Yang-Mills theory and QCD are well defined for any Lie group as gauge group. The choice ${\mathrm{G}}_2$ is of great interest, as it is the smallest group with trivial center and being at the same time accessible to simulations. This theory has been found to have many properties in common with SU(3) Yang-Mills theory and QCD, permitting us to study the role of the center. Herein, these investigations are extended to topological properties of ${\mathrm{G}}_2$ Yang-Mills theory. After giving the instanton construction for ${\mathrm{G}}_2$, topological lumps with instanton topological charge are identified in cooled lattice configurations. The corresponding topological susceptibility is determined in the vacuum and at low and high temperatures, showing a significant response to the phase structure of the theory.

We calculate the two-pion exchange potential between a heavy meson and a heavy baryon. We find this potential is as strong as the one-pion exchange potential between two heavy mesons and is enough to bind ${\Lambda }_b-\overline{B}$. Though our result is sensitive to the cutoff, the value of the cutoff is in the reasonable region.

We compare lattice data for the short-distance part of the static energy in $2+1$ flavor quantum chromodynamics (QCD) with perturbative calculations, up to next-to-next-to-next-to leading-logarithmic accuracy. We show that perturbation theory describes very well the lattice data at short distances, and exploit this fact to obtain a determination of the product of the lattice scale $r_0$ with the QCD scale ${\Lambda }_{\overline{\mathrm{MS}}}$. With the input of the value of $r_0$, this provides a determination of the strong coupling ${\alpha }_s$ at the typical distance scale of the lattice data. We obtain ${\alpha }_s(1.5\mathrm{GeV})=0.326\pm 0.019$, which provides a novel determination of ${\alpha }_s$ with three-loop accuracy (including resummation of the leading ultrasoft logarithms), and constitutes one of the few low-energy determinations of ${\alpha }_s$ available. When this value is evolved to the $Z$-mass scale $M_Z$, it corresponds to ${\alpha }_s(M_Z)={0.1156}_{-0.0022}^{+0.0021}$.

We study the ${\gamma }^{*}\Lambda \to {\Sigma }^0$ transition form factors by applying the covariant spectator quark model. Using the parametrization for the baryon core wave functions as well as for the pion cloud dressing obtained in a previous work, we calculate the dependence on the momentum transfer squared, $Q^2$, of the electromagnetic transition form factors. The magnetic form factor is dominated by the valence quark contributions. The final result for the transition magnetic moment, a combination of the quark core and pion cloud effects, turns out to give a value very close to the data. The pion cloud contribution, although small, pulls the final result towards the experimental value. The final result, ${\mu }_{\Lambda {\Sigma }^0}=-1.486{\mu }_N$, is about one and a half standard deviations from the central value in PDG, ${\mu }_{\Lambda {\Sigma }^0}=-1.61\pm 0.08{\mu }_N$. Thus, a modest improvement in the statistics of the experiment would permit the confirmation or rejection of the present result. Small but nonzero values for the electric form factor in the finite $Q^2$ region are also predicted, as a consequence of the pion cloud dressing.

We prove that $D^0-{\overline{D}}^0$ mixing in the standard model occurs only at second order in U-spin breaking. The U-spin subgroup of SU(3) is found to be a powerful tool for analyzing the cancellation of intermediate-state contributions to the $D^0-{\overline{D}}^0$ mixing parameter $y=\Delta \Gamma /(2\Gamma )$. Cancellations due to states within a single U-spin triplet are shown to be valid to first order in U-spin breaking. Illustrations are given for triplets consisting of (a) pairs of charged pions and kaons; (b) pairs of neutral pseudoscalar members of the meson octet; (c) charged vector-pseudoscalar pairs, and (d) states of four charged kaons and pions.

The observation of the $1.97\pm 0.04$ solar-mass neutronlike star gives constraint on the equation of state of cold, condensed matter. In this paper, the equation of state for both the pure quark star and the hybrid star with a quark core described by the quasiparticle model are considered. The parameters of the quasiparticle model that affect the mass of both the quark star and the hybrid star can be constrained by the observation.

We present a detailed study of the same-sign top pair production mediated by a nonuniversal $Z^{\prime }$ including production and decay at the Large Hadron Collider (LHC) at the QCD next-to-leading order (NLO) level, using the narrow width approximation and helicity amplitudes method. We find that the QCD NLO corrections can loosen the constraint on the model parameters and reduce the dependence of the total cross sections on the factorization scale significantly. We also study the signature and backgrounds of the process at the NLO level. In order to suppress the backgrounds, we further investigate the difference between the production rates of the positively and negatively charged dilepton at the LHC, and find that the same-sign dilepton signal of the new physics could be discovered more easily. Besides, we also discuss the uncertainty from the parton distribution at the NLO level.

In an effective operator approach, the full set of leading contributions to anomalous top couplings comprises various new trilinear as well as higher interaction vertices, some of which are related to one another by gauge symmetry or equations of motion. In order to study trilinear top couplings to Standard Model gauge bosons such as $tt\gamma$, $ttZ$, $tbW$ and $ttg$, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrization of the trilinear vertices alone. Four-fermion contact terms $qqtt$ and $udtb$ must be included if the relation to the operator basis is to be retained. In this paper, we point out how these interactions contribute to the single top search channels for anomalous trilinear $tbW$ couplings at the LHC and Tevatron, thus affecting the corresponding bounds. All results are based on full leading-order partonic matrix elements, thus automatically accounting for off-shell and interference effects as well as irreducible backgrounds. A discussion of the quantitative effects of going from on-shell tops to full matrix elements including acceptance cuts is also provided.

The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has been measured at midrapidity ($|y|<0.5$) in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ with ALICE at the LHC. Electrons were measured in the transverse momentum range $0.5<p_{\mathrm{t}}<8\mathrm{GeV}/c$. Predictions from a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data within the theoretical and experimental uncertainties.

We present a new measurement of the time-dependent $CP$ asymmetry of $B^0\to D^{*+}{D}^{*-}$ decays using ($471\pm 5$) million $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II $B$ Factory at the SLAC National Accelerator Laboratory. Using the technique of partial reconstruction, we measure the time-dependent $CP$ asymmetry parameters $S=-0.34\pm 0.12\pm 0.05$ and $C=+0.15\pm 0.09\pm 0.04$. Using the value for the $CP$-odd fraction $R_{\perp }=0.158\pm 0.028\pm 0.006$, previously measured by BABAR with fully reconstructed $B^0\to D^{*+}{D}^{*-}$ events, we extract the $CP$-even components $S_{+}=-0.49\pm 0.18\pm 0.07\pm 0.04$ and $C_{+}=+0.15\pm 0.09\pm 0.04$. In each case, the first uncertainty is statistical and the second is systematic; the third uncertainty on $S_{+}$ is the contribution from the uncertainty on $R_{\perp }$. The measured value of the $CP$-even component $S_{+}$ is consistent with the value of $\sin 2\beta$ measured in $b\to (c\overline{c})s$ transitions, and with the Standard Model expectation of small penguin contributions.

The first observation of the decays ${\overline{B}}_s^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ and ${\overline{B}}^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ are reported using an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$ recorded by the LHCb experiment. The branching fractions, normalized with respect to ${\overline{B}}_s^0\to D_s^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ and ${\overline{B}}_s^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$, respectively, are measured to be $\frac{\mathcal{B}({\overline{B}}_s^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-})}{\mathcal{B}({\overline{B}}_s^0\to D_s^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})}=(5.2\pm 0.5\pm 0.3)\times {10}^{-2}$ and $\frac{\mathcal{B}({\overline{B}}^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-})}{\mathcal{B}({\overline{B}}_s^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-})}=0.54\pm 0.07\pm 0.07$, where the first uncertainty is statistical and the second is systematic. The ${\overline{B}}_s^0\to D_s^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ decay is of particular interest as it can be used to measure the weak phase $\gamma$. First observation of the ${\overline{B}}_s^0\to D_{s1}(2536{)}^{+}{\pi }^{-}$, $D_{s1}^{+}\to D_s^{+}{\pi }^{-}{\pi }^{+}$ decay is also presented, and its branching fraction relative to ${\overline{B}}_s^0\to D_s^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ is found to be $\frac{\mathcal{B}({\overline{B}}_s^0\to D_{s1}(2536{)}^{+}{\pi }^{-},D_{s1}^{+}\to D_s^{+}{\pi }^{-}{\pi }^{+})}{\mathcal{B}({\overline{B}}_s^0\to D_s^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})}=(4.0\pm 1.0\pm 0.4)\times {10}^{-3}$.

We study the sensitivity of the LHC, with $20{\mathrm{fb}}^{-1}$ of data, to lepton flavor-violating Higgs boson decays $h\to {\tau }^{\pm }{\mu }^{\mp }$ (and $h\to {\tau }^{\pm }{e}^{\mp }$). We consider the large population of Higgses produced in gluon fusion, combined with leptonic decays of the $\tau$, and estimate that the LHC could set a 95% confidence level bound $\mathrm{BR}(h\to {\tau }^{\pm }{\mu }^{\mp })<4.5\times {10}^{-3}$. This corresponds to a coupling of the order of the Cheng-Sher ansatz $y_{\tau \mu }=\sqrt{m_{\tau }{m}_{\mu }/v^2}$.

Conformal field theories (CFTs) with a globally conserved U(1) charge $\mathcal{Q}$ can be deformed into compressible phases by modifying their Hamiltonian, $\mathcal{H}$, by a chemical potential $\mathcal{H}\to \mathcal{H}-\mu \mathcal{Q}$. We study $2+1$ dimensional CFTs upon which an explicit $S$ duality mapping can be performed. We find that this construction leads naturally to compressible phases which are superfluids, solids, or non-Fermi liquids which are more appropriately called “Bose metals” in the present context. The Bose metal preserves all symmetries and has Fermi surfaces of gauge-charged fermions, even in cases where the parent CFT can be expressed solely by bosonic degrees of freedom. Monopole operators are identified as order parameters of the solids, and the product of their magnetic charge and $\mathcal{Q}$ determines the area of the unit cell. We present implications for holographic theories on asymptotically ${\mathrm{AdS}}_4$ spacetimes: $S$ duality and monopole/dyon fields play important roles in this connection.

Two particles can collide in the vicinity of a rotating black hole producing the divergent energy in the center-of-mass frame [the Banados-Silk-West (BSW) effect]. However, it was shown recently that an observer at infinity can register quite modest energies $E$ and masses $m$ that obey some upper bounds. In the present work the counterpart of the original BSW effect is considered that may occur even for radial motion of colliding particles near charged static black holes. It is shown that in some scenarios there are no upper bounds on $E$ and $m$. Thus the high-energetic and superheavy products of the BSW effect in this situation are, in principle, detectable at infinity.

The effect of quantum torsion in theories of quantum gravity is usually described by an axionlike field which couples to matter and to gravitation and radiation gauge fields. In perturbation theory, the couplings of this torsion-descent axion field are of derivative type and so preserve a shift symmetry. This shift symmetry may be broken, if the torsion-descent axion field mixes with other axions, which could be related to moduli fields in string-inspired effective theories. In particular, the shift symmetry may break explicitly via nonperturbative effects, when these axions couple to fermions via chirality-changing Yukawa couplings with appropriately suppressed coefficients. We show how in such theories an effective right-handed Majorana neutrino mass can be generated at two loops by gravitational interactions that involve global anomalies related to quantum torsion. We estimate the magnitude of the gravitationally induced Majorana mass and find that it is highly model dependent, ranging from the multi-TeV to keV scale.

This is the first in a series of papers in which the gradient flows of fundamental curvature invariants are used to formulate a visualization of curvature. We start with the construction of strict Newtonian analogues (not limits) of solutions to Einstein’s equations based on the topology of the associated gradient flows. We do not start with any easy case. Rather, we start with the Curzon-Chazy solution, which, as history shows, is one of the most difficult exact solutions to Einstein’s equations to interpret physically. A substantial part of our analysis is that of the Curzon-Chazy solution itself. Eventually we show that the entire field of the Curzon-Chazy solution, up to a region very “close” to the intrinsic singularity, strictly represents that of a Newtonian ring, as has long been suspected. In this regard, we consider our approach very successful. As regards the local structure of the singularity of the Curzon-Chazy solution within a fully general relativistic analysis, however, whereas we make some advances, the full structure of this singularity remains incompletely resolved.

We consider the slowly rotating relativistic stars with a uniform angular velocity in scalar-tensor gravity, and examine the rotational effect around such compact objects. For this purpose, we derive a second order differential equation describing the frame dragging in scalar-tensor gravity and solve it numerically. As a result, we find that the total angular momentum is proportional to the angular velocity even in scalar-tensor gravity. We also show that one can observe the spontaneous scalarization in rotational effects as well as the other stellar properties, if the cosmological value of the scalar field is zero. On the other hand, if the cosmological value of the scalar field is nonzero, the deviation from general relativity can be seen in a wide range of coupling constants. Additionally, we find that, independently of the cosmological value of the scalar field, the deviation from general relativity becomes larger with more massive stellar models. Thus, via precise observations of astronomical phenomena associated with rotating relativistic stars, one may probe not only the gravitational theory in the strong-field regime, but also the existence of a scalar field.

In this paper we examine the validity of the linear perturbation theory near a bounce in the covariant analysis. Some linearity parameters are defined to set up conditions for a linear theory. Linear evolution of density perturbation and gravitational waves have been computed previously. We have calculated the vector and scalar induced parts of the shear tensor. For radiationlike and dustlike single fluid dominated collapsing Friedmann-Lemaître-Robertson-Walker background it is shown that the linearity conditions are not satisfied near a bounce.

We study the realization of cosmic inflation in bigravity theories. By analyzing the evolution of scalar, vector, and tensor perturbations in de Sitter-like spacetimes, we find strong stability constraints on the class of viable vacua offered by these theories. More specifically, the only stable de Sitter vacua contain two nondecoupled gravitons (one of which is massive) with different maximal propagation speeds. We derive an effective theory for the massless graviton, which is found to propagate at an intermediate speed, limited by the two maximal values. For inflation, while the spectrum of density perturbations remains nearly scale invariant, the power spectrum of tensor modes is found to depart from the usual prediction found in standard slow-roll inflation. In particular, both the tensor to scalar ratio $r$ and the spectral index of tensor modes $n_T$ receive sizable contributions from the couplings of the theory, leading to specific signals that may be tested in future cosmological probes of cosmic microwave background polarization.

The recent observation that the cosmic microwave background (CMB) may prefer a neutrino excess has triggered a number of works studying this possibility. The effect obtained by the noninteracting massless neutrino excess could be mimicked by some extra radiation component in the early Universe, such as a cosmological gravitational wave background. Prompted by the fact that a possible candidate to source those gravitational waves would be cosmic strings, we perform a parameter fitting study with models which consider both cosmic strings and the effective number of neutrinos as free parameters, using CMB and non-CMB data. We find that there is a correlation between cosmic strings and the number of extra relativistic species and that strings can account for all the extra radiation necessary. In fact, CMB data prefer strings at a $2\sigma$ level, paying the price of a higher extra radiation component. CMB data also give a moderate preference for a model with $n_s=1$. The inclusion of non-CMB data lowers the preference both for strings and for the extra relativistic species.