Machine learning techniques are used for treating jets as images to explore the performance of boosted top quark tagging. Tagging performances are studied in both hadronic and leptonic channels of top quark decay, employing a convolutional neural network (CNN) based technique along with boosted decision trees (BDT). This computer vision approach is also applied to distinguish between left and right polarized top quarks. In this context, an experimentally measurable asymmetry variable is proposed to estimate the polarization. Results indicate that the CNN based classifier is more sensitive to top quark polarization than the standard kinematic variables. It is observed that the overall tagging performance in the leptonic channel is better than the hadronic case, and the former also serves as a better probe for studying polarization.

The Cabibbo-Kobayashi-Maskawa matrix elements $|V_{cb}|$ and $|V_{ub}|$ can be obtained by combining data from the experiments with lattice QCD results for the semileptonic form factors for the $\overline{B}\to D^{*}\ell \overline{\nu }$ and $\overline{B}\to \pi \ell \overline{\nu }$ decays. It is highly desirable to use the Oktay-Kronfeld (OK) action for the form factor calculation on the lattice, since the OK action is designed to reduce the heavy quark discretization error down to the $\mathcal{O}(a^4{\mathrm{\Lambda }}^4)\simeq \mathcal{O}({\mathrm{\Lambda }}^4/(2m_Q{)}^4)$ level in the power counting rules of the heavy quark effective theory (HQET). Here, we present a matching calculation to improve heavy-heavy and heavy-light currents up to the ${\lambda }^3$ order in HQET, the same level of improvement as the OK action. Our final results for the improved currents are being used in a lattice QCD calculation of the semileptonic form factors for the $\overline{B}\to D^{*}\ell \overline{\nu }$ and $\overline{B}\to D\ell \overline{\nu }$ decays.

We consider an improved soft-wall AdS/QCD model coupled to an Einstein-dilaton system, which offers a way to study the deconfining and chiral transitions simultaneously. The correlation between these two transitions has been investigated in detail in the Einstein-dilaton-scalar system with the bulk scalar field representing the vacuum of matters in the flavor sector of the model. We find that the effects of the scaling dimension $\mathrm{\Delta }$ of the dual operator of the dilaton manifest in chiral transitions, although the equations of state can all be matched with the two-flavor lattice results for $\mathrm{\Delta }=2.5,3,3.5$ in the decoupling case of $\beta =0$. In the weak-coupling case with smaller $\beta$, both the equation of state and the chiral transition exhibit a crossover behavior and turn into first-order phase transitions with the increase of $\beta$.

Inspired by the observed $X(2900)$, we study systematically the mass spectra of the ground pentaquark states with the $qqqq\overline{Q}$ ($Q=c$, $b$; $q=n$, $s$; $n=u$, $d$) configuration in the framework of the Chromomagnetic Interaction model. We present a detailed analysis of their stabilities and decay behaviors. Our results indicate that there may exist narrow states or even stable states. We hope that the present study may inspire experimentalist’s interest in searching for such a type of the exotic pentaquark state.

In our previous work [Phys. Rev. D 101, 074025 (2020)], the photoproduction $\gamma p\to K^{+}{\mathrm{\Sigma }}^0(1385)$ has been investigated within an effective Lagrangian approach. There, the reaction amplitudes were constructed by considering the $t$-channel $K$ and $K^{*}(892)$ exchanges, $s$-channel $N$ contribution, $u$-channel $\mathrm{\Lambda }$ exchange, generalized contact term, and a minimum number of $s$-channel $N$ and $\mathrm{\Delta }$ resonance diagrams. It was found that the inclusion of one of the $N(1895){1/2}^{-}$, $\mathrm{\Delta }(1900){1/2}^{-}$, and $\mathrm{\Delta }(1930){5/2}^{-}$ resonances is essential to reproduce the available differential and total cross-section data for $\gamma p\to K^{+}{\mathrm{\Sigma }}^0(1385)$. In the present work, we employ the same model to study the photoproduction $\gamma n\to K^{+}{\mathrm{\Sigma }}^{-}(1385)$, with the purpose being to understand the reaction mechanism and, in particular, to figure out which one of the $N(1895){1/2}^{-}$, $\mathrm{\Delta }(1900){1/2}^{-}$, and $\mathrm{\Delta }(1930){5/2}^{-}$ resonances is really capable for a simultaneous description of the data for both $K^{+}{\mathrm{\Sigma }}^0(1385)$ and $K^{+}{\mathrm{\Sigma }}^{-}(1385)$ photoproduction reactions. The results show that the available data on differential and total cross sections and photobeam asymmetries for $\gamma n\to K^{+}{\mathrm{\Sigma }}^{-}(1385)$ can be reproduced only with the inclusion of the $\mathrm{\Delta }(1930){5/2}^{-}$ resonance rather than the other two. The generalized contact term and the $t$-channel $K$ exchange are found to dominate the background contributions. The resonance $\mathrm{\Delta }(1930){5/2}^{-}$ provides the most important contributions in the whole energy region considered, and it is responsible for the bump structure exhibited in the total cross sections.

Using an electron-positron collision data sample corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected with the BESIII detector at a center-of-mass energy of 3.773 GeV, we search for the baryon-number and lepton-number violating decays $D^0\to \overline{p}{e}^{+}$ and $D^0\to p{e}^{-}$. No obvious signals are found with the current statistics. The upper limits on the branching fractions for $D^0\to \overline{p}{e}^{+}$ and $D^0\to p{e}^{-}$ are set to be $1.2\times {10}^{-6}$ and $2.2\times {10}^{-6}$ at 90% confidence level, respectively.

The discovery of diffuse sub-PeV gamma-rays by the Tibet ${\mathrm{AS}}_{\gamma }$ Collaboration promises to revolutionize our understanding of the high-energy astrophysical universe. It has been shown that these data broadly agree with prior theoretical expectations. We study the impact of this discovery on a well-motivated new physics scenario: PeV-scale decaying dark matter (DM). Considering a wide range of final states in DM decay, a number of DM density profiles, and numerous astrophysical background models, we find that these data provide the most stringent limit on DM lifetime for various Standard Model final states. In particular, we find that the strongest constraints are derived for DM masses in between a few PeV to a few tens of PeV. Near-future data of these high-energy gamma-rays can be used to discover PeV-scale decaying DM.

I show that the neutral pion decay in $B\to K^{(*)}{\pi }^0\gamma$, with ${\pi }^0\to ee\gamma$, might generate large sources of lepton flavor universality violation (LFUV) in measurements of the ratios, $R_{K^{(*)}}$: If the photons in the $K^{(*)}ee\gamma \gamma$ final state are reconstructed as bremsstrahlung, the recovered electron-positron invariant mass can be pushed into the $1–6{\mathrm{GeV}}^2$ signal region, artificially enhancing the measured $B\to K^{(*)}ee$ branching ratio compared to $B\to K^{(*)}\mu \mu$. I present a conservative estimate and simulation of the $B\to K{\pi }^0\gamma$ LFUV background at LHCb, that together suggest this effect could reduce the recovered $R_K$ up to several percent. A reliable assessment of the size of this effect will require dedicated simulations within experimental frameworks themselves.

The prospects of measuring a single-differential dijet cross section during the proposed short proton-oxygen data taking at LHC Run 3 are studied using next-to-leading-order perturbative QCD predictions. With reasonable experimental cuts and luminosity estimates, such a measurement is found to be feasible, and a few inverse nanobarns of integrated luminosity is estimated to be enough to yield new constraints on parton distribution functions (PDFs) of light nuclei. In the absence of a dedicated proton-proton reference, a mixed-energy nuclear modification ratio is proposed for canceling free-proton PDF uncertainties to obtain a direct access to the nuclear modifications of the parton distributions in oxygen.

We show that double field theory arises from the color-kinematic double copy of Yang-Mills theory. A precise double copy prescription for the Yang-Mills action at quadratic and cubic order is provided that yields the double field theory action in which the duality invariant dilaton has been integrated out. More precisely, at quadratic order this yields the gauge-invariant double field theory, while at cubic order it yields the cubic double field theory action subject to a gauge condition that originates from Siegel gauge in string field theory.

We consider a $f(R)$ gravity theory in ($2+1$)-dimensions with a self-interacting scalar field nonminimally coupled to gravity. Without specifying the form of the $f(R)$ function, solving the field equations we find that the Ricci scalar receives a nonlinear correction term which breaks the conformal invariance and leads to a massless black hole solution. When the nonlinear term decouples, we get a well-known hairy black hole solution with the scalar field conformally coupled to gravity. We also find that the entropy of our black hole may be higher than the corresponding conformal black hole which indicates that our solution may be thermodynamically preferred.

We reexamine a loosely trapped surface proposed as an indicator for strong gravity and an attractive gravity probe surface as that for gravity. Refined inequalities for them are derived by taking account of angular momentum, gravitational waves, and matters.

In this work, we analyze some judiciously chosen solutions of Kerr black holes with scalar hair (KBHsSH) of special interest for gravitational wave events originated from extreme mass ratio inspirals (EMRIs). Because of the off-center distribution of energy density, these spacetimes are warped in such a way that not all metric functions behave monotonically on the equatorial plane as in the exterior region of Kerr black holes (KBHs). This has great impact on the orbital parameters, which in turn affect the imprints on signals descendant from EMRIs in an adiabatic evolution. By investigating circular obit parameters, we unveil what qualitative features could be present in the signals that are new and distinct compared to KBHs, and we evolve some inspirals by employing the usual quadrupole formula approximation. We show that the frequencies of the emitted signals behave nonmonotonically, i.e., they can backward chirp, and for some particular cases they can become arbitrarily small, falling below LISA’s sensibility range. Finally, we present two sets of waveforms produced by a noncircular EMRI in which the compact object follows a type of geodesic motion typically present in spacetimes with a static ring, in which the compact object is periodically momentarily at rest.

We construct an inspiral-merger-ringdown eccentric gravitational-wave (GW) model for binary black holes with non-precessing spins within the effective-one-body formalism. This waveform model, SEOBNRv4EHM, extends the accurate quasi-circular SEOBNRv4HM model to eccentric binaries by including recently computed eccentric corrections up to 2PN order in the gravitational waveform modes, notably the $(l,|m|)=(2,2),(2,1),(3,3),(4,4),(5,5)$ multipoles. The waveform model reproduces the zero eccentricity limit with an accuracy comparable to the underlying quasicircular model, with the unfaithfulness of $\lesssim 1\%$ against quasicircular numerical-relativity (NR) simulations. When compared against 28 public eccentric NR simulations from the Simulating eXtreme Spacetimes catalog with initial orbital eccentricities up to $e\simeq 0.3$ and dimensionless spin magnitudes up to $+0.7$, the model provides unfaithfulness $<1\%$, showing that both the $(2,|2|)$-modes and the higher-order modes are reliably described without calibration to NR datasets in the eccentric sector. The waveform model SEOBNRv4EHM is able to qualitatively reproduce the phenomenology of dynamical captures, and can be extended to include spin-precession effects. It can be employed for upcoming observing runs with the LIGO-Virgo-KAGRA detectors and used to re-analyze existing GW catalogs to infer the eccentricity parameters for binaries with $e\lesssim 0.3$ (at 20 Hz or lower) and spins up to $\lesssim 0.9–0.95$. The latter is a promising region of the parameter space where some astrophysical formation scenarios of binaries predict mild eccentricity in the ground-based detectors’ bandwidth. Assessing the accuracy and robustness of the eccentric waveform model SEOBNRv4EHM for larger eccentricities and spins will require comparisons with, and, likely, calibration to eccentric NR waveforms in a larger region of the parameter space.

We study the existence and nature of Aretakis charge and its potentially observable imprint at a finite distance from the horizon (Ori coefficient) in near-extremal black hole backgrounds. Specifically, we consider the time evolution of horizon penetrating scalar and gravitational perturbations with compact support on near-extremal Reissner-Nordström and Kerr. We do this by numerically solving the Teukolsky equation and determining the Aretakis charge values on the horizon and at a finite distance from the black hole. We demonstrate that these values are no longer strictly conserved in the nonextremal case; however, their decay rate can be arbitrarily slow as the black hole approaches extremality allowing for the possibility of their observation as a transient hair.

In terms of the complex angular momentum method, we compute the absorption cross section by analyzing a massless test scalar field around conformally related black holes. First, we investigate circular null geodesics and thereby prove a precondition for calculating the absorption cross section in the context of conformally related black holes. Then we use the WKB approximation method to derive the analytic expression of Regge frequency and the oscillation part of absorption cross sections. We find that this oscillation part depends on the scale factor of conformal transformations. By taking the conformally related Schwarzschild-Tangherlini black hole as an example, we show that this regular black hole has substantially distinctive absorption behavior compared with singular black holes. Our result provides a new approach to distinguish a regular black hole from a singular one.

Black holes are expected to evaporate through the process of Hawking radiation. This process is expected to cause the uncertainty in a black hole’s position to grow to $\sim M^2/M_{Pl}^3$ over the course of it’s lifetime, even as its momentum spreads only by $\sim M_{Pl}$. For the black holes that have been observed, which have $M\ge M_{\odot }$, this greatly exceeds the Hubble volume. However, the decay of black holes and their quantum spreading, are delayed in the Universe while the influx of energy into the black holes exceeds their Hawking luminosity. We show that for these $M\ge M_{\odot }$ black holes, their decay outside galaxies and clusters is prevented far longer than it takes the black holes to be dragged well beyond the Hubble horizon, where their eventual decay occurs away from the prying eyes of any observer who has not hitched a ride with them. Meanwhile, black holes in an observer’s galaxy or cluster are themselves prevented from decaying long past the extinction of the last stars, and at least until their galaxy/cluster is swept clean of dark matter, in $\gg {10}^{25}\mathrm{y}$. Even then, if the black holes become unbound, then they are dragged beyond the Hubble radius before undergoing significant decay; if not, they remain in bound orbits, spreading at most over a subvolume of the galaxy/cluster, and long localized by scatterings to much smaller volumes.

We study the merger rate of primordial black holes (PBHs) in self-interacting dark matter (SIDM) halo models. To explore a numerical description of the density profile of SIDM halo models, we use the result of a previously performed simulation for SIDM halo models with $\sigma /m=10{\mathrm{cm}}^2{\mathrm{g}}^{-1}$. We also propose a concentration-mass-time relation that can explain the evolution of the halo density profile related to SIDM models. Furthermore, we investigate the encounter condition of PBHs that may have been randomly distributed in the medium of dark matter halos. Under these assumptions, we calculate the merger rate of PBHs within each halo considering SIDM halo models and compare the results with that obtained for cold dark matter (CDM) halo models. To do this, we employ the definition of the time after halo virialization as a function of halo mass. Also, by unifying the transition time for all halos using a quantity that depends on the halo mass and cross section of SIDM particles, we indicate that SIDM halo models, for $f_{\mathrm{PBH}}>0.32$, can generate sufficient PBH mergers in such a way that their numbers exceed the corresponding results obtained from CDM halo models. By considering the spherical-collapse halo mass function, we obtain similar results for the cumulative merger rate of PBHs, for $f_{\mathrm{PBH}}=1$. Moreover, we calculate the evolution of the PBH total merger rate as a function of redshift. The results show that SIDM models, when considering $f_{\mathrm{PBH}}>0.32$, could have generated more significant PBH mergers than CDM models at higher redshifts. To determine a constraint on the PBH abundance, we study the merger rate of PBHs in terms of their fraction and masses and compare those with the black hole merger rate estimated by the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detectors during the third observing run. The results demonstrate that within the context of SIDM halo models, the merger rate of $10M_{\odot }-10M_{\odot }$ events can potentially fall within the aLIGO window. We also estimate a relation between the fraction of PBHs and their masses, which is well consistent with our findings.

Cosmological backreaction corresponds to the effect of inhomogeneities of structure on the global expansion of the Universe. The main question surrounding this phenomenon is whether or not it is important enough to lead to measurable effects on the scale factor evolution, eventually explaining its acceleration or the Hubble tension. One of the most important results on this subject is the Buchert-Ehlers theorem [T. Buchert and J. Ehlers, Astron. Astrophys. 320, 1 (1997)] stating that backreaction is exactly zero when calculated using Newton’s theory of gravitation, which may not be the case in general relativity. It is generally said that this result implies that backreaction is a purely relativistic effect. We will show that this is not necessarily the case, in the sense that this implication does not apply to a universe which is still well-described by Newton’s theory on small scales but has a non-Euclidean topology. The theorem should therefore be generalized to account for such a scenario. In a heuristic calculation where we construct a theory which is locally Newtonian but defined on a non-Euclidean topology, we show that the backreaction is nonzero, meaning that it might be nonrelativistic depending on the topological class of our Universe. However, that construction is not unique and remains to be justified from a nonrelativistic limit of general relativity.