QCD with imaginary chemical potential is free of the sign problem and exhibits a rich phase structure constraining the phase diagram at real chemical potential. We simulate the critical end point of the Roberge-Weiss transition at imaginary chemical potential for ${\mathrm{N}}_{\mathrm{f}}=2$ QCD on ${\mathrm{N}}_{\tau }=6$ lattices with standard Wilson fermions. As found on coarser lattices, the Roberge-Weiss end point is a triple point connecting the deconfinement/chiral transitions in the heavy/light quark mass region and changes to a second-order end point for intermediate masses. These regimes are separated by two tricritical values of the quark mass, which we determine by extracting the critical exponent $\nu$ from a systematic finite size scaling analysis of the Binder cumulant of the imaginary part of the Polyakov loop. We are able to explain a previously observed finite size effect afflicting the scaling of the Binder cumulant in the regime of three-phase coexistence. Compared to ${\mathrm{N}}_{\tau }=4$ lattices, the tricritical masses are significantly shifted. Exploratory results on ${\mathrm{N}}_{\tau }=8$ as well as comparison with staggered simulations suggest that much finer lattices are needed before a continuum extrapolation becomes feasible.

Through analyzing the $B_{(s)}$ charmed decays $B^0\to {\overline{D}}_0{f}_0(980)$ and $B_s\to {\overline{D}}_0{f}_0(980)$ within the framework of the perturbative QCD factorization approach and comparing with the current data, we find that there are two possible regions for the $f_0(980)-f_0(500)$ mixing angle $\theta$: one is centered at 34°–38° and the other falls into 142°–154°. The former can overlap mostly with one of the allowed angle regions extracted from the decay $B^0\to {\overline{D}}_0{f}_0(500)$. The branching fractions of $B_s$ decay modes are less sensitive to the mixing angle compared with those of $B$ decay modes. Especially, for the decay $B_s\to D^0{f}_0(980)$, its branching fraction changes only slightly between $(1.2–1.8)\times {10}^{-7}$ when the mixing angle $\theta$ runs from 0° to 180°. All of our results support the picture that the $f_0(980)$ is dominated by the two-quark component in the $B$ decay dynamic mechanism. Furthermore, the $s\overline{s}$ component is more important than the $q\overline{q}=(u\overline{u}+d\overline{d})/\sqrt{2}$ component. This point is different from $f_0(500)/\sigma$. Last but not least, our picture is not in conflict with the popular four-quark explanation.

We carry out a global analysis of the experimental data on the ${\chi }_c$ production cross section and the ratio $\sigma ({\chi }_{c2})/\sigma ({\chi }_{c1})$ at the LHC and the Tevatron. The related long-distance matrix elements (LDMEs) at both leading order (LO) and next-to-leading order (NLO) in the QCD coupling constant are renewed. We also present the transverse momentum distribution of the ${\chi }_c$ production cross section and the ratio $\sigma ({\chi }_{c2})/\sigma ({\chi }_{c1})$ for several experimental conditions and find that NLO predictions agree with all sets of experimental data. By contrast, at LO, one cannot explain all the data with a unique value of the color-octet LDME. A brief analysis of the nonrelativistic QCD scale dependence of the cross sections shows that, for the conditions we are concerned with in this paper, the dependence can be almost totally absorbed into the LDME.

We investigate the processes $e^{+}{e}^{-}\to \gamma J/\psi \varphi$, $\gamma J/\psi \omega$, and ${\pi }^{0}J/\psi \eta$ to search for the charmoniumlike states with hidden $s\overline{s}$, such as $Y(4140)$, $Y(4274)$, $X(4350)$, and $X(3915)$. These processes receive contributions from the charmed-strange meson rescatterings. When the center-of-mass energies of $e^{+}{e}^{-}$ scatterings are taken around the $D_{s0}(2317)D_s^{*}$, $D_{s1}(2460)D_s$, or $D_{s1}(2460)D_s^{*}$ threshold, the anomalous triangle singularities can be present in the rescattering amplitudes, which implies a nonresonance explanation about the resonancelike structures. The positions of the anomalous triangle singularities are sensitive to the kinematics, which offers us a criterion to distinguish the kinematic singularities from genuine particles.

We present a factorization formula for the inclusive production of the Higgs boson at large transverse momentum $P_T$ that includes all terms with the leading power of $1/P_T^2$. The cross section is factorized into convolutions of parton distributions, infrared-safe hard-scattering cross sections for producing a parton, and fragmentation functions that give the distribution of the longitudinal momentum fraction of the Higgs relative to the fragmenting parton. The infrared-safe cross sections and the fragmentation functions are perturbatively calculable. The most important fragmentation functions are those for which the fragmenting parton is the top quark, gluon, $W$, $Z$, and the Higgs itself. We calculate the fragmentation functions at leading order in the Standard Model coupling constants. The factorization formula enables the resummation of large logarithms of $P_T/M_H$ due to final-state radiation by integrating evolution equations for the fragmentation functions. By comparing the cross section for the process $q\overline{q}\to Ht\overline{t}$ from the leading-power factorization formula at leading order in the coupling constants with the complete leading-order cross section, we infer that the error in the factorization formula decreases to less than 5% for $P_T>600\mathrm{GeV}$ at a future 100 TeV collider.

A measurement of vector boson ($V$) production in conjunction with a $D^{*}(2010{)}^{+}$ meson is presented. Using a data sample corresponding to $9.7{\mathrm{fb}}^{-1}$ of proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$ produced by the Fermilab Tevatron, we reconstruct $V+D^{*+}$ samples with the CDF II detector. The $D^{*+}$ is fully reconstructed in the $D^{*}(2010{)}^{+}\to D^0(\to K^{-}{\pi }^{+}){\pi }^{+}$ decay mode. This technique is sensitive to the associated production of vector boson plus charm or bottom mesons. We measure the ratio of production cross sections $\sigma (W+D^{*})/\sigma (W)=[1.75\pm 0.13(\mathrm{stat})\pm 0.09(\mathrm{stat})]\%$ and $\sigma (Z+D^{*})/\sigma (Z)=[1.5\pm 0.4(\mathrm{stat})\pm 0.2(\mathrm{stat})]\%$ and perform a differential measurement of $d\sigma (W+D^{*})/d{p}_T(D^{*})$. Event properties are utilized to determine the fraction of $V+D^{*}(2010{)}^{+}$ events originating from different production processes. The results are in agreement with the predictions obtained with the pythia program, limiting possible contribution from non-standard-model physics processes.

Recently, an interesting inflationary scenario, named Gauss-Bonnet inflation, was proposed by Kanti et al. [Phys. Rev. D 92, 041302 (2015); Phys. Rev. D 92, 083524 (2015)]. In the model, there is no inflaton potential, but the inflaton couples to the Guass-Bonnet term. In the case of quadratic coupling, they find inflation occurs with a graceful exit. The scenario is attractive because of the natural setup. However, we show there exists a gradient instability in the tensor perturbations in this inflationary model. We further prove the no-go theorem for Gauss-Bonnet inflation without an inflaton potential.

In this paper, we find the Yangian algebra responsible for the integrability of the ${\mathrm{AdS}}_2\times S^2\times T^6$ superstring in the planar limit. We demonstrate the symmetry of the corresponding exact $S$ matrix in the massive sector, including the presence of the secret symmetry. We give two alternative presentations of the Hopf algebra. The first takes the usual canonical form, which, as the relevant representations are long, leads to a Yangian representation that is not of evaluation type. After investigating the relationship between cocommutativity, evaluation representations and the shortening condition, we find an alternative realization of the Yangian whose representation is of the evaluation type. Finally, we explore two limits of the $S$ matrix. The first is the classical $r$ matrix, where we rediscover the need for a secret symmetry also in this context. The second is the simplifying zero-coupling limit. In this limit, taking the $S$ matrix as a generating $R$ matrix for the algebraic Bethe ansatz, we obtain an effective model of free fermions on a periodic spin-chain. This limit should provide hints to the one-loop anomalous dimension of the mysterious superconformal quantum mechanics dual to the superstring theory in this geometry.

We exploit a recent advance in the study of interacting topological superconductors to propose a solution to the family puzzle of particle physics in the context of $SO(18)$ [or more correctly, $\text{Spin}(18)$] grand unification. We argue that Yukawa couplings of intermediate strength may allow the mirror matter and extra families to decouple at arbitrarily high energies. As was clear from the existing literature, we have to go beyond the Higgs mechanism in order to solve the family puzzle. A pattern of symmetry breaking which results in the $SU(5)$ grand unified theory with horizontal or family symmetry $USp(4)=\text{Spin}(5)$ [or more loosely, $SO(5)$] leaves exactly three light families of matter and seems particularly appealing. We comment briefly on an alternative scheme involving discrete non-Abelian family symmetries. In a few lengthy Appendices we review some of the pertinent condensed matter theory.

In this work, we consider a particle moving in front of a dielectric plate and study two of the most relevant effects of the vacuum field fluctuations: the dissipation and the decoherence of the particle’s internal degrees of freedom. We consider the particle to follow a classical, macroscopically fixed trajectory. To study the dissipative effects, we calculate the in-out effective action by functionally integrating over the vacuum field and the microscopic degrees of freedom of both the plate and the particle. This in-out effective action develops an imaginary part and, hence, a nonvanishing probability for the decay (because of friction) of the initial vacuum state. We analyze how the dissipation is affected by the relative velocity between the particle and the plate and the properties of the microscopic degrees of freedom. In order to study the effects of decoherence over the internal degrees of freedom of the particle, we calculate the closed time path or Schwinger-Keldysh influence action, by functionally integrating over the vacuum field and the microscopic degrees of freedom of the plate. We estimate the decoherence time as the time needed by two different quantum configurations (of the internal degree of freedom of the particle) to be possible to differentiate from one another. We analyze the way in which the presence of the mirror affects the decoherence and the possible ways to maximize or reduce its effects.

Using the background field method and the Batalin-Vilkovisky formalism, we prove a key theorem on the cohomology of perturbatively local functionals of arbitrary ghost numbers in renormalizable and nonrenormalizable quantum field theories whose gauge symmetries are general covariance, local Lorentz symmetry, non-Abelian Yang-Mills symmetries and Abelian gauge symmetries. Interpolating between the background field approach and the usual, nonbackground approach by means of a canonical transformation, we take advantage of the properties of both approaches and prove that a closed functional is the sum of an exact functional plus a functional that depends only on the physical fields and possibly the ghosts. The assumptions of the theorem are the mathematical versions of general properties that characterize the counterterms and the local contributions to the potential anomalies. This makes the outcome a theorem on the cohomology of renormalization, rather than the whole local cohomology. The result supersedes numerous involved arguments that are available in the literature.

An inflationary universe scenario in the context of a tachyon field is studied. This study is carried out using an ansatz for the effective potential of cosmological perturbations $U(\eta )$. We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different Ansätze for the effective potential of cosmological perturbations: Easther’s model and an effective potential similar to power-law inflation. Also, we find from the background equations that the effective tachyonic potentials $V(\phi )$ in both models satisfy the properties of a tachyonic potential. We consider the recent data from the Planck to constrain the parameters in our effective potential generating the cosmological perturbations.

The light cone sum rules method is used in studying the radiative decays ${\mathrm{\Sigma }}_Q\to {\mathrm{\Lambda }}_Q\gamma$ and ${\mathrm{\Xi }}_Q^{\prime }\to {\mathrm{\Xi }}_Q\gamma$. First, the sum rules for the form factor $F_2(Q^2=0)$ responsible for these transitions is constructed. Using this result, the decay widths of the above-mentioned decays are calculated and analyzed. A comparison of our predictions on the decay widths of considered transitions with the predictions of the other approaches is presented.

We examine the implication of the 750 GeV diphoton resonance on the two-Higgs-doublet model by imposing various theoretical and experimental constraints. The production rate of the two-Higgs-doublet model is smaller than the cross section observed at the LHC by 2 orders of magnitude. In order to accommodate the 750 GeV diphoton resonance, we extend the two-Higgs-doublet model by introducing additional Higgs fields, and focus on two different extensions: an inert complex Higgs triplet and a real scalar septuplet. As the 125 GeV Higgs is in agreement with the observed data, the production rate for the 750 GeV diphoton resonance can be enhanced to 0.6 fb for the former and 4.5 fb for the latter. The results of the latter are well consistent with the 750 GeV diphoton excess at the LHC.

We discuss the parameter space of the inert doublet model, a two Higgs doublet model with a dark matter candidate. An extensive set of theoretical and experimental constraints on this model is considered, where both collider as well as astroparticle data limits, the latter in the form of dark matter relic density as well as direct detection, are taken into account. We discuss the effects of these constraints on the parameter space of the model. In particular, we do not require the inert doublet model to provide the full dark matter content of the Universe, which opens up additional regions in the parameter space accessible at collider experiments. The combination of all constraints leads to a relatively strong mass degeneracy in the dark scalar sector for masses $\gtrsim 200\mathrm{GeV}$, and to a minimal scale $\sim 45\mathrm{GeV}$ for the dark scalar masses. We also observe a stringent mass hierarchy $M_H^{\pm }>M_A$. We propose benchmark points and benchmark planes for dark scalar pair production for the current LHC run being in compliance with all theoretical as well as experimental bounds.

The $B_c$ production rate in Higgs boson decays is evaluated in the nonrelativistic QCD framework. Given that the Higgs total decay width is about 4.20 MeV and the vector $B_c^{*}$ meson decays completely to the ground state, we find that the branching fraction of $B_c$ meson production in Higgs decays is $8.50\times {10}^{-4}$, where both leading QCD and QED contributions are included. This process is hence detectable in the high-luminosity/-energy LHC. It is found that the coupling of $Hb\overline{b}$ dominates the processes, and contributions from the triangle top-quark loop and other couplings ($Hc\overline{c}$, $HWW$ and $HZZ$) are small. In confronting the quarkonia production, we find that the fraction rate of $B_c$ production is more than an order of magnitude bigger than those of charmonium and bottomonium production in Higgs decays. Moreover, various uncertainties and differential distributions of the concerned processes are analyzed carefully.

We investigate the reach of the LHC Run 2 and that of a future circular hadron collider with up to 100 TeV center of mass energy for the exploration of potential dark matter sectors. These dark sectors are conveniently and broadly described by simplified models. The simplified models we consider provide microscopic descriptions of interactions between the standard model partons and the dark sector particles mediated by the four basic types of ($s$-channel) messenger fields: scalar, pseudoscalar, vector or axial-vector. Our analysis extends and updates the previously available results for the LHC at 8 and 14 TeV to 100 TeV for models with all four messenger types. We revisit and improve the analysis at 14 TeV, by studying a variety of analysis techniques, concluding that the most discriminating variables correspond to the missing transverse energy and the azimuthal angle between jets in the final state. Going to 100 TeV, the limits on simplified models of dark matter are enhanced significantly, in particular for heavier mediators and dark sector particles, for which the available phase space at the LHC is restricted. The possibility of a 100 TeV collider provides an unprecedented coverage of the dark sector basic parameters and a unique opportunity to pin down the particle nature of dark matter and its interactions with the standard model.

This is the second paper of the series aimed at understanding the ensemble of instanton-dyons, now with two flavors of light dynamical quarks. The partition function is appended by the fermionic factor, $(\det T{)}^{N_f}$, and Dirac eigenvalue spectra at small values are derived from the numerical simulation of 64 and 128 dyons. Those spectra show a clear chiral symmetry breaking pattern at high dyon density.

Based on the knowledge of the QCD radiation pattern, observables to distinguish jets containing one and two $b$ hadrons are discussed. A simple method is used to combine pairs of the most sensitive observables—girth, number of charged tracks and the energy or momentum fraction of the leading $b$ hadron with respect to the jet—into one discriminator. Their efficiencies, on the particle level, are estimated and found to improve the performance and the robustness of the observables in different momentum slices.

Using a data sample of $1.31\times {10}^9$ $J/\psi$ events accumulated with the BESIII detector, the decay $J/\psi \to p\overline{p}\varphi$ is studied via two decay modes, $\varphi \to K_S^0{K}_L^0$ and $\varphi \to K^{+}{K}^{-}$. The branching fraction of $J/\psi \to p\overline{p}\varphi$ is measured to be $\mathcal{B}(J/\psi \to p\overline{p}\varphi )=[5.23\pm 0.06(\mathrm{stat})\pm 0.33(\mathrm{syst})]\times {10}^{-5}$, which agrees well with a previously published measurement, but with a significantly improved precision. No evident enhancement near the $p\overline{p}$ mass threshold, denoted as $X(p\overline{p})$, is observed, and the upper limit on the branching fraction of $J/\psi \to X(p\overline{p})\varphi \to p\overline{p}\varphi$ is determined to be $\mathcal{B}(J/\psi \to X(p\overline{p})\varphi \to p\overline{p}\varphi )<2.1\times {10}^{-7}$ at the 90% confidence level.