We investigate the prospects of searching dark sector models via exotic $Z$-boson decay at future $e^{+}{e}^{-}$ colliders with Giga $Z$ and Tera $Z$ options. Four general categories of dark sector models, Higgs portal dark matter, vector-portal dark matter, inelastic dark matter, and axionlike particles, are considered. Focusing on channels motivated by the dark sector models, we carry out a model-independent study of the sensitivities of $Z$ factories in probing exotic decays. The limits on branching ratios of the exotic $Z$ decay are typically $\mathcal{O}({10}^{-6}–{10}^{-8.5})$ for the Giga $Z$ and $\mathcal{O}({10}^{-7.5}–{10}^{-11})$ for the Tera $Z$, and they are compared with the projection for the high luminosity LHC. We demonstrate that future $Z$ factories can provide its unique and leading sensitivity and highlight the complementarity with other experiments, including the indirect and direct dark matter search limits and the existing collider limits. Future $Z$ factories will play a leading role in uncovering the hidden sector of the Universe in the future.

In the framework of BLMSSM, the Higgs decays $h^0\to Z\gamma$ and $h^0\to m_{V}Z$ are studied where $m_V$ represents a vector meson ($\rho ,\omega ,\varphi ,J/\psi ,\mathrm{\Upsilon }$, etc.). Corrections to the $CP$-even and $CP$-odd $h^0\gamma Z$ couplings occur via loop diagrams where new particles are involved. Actually both of them obviously influence the decay rates of $h^0\to Z\gamma$ and $h^0\to m_{V}Z$. Concretely, our obtained numerical result shows that the decay width of $h^0\to Z\gamma$ can be 1.3 times larger than the prediction of the Standard Model (SM). For the light mesons ($\rho$, $\omega$), the corrections to $h^0\to m_{V}Z$ are within 15%–20%, still consistent with the SM results. The results of this work would encourage a detection on $h^0\to Z\gamma$ at LHC for exploring new physics beyond SM.

We perform a systematic study of the Dirac neutrino masses which arise from a dimension five effective operator with a singlet scalar. We identify all possible realizations of this operator at tree level and one-loop level. The corresponding predictions for the particle content and neutrino mass matrix are presented. We add a $Z_2$ symmetry to forbid the renormalizable Yukawa coupling, and non-Abelian discrete flavor symmetry can be used to forbid tree level diagrams in non-genuine one-loop models. The electrically neutral particle mediating the loop diagram could be dark matter candidate. We give the possible dark matter particles and the restrictions on the parameter $\alpha$ for each model.

We present a general technique for addressing sign problems that arise in Monte Carlo simulations of field theories. This method deforms the domain of the path integral to a manifold in complex field space that maximizes the average sign (therefore reducing the sign problem) within a parametrized family of manifolds. We presents results for the $1+1$ dimensional Thirring model with Wilson fermions on lattice sizes up to $40\times 10$. This method reaches higher $\mu$ than previous techniques while substantially decreasing the computational time required.

We discuss a scenario in which the $P_c(4450{)}^{+}$ heavy pentaquark is a ${\mathrm{\Sigma }}_c{\overline{D}}^{*}\text{−}{\mathrm{\Lambda }}_c(2595)\overline{D}$ molecule. The ${\mathrm{\Lambda }}_{c1}\overline{D}\to {\mathrm{\Sigma }}_c{\overline{D}}^{*}$ transition is mediated by the exchange of a pion almost on the mass shell that generates a long-range $1/r^2$ potential. This is analogous to the effective force that is responsible for the Efimov spectrum in three-boson systems interacting through short-range forces. The equations describing this molecule exhibit approximate scale invariance, which is anomalous and broken by the solutions. If the $1/r^2$ potential is strong enough this symmetry survives in the form of discrete scale invariance, opening the prospect of an Efimov-like geometrical spectrum in two-hadron systems. For a molecular pentaquark with quantum numbers ${\frac{3}{2}}^{-}$ the attraction is not enough to exhibit discrete scale invariance, but this prospect might very well be realized in a ${\frac{1}{2}}^{+}$ pentaquark or in other hadron molecules involving transitions between particle channels with opposite intrinsic parity and a pion near the mass shell. A very good candidate is the ${\mathrm{\Lambda }}_c(2595){\overline{\mathrm{\Xi }}}_b-{\mathrm{\Sigma }}_c{{\overline{\mathrm{\Xi }}}_b}^{\prime }$ molecule. Independently of this, the $1/r^2$ force is expected to play a very important role in the formation of this type of hadron molecule, which points to the existence of ${\frac{1}{2}}^{+}$ ${\mathrm{\Sigma }}_c{D}^{*}\text{−}{\mathrm{\Lambda }}_c(2595)D$ and $1^{+}$ ${\mathrm{\Lambda }}_c(2595){\mathrm{\Xi }}_b-{\mathrm{\Sigma }}_c{\mathrm{\Xi }}_b^{\prime }$ molecules and $0^{+}/1^{-}$ ${\mathrm{\Lambda }}_c(2595){\overline{\mathrm{\Xi }}}_b-{\mathrm{\Sigma }}_c{{\overline{\mathrm{\Xi }}}_b}^{\prime }$ baryonia.

We have investigated ${\mathrm{\Omega }}_c$ states that are dynamically generated from the meson-baryon interaction. We use an extension of the local hidden gauge to obtain the interaction from the exchange of vector mesons. We show that the dominant terms come from the exchange of light vectors, where the heavy quarks are spectators. This has as a consequence that heavy quark symmetry is preserved for the dominant terms in the ($1/m_Q$) counting, and also that the interaction in this case can be obtained from the SU(3) chiral Lagrangians. We show that for a standard value for the cutoff regulating the loop, we obtain two states with $J^P={1/2}^{-}$ and two more with $J^P={3/2}^{-}$, three of them in remarkable agreement with three experimental states in mass and width. We also make predictions at higher energies for states of vector-baryon nature.

The next-to-next-to-leading-order (NNLO) pQCD prediction for the $\gamma {\gamma }^{*}\to {\eta }_c$ form factor was evaluated in 2015 using nonrelativistic QCD (NRQCD). A strong discrepancy between the NRQCD prediction and the BABAR measurements was observed. Until now there has been no solution for this puzzle. In this paper, we present a NNLO analysis by applying the Principle of Maximum Conformality (PMC) to set the renormalization scale. By carefully dealing with the light-by-light diagrams at the NNLO level, the resulting high precision PMC prediction agrees with the BABAR measurements within errors, and the conventional renormalization scale uncertainty is eliminated. The PMC is consistent with all of the requirements of the renormalization group, including scheme-independence. The application of the PMC thus provides a rigorous solution for the $\gamma {\gamma }^{*}\to {\eta }_c$ form factor puzzle, emphasizing the importance of correct renormalization scale-setting. The results also support the applicability of NRQCD to hard exclusive processes involving charmonium.

The present article is the follow-up work of Phys. Rev. D 94, 094006 (2016), where we have extended the study of quarkonia dissociation in (momentum) anisotropic hot QCD medium. As evident by the experimentally observed collective flow at the RHIC and LHC, the momentum anisotropy is present at almost all the stages after the collision, and therefore, it is important to include its effects in the analysis. Employing the in-medium (corrected) potential while considering the anisotropy (both oblate and prolate cases) in the medium, the thermal widths and the binding energies of the heavy quarkonia states ($s$-wave charmonia and $s$-wave bottomonia specifically, for radial quantum numbers $n=1$ and 2) have been determined. The hot QCD medium effects have been included by employing a quasiparticle description. The presence of anisotropy has modified the potential and then the thermal widths and binding energies of these states in a significant manner. The results show a quite visible shift in the values of dissociation temperatures as compared to the isotropic case. Further, the hot QCD medium interaction effects suppress the dissociation temperature as compared to the case where we consider the medium as a noninteracting ultrarelativistic gas of quarks (antiquarks) and gluons.

We study the dual chiral density wave (DCDW) in nuclear matter using a hadronic model with the parity doublet structure. We first extend the ordinary DCDW ansatz so as to incorporate the effect of an explicit chiral symmetry breaking. Then via numerically evaluating and minimizing the effective potential, we determine the phase structure. We find, in addition to the ordinary DCDW phase where the space average of the chiral condensate vanishes, a new DCDW phase with a nonvanishing space average depending on the value of the chiral invariant mass parameter.

Using the local hidden gauge approach, we study the possibility of the existence of bottom strange molecular states with isospin 0. We find three bound states with spin parity $0^{+}$, $1^{+}$, and $2^{+}$ generated by the ${\overline{K}}^{*}{B}^{*}$ and $\omega B_s^{*}$ interaction, among which the state with spin 2 can be identified as $B_{s2}^{*}(5840)$. In addition, we also study the ${\overline{K}}^{*}B$ and $\omega B_s$ interaction and find a bound state which can be associated to $B_{s1}(5830)$. In addition, the $\overline{K}{B}^{*}$, $\eta B_s^{*}$, $\overline{K}B$, and $\eta B_s$ systems are studied, and two bound states are predicted. We expect that further experiments can confirm our predictions.

The charm semileptonic decays $D^{+}\to \eta e^{+}{\nu }_e$ and $D^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e$ are studied with a sample of $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector. We measure the branching fractions for $D^{+}\to \eta e^{+}{\nu }_e$ to be $(10.74\pm 0.81\pm 0.51)\times {10}^{-4}$, and for $D^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e$ to be $(1.91\pm 0.51\pm 0.13)\times {10}^{-4}$, where the uncertainties are statistical and systematic, respectively. In addition, we perform a measurement of the form factor in the decay $D^{+}\to \eta e^{+}{\nu }_e$. All the results are consistent with those obtained by the CLEO-c experiment.

We explore the transition to hydrodynamics in a weakly coupled model of quark-gluon plasma given by kinetic theory in the relaxation-time approximation with conformal symmetry. We demonstrate that the gradient expansion in this model has a vanishing radius of convergence due to the presence of a transient (nonhydrodynamic) mode, in a way similar to results obtained earlier in strongly coupled gauge theories. This suggests that the mechanism by which hydrodynamic behavior emerges is the same, which we further corroborate by a novel comparison between solutions of different weakly and strongly coupled models. However, in contrast with other known cases, we find that not all the singularities of the analytic continuation of the Borel transform of the gradient expansion correspond to transient excitations of the microscopic system; some of them reflect analytic properties of the kinetic equation when the proper time is continued to complex values.

Curved momentum spaces associated to the $\kappa$-deformation of the ($3+1$) de Sitter and anti–de Sitter algebras are constructed as orbits of suitable actions of the dual Poisson-Lie group associated to the $\kappa$-deformation with nonvanishing cosmological constant. The $\kappa$-de Sitter and $\kappa$-anti–de Sitter curved momentum spaces are separately analyzed, and they turn out to be, respectively, half of the ($6+1$)-dimensional de Sitter space and half of a space with $\mathrm{SO}(4,4)$ invariance. Such spaces are made of the momenta associated to spacetime translations and the “hyperbolic” momenta associated to boost transformations. The known $\kappa$-Poincaré curved momentum space is smoothly recovered as the vanishing cosmological constant limit from both of the constructions.

The baby Skyrme model is studied in the presence of an isospin chemical potential. The inclusion of the chemical potential leads to an asymmetric vacuum. As a result, the residual $SO(2)$ symmetry of the model is broken into the discrete ${\mathbb{Z}}_2$ group. Nontrivial topological field configurations are found to be allowed in the model. We obtained numerical solutions for the solitons on top of the new vacuum by minimizing the energy functional using a simulated annealing algorithm. All the calculations were performed by relaxing the rotational symmetry inherent to the hedgehog approximation. The corresponding soliton solutions exhibit discrete symmetries imposed by the new vacuum.

We develop a resummation approach based on Meijer-$G$ functions and apply it to approximate the Borel sum of divergent series and the Borel-Écalle sum of resurgent transseries in quantum mechanics and quantum field theory (QFT). The proposed method is shown to vastly outperform the conventional Borel-Padé and Borel-Padé-Écalle summation methods. The resulting Meijer-$G$ approximants are easily parametrized by means of a hypergeometric ansatz and can be thought of as a generalization to arbitrary order of the Borel-hypergeometric method [Mera et al., Phys. Rev. Lett. 115, 143001 (2015)]. Here we demonstrate the accuracy of this technique in various examples from quantum mechanics and QFT, traditionally employed as benchmark models for resummation, such as zero-dimensional ${\varphi }^4$ theory; the quartic anharmonic oscillator; the calculation of critical exponents for the $N$-vector model; ${\varphi }^4$ with degenerate minima; self-interacting QFT in zero dimensions; and the summation of one- and two-instanton contributions in the quantum-mechanical double-well problem.

The final stage of a binary black hole merger is ringdown, in which the system is described by a Kerr black hole with quasinormal mode perturbations. It is far from straightforward to identify the time at which the ringdown begins. Yet determining this time is important for precision tests of the general theory of relativity that compare an observed signal with quasinormal mode descriptions of the ringdown, such as tests of the no-hair theorem. We present an algorithmic method to analyze the choice of ringdown start time in the observed waveform. This method is based on determining how close the strong field is to a Kerr black hole (Kerrness). Using numerical relativity simulations, we characterize the Kerrness of the strong-field region close to the black hole using a set of local, gauge-invariant geometric and algebraic conditions that measure local isometry to Kerr. We produce a map that associates each time in the gravitational waveform with a value of each of these Kerrness measures; this map is produced by following outgoing null characteristics from the strong and near-field regions to the wave zone. We perform this analysis on a numerical relativity simulation with parameters consistent with GW150914—the first gravitational-wave detection. We find that the choice of ringdown start time of 3 ms after merger used in the GW150914 study [B. P. Abbott et al. (Virgo Collaboration and LIGO Scientific Collaboration), Phys. Rev. Lett. 116, 221101 (2016).] to test general relativity corresponds to a high dimensionless perturbation amplitude of $\sim 7.5\times {10}^{-3}$ in the strong-field region. This suggests that in higher signal-to-noise detections, one would need to start analyzing the signal at a later time for studies that depend on the validity of black hole perturbation theory.

An analogue model for the ${\mathrm{AdS}}_2$ spacetime has been recently introduced by Mosna et al. [Phys. Rev. D 94, 104065 (2016)] by considering sound waves propagating on a fluid with an ill-defined velocity profile at its source/sink. The wave propagation is then uniquely defined only when one imposes an extra boundary condition at the source/sink (which corresponds to the spatial infinity of ${\mathrm{AdS}}_2$). Here we show that, once this velocity profile is smoothed out at the source/sink, the need for extra boundary conditions disappears. This, in turn, corresponds to deformations of the ${\mathrm{AdS}}_2$ spacetime near its spatial infinity. We also examine how this regularization of the velocity profile picks up a specific boundary condition for the idealized system, so that both models agree in the long wavelength limit.

Chameleon theories of gravity predict that the gaseous component of isolated dwarf galaxies rotates with a faster velocity than the stellar component. In this paper, we exploit this effect to obtain new constraints on the model parameters using the measured rotation curves of six low surface brightness galaxies. For $f(R)$ theories, we rule out values of $f_{R0}>{10}^{-6}$. For more general theories, we find that the constraints from Cepheid variable stars are currently more competitive than the bounds we obtain here but we are able to rule out self-screening parameters ${\chi }_c>{10}^{-6}$ for fifth-force strengths (coupling of the scalar to matter) as low as 0.05 the Newtonian force. This region of parameter space has hitherto been inaccessible to astrophysical probes. We discuss the future prospects for improving these bounds.

Adopting the Landau-Lifshiftz method of classical fluctuations, we determine the statistical average strength of the fluctuations of the energy flux on the apparent horizon of a homogeneous and isotropic universe described by Einstein gravity. We find that the fluctuations increase with the temperature of the horizon and decrease with its area, in accordance with the features of systems where gravity can be neglected. We further find, on the one hand, that the fluctuations vanish in the cosmological constant dominated de Sitter expansion and, on the other hand, that the domination of phantom fields is excluded. The reasonableness of the results we have obtained lend support to the view that the Universe behaves as a normal thermodynamic system.

We apply a recently developed method to directly measure the gravitational lensing power spectrum from CMB power spectra to the Planck satellite data. This method allows us to analyze the tension between the temperature power spectrum and lens reconstruction in a model-independent way. Even when allowing for arbitrary variations in the lensing power spectrum, the tension remains at the $2.4\sigma$ level. By separating the lensing and unlensed high redshift information in the CMB power spectra, we also show that under $\mathrm{\Lambda }\mathrm{CDM}$ the two are in tension at a similar level, whereas the unlensed information is consistent with lensing reconstruction. These anomalies are driven by the smoother acoustic peaks relative to $\mathrm{\Lambda }\mathrm{CDM}$ at $\ell \sim 1250–1500$. Both tensions relax slightly when polarization data are considered. This technique also isolates the one combination of the lensing power spectrum multipoles that the Planck CMB power spectra currently constrain and can be straightforwardly generalized to future data when CMB power spectra constrain multiple aspects of lensing which are themselves correlated with lensing reconstruction.