We analyze the bounds on the spectrum of composite Higgs models that come from flavor observables, by means of simple two-site effective Lagrangians, which incorporate a custodial symmetry and a left-right parity, and which could also be adopted in further phenomenological studies on composite Higgs models. We derive, in particular, an important constraint on the masses of the $(t_L,b_L)$ partners, which does not depend on the flavor structure of the sector beyond the Standard Model. This bound is obtained from the “infrared” contribution to $b\to s\gamma$ induced by the flavor-conserving effective vertex $W{t}_R{b}_R$. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling and, as a consequence, in attenuating the constraint, which, however, remains of the order of 1 TeV. In addition to this bound, we calculate the constraints from the “ultraviolet” contribution to $b\to s\gamma$, induced by loops of heavy fermions, and to ${ϵ}^{\prime }/{ϵ}_K$.

We interpret the recent discovery of a 125 GeV Higgs-like state in the context of a two-Higgs-doublet model with a heavy fourth sequential generation of fermions, in which one Higgs doublet couples only to the fourth-generation fermions, while the second doublet couples to the lighter fermions of the first three families. This model is designed to accommodate the apparent heaviness of the fourth-generation fermions and to effectively address the low-energy phenomenology of a dynamical electroweak-symmetry-breaking scenario. The physical Higgs states of the model are, therefore, viewed as composites primarily of the fourth-generation fermions. We find that the lightest Higgs, $h$, is a good candidate for the recently discovered 125 GeV spin-zero particle, when $\tan \beta \sim \mathcal{O}(1)$, for typical fourth-generation fermion masses of $M_{4\mathrm{G}}=400–600\mathrm{GeV}$, and with a large $t\mathrm{\text{−}}{t}^{\prime }$ mixing in the right-handed quark sector. This, in turn, leads to $\mathrm{BR}(t^{\prime }\to th)\sim \mathcal{O}(1)$, which drastically changes the $t^{\prime }$ decay pattern. We also find that, based on the current Higgs data, this two-Higgs-doublet model generically predicts an enhanced production rate (compared to the Standard Model) in the $pp\to h\to \tau \tau$ channel, and reduced rates in the $VV\to h\to \gamma \gamma$ and $p\overline{p}/pp\to V\to hV\to Vbb$ channels. Finally, the heavier $CP$-even Higgs is excluded by the current data up to $m_H\sim 500\mathrm{GeV}$, while the pseudoscalar state, $A$, can be as light as 130 GeV. These heavier Higgs states and the expected deviations from the Standard Model din some of the Higgs production channels can be further excluded or discovered with more data.

Motivated by the statistical fluctuation of Dirac spectrum of QCD-like theories subjected to (pseudo)reality-violating perturbations and in the $\epsilon$ regime, we compute the smallest eigenvalue distribution and the level spacing distribution of chiral and nonchiral parametric random matrix ensembles of Dyson-Mehta-Pandey type. To this end we employ the Nyström-type method to numerically evaluate the Fredholm Pfaffian of the integral kernel for the chG(O,S)E-chGUE and G(O,S)E-GUE crossover. We confirm the validity and universality of our results by comparing them with several lattice models, namely fundamental and adjoint staggered Dirac spectra of SU(2) quenched lattice gauge theory under the twisted boundary condition (imaginary chemical potential) or perturbed by phase noise. Both in the zero-virtuality region and in the spectral bulk, excellent one-parameter fitting is achieved already on a small $4^4$ lattice. Anticipated scaling of the fitting parameter with the twisting phase, mean level spacing, and the system size allows for precise determination of the pion decay (diffusion) constant $F$ in the low-energy effective Lagrangian.

The bulk and shear viscosities ($\eta$ and $\zeta$) have been studied for quark-gluon plasma produced in relativistic heavy ion collisions within semiclassical transport theory, in a recently proposed quasiparticle model of ($2+1$)-flavor lattice QCD equation of state. These transport parameters have been found to be highly sensitive to the interactions present in hot QCD. Contributions to the transport coefficients from both the gluonic sector and the matter sector have been investigated. The matter sector is found to be significantly dominating over the gluonic sector in the cases of both $\eta$ and $\zeta$. The temperature dependences of the quantities $\zeta /\mathcal{S}$ and $\zeta /\eta$ indicate a sharply rising trend for the $\zeta$, closer to the QCD transition temperature. Both $\eta$ and $\zeta$ are shown to be equally significant for the temperatures that are accessible in the relativistic heavy ion collision experiments and hence play a crucial role in investigating the properties of the quark-gluon plasma.

We make a theoretical study of the $\eta (1405)\to {\pi }^0{f}_0(980)$ and $\eta (1405)\to {\pi }^0{a}_0(980)$ reactions with an aim to determine the isospin violation and the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We make use of the chiral unitary approach where these two resonances appear as composite states of two mesons, dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the $f_0(980)$ production in agreement with a BES experiment. As to the amount of isospin violation, or $f_0(980)$ and $a_0(980)$ mixing, assuming constant vertices for the primary $\eta (1405)\to {\pi }^{0}K\overline{K}$ and $\eta (1405)\to {\pi }^0{\pi }^0\eta$ production, we find results which are much smaller than found in the recent experimental BES paper, but consistent with results found in two other related BES experiments. We have tried to understand this anomaly by assuming an $I=1$ mixture in the $\eta (1405)$ wave function, but this leads to a much bigger width of the $f_0(980)$ mass distribution than observed experimentally. The problem is solved by using the primary production driven by ${\eta }^{\prime }\to K^{*}\overline{K}$ followed by $K^{*}\to K\pi$, which induces an extra singularity in the loop functions needed to produce the $f_0(980)$ and $a_0(980)$ resonances. Improving upon earlier work along the same lines, and using the chiral unitary approach, we can now predict absolute values for the ratio $\Gamma ({\pi }^0,{\pi }^{+}{\pi }^{-})/\Gamma ({\pi }^0,{\pi }^0\eta )$ which are in fair agreement with experiment. We also show that the same results hold if we had the $\eta (1475)$ resonance or a mixture of these two states, as seems to be the case in the BES experiment.

Belle data on $\gamma \gamma \to {\eta }^{\prime }\pi \pi$ are refitted using a broad $J^{PC}=0^{-+}$ peaking in the mass range 2250–2300 and $X(1835)$, but without $\eta (1760)$. There is the possibility that the broad $0^{-+}$ signal may be identified with the $0^{-+}$ glueball predicted originally by Morningstar and Peardon. The $X(1835)$ is confirmed to have a resonant phase variation.

We analyze a sample of $3\times {10}^6$ quantum-correlated $D^0{\overline{D}}^0$ pairs from $818{\mathrm{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected with the CLEO-c detector at $E_{\mathrm{cm}}=3.77\mathrm{GeV}$, to give an updated measurement of $\cos \delta$ and a first determination of $\sin \delta$, where $\delta$ is the relative strong phase between doubly Cabibbo-suppressed $D^0\to K^{+}{\pi }^{-}$ and Cabibbo-favored ${\overline{D}}^0\to K^{+}{\pi }^{-}$ decay amplitudes. With no inputs from other experiments, we find $\cos \delta ={0.81}_{-0.18-0.05}^{+0.22+0.07}$, $\sin \delta =-0.01\pm 0.41\pm 0.04$, and $|\delta |=({10}_{-53-0}^{+28+13})°$. By including external measurements of mixing parameters, we find alternative values of $\cos \delta ={1.15}_{-0.17-0.08}^{+0.19+0.00}$, $\sin \delta ={0.56}_{-0.31-0.20}^{+0.32+0.21}$, and $\delta =({18}_{-17}^{+11})°$. Our results can be used to improve the world average uncertainty on the mixing parameter $y$ by approximately 10%.

A conserved current for generic quadratic curvature gravitational models is defined, and it is shown that, at the linearized level, it corresponds to the Deser-Tekin charges. An explicit expression for the charge for new massive gravity in three dimensions is given. Some implications of the linearized equations are discussed.

The one-loop quantum corrections of Chern-Simons spinor electrodynamics in the light-cone gauge has been investigated. We have calculated the vacuum polarization tensor, fermionic self-energy, and on-shell vertex correction with a hybrid regularization consisting of a higher covariant derivative regularization and dimensional continuation. The Mandelstam-Leibbrandt prescription is used to handle the spurious light-cone singularity in the gauge field propagator. We then perform the finite renormalization to define the quantum theory. The generation of the parity-even Maxwell term and the arising of anomalous magnetic moment from quantum corrections are reproduced as in the case of a covariant gauge choice. The Ward identities in the light-cone gauge are verified to satisfy explicitly. Further, we have found the light-cone vector dependent sector of local quantum effective action for the fermion is explicitly gauge invariant, and hence the Lorentz covariance of $S$-matrix elements of the theory can be achieved.

We consider the $O(N)$ linear $\sigma$ model and introduce an auxiliary field to eliminate the scalar self-interaction. Using a suitable limiting process this model can be continuously transformed into the nonlinear version of the $O(N)$ model. We demonstrate that up to two-loop order in the Cornwall-Jackiw-Tomboulis formalism, the effective potential of the model with auxiliary field is identical to the one of the standard $O(N)$ linear $\sigma$ model if the auxiliary field is eliminated using the stationary values for the corresponding one- and two-point functions. We numerically compute the chiral condensate and the $\sigma$- and $\pi$-meson masses at nonzero temperature in the one-loop approximation of the Cornwall-Jackiw-Tomboulis formalism. The order of the chiral phase transition depends sensitively on the choice of the renormalization scheme. In the linear version of the model and for explicitly broken chiral symmetry, it turns from crossover to first order as the mass of the $\sigma$ particle increases. In the nonlinear case, the order of the phase transition turns out to be of first order. In the region where the parameter space of the model allows for physical solutions, Goldstone’s theorem is always fulfilled.

We investigate the existence of nonaxisymmetric solutions in the six-dimensional baby-Skyrme brane model. The brane is described by a localized solution to the baby-Skyrme model extending in the extra dimensions. Such nonsymmetric branes have already been constructed in the original $2+1$-dimensional baby-Skyrme model in flat space. We generalize this result to the case of gravitating baby Skyrme and in the context of extra dimensions. These nontrivial deformations from the axisymmetric shape appear for higher values of the topological charge, so we consider the cases of $B=3$, 4, where $B$ is the topological charge. We solve the coupled system of the Einstein and baby-Skyrme equations by the $\mathrm{\text{successive}}$ over-relaxation method. We argue that the result may be a possible resolution for the fermion mass hierarchy puzzle.

We study the thermodynamics of the two flavor massless Schwinger model on a torus at a finite chemical potential. We show that the physics only depends on the isospin chemical potential, and there are marked deviations from a free fermion theory. We argue that spatial inhomogeneities can develop in the system at very low temperatures.

Ever since Schwinger published his influential paper [J. Schwinger, Phys. Rev. 82, 664 (1951)], the maxim that there can be no pair creation in a plane wave has been often cited. We advance an analysis that indicates that in any real situation, where thermal effects are present, in a single plane-wave field, even in the limit of zero frequency (a constant crossed field), thermal photons can seed pair creation. Interestingly, the pair-production rate is found to depend nonperturbatively on both the amplitude of the constant crossed field and on the temperature.

Models with higher order derivative terms in the kinetic energy not only appear as effective theories but also can be considered as elementary, renormalizable models in their own right. The extension of the Higgs mechanism is discussed for Yang-Mills-Higgs models, where the kinetic energy of the scalar field contains higher order derivatives. The connection term of the covariant derivatives generates a local potential for the gauge field in the phase with spontaneously broken global gauge symmetry that may break Lorentz symmetry in the vacuum. The relativistic, massless gauge bosons spectrum is found for small fluctuations, where the only remnant of the breakdown of the Lorentz symmetry is a shift of the energy induced by the expectation value of the temporal component of the gauge field, reminiscent of a chemical potential.

We study the interplay between the stripe order and the superconducting order in a strongly coupled striped superconductor using gauge/gravity duality. In particular, we study the effects of inhomogeneity introduced by the stripe order on the superconducting transition temperature beyond the mean field level by including the effects of backreaction onto the spacetime geometry in the dual gravitational picture. We find that inhomogeneity enhances the critical temperature relative to its value for the uniform system.

We show that sine-Gordon solitons appear in the low-energy effective theory of a domain wall in a $U(1)$ gauge theory with two charged complex scalar fields with masses if we introduce the Josephson interaction term between the scalar fields. We identify these sine-Gordon solitons as vortices or $\mathbf{C}{P}^1$ sigma model instantons in the bulk, which are absorbed into the domain wall world volume. These vortices can be called Josephson vortices since they appear in Josephson junctions of two superconductors. This setup gives a physical realization of a lower-dimensional analogue of Atiyah-Manton construction of Skyrmions from instanton holonomy.

The flow equations of the functional renormalization group are applied to the $O(N)$-symmetric scalar theory, for $N=1$ and $N=4$, in four Euclidean dimensions, $d=4$, to determine the effective potential and the renormalization function of the field in the broken phase. In our numerical analysis, the infrared limit, corresponding to the vanishing of the running momentum scale in the equations, is approached to obtain the physical values of the parameters by extrapolation. In the $N=4$ theory a nonperturbatively large value of the physical renormalization of the longitudinal component of the field is observed. The dependence of the field renormalization on the UV cutoff and on the bare coupling is also investigated.

We consider the nonequilibrium dynamics of a real quantum scalar field. We show the formal equivalence of the exact evolution equations for the statistical and spectral two-point functions with a fictitious Langevin process and examine the conditions under which a local Markovian dynamics is a valid approximation. In quantum field theory, the memory kernel and the noise correlator typically exhibit long time power laws and are thus highly nonlocal, thereby questioning the possibility of a local description. We show that despite this fact, there is a finite time range during which a local description is accurate. This requires the theory to be (effectively) weakly coupled. We illustrate the use of such a local description for studies of decoherence and entropy production in quantum field theory.

The construction of the Agua Negra tunnels that will link Argentina and Chile under the Andes, the world’s longest mountain range, opens the possibility of building the first deep underground laboratory in the Southern Hemisphere. This laboratory has the acronym ANDES (Agua Negra Deep Experiment Site) and its overburden could be as large as $\sim 1.7\mathrm{km}$ of rock, or 4500 mwe, providing an excellent low background environment to study physics of rare events like the ones induced by neutrinos and/or dark matter. In this paper we investigate the physics potential of a few kiloton size liquid scintillator detector, which could be constructed in the ANDES laboratory as one of its possible scientific programs. In particular, we evaluate the impact of such a detector for the studies of geoneutrinos and Galactic supernova neutrinos, assuming a fiducial volume of 3 kilotons as a reference size. We emphasize the complementary roles of such a detector to the ones of the Northern Hemisphere neutrino facilities, given the advantages of its geographical location.