We find unitary and local theories of higher curvature gravity in the vielbein formalism, known as Poincaré gauge theory, by utilizing the equivalence to ghost-free massive bigravity. We especially focus on three and four dimensions, but extensions into a higher-dimensional spacetime are straightforward. In three dimensions, quadratic gravity $\mathcal{L}=R+T^2+R^2$, where $R$ is the curvature and $T$ is the torsion with indices omitted, is shown to be equivalent to zwei-dreibein gravity and free from the ghost at fully nonlinear orders. In a special limit, new massive gravity is recovered. When the model is applied to the $\mathrm{AdS}/\mathrm{CFT}$ correspondence, unitarity both in the bulk theory and in the boundary theory implies that the torsion must not vanish. On the other hand, in four dimensions, the absence of a ghost at nonlinear order requires an infinite number of higher curvature terms, and these terms can be given by a schematic form $R(1+R/\alpha m^2{)}^{-1}R$, where $m$ is the mass of the massive spin-2 mode originating from the higher curvature terms and $\alpha$ is an additional parameter that determines the amplitude of the torsion. We also provide another four-dimensional ghost-free higher curvature theory that contains a massive spin-0 mode as well as a massive spin-2 mode.

We revisit our previous proposed conjecture—the horizon creates a local instability which acts as the source of the quantum temperature of a black hole. It is found that a chargeless massless particle moving along the null trajectory in Eddington-Finkelstein (EF) coordinates feels instability in the vicinity of the horizon. Such instability is observer independent for this particle motion. Moreover, an observer associated with EF coordinates finds the local Hamiltonian as $xp$, where $p$ is the canonical momentum corresponding to the coordinate $x$. Finally, using this Hamiltonian, we notice that, at the quantum level, this class of observers feels the horizon as a thermal object with the temperature given by the Hawking expression. We provide this by using various techniques in quantum mechanics and, thereby, bolster our earlier claim—the automatic local instability can be a mechanism for emerging the horizon as a thermal object. In this process, the present analysis provides another set of coordinates (namely, the EF frame), in addition to our earlier Painlevé ones, in which the null trajectory of the massless particle is governed by an $xp$-type Hamiltonian in the near-horizon regime.

We consider the gravitational quasinormal modes of the static and spherically-symmetric dirty black holes in the effective theory of gravity with the third order curvature term inspired by the Goroff-Sagnotti calculation. It is demonstrated that using the WKB-Padé summation proposed in [J. Matyjasek and M. Opala, Phys. Rev. D 96, 024011 (2017)] one can achieve sufficient accuracy to calculate corrections to the complex frequencies of the quasinormal modes caused by the Goroff-Sagnotti curvature term. It is shown that the curvature correction (with our choice of the sign of the coupling constant) increases damping of the fundamental modes (except for the lowest fundamental mode) and decreases their frequencies. We argue that the methods adopted in this paper can be used in the analysis of the influence of the higher-order curvature terms upon the quasinormal modes and in a number of related problems that require high accuracy.

Using a simple model of low-mass stellar objects we have shown modified gravity impact on their early evolution, such as Hayashi tracks, radiative core development, effective temperature, masses, and luminosities. We have also suggested that the upper mass’ limit of fully convective stars on the main sequence might be different than commonly adopted.

We readdress the thermodynamic structure of geometrical relations on a generic null surface. Among three potential candidates, originating from different components of $R_{ab}$ along the null vectors for the surface (i.e., $R_{ab}{q}_c^a{l}^b$, $R_{ab}{l}^a{l}^b$, and $R_{ab}{l}^a{k}^b$ where $q_{ab}$ is the projector on the null surface and $l^a$, $k^a$ are null normal and corresponding auxiliary vectors of it, respectively), the first one leads to a Navier-Stokes-like equation. Here we devote our investigation to the other two members. We find that $R_{ab}{l}^a{l}^b$, which yields the evolution equation for the expansion parameter corresponding to $l^a$ along itself, can be interpreted as a thermodynamic relation when integrated on the two-dimensional transverse subspace of the null hypersurface along with a virtual displacement in the direction of $l^a$. Moreover, for a stationary background, the integrated version of it yields the general form of the Smarr formula. Although this is more or less known in literature, a similar argument for the evolution equation of the expansion parameter corresponding to $k^a$ along $l^a$, provided by $R_{ab}{l}^a{k}^b$, leads to a more convenient form of thermodynamic relation. In this analysis, contrary to earlier approaches, the identified thermodynamic entities come out to be in covariant forms and also are foliation independent. Hence, these can be applied to any coordinate system adapted to the null hypersurface. Moreover, these results are not restricted to any specific parametrization of $k^a$ and also $k^a$ need not be hypersurface orthogonal. In addition, here any particular dynamical equation for the metric is not being explicitly used and therefore we feel that our results are solely based on the properties of the null surface.

We study nanohertz gravitational waves relevant to pulsar timing array experiments from quantum fluctuations in the early universe with null energy condition (NEC) violation. The NEC violation admits accelerated expansion with the scale factor $a\propto (-t{)}^{-p}$ ($p>0$), which gives the tensor spectral index $n_t=2/(p+1)>0$. To evade the constraint from big bang nucleosynthesis (BBN), we connect the NEC-violating phase to a subsequent short slow-roll inflationary phase which ends with standard reheating, and thereby reduce the high-frequency part of the spectrum. An explicit model is constructed within the cubic Horndeski theory which allows for stable violation of the NEC. We present numerical examples of the background evolution having the different maximal Hubble parameters (which determine the peak amplitude of gravitational waves), the different inflationary Hubble parameters (which determine the amplitudes of high-frequency gravitational waves), and different durations of the inflationary phase (which essentially determine the peak frequency of the spectrum). We display the spectra with $n_t=0.8$, 0.9, and 0.95 for $f\lesssim 1/\mathrm{yr}$, which are consistent with the recent NANOGrav result. We also check that they do not contradict the BBN constraint. We discuss how the nearly scale-invariant spectrum of curvature perturbations is produced in the NEC-violating phase.

Risaliti, Lusso, and collaborators have constructed a high-redshift Hubble diagram of supernovae (SNe), quasars (QSO), and gamma-ray bursts (GRBs) that shows a “$\sim 4\sigma$ tension with the $\mathrm{\Lambda }\mathrm{CDM}$ model” based on a log polynomial cosmographic expansion [1,2]. In this work, we demonstrate that the log polynomial expansion generically fails to recover flat $\mathrm{\Lambda }\mathrm{CDM}$ beyond $z\sim 2$, thus undermining the $\sim 4\sigma$ tension claim. Moreover, through direct fits of both the flat $\mathrm{\Lambda }\mathrm{CDM}$ and the log polynomial model to the $\mathrm{SNe}+\mathrm{QSO}+\mathrm{GRB}$ data set, we confirm that the flat $\mathrm{\Lambda }\mathrm{CDM}$ model is preferred. Ultimately, we trace the tension to the QSO data and show that a best fit of the flat $\mathrm{\Lambda }\mathrm{CDM}$ model to the QSO data leads to a flat $\mathrm{\Lambda }\mathrm{CDM}$ universe with no dark energy within $1\sigma$. This marks an irreconcilable tension between the Risaliti-Lusso QSOs and flat $\mathrm{\Lambda }\mathrm{CDM}$.

We perform a statistical inference of the astrophysical population of binary black hole (BBH) mergers observed during the first two observing runs of Advanced LIGO and Advanced Virgo, including events reported in the GWTC-1 and IAS catalogs. We derive a novel formalism to fully and consistently account for events of arbitrary significance. We carry out a software injection campaign to obtain a set of mock astrophysical events subject to our selection effects, and use the search background to compute the astrophysical probabilities $p_{\text{astro}}$ of candidate events for several phenomenological models of the BBH population. We emphasize that the values of $p_{\text{astro}}$ depend on both the astrophysical and background models. Finally, we combine the information from individual events to infer the rate, spin, mass, mass-ratio and redshift distributions of the mergers. The existing population does not discriminate between random spins with a spread in the effective spin parameter, and a small but nonzero fraction of events from tidally torqued stellar progenitors. The mass distribution is consistent with one having a cutoff at $m_{\max }={41}_{-5}^{+10}{\mathrm{M}}_{\odot }$, while the mass ratio favors equal masses; the mean mass ratio $\overline{q}>0.67$. The rate shows no significant evolution with redshift. We show that the merger rate restricted to BBHs with a primary mass between $20–30{\mathrm{M}}_{\odot }$, and a mass ratio $q>0.5$, and at $z\sim 0.2$, is $1.5–5.3{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ (90% c.l.); these bounds are model independent and a factor of $\sim 3$ tighter than that on the local rate of all BBH mergers, and hence are a robust constraint on all progenitor models. Including the events in our catalog increases the Fisher information about the BBH population by $\sim 47\%$, and tightens the constraints on population parameters.

The Murchison Widefield Array (MWA) recorded impulsive radio events in the quiet solar corona at frequencies 98, 120, 132, and 160 MHz [S. Mondal, D. Oberoi, and A. Mohan, Astrophys. J. 895, L39 (2020)]. We propose that these radio events are the direct manifestation of dark matter annihilation events within the axion quark nugget (AQN) framework. It has been argued [A. Zhitnitsky, J. Cosmol. Astropart. Phys. 10 (2017) 050; N. Raza, L. vanWaerbeke, and A. Zhitnitsky, Phys. Rev. D 98, 103527 (2018)] that the AQN-annihilation events in the quiet solar corona can be identified with the nanoflares conjectured by Parker [Astrophys. J. 264, 642 (1983)]. We further support this claim by demonstrating that observed impulsive radio events [S. Mondal, D. Oberoi, and A. Mohan, Astrophys. J. 895, L39 (2020)], including their rate of appearance, their temporal and spatial distributions, and their energetics, are matching the generic consequences of AQN annihilations in the quiet corona. We propose to test this idea by analyzing the correlated clustering of impulsive radio events in different frequency bands. These correlations are expressed in terms of the time delays between radio events in different frequency bands measured in seconds. We also make generic predictions for low (80 and 89 MHz) and high (179, 196, 217, and 240 MHz) frequency bands, that have been recorded, but not published, by Mondal et al. [Astrophys. J. 895, L392020]. We finally suggest to test our proposal by studying possible cross-correlation between MWA radio signals and Solar Orbiter recording of extreme UV photons (aka “campfires”).

We investigate the $B_{d,s}^0\to f_1{f}_1$ decays in the framework of perturbative QCD (PQCD) approach with a referenced value ${\varphi }_{f_1}\sim 24°$. Here, $f_1$ denotes the axial-vector mesons $f_1(1285)$ and $f_1(1420)$ with mixing angle ${\varphi }_{f_1}$ in the quark-flavor basis. The observables such as branching ratios, direct $CP$ violations, and polarization fractions of the $B_s^0\to f_1{f}_1$ decays are predicted for the first time. We find that (i) the almost pure penguin modes $B_s^0\to f_1{f}_1$ have large branching ratios in the order of ${10}^{-6}\sim {10}^{-5}$ due to the Cabibbo-Kobayashi-Maskawa enhancement and generally constructive interferences between the amplitudes of $B_s^0\to f_n{f}_s$ and $B_s^0\to f_s{f}_s$ with $f_n$ and $f_s$ being the quark-flavor states of $f_1$ mesons. (ii) The observables receive important contributions from the weak annihilation diagrams in the PQCD approach. In particular, without the annihilation contributions, the $B_s^0\to f_1(1420)f_1(1420)$ branching ratio will decrease about 81% and its longitudinal polarization fraction will reduce around 43%. And (iii) the dependence of the $B_{d,s}^0\to f_1{f}_1$ decay rates on ${\varphi }_{f_1}$ exhibits some interesting line shapes, whose confirmations would be helpful to constrain the determination of ${\varphi }_{f_1}$ inversely. All the PQCD predictions await for the (near) future examinations at Large Hadron Collider beauty and/or Belle-II experiments to further understand the properties of the axial-vector mesons and the perturbative dynamics released from the considered decay modes.

We present a comprehensive analysis of leptonic unitarity triangles, using both current neutrino oscillation data and projections of next-generation oscillation measurements. Future experiments, sensitive to the degree of $CP$ violation in the lepton sector, will enable the construction of precise triangles. We show how unitarity violation could manifest in the triangles and discuss how they serve as unitarity tests. We also propose the use of Jarlskog factors as a complementary means of probing unitarity. This analysis highlights the importance of testing the unitarity of the leptonic mixing matrix, an understanding of which is crucial for deciphering the nature of the neutrino sector.

Besides $CP$-preserving interactions, axions and axion-like particles may also have small $CP$-violating scalar Yukawa interactions with nucleons and electrons. Any such interaction will generate macroscopic monopole-dipole forces which can be searched for experimentally. When the best experimental limits on scalar interactions are combined with stellar energy-loss arguments constraining pseudoscalar interactions, strong bounds can be set on $CP$-violating axion couplings which almost intersect the expectation for QCD models. Over the years, both astrophysical and laboratory tests have improved. We provide a much-needed up-to-date compilation of these constraints, showing improvements in some regions of parameter space by factors between 40 and 130. We advocate experimental opportunities, without astrophysical or dark-matter assumptions, to track down the axion in the lesser-explored corners of its parameter space.

We perform a comprehensive analysis of the secluded supersymmetric ${U(1)}^{\prime }$ model, consistent with present experimental constraints. We find that, in this model, the additional $Z^{\prime }$ gauge boson can be leptophobic without resorting to gauge kinetic mixing and consequently, also $d$-quark-phobic, thus lowering the LHC bounds on its mass. The model can accommodate very light singlinos as DM candidates, consistent with present day cosmological and collider constraints. Light charginos and neutralinos are responsible for muon anomalous magnetic predictions within $1\sigma$ of the measured experimental value. Finally, we look at the possibility that a lighter $Z^{\prime }$, expected to decay mainly into chargino pairs and followed by the decay into lepton pairs, could be observed at 27 TeV.

We propose a next-to-minimal supersymmetric Standard Model (NMSSM) extended by an ${\mathbb{A}}_4\times {\mathit{Z}}_3$ flavor symmetry and three right-handed neutrinos providing a detailed study of the neutrino sector and a solution to the domain wall problem. In this proposal, neutrino masses are generated through Type I seesaw mechanism while the mixing angles are described by the trimaximal mixing realized using the NMSSM singlet $S$ and only two flavon fields. The phenomenology of neutrino parameters is studied for normal and inverted mass hierarchies. In particular, we numerically evaluated the observables related to neutrino masses and mixing, namely, $\sum m_i$, $m_{ee}$, $m_{{\nu }_e}$, and ${\delta }_{CP}$ where we find that the ranges of $m_{ee}$ and $m_{{\nu }_e}$ are accessible by current and future experiments while the obtained ranges of $\sum m_i$ and ${\delta }_{CP}$ lie within the current experimental data. Another attractive feature we discussed in this paper is the circumvention of the domain wall problem induced by the spontaneous breaking of the ${\mathbb{A}}_4\times {\mathit{Z}}_3$ discrete symmetry. We first showed that the domain walls in the charged lepton sector occur at high energy scale leading to unproblematic domain walls, while in the neutrino sector they are inevitable. Then, to solve this problem, we reconsidered the well-known approach that relies on the explicit breaking of the discrete symmetry through the insertion of Planck-suppressed operators induced by supergravity.

Recently, Singh and Chandrasekharan [Phys. Rev. D 100, 054505 (2019)] showed that fixed points of the nonlinear $O(3)$ sigma model can be reproduced near a quantum phase transition of a spin model with just two qubits per lattice site. In a paper by the NuQS Collaboration [Phys. Rev. Lett. 123, 090501 (2019)], the proposal is made to simulate such field theories on a quantum computer using the universal properties of a similar model. In this paper, following that direction, we demonstrate how to prepare the ground state of the model from Singh and Chandrasekharan and measure a dynamical quantity of interest, the $O(3)$ Noether charge, on a quantum computer. In particular, we apply Trotter methods to obtain results for the complexity of adiabatic ground state preparation in both the weak-coupling and quantum-critical regimes and use shadow tomography to measure the dynamics of local observables. We then present and analyze a quantum algorithm based on nonunitary randomized simulation methods that may yield an approach suitable for intermediate-term noisy quantum devices.

Efficient digitization is required for quantum simulations of gauge theories. Schemes based on discrete subgroups use fewer qubits at the cost of systematic errors. We systematize this approach by deriving a single plaquette action for approximating general continuous gauge groups through integrating out field fluctuations. This provides insight into the effectiveness of these approximations, and how they could be improved. We accompany the scheme by simulations of pure gauge over the largest discrete subgroup of $SU(3)$ up to the third order.

Based on the nonrelativistic QCD framework, we study $\mathrm{\Upsilon }$ production in semi-inclusive deep inelastic electron-proton scattering (SIDIS) at HERA, EIC, and LHeC, with the main aim of assessing the viability of observing $\mathrm{\Upsilon }$ electroproduction at the three colliders. The color-octet (CO) contributions are found to have a crucial effect on both the integrated and differential cross sections, serving to further establish the significance of the CO mechanism. By setting the kinematic cuts to $p_{t,\mathrm{\Upsilon }}^{\star 2}>1{\mathrm{GeV}}^2$, $W>50\mathrm{GeV}$, $2<Q^2<100{\mathrm{GeV}}^2$, and $0.3<z<0.9$, only a few electroproduced $\mathrm{\Upsilon }$ events can be generated at HERA, partially accounting for its lack of measured $\mathrm{\Upsilon }$ electroproduction. However, under the same cut conditions, the EIC and LHeC can accumulate about $8.7\times {10}^2$ and $3.7\times {10}^4$ reconstructed $\mathrm{\Upsilon }$ events in one operation year, respectively, which manifestly indicates the prospect of detecting the $\mathrm{\Upsilon }$-related SIDIS processes at the two forthcoming $ep(eA)$ colliders.

Masses of the ground-state tetraquarks composed from heavy $c$ and $b$ quarks and antiquarks are calculated in the diquark-antidiquark picture in the framework of the relativistic quark model based on the quasipotential approach. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole, and the internal structure of the diquarks is taken into account. All such tetraquarks are found above the thresholds of decays to two heavy quarkonia. This is a result of the consideration of the diquark not to be a pointlike object. Therefore, such tetraquarks can be observed as broad structures decaying dominantly to quarkonia. The broad structure next to the di-$J/\psi$ mass threshold, recently observed by the LHCb Collaboration, can correspond to the ground $2^{++}$-state tetraquark consisting of four charm quarks.