We discuss the link between the chiral symmetry of QCD and the numerical results of the light-front quark model (LFQM), analyzing both the two-point and three-point functions of a pseudoscalar meson from the perspective of the vacuum fluctuation consistent with the chiral symmetry of QCD. The two-point and three-point functions are exemplified in this work by the twist-2 and twist-3 distribution amplitudes of a pseudoscalar meson and the pion elastic form factor, respectively. The present analysis of the pseudoscalar meson commensurates with the previous analysis of the vector meson two-point function and fortifies our observation that the LFQM with effective degrees of freedom represented by the constituent quark and antiquark may provide the view of effective zero-mode cloud around the quark and antiquark inside the meson. Consequently, the constituents dressed by the zero-mode cloud may be expected to satisfy the chiral symmetry of QCD. Our results appear consistent with this expectation and effectively indicate that the constituent quark and antiquark in the LFQM may be considered as the dressed constituents including the zero-mode quantum fluctuations from the vacuum.

The final ATLAS Run 1 measurements of Higgs boson production and couplings in the decay channel $H\to Z{Z}^{*}\to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}$, where $\ell$, ${\ell }^{\prime }=e$ or $\mu$, are presented. These measurements were performed using $pp$ collision data corresponding to integrated luminosities of 4.5 and $20.3{\mathrm{fb}}^{-1}$ at center-of-mass energies of 7 and 8 TeV, respectively, recorded with the ATLAS detector at the LHC. The $H\to Z{Z}^{*}\to 4\ell$ signal is observed with a significance of 8.1 standard deviations, with an expectation of 6.2 standard deviations, at $m_H=125.36\mathrm{GeV}$, the combined ATLAS measurement of the Higgs boson mass from the $H\to \gamma \gamma$ and $H\to Z{Z}^{*}\to 4\ell$ channels. The production rate relative to the Standard Model expectation, the signal strength, is measured in four different production categories in the $H\to Z{Z}^{*}\to 4\ell$ channel. The measured signal strength, at this mass, and with all categories combined, is ${1.44}_{-0.33}^{+0.40}$. The signal strength for Higgs boson production in gluon fusion or in association with $t\overline{t}$ or $b\overline{b}$ pairs is found to be ${1.7}_{-0.4}^{+0.5}$, while the signal strength for vector-boson fusion combined with $WH/ZH$ associated production is found to be ${0.3}_{-0.9}^{+1.6}$.

The canonical recursive Dyson-Schwinger equations for the three-gluon and ghost-gluon vertices are solved numerically. The employed truncation includes several previously neglected diagrams and includes back-coupling effects. We find an infrared finite ghost-gluon vertex and an infrared diverging three-gluon vertex. We also compare our results with those obtained in previous calculations, where bare vertices were used in the loop diagrams.

We discuss eternal inflation in the context of classical probability spaces defined by a triplet: sample space, $\sigma$-algebra, and probability measure. We show that the measure problem is caused by the countable additivity axiom applied to the maximal $\sigma$-algebra of countably infinite sample spaces. This is a serious problem if the bulk space-time is treated as a sample space which is thought to be effectively countably infinite due to local quantum uncertainties. However, in semiclassical description of eternal inflation the physical space expands exponentially which makes the sample space of infinite trajectories uncountable and the (future) boundary space effectively continuous. Then the measure problem can be solved by defining a probability measure on the continuum of trajectories or holographically on the future boundary. We argue that the probability measure which is invariant under the symmetries of the tree-like structure of eternal inflation can be generated from the Lebesgue measure on unit interval. According to Vitali theorem the Lebesgue measure leaves some sets without a measure which means that there are certain probabilistic questions in eternal inflation that cannot be answered.

We update the indirect constraints on the Georgi-Machacek model from $B$-physics and electroweak precision observables, including new constraints from $b\to s\gamma$ and $B_s^0\to {\mu }^{+}{\mu }^{-}$. We illustrate the effect of these constraints on the couplings of the Standard-Model-like Higgs boson by performing scans using the most general scalar potential, subject to vacuum stability and perturbativity constraints. We find that simultaneous enhancements of all the Higgs production cross sections by up to 39% are still allowed after imposing these constraints. LHC rate measurements on the Higgs pole could be blind to these enhancements if unobserved nonstandard Higgs decays are present.

Recently experimentalists have discovered several charged charmoniumlike hadrons $Z_c^{+}$ with unconventional quark content $\overline{c}c\overline{d}u$. We perform a search for $Z_c^{+}$ with mass below 4.2 GeV in the channel $I^G(J^{PC})=1^{+}(1^{+-})$ using lattice QCD. The major challenge is presented by the two-meson states $J/\psi \pi$, ${\psi }_{2S}\pi$, ${\psi }_{1D}\pi$, $D{\overline{D}}^{*}$, $D^{*}{\overline{D}}^{*}$, ${\eta }_c\rho$ that are inevitably present in this channel. The spectrum of eigenstates is extracted using a number of meson-meson and diquark-antidiquark interpolating fields. For our pion mass of 266 MeV we find all the expected two-meson states but no additional candidate for $Z_c^{+}$ below 4.2 GeV. Possible reasons for not seeing an additional eigenstate related to $Z_c^{+}$ are discussed. We also illustrate how a simulation incorporating interpolators with a structure resembling low-lying two-meson states seems to render a $Z_c^{+}$ candidate, which is however not robust after further two-meson states around 4.2 GeV are implemented.

The vector meson $\rho$ in the presence of an external magnetic field has been investigated in the framework of the Nambu–Jona-Lasinio model, in which mesons are constructed by the infinite sum of quark-loop chains by using random phase approximation. The quark loop of $\rho$ meson polarization function is calculated to the leading order of $1/N_c$ expansion by taking the quark propagator in Ritus form as well the Landau level representation. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson ${\rho }^0$ with spin component $s_z=0,\pm 1$, and the charged vector meson ${\rho }^{\pm }$ with $s_z=0$ also increases with magnetic field. However, the mass square of the charged vector meson ${\rho }^{+}$ (${\rho }^{-}$) with $s_z=+1$ ($s_z=-1$) decreases linearly with magnetic field and drops to zero at the critical magnetic field $e{B}_c\simeq 0.2{\mathrm{GeV}}^2$, which indicates the possible condensation of a charged vector meson in the vacuum. The value of the critical magnetic field is the same by using the Ritus quark propagator as well the Landau level representation of the quark propagator, which is much lower than the value $e{B}_c\simeq 0.6{\mathrm{GeV}}^2$ predicted by a pointlike vector meson.

While the muon $g-2$ anomaly can be successfully explained by some new physics models, most of them are severely constrained by the $\mu \to e\gamma$ bound. This tension is more transparent from the effective field theory perspective, in which the two phenomena are encoded in two very similar operators. However, with the $\mathcal{O}(1)$ Wilson coefficients, the current upper bound on $\mu \to e\gamma$ indicates a new physics cutoff scale being 5 orders smaller than that needed to eliminate the $(g-2{)}_{\mu }$ anomaly. By summarizing all the formulas from the one-loop contributions to the muon $g-2$ with the internal-particle spin not larger than 1, we point out two general methods to reconcile the conflict between the muon $g-2$ and $\mu \to e\gamma$: the Glashow-Iliopoulos-Maiani mechanism and the nonuniversal couplings. For the latter method, we use a simple scalar leptoquark model as an illustration.

One version of the membrane paradigm states that, as far as outside observers are concerned, black holes can be replaced by a dissipative membrane with simple physical properties located at the stretched horizon. We demonstrate that such a membrane paradigm is incomplete in several aspects. We argue that it generically fails to capture the massive quasinormal modes, unless we replace the stretched horizon by the exact event horizon, and illustrate this with a scalar field in a Banados-Teitelboim-Zanelli (BTZ) black hole background. We also consider as a concrete example linearized metric perturbations of a five-dimensional AdS-Schwarzschild black brane and show that a spurious excitation appears in the long-wavelength response that is only removed from the spectrum when the membrane paradigm is replaced by ingoing boundary conditions at the event horizon. We interpret this excitation in terms of an additional Goldstone boson that appears due to symmetry breaking by the classical solution ending on the stretched horizon rather than the event horizon.

We consider the zero-point field fluctuations, and the related field energy densities, inside a one-dimensional and a three-dimensional cavity with a mobile wall. The mechanical degrees of freedom of the mobile wall are described quantum mechanically, and they are fully included in the overall system dynamics. In this optomechanical system, the field and the wall can interact with each other through the radiation pressure on the wall, given by the photons inside the cavity or even by vacuum fluctuations. We consider two cases—the one-dimensional electromagnetic field and the three-dimensional scalar field—and use the Green’s functions formalism, which allows extension of the results obtained for the scalar field to the electromagnetic field. We show that the quantum fluctuations of the position of the cavity’s mobile wall significantly affect the field energy density inside the cavity, in particular at the very proximity of the mobile wall. The dependence of this effect from the ultraviolet cutoff frequency, related to the plasma frequency of the cavity walls, is discussed. We also compare our new results for the one-dimensional electromagnetic field and the three-dimensional massless scalar field to results recently obtained for the one-dimensional massless scalar field. We show that the presence of a mobile wall also changes the Casimir-Polder force on a polarizable body placed inside the cavity, giving the possibility to detect experimentally the new effects we have considered.

We investigate the vector and axial currents induced by external electromagnetic fields and chemical potentials in chiral systems at finite temperature. Similar to the normal Hall effect, we find that an axial Hall current is generated in the presence of the electromagnetic fields along with an axial chemical potential, which may be dubbed as the “chiral Hall effect” (CHE). The CHE is related to the interactions of chiral fermions and exists with a nonzero axial chemical potential. We argue that the CHE could lead to nontrivial charge distributions at different rapidity in asymmetric heavy ion collisions. Moreover, we study the chiral electric waves led by the fluctuations of the vector and axial chemical potentials along with the chiral electric separation effect, where a density wave propagates along the applied electric field. Combining with the normal/chiral Hall effects, the fluctuations of chemical potentials thus result in Hall density waves. The Hall density waves may survive even at zero chemical potentials and become nondissipative. We further study the transport coefficients including the Hall conductivities, damping times, wave velocities, and diffusion constants of chiral electric waves in a strongly coupled plasma via the AdS/CFT correspondence.

In Hořava-Lifshitz cosmology we use the holographic Ricci-like cutoff for the energy density proposed by L. N. Granda and A. Oliveros and under this framework we study, through the cosmic evolution at late times, the sign change in the amount of nonconservation energy ($Q$) present in this cosmology. We revise the early stage (curvature-dependent) of this cosmology, where a term reminiscent of stiff matter is the dominant, and in this stage we find a power-law solution for the cosmic scale factor although $\omega =-1$. Late and early phantom schemes are obtained without requiring $\omega <-1$. Nevertheless, these schemes are not feasible according to what is shown in this paper. We also show that $\omega =-1$ alone does not imply a de Sitter phase in the present cosmology. Thermal aspects are revised by considering the energy interchange between the bulk and the spacetime boundary and we conclude that there is no thermal equilibrium between them. Finally, a ghost scalar graviton (extra degree of freedom in HL gravity) is required by the observational data.

We propose an alternative to particle dark matter that borrows ingredients of modified Newtonian dynamics (MOND) while adding new key components. The first new feature is a dark matter fluid, in the form of a scalar field with small equation of state and sound speed. This component is critical in reproducing the success of cold dark matter for the expansion history and the growth of linear perturbations, but does not cluster significantly on nonlinear scales. Instead, the missing mass problem on nonlinear scales is addressed by a modification of the gravitational force law. The force law approximates MOND at large and intermediate accelerations, and therefore reproduces the empirical success of MOND at fitting galactic rotation curves. At ultralow accelerations, the force law reverts to an inverse-square law, albeit with a larger Newton’s constant. This latter regime is important in galaxy clusters and is consistent with their observed isothermal profiles, provided the characteristic acceleration scale of MOND is mildly varying with scale or mass, such that it is 12 times higher in clusters than in galaxies. We present an explicit relativistic theory in terms of two scalar fields. The first scalar field is governed by a Dirac-Born-Infeld action and behaves as a dark matter fluid on large scales. The second scalar field also has single-derivative interactions and mediates a fifth force that modifies gravity on nonlinear scales. Both scalars are coupled to matter via an effective metric that depends locally on the fields. The form of this effective metric implies the equality of the two scalar gravitational potentials, which ensures that lensing and dynamical mass estimates agree. Further work is needed in order to make both the acceleration scale of MOND and the fraction at which gravity reverts to an inverse-square law explicitly dynamical quantities, varying with scale or mass.

We report a new class of $SO(3,\mathbb{C})$ and diffeomorphism invariant formulations for general relativity with either a vanishing or a nonvanishing cosmological constant, which depends functionally on a $SO(3,\mathbb{C})$ gauge connection and a complex-valued 4-form via a holomorphic function of the trace of a symmetric $3\times 3$ matrix that is constructed from these variables. We present two members of this class, one of which results from the implementation of a method for obtaining action principles belonging to the class. For the case of a nonvanishing cosmological constant, we solve for the complex-valued 4-form and get pure connection action principles. We perform the canonical analysis of the class. The analysis shows that only the Hamiltonian constraint is modified with respect to the Ashtekar formulation and that the members of the class have two physical degrees of freedom per space point.

A model of high scale inflation is presented where the radial part of the Peccei-Quinn (PQ) field with a non-minimal coupling to gravity plays the role of the inflaton, and the QCD axion is the dark matter. A quantum fluctuation of $\mathcal{O}(H/2\pi )$ in the axion field will result in a smaller angular fluctuation if the PQ field is sitting at a larger radius during inflation than in the vacuum. This changes the effective axion decay constant, $f_a$, during inflation and dramatically reduces the production of isocurvature modes. This mechanism opens up a new window in parameter space where an axion decay constant in the range $10^{12}\mathrm{GeV}\lesssim f_a\lesssim 10^{15}\mathrm{GeV}$ is compatible with observably large $r$. The exact range allowed for $f_a$ depends on the efficiency of reheating. This model also predicts a minimum possible value of $r=10^{-3}$. The new window can be explored by a measurement of $r$ possible with SPIDER and the proposed CASPEr experiment search for high $f_a$ axions.

We systematically study the null-test for the growth rate data first presented in [S. Nesseris and D. Sapone, arXiv:1409.3697.] and we reconstruct it using various combinations of data sets, such as the $f{\sigma }_8$ and $H(z)$ or type Ia supernovae data. We perform the reconstruction in two different ways, either by directly binning thedata or by fitting various dark energy models. We also examine how well the null-test can be reconstructed by future data by creating mock catalogs based on the cosmological constant model, a model with strong dark energy perturbations, the $f(R)$ and $f(G)$ models, and the large void Lemaitre-Tolman-Bondi model that exhibit different evolution of the matter perturbations. We find that with future data similar to an LSST-like survey, the null-test will be able to successfully discriminate between these different cases at the $5\sigma$ level.

It is well known that the vacuum state of a quantum field is spatially entangled. This is true in both free and confined spaces, for example, in an optical cavity. The obvious consequence of this, however, is surprising and intuitively challenging: namely, that in a mathematical sense, half of an empty cavity is not empty. Formally this is clear, but what does this physically mean in terms of, say, measurements that can actually be made? In this paper we utilize a local quantization procedure along with the tools of Gaussian quantum mechanics to characterize the particle content in the reduced state of a subregion within a cavity and expose the spatial profile of its entanglement with the opposite region. We then go on to discuss a thought experiment in which a mirror is very quickly introduced between the regions. In so doing we expose a simple and physically concrete answer to the above question: the real excitations created by slamming down the mirror are mathematically equivalent to those previously attributed to the reduced states of the subregions. Performing such an experiment in the laboratory may be an excellent method of verifying vacuum entanglement, and we conclude by discussing different possibilities of achieving this aim.

The structure of the Higgs sector is a major issue in the quest of a detailed description of the electroweak interactions. Most of the effort is devoted to the study of the standard model–like Higgs boson at 126 GeV; however, the experimental collaborations at the LHC are also searching for extra scalar particles whose presence may hint at an extended Higgs sector, typical of many extensions of the standard model. We study a model-independent parametrization of a scalar particle lighter than the 126 GeV Higgs boson, which may be easily implemented in the ongoing searches by ATLAS and CMS. Indeed, many effective Lagrangians and parametrizations used at present for the description of the Higgs sector implicitly assume that no light particles other than the standard model ones are present in the spectrum. We therefore introduce a parametrization of a model with two scalars, one corresponding to the 126 GeV Higgs boson and the other to a lighter scalar. After the introduction of this parametrization, we consider two typical examples falling in this category: the two-Higgs-doublet model and the next-to-minimal supersymmetric standard model. We do this for two purposes: to illustrate the use of our parametrization and also show that some well-motivated models giving such a situation can be probed at LHC, advocating for such a search. Our results agree with the specific studies performed for these models. Furthermore, employing such a generic parametrization allows us to translate the bounds to any model beyond the standard model falling into this class.