We investigate a new bound on the low reheating temperature in a scenario where the Universe experiences early matter domination before reheating after which the standard big bang cosmology begins. In many models of dark matter (DM), the small scale fluctuations of DM grow during the early matter-domination era and seed the formation of the ultracompact minihalos (UCMHs). Using the constraints on the number of UCMHs from gamma-ray observations, we find a lower bound on the reheating temperature between $\mathcal{O}(10)–\mathcal{O}(100)\mathrm{MeV}$ for WIMP dark matter depending on the nature of DM. A similar bound could be obtained for non-WIMP dark matter by observing UCMHs gravitationally such as pulsar timing, microlensing and so on, in some future observations.

We present a study of transverse single-spin asymmetries (SSAs) in $p^{\uparrow }p\to J/\psi X$ and $p^{\uparrow }p\to DX$ within the framework of the generalized parton model (GPM), which includes both spin and transverse momentum effects, and show how they can provide useful information on the still almost unknown gluon Sivers function. Moreover, by adopting a modified version of this model, named color gauge invariant (CGI) GPM, we analyze the impact of the initial- and final-state interactions on our predictions. As a consequence, we find that these two processes are sensitive to different gluon Sivers functions, which can be expressed as linear combinations of two distinct, universal gluon distributions. We therefore define proper observables which could allow for a separate extraction of these two independent Sivers functions. At the same time, we show how it would be possible to discriminate between the GPM and the CGI-GPM approaches by comparing the corresponding estimates of SSAs with present and future experimental results at RHIC.

We analyze the lepton number violating (LNV) meson decays that arise in a TeV scale left-right symmetry model. The right-handed Majorana neutrino $N$ along with the right-handed or Standard Model gauge bosons mediate the meson decays and provide a resonant enhancement of the rates if the mass of $N$ ($M_N$) lies in the range $\sim (100\mathrm{MeV}–5\mathrm{GeV})$. Using the expected upper limits on the number of events for the LNV decay modes $M_1^{+}\to {\ell }^{+}{\ell }^{+}{\pi }^{-}$ ($M_1=B$, $D$, $D_s$, $K$), we derive constraints plausible on the mass of the right handed charged gauge boson by future searches at the ongoing NA62 and LHCb experiments at CERN, the upcoming Belle II at SuperKEK, as well as at the proposed future experiments, SHiP and FCC-ee. These bounds are complimentary to the limits from the same-sign dilepton search at the Large Hadron Collider (LHC). The very high intensity of charmed mesons expected to be produced at SHiP will result in a far more stringent bound, $M_{W_R}>18.4\mathrm{TeV}$ (corresponding to $M_N=1.46\mathrm{GeV}$), than the other existing bounds from collider and neutrinoless double beta decay searches.

We explore double Higgs production via gluon fusion in the $b\overline{b}\gamma \gamma$ channel at the high-luminosity LHC using machine learning tools. We first propose a Bayesian optimization approach to select cuts on kinematic variables, obtaining a 30%–50% increase in the significance compared to current results in the literature. We show that this improvement persists once systematic uncertainties are taken into account. We next use boosted decision trees (BDT) to further discriminate signal and background events. Our analysis shows that a joint optimization of kinematic cuts and BDT hyperparameters results in an appreciable improvement in the significance. Finally, we perform a multivariate analysis of the output scores of the BDT. We find that assuming a very low level of systematics, the techniques proposed here will be able to confirm the production of a pair of standard model Higgs bosons at $5\sigma$ level with $3{\mathrm{ab}}^{-1}$ of data. Assuming a more realistic projection of the level of systematics, around 10%, the optimization of cuts to train BDTs combined with a multivariate analysis delivers a respectable significance of $4.6\sigma$. Even assuming large systematics of 20%, our analysis predicts a $3.6\sigma$ significance, which represents at least strong evidence in favor of double Higgs production. We carefully incorporate background contributions coming from light flavor jets or $c$ jets being misidentified as $b$ jets and jets being misidentified as photons in our analysis.

On the basis of Lüscher’s finite volume formula, a simple test (consistency check or sanity check) is introduced and applied to inspect the recent claims of the existence of the nucleon-nucleon ($NN$) bound state(s) for heavy quark masses in lattice QCD. We show that the consistency between the scattering phase shifts at $k^2>0$ and/or $k^2<0$ obtained from the lattice data and the behavior of phase shifts from the effective range expansion (ERE) around $k^2=0$ exposes the validity of the original lattice data; otherwise, such information is hidden in the energy shift $\mathrm{\Delta }E$ of the two nucleons on the lattice. We carry out this consistency check for all the lattice results in the literature claiming the existence of the $NN$ bound state(s) for heavy quark masses and find that (i) some of the $NN$ data show a clear inconsistency between the behavior of ERE at $k^2>0$ and that at $k^2<0$, (ii) some of the $NN$ data exhibit a singular behavior of the low-energy parameter (such as the divergent effective range) at $k^2<0$, (iii) some of the $NN$ data have the unphysical residue for the bound-state pole in the $S$ matrix, and (iv) the rest of the $NN$ data are inconsistent among themselves. Furthermore, we raise a caution of using the ERE in the case of the multiple bound states. Our finding, together with the fake plateau problem previously pointed out by the present authors, brings a serious doubt on the existence of the $NN$ bound states for pion masses heavier than 300 MeV in the previous studies.

Recent $N_f=2+1$ lattice data for meson-meson scattering in the $p$-wave and with isospin $I=1$ are analyzed using a unitarized model inspired by chiral perturbation theory in the inverse-amplitude formulation for two and three flavors. Chiral extrapolations are performed that postdict phase shifts extracted from experiment quite well. In addition, the low-energy constants are compared to the ones from a recent analysis of $N_f=2$ lattice QCD simulations to check for the consistency of the hadronic model used here. Some inconsistencies are detected in the fits to $N_f=2+1$ data, in contrast to the previous analysis of $N_f=2$ data.

We employ dimension-4 operators to improve the local vector and axial-vector currents and calculate the nucleon isovector axial coupling $g_A^3$ with overlap valence on $2+1$-flavor domain wall fermion (DWF) sea. Using the equality of $g_A^3$ from the spatial and temporal components of the axial-vector current as a normalization condition, we find that $g_A^3$ is increased by a few percent towards the experimental value. The excited-state contamination has been taken into account with three time separations between the source and sink. The improved axial charges $g_A^3(24I)=1.22(4)(3)$ and $g_A^3(32I)=1.21(3)(3)$ are obtained on a $24^3\times 64$ lattice at pion mass of 330 MeV and a $32^3\times 64$ lattice at pion mass 300 MeV and are increased by 3.4% and 1.7% from their unimproved values, respectively. We have also used clover fermions on the same DWF configurations and find the same behavior for the local axial charge as that with overlap fermions.

This paper is devoted to the study of vortical susceptibility of chiral condensate. We show that this parameter can be derived in two ways. First we obtain this using the spectrum of the Dirac operator in a metric of a curved space-time, which corresponds to rotation. Second we propose some variants of computation of the expression for the susceptibility via the holographic approach to QCD.

In the extended quasidilaton massive gravity we perform a nonlinear transformation of the shift vector and then calculate the second derivatives of the Hamiltonian density with respect to the lapse function and the (nonlinearly transformed) shift vector. It is then shown that the $4\times 4$ Hessian matrix is invertible, meaning that the equations of motion for the lapse function and the shift vector simply determine themselves. Therefore, there is no primary constraint that removes the Boulware-Deser ghost.

Binary black hole systems are among the most important sources for gravitational wave detection. They are also good objects for theoretical research for general relativity. A gravitational waveform template is important to data analysis. An effective-one-body-numerical-relativity (EOBNR) model has played an essential role in the LIGO data analysis. For future space-based gravitational wave detection, many binary systems will admit a somewhat orbit eccentricity. At the same time, the eccentric binary is also an interesting topic for theoretical study in general relativity. In this paper, we construct the first eccentric binary waveform model based on an effective-one-body-numerical-relativity framework. Our basic assumption in the model construction is that the involved eccentricity is small. We have compared our eccentric EOBNR model to the circular one used in the LIGO data analysis. We have also tested our eccentric EOBNR model against another recently proposed eccentric binary waveform model; against numerical relativity simulation results; and against perturbation approximation results for extreme mass ratio binary systems. Compared to numerical relativity simulations with an eccentricity as large as about 0.2, the overlap factor for our eccentric EOBNR model is better than 0.98 for all tested cases, including spinless binary and spinning binary, equal mass binary, and unequal mass binary. Hopefully, our eccentric model can be the starting point to develop a faithful template for future space-based gravitational wave detectors.

The ${\overline{B}}_q^{*}\to DP$, $DV$ weak decays are studied with the perturbative QCD approach, where $q=u$, $d$ and $s$; $P$ and $V$ denote the ground $SU(3)$ pseudoscalar and vector meson nonet. It is found that the branching ratios for the color-allowed ${\overline{B}}_q^{*}\to D_q{\rho }^{-}$ decays can reach up to ${10}^{-9}$ or more and should be promisingly measurable at the running LHC and forthcoming SuperKEKB experiments in the near future.

Due to its relevance for the characterization of the quark-gluon plasma (QGP) produced in ultrarelativistic heavy-ion collisions, conductivity is among the most important transport coefficients of QGP. By employing kinetic theory and the Kubo formula, we present a general derivation of electric and Hall conductivity of relativistic quark-gluon gas in the magnetic field. Furthermore, we investigate the temperature dependence of electric conductivity and Hall conductivity of QGP in magnetic field. We find that presence of the magnetic field leads to a decrease of the electric conductivity, especially at low temperatures. Finally, we present the relationship between conductivity and the polarization tensor of QGP.

In this paper, a general case of conformal invariant vacuum nonlinear electrodynamics is studied. We analyze the consistency of this electrodynamics model with fundamental principles such as causality, unitarity, and the Ellis-Hawking dominant energy condition. Certain features of the electromagnetic waves in this model are investigated.

We have recently studied theoretical constraints on the parameters of a two Higgs doublet model (2HDM) augmented with a color-octet scalar. In this paper we consider the consequences of requiring the model to remain valid up to very high energy scales. The acceptable region of parameter space is reduced when one insists on vacuum stability, perturbative unitarity and the absence of Landau poles below a given scale. As the scale to which we require the model to be valid is increased, the acceptable region of parameter space for the 2HDM sector is reduced in such a way that it approaches the alignment limit, $\cos (\beta -\alpha )\to 0$, and the masses of $H^0$, $A$ and $H^{\pm }$ are pushed closer to each other. The parameters of the color-octet sector are also restricted to an increasingly smaller region.

We revisit a scenario with an enhanced top Yukawa coupling in vectorlike quark (VLQ) models, where the top Yukawa coupling is larger than the standard model value and the lightest VLQ has a negative Yukawa coupling. We find that the parameter space satisfying the LHC bounds of the Higgs signal strengths consistently with the precision measurements is rather wide. Because the Lagrangian parameters of the Yukawa couplings are large, such scenario can be realized in some strongly interacting theories. It also turns out that there is a noticeable relation between the contributions of the triangle and box diagrams in the $gg\to hh$ process by using the lowest order of the $1/M$ expansion where $M$ is the heavy mass running in the loops.

We investigate the spectrum and IR properties of the SU(3) “sextet” model with two Dirac fermions in the two-index symmetric representation via lattice simulations. This model is a prime candidate for a realization of walking technicolor, which features a minimal matter content and it is expected to be inside or very close to the lower boundary of the conformal window. We use the Wilson discretization for the fermions and map the phase structure of the lattice model. We study several spectral and gradient flow observables both in the bulk and the weak coupling phases. While in the bulk phase we find clear signs of chiral symmetry breaking, in the weak coupling phase there is no clear indication for it, and instead the chiral limit of the model seems compatible with an IR-conformal behavior.

Fluctuations of conserved charges allow us to study the chemical composition of hadronic matter. A comparison between lattice simulations and the hadron resonance gas (HRG) model suggested the existence of missing strange resonances. To clarify this issue we calculate the partial pressures of mesons and baryons with different strangeness quantum numbers using lattice simulations in the confined phase of QCD. In order to make this calculation feasible, we perform simulations at imaginary strangeness chemical potentials. We systematically study the effect of different hadronic spectra on thermodynamic observables in the HRG model and compare to lattice QCD results. We show that, for each hadronic sector, the well-established states are not enough in order to have agreement with the lattice results. Additional states, either listed in the Particle Data Group booklet (PDG) but not well established, or predicted by the quark model (QM), are necessary in order to reproduce the lattice data. For mesons, it appears that the PDG and the quark model do not list enough strange mesons, or that, in this sector, interactions beyond those included in the HRG model are needed to reproduce the lattice QCD results.

As with parton distributions, flexible phenomenological parametrizations of generalized parton distributions (GPDs) are essential for their extraction from data. The large number of constraints imposed on GPDs make simple Lorentz covariant models viable; but, such models are often incomplete in that they employ the impulse approximation. Using the GPD of the pion as a test case, we show that the impulse approximation can lead to violation of the positivity bound required of GPDs. We focus on a particular model of the pion bound-state vertex that was recently proposed and demonstrate that satisfying the bound is not guaranteed by Lorentz covariance. Violation of the positivity bound is tied to a problematic mismatch between the behavior of the quark distribution at the end point and the crossover value of the GPD.

In the framework of the $k_T$-factorization approach, the production and polarization of prompt $J/\psi$ mesons at the LHC energies is studied. Our consideration is based on the nonrelativistic QCD formalism for bound states and off-shell amplitudes for hard partonic subprocesses. Both the direct production mechanism and feed-down contributions from ${\chi }_c$ and $\psi (2S)$ decays are taken into account. The transverse momentum dependent (or unintegrated) gluon densities in a proton were derived from Ciafaloni-Catani-Fiorani-Marchesini evolution equation or, alternatively, were chosen in accordance with Kimber-Martin-Ryskin prescription. The nonperturbative color-octet matrix elements were first deduced from the fits to the latest CMS data on $J/\psi$ transverse momentum distributions and then applied to describe the ATLAS and LHCb data on $J/\psi$ production and polarization at $\sqrt{s}=7$, 8 and 13 TeV. We perform an estimation of polarization parameters ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$, and ${\lambda }_{\theta \varphi }$ which determine $J/\psi$ spin density matrix and demonstrate that treating the soft gluon emission as a series of explicit color-electric dipole transitions within NRQCD leads to unpolarized $J/\psi$ production at high transverse momenta, that is in qualitative agreement with the LHC data.

Within the QCD light-cone sum rule (LCSR) approach, we investigate the transition form factors of $D\to a_0(980)$ up to the twist-3 light-cone distribution amplitudes (LCDAs) of the scalar meson $a_0(980)$ in the two-quark picture. Using these form factors, we calculate the differential decay widths and branching ratios of the $D\to a_0(980)e^{+}{\nu }_e$ semileptonic decays. We obtain $\mathcal{B}(D^0\to a_0^{-}(980)e^{+}{\nu }_e)=(4.08_{-1.22}^{+1.37})\times {10}^{-4}$ and $\mathcal{B}(D^{+}\to a_0^0(980)e^{+}{\nu }_e)=(5.40_{-1.59}^{+1.78})\times {10}^{-4}$. The results are sensitive to the $a_0(980)$ inner structure. These decays can be searched for at the BESIII experiment, and any experimental observations will be useful to identify internal quark contents of the $a_0(980)$ meson, which will shed light on understanding theoretical models.