The stringent constraints from the direct searches for exotic scalars at the LHC, as well as indirect bounds from flavor physics measurements, have imposed severe restrictions on the parameter space of new physics models featuring extended Higgs sectors. In the type-II two-Higgs-doublet model (2HDM), this implies a lower bound on the charged Higgs masses of $\mathcal{O}(600\mathrm{GeV})$. In this work we analyze the phenomenology of a $Z_3$ symmetric three-Higgs-doublet model in the alignment limit focusing on the impact of flavor physics constraints on its parameter space. We show that the couplings of the two charged Higgs bosons in this model feature an additional suppression factor compared to type-II 2HDM. This gives rise to a significant relaxation of the flavor physics constraints in this model, allowing the charged Higgs masses to be as low as $\mathcal{O}(200\mathrm{GeV})$. We also consider the constraints coming from precision electroweak observables and the observed diphoton decay rate of the 125 GeV Higgs boson at the LHC. The bounds coming from the direct searches of nonstandard Higgs bosons at the LHC, particularly those from resonance searches in the ditau channel, prove to be very effective in constraining this scenario further.

We present a determination of the ratio of kaon and pion leptonic decay constants in isosymmetric QCD (ISOQCD), $f_K/f_{\pi }$, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration with $N_f=2+1+1$ flavors of Wilson-clover twisted-mass quarks, including configurations close to the physical point for all dynamical flavors. The simulations are carried out at three values of the lattice spacing ranging from $\sim 0.068$ to $\sim 0.092\mathrm{fm}$ with linear lattice size up to $L\sim 5.5\mathrm{fm}$. The scale is set by the particle data group (PDG) value of the pion decay constant, $f_{\pi }^{\text{ISO}\mathrm{QCD}}=130.4(2)\mathrm{MeV}$, at the ISOQCD pion point, $M_{\pi }^{\text{ISO}\mathrm{QCD}}=135.0(2)\mathrm{MeV}$, obtaining for the gradient-flow scales the values $w_0=0.17383(63)\mathrm{fm}$, $\sqrt{t_0}=0.14436(61)\mathrm{fm}$ and $t_0/w_0=0.11969(62)\mathrm{fm}$. The data are analyzed within the framework of SU(2) chiral perturbation theory without resorting to the use of renormalized quark masses. At the ISOQCD kaon point $M_K^{\text{ISO}\mathrm{QCD}}=494.2(4)\mathrm{MeV}$ we get $(f_K/f_{\pi }{)}^{\text{ISO}\mathrm{QCD}}=1.1995(44)$, where the error includes both statistical and systematic uncertainties. Implications for the Cabibbo-Kobayashi-Maskawa matrix element $|V_{us}|$ and for the first-row Cabibbo-Kobayashi-Maskawa unitarity are discussed.

High-accuracy $\mathrm{\Upsilon }$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $\gamma p\to \mathrm{\Upsilon }p$, from which the absolute value of the $\mathrm{\Upsilon }p$-scattering length, $|{\alpha }_{\mathrm{\Upsilon }p}|$, can be extracted using a vector-meson dominance model. For this evaluation, we used $\mathrm{\Upsilon }$-meson photoproduction quasidata from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|{\alpha }_{\mathrm{\Upsilon }p}|$ with the recently determined scattering lengths for $\omega p$, $\varphi p$, and $J/\psi p$ using the A2, CLAS, and GlueX experimental data are performed. The role of the “young” vector-meson effect is evaluated.

We calculate the leading-order QED radiative corrections to the process $e^{-}p\to e^{-}p{l}^{-}{l}^{+}$ in the soft-photon approximation, in two different energy regimes which are of relevance to extract nucleon structure information. In the low-energy region, this process is studied to better constrain the hadronic corrections to precision muonic hydrogen spectroscopy. In the high-energy region, the beam-spin asymmetry for double-virtual Compton scattering allows us to directly access the generalized parton distributions. We find that the soft-photon radiative corrections have a large impact on the cross sections and are therefore of paramount importance to extract the nucleon structure information from this process. For the forward-backward asymmetry, the radiative corrections are found to affect the asymmetry only around or below the 1% level, whereas the beam-spin asymmetry is not affected at all in the soft-photon approximation, which makes them gold-plated observables to extract nucleon structure information in both the low- and high-energy regimes.

Experimentally probing the charm-Yukawa coupling in the LHC experiments is important, but very challenging due to an enormous QCD background. We study a new channel that can be used to search for the Higgs decay $H\to c\overline{c}$, using the vector boson fusion (VBF) mechanism with an associated photon. In addition to suppressing the QCD background, the photon gives an effective trigger handle. We discuss the trigger implications of this final state that can be utilized in ATLAS and CMS. We propose a novel search strategy for $H\to c\overline{c}$ in association with VBF jets and a photon, where we find a projected sensitivity of about 13 times the SM charm-Yukawa coupling at 95% ${\mathrm{CL}}_s$ at High Luminosity LHC (HL-LHC). Our result is comparable and complementary to existing projections at the HL-LHC. We also discuss the implications of increasing the center of mass collision energy to 30 TeV and 100 TeV.

A search for time-dependent violation of the charge-parity symmetry in $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ decays is performed at the LHCb experiment using proton-proton collision data recorded from 2015 to 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. The $D^0$ meson is required to originate from a $D^{*}(2010{)}^{+}\to D^0{\pi }^{+}$ decay, such that its flavor at production is identified by the charge of the accompanying pion. The slope of the time-dependent asymmetry of the decay rates of $D^0$ and ${\overline{D}}^0$ mesons into the final states under consideration is measured to be $\mathrm{\Delta }{Y}_{K^{+}{K}^{-}}=(-2.3\pm 1.5\pm 0.3)\times {10}^{-4}$, $\mathrm{\Delta }{Y}_{{\pi }^{+}{\pi }^{-}}=(-4.0\pm 2.8\pm 0.4)\times {10}^{-4}$, where the first uncertainties are statistical and the second are systematic. These results are compatible with the conservation of the charge-parity symmetry at the level of 2 standard deviations and improve the precision by nearly a factor of 2.

Combining with the small-large black hole phase transition, the thermodynamic geometry has been well applied to study the microstructure for the charged anti–de Sitter (AdS) black hole. In this paper, we extend the geometric approach to the rotating Kerr-AdS black hole and aim to develop a general approach for the Kerr-AdS black hole. Treating the entropy and pressure as the fluctuation coordinates, we construct the Ruppeiner geometry for the Kerr-AdS black hole by making use of the Christodoulou-Ruffini-like squared-mass formula, which is quite different from the charged case. Employing the empirical observation of the corresponding scalar curvature, we find that, for the near-extremal Kerr-AdS black hole, the repulsive interaction dominates among its microstructure, while for far-from-extremal Kerr-AdS black hole, the attractive interaction dominates. The critical phenomenon is also observed for the scalar curvature. These results uncover the characteristic microstructure of the Kerr-AdS black hole. Such general thermodynamic geometry approach is worth generalizing to other rotating AdS black holes, and more interesting microstructure is expected to be discovered.

In this second part of a two-part paper, we discuss numerical simulations of a head-on merger of two nonspinning black holes. We resolve the fate of the original two apparent horizons by showing that after intersecting, their world tubes “turn around” and continue backwards in time. Using the method presented in the first paper [Phys. Rev. D 084083 (2021)] to locate these surfaces, we resolve several such world tubes evolving and connecting through various bifurcations and annihilations. This also draws a consistent picture of the full merger in terms of apparent horizons, or more generally, marginally outer trapped surfaces (MOTSs). The MOTS stability operator provides a natural mechanism to identify MOTSs which should be thought of as black hole boundaries. These are the two initial ones and the final remnant. All other MOTSs lie in the interior and are neither stable nor inner trapped.

In classical numerical relativity, marginally outer trapped surfaces (MOTSs) are the main tool to locate and characterize black holes. For five decades it has been known that during a binary merger, a new outer horizon forms around the initial apparent horizons of the individual holes once they are sufficiently close together. However the ultimate fate of those initial horizons has remained a subject of speculation. Recent axisymmetric studies have shed new light on this process and this pair of papers essentially completes that line of research: we resolve the key features of the post-swallowing axisymmetric evolution of the initial horizons. This first paper introduces a new shooting-method for finding axisymmetric MOTSs along with a reinterpretation of the stability operator as the analogue of the Jacobi equation for families of MOTSs. Here, these tools are used to study exact solutions and initial data. In the sequel paper [Phys. Rev. D 104, 084084 (2021)] they are applied to black hole mergers.

We investigate the quark deconfinement phase transition in the context of binary neutron star (BNS) mergers. We treat hadronic matter using a Brueckner-Hartree-Fock quantum many-body approach and modern two-body and three-body nuclear interactions derived within chiral effective field theory. Quark matter is modeled using an extended version of the bag model. We combine these approaches to construct a new finite-temperature composition-dependent equation of state (EOS) with a first-order phase transition between hadrons and deconfined quarks. We perform numerical relativity simulations of BNS mergers with this new EOS and compare results obtained with or without the deconfinment phase transition. We find that deconfined quark production in a neutron star merger results from matter crossing the phase boundary over a wide range of temperatures and densities. The softening of the EOS due to the phase transition causes the merger remnants to be more compact and to collapse to a black hole at earlier times. The phase transition is imprinted on the postmerger gravitational wave (GW) signal duration, amplitude, and peak frequency. However, this imprint is only detectable for binaries with sufficiently long-lived remnants. Moreover, the phase transition does not result in significant deviations from quasiuniversal relations for the postmerger GW peak frequency. Consequently, the postmerger GW peak frequency alone is not sufficient to conclusively exclude or confirm the presence of a phase transition in a BNS merger. We also study the impact of the phase transition on dynamical ejecta, remnant accretion disk masses, $r$-process nucleosynthetic yields and associated electromagnetic counterparts. While there are differences in the electromagnetic counterparts and nucleosynthesis yields between the purely hadronic models and the models with phase transitions, these can be primarily ascribed to the difference in remnant collapse time between the two, so they are degenerate with other effects. An exception is the nonthermal afterglow caused by the interaction of the fastest component of the dynamical ejecta and the interstellar medium, which is systematically boosted in the binaries with phase transition as a consequence of the more violent merger they experience.

High-energy positrons can be efficiently created through high-energy photons splitting into electron-positron pairs under the influence of the Coulomb field. Here we show that a new degree of freedom—the intrinsic orbital angular momentum (OAM)—can be introduced into relativistic positrons when the incident photons are twisted. We develop the full-twisted scattering theory to describe the transfer of angular momentum before and after the interaction. It is found that the total angular momentum (TAM) of the photon is equally distributed between the positron and electron. For each photon TAM value, the generated leptons gain a higher average OAM number when the photon spin is antiparallel to its TAM. The impact of photon polarization on the OAM spectrum profile and the scattering probability is more significant at small photon TAM numbers, owing to the various interaction channels influenced by flipping the photon spin. Our work provides the theoretical basis to study OAM physics in particle scattering and to obtain copious relativistic vortex positrons through the Beth-Heitler process.

From analysis of data produced by the BABAR experiment, the first upper bounds (90% C.L.) were obtained on the branching ratios $\mathrm{Br}(\tau \to e\gamma \gamma )<2.5\times {10}^{-4}$ and $\mathrm{Br}(\tau \to \mu \gamma \gamma )<5.8\times {10}^{-4}$. In addition, improved upper bounds (95% C.L.) were found on branching ratios $\mathrm{Br}(\tau \to eX)<1.4\times {10}^{-3}$ and $\mathrm{Br}(\tau \to \mu X)<2.0\times {10}^{-3}$, where $X$ is an undetected weakly interacting boson with mass $m_X<1.6\mathrm{GeV}/c^2$.

In the minimal supersymmetric extension of the Standard Model (MSSM) the Higgsino mass parameter $\mu$ appears both in the masses of the Higgs bosons and in the neutralino mass matrix. Electroweak finetuning therefore prefers small values of $|\mu |$. On the other hand, binolike neutralinos make a good dark matter candidate. We show that current direct search limits then impose a strong lower bound on $|\mu |$, in particular for $\mu >0$ or if the masses of the heavy Higgs bosons of the MSSM are near their current limit from LHC searches; these bounds on $|\mu |$ are typically much stronger than the ones from collider physics. There is therefore some tension between fine-tuning and neutralino dark matter in the MSSM. We also provide simple analytical expressions which in most cases closely reproduce the numerical results.

We apply a quantum teleportation protocol based on the Hayden-Preskill thought experiment to quantify how scrambling a given quantum evolution is. It has an advantage over the direct measurement of out-of-time ordered correlators when used to diagnose the information scrambling in the presence of decoherence effects stemming from a noisy quantum device. We demonstrate the protocol by applying it to two physical systems: Ising spin chain and SU(2) lattice Yang-Mills theory. To this end, we numerically simulate the time evolution of the two theories in the Hamiltonian formalism. The lattice Yang-Mills theory is implemented with a suitable truncation of Hilbert space on the basis of the Kogut-Susskind formalism. On a two-leg ladder geometry and with the lowest nontrivial spin representations, it can be mapped to a spin chain, which we call the Yang-Mills-Ising model and is also directly applicable to future digital quantum simulations. We find that the Yang-Mills-Ising model shows the signal of information scrambling at late times.

The decay $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}\eta$ is observed for the first time, using $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of $6.32{\mathrm{fb}}^{-1}$, collected by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV. The absolute branching fraction for this decay is measured to be $\mathcal{B}(D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}\eta )=(3.12\pm 0.13_{\mathrm{stat}}\pm 0.09_{\mathrm{syst}})\%$. The first amplitude analysis of this decay reveals the substructures in $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}\eta$ and determines the relative fractions and the phases among these substructures. The dominant intermediate process is $D_s^{+}\to a_1(1260{)}^{+}\eta ,a_1(1260{)}^{+}\to \rho (770{)}^0{\pi }^{+}$ with a branching fraction of $(1.73\pm 0.14_{\mathrm{stat}}\pm 0.08_{\mathrm{syst}})\%$. We also observe the $W$-annihilation process $D_s^{+}\to a_0(980{)}^{+}\rho (770{)}^0$, $a_0(980{)}^{+}\to {\pi }^{+}\eta$ with a branching fraction of $(0.21\pm 0.08_{\mathrm{stat}}\pm 0.05_{\mathrm{syst}})\%$, which is larger than the branching fractions of other measured pure $W$-annihilation decays by 1 order of magnitude.

In the context of the gauge/gravity duality, using the proposed candidate $c$-function, which is derived from the entanglement entropy of a strip-shaped region, we investigate the RG flow for $d+1$-dimensional quantum field theories with broken Lorentz and rotational symmetries in the IR, but preserved conformal invariance in the UV boundary. We examine conditions of monotonicity of the $c$-function for holographic anisotropic theories dual to the Einstein gravity via the constraints imposed by the null energy conditions. We consider near UV and IR behaviors and identify the sufficient conditions that guarantee the $c$ function decreases monotonically along the RG flows.

Scattering amplitudes computed by superstring perturbation theory are known to holomorphically split into chiral half-integrands at fixed internal loop momentum. It is established by direct computation that, upon reduction to the ordinary moduli space, the chiral half-integrands of the superstring match those computed by the ambitwistor string in the limit of zero tension (${\alpha }^{\prime }\to \infty$). Subtleties that arise at higher genus due to the nonprojectedness of the supermoduli space are considered and arguments as to their resolution are furnished.

We implement a dynamical resummation method (DRM) as an extension of the dynamical renormalization group to study the time evolution of infrared dressing in nongauge theories. Super renormalizable and renormalizable models feature infrared divergences similar to those of a theory at a critical point, motivating a renormalization group improvement of the propagator that yields a power-law decay of the survival probability $\propto t^{-\mathrm{\Delta }}$. The DRM confirms this decay, yields the dressed state, and determines that the anomalous dimension $\mathrm{\Delta }$ is completely determined by the slope of the spectral density at threshold independent of the ultraviolet behavior, suggesting certain universality for infrared phenomena. The dressed state is an entangled state of the charged and massless quanta. The entanglement entropy is obtained by tracing over the unobserved massless quanta. Its time evolution is determined by the DRM, is infrared finite, and describes the information flow from the initial single particle to the asymptotic multiparticle dressed state. We show that effective field theories of massless axionlike particles coupled to fermion fields do not feature infrared divergences and provide a criterion for infrared divergences in effective field theories valid for nongauge theories up to one loop.

A quantum-optics approach is used to study the nature of the acceleration radiation due to a random atomic cloud falling freely into a generalized Schwarzschild black hole through a Boulware vacuum. The properties of this horizon brightened acceleration radiation (HBAR) are analyzed with a master equation that is fully developed in a multimode format. A scheme for the coarse-graining average for an atomic cloud is considered, with emphasis on the random injection scenario, which is shown to generate a thermal state. The role played by conformal quantum mechanics (CQM) is shown to be critical for detailed balance via a Boltzmann factor governed by the near-horizon physics, with the unique selection of the Hawking temperature. The HBAR thermal state is the basis for a thermodynamic framework that parallels black hole thermodynamics.