We study the Casimir effect for parallel plates with massless Majorana fermions obeying the bag boundary conditions at finite temperature. The thermal influence will modify the effect. It is found that the sign of the Casimir energy remains negative if the product of the plate distance and the temperature is larger than a special value, otherwise the energy will change to positive. The Casimir energy rises with the stronger thermal influence. We show that the attractive Casimir force between two parallel plates becomes greater with increasing temperature. In the case of the piston system involving the same Majorana fermions with the same boundary conditions, the attractive force on the piston will be weaker in higher-temperature surroundings.

We examine the picture of emergent geometry arising from a mass-deformed matrix model. Because of the mass deformation, a vacuum geometry turns out to be a constant curvature spacetime such as $d$-dimensional sphere and (anti-)de Sitter spaces. We show that the mass-deformed matrix model giving rise to the constant curvature spacetime can be derived from the $d$-dimensional Snyder algebra. The emergent geometry beautifully confirms all the rationale inferred from the algebraic point of view that the $d$-dimensional Snyder algebra is equivalent to the Lorentz algebra in $(d+1)$-dimensional flat spacetime. For example, a vacuum geometry of the mass-deformed matrix model is completely described by a $G$-invariant metric of coset manifolds $G/H$ defined by the Snyder algebra. We also discuss a nonlinear deformation of the Snyder algebra.

We present a complete explicit $N=1$, $d=4$ supergravity action in an arbitrary Jordan frame with nonminimal scalar-curvature coupling of the form $\Phi (z,\overline{z})R$. The action is derived by suitably gauge fixing the superconformal action. The theory has a modified Kähler geometry, and it exhibits a significant dependence on the frame function $\Phi (z,\overline{z})$ and its derivatives over scalars, in the bosonic as well as in the fermionic part of the action. Under certain simple conditions, the scalar kinetic terms in the Jordan frame have a canonical form. We consider an embedding of the next-to-minimal supersymmetric standard model (NMSSM) gauge theory into supergravity, clarifying the Higgs inflation model recently proposed by Einhorn and Jones. We find that the conditions for canonical kinetic terms are satisfied for the NMSSM scalars in the Jordan frame, which leads to a simple action. However, we find that the gauge singlet field experiences a strong tachyonic instability during inflation in this model. Thus, a modification of the model is required to support the Higgs-type inflation.

We study the consequences of further modification of $f(R,R_{\mu \nu }{R}^{\mu \nu },R_{\mu \nu \sigma \rho }{R}^{\mu \nu \sigma \rho })/f(R)$ theories by means of the Dirac-Born-Infeld procedure, which is the replacement of $f$ by $\lambda (\sqrt{1+2f/\lambda }-1)$ (the free parameter $\lambda$ fixes an additional energy scale). We pay special attention to the definition of masses of the linearized propagating degrees of freedom because they are important to judge the stability of the linearization around vacuum background spaces. In this context we discuss the subtleties associated with expanding $f(R,R_{\mu \nu }{R}^{\mu \nu },R_{\mu \nu \sigma \rho }{R}^{\mu \nu \sigma \rho })$ Lagrangians around maximally symmetric spaces of constant curvature, as well as with equivalence of the linearized Lagrangian to a scalar-tensor theory. Investigation of the consequences of applying the Dirac-Born-Infeld (DBI) strategy to further modify quadratic theories on the stability of de Sitter vacuum, as well as its impact on the cosmological dynamics, are the main concern of this paper. We show that (i) although the DBI deformation does not affect the Ostrogradski stability, other important instabilities such as the Ricci and scalar-tachyon ones, may be indeed surmounted (sometimes at the cost of renouncing to the original motivation of the DBI strategy, to avoid singularities), and (ii) DBI transforming the original theory broadens its possibilities to do cosmology since the asymptotic structure of the DBI-dual theory is richer than in the standard case. In particular, either the dimension of the phase space is increased, or there appear bifurcations in the control-parameter space.

We present a new signature by which one could potentially discriminate between a spectrum of gravitational radiation generated by a self-ordering scalar field vs that of inflation, specifically a comparison of the magnitude of a flat spectrum at frequencies probed by future direct detection experiments to the magnitude of a possible polarization signal in the cosmic microwave background radiation. In the process we clarify several issues related to the proper calculation of such modes, focusing on the effect of post-horizon-crossing evolution.

In this paper, the Dvali-Gabadadze-Porrati (DGP) brane model is confronted by current cosmic observational data sets from geometrical and dynamical perspectives. On the geometrical side, the recently released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation from the Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey (transverse and radial to line-of-sight data points), the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations [shift parameters $R$, $l_a(z_{*})$ and redshift at the last scatter surface $z_{*}$], ages of high redshifts galaxies, i.e., the lookback time and the high redshift gamma ray bursts are used. On the dynamical side, data points about the growth function of matter linear perturbations are used. Using the same data set combination, we also constrain the flat $\Lambda \mathrm{CDM}$ model as a comparison. The results show that current geometrical and dynamical observational data sets much favor the flat $\Lambda \mathrm{CDM}$ model and the departure from it is above $4\sigma (6\sigma )$ for the spatially flat DGP model with (without) SN systematic errors. The consistence of growth function data points is checked in terms of a relative departure of redshift-distance relation.

We reconsider nonminimal $\lambda {\varphi }^4$ chaotic inflation which includes the gravitational coupling term $\xi \mathcal{R}{\varphi }^2$, where $\varphi$ denotes a gauge singlet inflaton field and $\mathcal{R}$ is the Ricci scalar. For $\xi \gg 1$, we require, following recent discussions, that the energy scale ${\lambda }^{1/4}{m}_P/\sqrt{\xi }$ for inflation should not exceed the effective UV cutoff scale $m_P/\xi$, where $m_P$ denotes the reduced Planck scale. The predictions for the tensor-to-scalar ratio $r$ and the scalar spectral index $n_s$ are found to lie within the Wilkinson Microwave Anisotropy Probe $1\mathrm{\text{−}}\sigma$ bounds for ${10}^{-12}\lesssim \lambda \lesssim {10}^{-4}$ and ${10}^{-3}\lesssim \xi \lesssim {10}^2$. In contrast, the corresponding predictions of minimal $\lambda {\varphi }^4$ chaotic inflation lie outside the Wilkinson Microwave Anisotropy Probe $2\mathrm{\text{−}}\sigma$ bounds. We also find that $r\gtrsim 0.002$, provided the scalar spectral index $n_s\ge 0.96$. In estimating the lower bound on $r$, we take into account possible modifications due to quantum corrections of the tree level inflationary potential.

We discuss the additional perturbation introduced during inflation by quantum stress tensor fluctuations of a conformally invariant field such as the photon. We consider both a kinematical model, which deals only with the expansion fluctuations of geodesics, and a dynamical model which treats the coupling of the stress tensor fluctuations to a scalar inflaton. In neither model do we find any growth at late times, in accordance with a theorem due to Weinberg. What we find instead is a correction which becomes larger the earlier one starts inflation. This correction is non-Gaussian and highly scale dependent, so the absence of such effects from the observed power spectra may imply a constraint on the total duration of inflation. We discuss different views about the validity of perturbation theory at very early times during which currently observable modes are trans-Planckian.

Neutrino mass patterns and mixing have been studied in the context of the next-to-minimal supersymmetric standard model (NMSSM) with three gauge singlet neutrino superfields. We consider the case with the assumption of $R$-parity conservation. The vacuum expectation value of the singlet scalar field $S$ of NMSSM induces the Majorana masses for the right-handed neutrinos as well as the usual $\mu$ term. The contributions to the light neutrino mass matrix at the tree level as well as one-loop level are considered, consistent with the tribimaximal pattern of neutrino mixing. Light neutrino masses arise at the tree level through a TeV-scale seesaw mechanism involving the right-handed neutrinos. Although all the three light neutrinos acquire nonzero masses at the tree level, we show that the one-loop contributions can be comparable in size under certain conditions. Possible signatures to probe this model at the LHC and its distinguishing features compared to other models of neutrino mass generation are briefly discussed.

We calculate finite-volume effects on the pion masses and decay constant in twisted mass lattice QCD at finite lattice spacing. We show that the lighter neutral pion in twisted mass lattice QCD gives rise to finite-volume effects that are exponentially enhanced when compared to those arising from the heavier charged pions. We demonstrate that the recent two flavor twisted mass lattice data can be better fitted when twisted mass effects in finite-volume corrections are taken into account.

The weak kaon production off the nucleon induced by neutrinos is studied at the low and intermediate energies of interest for some ongoing and future neutrino oscillation experiments. This process is also potentially important for the analysis of proton decay experiments. We develop a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are $f_{\pi }$, the pion decay constant, Cabibbo’s angle, the proton and neutron magnetic moments, and the axial vector coupling constants for the baryons octet, $D$ and $F$, that are obtained from the analysis of the semileptonic decays of neutron and hyperons. The studied mechanisms are the main source of kaon production for neutrino energies up to 1.2 to 1.5 GeV for the various channels and the cross sections are large enough to be amenable to be measured by experiments such as Minerva and T2K.

We study a holographic model realizing an “antiferromagnetic” phase in which a global $SU(2)$ symmetry representing spin is broken down to a $U(1)$ by the presence of a finite electric charge density. This involves the condensation of a neutral scalar field in a charged anti–de Sitter black hole. We observe that the phase transition for both neutral and charged (as in the standard holographic superconductor) order parameters can be driven to zero temperature by a tuning of the UV conformal dimension of the order parameter, resulting in a quantum phase transition of the Berezinskii-Kosterlitz-Thouless–type. We also characterize the antiferromagnetic phase and an externally forced ferromagnetic phase by showing that they contain the expected spin waves with linear and quadratic dispersions, respectively.

For spatially bounded free fields, the Bekenstein bound states that the specific entropy satisfies the inequality $\frac{S}{E}\le 2\pi R$, where $R$ stands for the radius of the smallest sphere that circumscribes the system. The validity of the Bekenstein bound in the asymptotically free side of the Euclidean $(\lambda {\phi }^4{)}_d$ scalar field theory is investigated. We consider the system in thermal equilibrium with a reservoir at temperature ${\beta }^{-1}$ and defined in a compact spatial region without boundaries. Using the effective potential, we discuss the thermodynamic of the model. For low and high temperatures the system presents a condensate. We present the renormalized mean energy $E$ and entropy $S$ for the system and show in which situations the specific entropy satisfies the quantum bound.

Bayesian inferences in high energy physics often use uniform prior distributions for parameters about which little or no information is available before data are collected. The resulting posterior distributions are therefore sensitive to the choice of parametrization for the problem and may even be improper if this choice is not carefully considered. Here we describe an extensively tested methodology, known as reference analysis, which allows one to construct parametrization-invariant priors that embody the notion of minimal informativeness in a mathematically well-defined sense. We apply this methodology to general cross section measurements and show that it yields sensible results. A recent measurement of the single-top quark cross section illustrates the relevant techniques in a realistic situation.

We use the “general gauge mediation” (GGM) formalism to describe a five-dimensional setup with an $S^1/{\mathbb{Z}}_2$ orbifold. We first consider a model independent supersymmetry breaking hidden sector on one boundary and generic chiral matter on another. Using the definition of GGM, the effects of the hidden sector are contained in a set of global symmetry current correlator functions and is mediated through the bulk. We find the gaugino, sfermion and hyperscalar mass formulas for minimal and generalized messengers in different regimes of a large, small and intermediate extra dimension. Then we use the five-dimensional GGM formalism to construct a model in which an $SU(5)$ Intriligator, Seiberg and Shih (ISS) model is located on the hidden boundary. We weakly gauge a global symmetry of the ISS model and associate it with the bulk vector superfield. Compared to four-dimensional GGM, there is a natural way to adjust the gaugino versus sfermion mass ratio by a factor $(M\ell {)}^2$, where $M$ is a characteristic mass scale of the supersymmetry breaking sector and $\ell$ is the length of the extra dimension.

We present the first $2+1$ flavor spectrum measurements of glueball states using high statistics simulations with improved staggered fermions. We find a spectrum consistent with quenched measurements of scalar, pseudoscalar, and tensor glueball states. The measurements were made using 5000 configurations at a lattice spacing of 0.123 fm and pion mass of 280 MeV and 3000 configurations at 0.092 fm with a pion mass of 360 MeV. We see some evidence of coupling to $2\pi$ states. We compare our results with the experimental glueball candidate spectrum as well as quenched glueball estimates.

We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles produced in association with a large transverse momentum jet ($\sim 2.2{\mathrm{fb}}^{-1}$) or with a Drell-Yan lepton pair ($\sim 2.7{\mathrm{fb}}^{-1}$) in the $Z$-boson mass region [$70<M(\mathrm{\text{pair}})<110\mathrm{GeV}/c^2$] as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton pair or the leading jet in each event to define regions of $\eta \mathrm{\text{−}}\varphi$ space that are sensitive to the modeling of the underlying event. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte Carlo models.

We propose another method to compute the Casimir force in noncommutative Randall-Sundrum braneworld model considered by K. Nouicer and Y. Sabri, Phys. Rev. D 80, 086013 (2009). recently. Our method can be used to compute the Casimir force to any order in the noncommutative parameter. Contrary to the claim made by K. Nouicer and Y. Sabri that repulsive Casimir force can appear in the first order approximation, we show that the Casimir force is always attractive at any order of approximation.

We study a gauge theory model where there is an intermediate symmetry breaking to a metastable vacuum that breaks a simple gauge group to a $U(1)$ factor. Such a model admits the existence of metastable magnetic monopoles, which we dub false monopoles. We prove the existence of these monopoles in the thin-wall approximation. We determine the instantons for the collective coordinate that corresponds to the radius of the monopole wall and we calculate the semiclassical tunneling rate for the decay of these monopoles. The monopole decay consequently triggers the decay of the false vacuum. As the monopole mass is increased, we find an enhanced rate of decay of the false vacuum relative to the celebrated homogeneous tunneling rate due to S. R. Coleman [Subnuclear series 13, 297 (1977).].

Restricting the functional integral to the Gribov region $\Omega$ leads to a deep modification of the behavior of Euclidean Yang-Mills theories in the infrared region. For example, a gluon propagator of the Gribov type, $\frac{k^2}{k^4+{\widehat{\gamma }}^4}$, can be viewed as a propagating pair of unphysical modes, called here $i$-particles, with complex masses $\pm i{\widehat{\gamma }}^2$. From this viewpoint, gluons are unphysical and one can see them as being confined. We introduce a simple toy model describing how a suitable set of composite operators can be constructed out of $i$-particles whose correlation functions exhibit only real branch cuts, with associated positive spectral density. These composite operators can thus be called physical and are the toy analogy of glueballs in the Gribov-Zwanziger theory.