2009.04361]. It is found that in the limit of weak interactions of hypothetical heavy baryons with the primeval plasma the effect can be strongly enhanced and the observed magnitude of the asymmetry can be obtained for a wide range of the model parameters.

The reconstruction of the spectral function from the correlation function in Euclidean space is a challenging task. In this paper, we employ the machine learning techniques in terms of the radial basis functions networks to reconstruct the spectral function from a finite number of correlation data. To test our method, we first generate one type of correlation data using a mock spectral function by mixing several Breit-Wigner propagators. We found that compared with other traditional methods, e.g., truncated singular value decomposition, Tikhonov, and maximum entropy methods, our approach gives a continuous and unified reconstruction for both positive definite and negative spectral functions, which is especially useful for studying the QCD phase transition. Moreover, our approach has considerably better performance in the low-frequency region. This has advantages for the extraction of transport coefficients which are related to the zero frequency limit of the spectral function. With the mock data generated through a model spectral function of stress energy tensor, we find our method gives a precise and stable extraction of the transport coefficients.

We present a class of models in which the coupling of the photon to an ultralight scalar field that has a time-dependent vacuum expectation value causes the fine structure constant to oscillate in time. The scalar field is assumed to constitute all or part of the observed dark matter. Its mass is protected against radiative corrections by a discrete ${\mathbb{Z}}_N$ exchange symmetry that relates the Standard Model to several copies of itself. The abundance of dark matter is set by the misalignment mechanism. We show that the oscillations in the fine structure constant are large enough to be observed in current and near-future experiments.

We propose a new portal coupling to dark matter by taking advantage of the nonminimally coupled portal sector to the Ricci scalar. Such a portal sector conformally induces couplings to the trace of the energy-momentum tensor of matters including highly secluded dark matter particles. The portal coupling is so feeble that dark matter is produced by freeze-in processes of scatterings and/or the decay of the mediator. We consider two concrete realizations of the portal: conformally induced Higgs portal and conformally induced mediator portal. The former case is compatible with the Higgs inflation, while the latter case can be tested by dark matter direct detection experiments.

We consider hadronic axion models that extend the Standard Model by one complex scalar field and one or more new heavy quarks, i.e., $N_{\mathcal{Q}}\ge 1$. We review previously suggested selection criteria as well as categorize and catalog all possible models for $N_{\mathcal{Q}}\le 9$. In particular, allowing for $N_{\mathcal{Q}}>1$ can introduce models that spoil the axion solution of the strong $CP$ problem. Demanding that Landau poles do not appear below some energy scale limits the number of preferred models to a finite number. For our choice of criteria, we find that $N_{\mathcal{Q}}\le 28$ and only 820 different anomaly ratios $E/N$ exist (443 when considering additive representations, 12 when all new quarks transform under the same representation). We analyze the ensuing $E/N$ distributions, which can be used to construct informative priors on the axion-photon coupling. The hadronic axion model band may be defined as the central region of one of these distributions, and we show how the band for equally probable, preferred models compares to present and future experimental constraints.

We revisit dark matter annihilation as an explanation of the positron excess reported recently by the AMS-02 satellite-borne experiment. To this end, we propose a particle dark matter model by considering a two Higgs doublet model (2HDM) extended with an additional singlet boson and a singlet fermion. The additional (light) boson mixes with the pseudoscalar inherent in the 2HDM, and the singlet fermion, which is the dark matter candidate, annihilates via this bosonic portal. The dark matter candidate is made leptophilic by choosing the lepton-specific 2HDM and a suitable high value of $\tan \beta$. We identify the model parameter space which explains the muon g-2 anomaly while evading the experimental constraints. After establishing the viability of the singlet fermion to be a dark matter candidate, we calculate the positron excess produced from its annihilation to the light bosons which primarily decay to muons. Incorporating the Sommerfeld effect caused by the light mediator and an appropriate boost factor, we find that our proposed model can satisfactorily explain the positron fraction excess as well as the positron spectrum data reported by the AMS-02 experiment.

In the present work, we investigate the decays of $Z_{cs}^{-}(3985)$ in the $D_s^{-}{D}^{*0}+D_s^{*-}{D}^0$ molecular frame. By using an effective Lagrangian approach, the branching ratios of $Z_{cs}^{-}\to J/\psi K^{-}$ and $Z_{cs}^{-}\to {\eta }_c{K}^{*-}$ are estimated. It is found that the dominating decay mode of $Z_{cs}^{-}(3985)$ is open charm channel, while, the branching ratio of the hidden charm decay channels is about 20%. In particular, the branching ratios of $Z_{cs}^{-}\to J/\psi K^{-}$ and $Z_{cs}^{-}\to {\eta }_c{K}^{*-}$ are predicted to be an order of 10%. Moreover, our estimation indicates that the fraction of the quasi-two-body cascade decay via $Z_{cs}(3985)$ and the total cross section of $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ around 4.68 GeV is $(6.8_{-6.2}^{+10.5})\%$. All the predicted branching ratios in the present work could be tested by further measurements in BESIII and Belle II.

How to hunt for higher $P$-wave states of charmonium is still an open topic when $2P$ charmonia were identified. In this work, we present an unquenched quark model calculation to illustrate the spectroscopy behavior of these $3P$, $4P$, and $5P$ states in charmonium family. For the $3P$ charmonia, the predicted masses are around 4.2 GeV and their two-body open-charm decay behaviors were given, by which we propose that searching for these $3P$ states via their open-charm decay channels from $\gamma \gamma$ fusion and $B$ decay can be accessible at future experiment like LHCb and Belle II. We continue to calculate the masses of these $4P$ and $5P$ charmonia. Combing with these calculated results of higher $P$-wave states of charmonium, we find that the coupled-channel effect becomes more obvious with increasing the radial quantum number, which can be understood well by the modified Godfrey-Isgur model with screened potential.

We study a Jackiw-Teitelboim (JT) supergravity theory, defined as a Euclidean path integral over orientable supermanifolds with constant negative curvature, which was argued by Stanford and Witten to be captured by a random matrix model in the $\mathit{\beta }=2$ Dyson-Wigner class. We show that the theory is a double-cut matrix model tuned to a critical point where the two cuts coalesce. Our formulation is fully nonperturbative and manifestly stable, providing for explicit unambiguous computation of observables beyond the perturbative recursion relations derivable from loop equations. Our construction shows that this JT supergravity theory may be regarded as a particular combination of certain type 0B minimal string theories, and is hence a natural counterpart to another family of JT supergravity theories recently shown to be built from type 0A minimal strings. We conjecture that certain other JT supergravities can be similarly defined in terms of double-cut matrix models.

Compactifications of the Chaudhuri-Hockney-Lykken (CHL) string to eight dimensions can be characterized by embeddings of root lattices into the rank 12 momentum lattice ${\mathrm{\Lambda }}_M$, the so-called Mikhailov lattice. Based on these data, we devise a method to determine the global gauge group structure including all $U(1)$ factors. The key observation is that, while the physical states correspond to vectors in the momentum lattice, the gauge group topology is encoded in its dual. Interpreting a nontrivial ${\pi }_1(G)\equiv \mathcal{Z}$ for the non-Abelian gauge group $G$ as having gauged a $\mathcal{Z}$ 1-form symmetry, we also prove that all CHL gauge groups are free of a certain anomaly [1] that would obstruct this gauging. We verify this by explicitly computing $\mathcal{Z}$ for all 8D CHL vacua with $\mathrm{rank}(G)=10$. Since our method applies also to $T^2$ compactifications of heterotic strings, we further establish a map that determines any CHL gauge group topology from that of a “parent” heterotic model.

The knots-quivers correspondence states that various characteristics of a knot are encoded in the corresponding quiver and the moduli space of its representations. However, this correspondence is not a bijection: more than one quiver may be assigned to a given knot and encode the same information. In this work we study this phenomenon systematically and show that it is generic rather than exceptional. First, we find conditions that characterize equivalent quivers. Then we show that equivalent quivers arise in families that have the structure of permutohedra, and the set of all equivalent quivers for a given knot is parametrized by vertices of a graph made of several permutohedra glued together. These graphs can be also interpreted as webs of dual three-dimensional $\mathcal{N}=2$ theories. All these results are intimately related to properties of homological diagrams for knots, as well as to multicover skein relations that arise in the counting of holomorphic curves with boundaries on Lagrangian branes in Calabi-Yau three-folds.

The two-loop correction to the mass of the ${\varphi }^4$ kink is $0.0126\lambda /m$ in terms of the coupling $\lambda$ and the meson mass $m$ evaluated at the minimum of the potential. This is calculated using a recently proposed alternative to collective coordinates. Both the kink energy and the vacuum energy are IR divergent at this order. To cancel the divergence, the two energy densities are subtracted before integrating over space, or equivalently a finite counterterm is added to the Hamiltonian density to cancel the vacuum energy density. All spatial integrals are performed analytically. However in the last step of our calculation, integrals over virtual momenta are performed numerically.

We present new developments and comparisons of competing inspiral and waveform models for highly eccentric nonspinning extreme and intermediate mass-ratio inspirals (EMRIs and IMRIs). Starting from our high eccentricity self-force library, we apply the near-identity transform (NIT) technique to rapidly compute highly eccentric self-forced inspirals for the first time. Upon evaluating our approximate NIT results via comparison with full self-force inspirals, we couple our accurate and streamlined inspiral data to potential waveform generation schemes. We find that, although high eccentricity strains the NIT method, NIT inspirals are consistent with full self-force inspirals for EMRIs. However, our NIT implementation at first postadiabatic order) is not able to achieve Laser Interferometer Space Antenna-motivated accuracy goals for highly eccentric IMRIs. Our most sophisticated waveforms are devised through a new technique that efficiently connects NIT orbital parameters to Teukolsky amplitudes and phases. We compare these sophisticated Teukolsky waveforms to those with synthesized (summing over harmonics) amplitudes based on a kludge. We find that, assuming identical worldlines (so that dephasing is negligible), kludge waveforms compare favorably to Teukolsky waveforms for nonspinning bodies.

Quantum aspects of black holes may have observational imprints on their absorption and emission spectrum. In this work, we consider the possibility of nonuniform area quantization and its effects on the phasing of a gravitational waveform from coalescing black hole inspirals. These observations may provide detectable effects distinct from that of a uniform area quantization and allow us to put bounds on various parameters of the underlying model. Our work can also be regarded as a novel test for the area-entropy proportionality of black hole solutions in general relativity.

We study the propagation of charged scalar fields in the background of $2+1$-dimensional Coulomb-like AdS black holes, and we show that such propagation is unstable under Dirichlet boundary conditions. However, all the unstable modes are superradiant and all the stable modes are nonsuperradiant, according with the superradiant condition. Mainly, we show that when the scalar field is charged the quasinormal frecuencies (QNFs) are always complex, contrary to the uncharged case, where for small values of the black hole charge the complex QNFs are dominant, while that for bigger values of the black hole charge the purely imaginary QNFs are dominant.

We present a new choice of initial data for binary black hole simulations that significantly improves the efficiency of high-spin simulations. We use spherical Kerr-Schild coordinates, where the horizon of a rotating black hole is spherical, for each black hole. The superposed spherical Kerr-Schild initial data reduce the runtime by a factor of 2 compared to standard superposed Kerr-Schild for an intermediate resolution spin-0.99 binary-black-hole simulation. We also explore different variations of the gauge conditions imposed during the evolution, one of which produces an additional speed-up of 1.3.