A generic lesson of string theory is that the coupling constants of an effective low energy theory are determined by the vacuum values of a set of fields—the so-called moduli—some of which are stabilized at relatively low masses by nonperturbative effects. We argue that the physics of these moduli cannot be separated from the issues of dynamical and gauge mediated supersymmetry breaking. To illustrate this point we present a modified version of the type IIB Kachru-Kallosh-Linde-Trivedi model where the criteria for gauge mediated supersymmetry breaking may be realized.

We use a functional approach to study various aspects of the quantum effective dynamics of moving, planar, dispersive mirrors, coupled to scalar or Dirac fields, in different numbers of dimensions. We first compute the Euclidean effective action, and use it to derive the imaginary part of the “in-out” effective action. We also obtain, for the case of the real scalar field in $1+1$ dimensions, the Schwinger-Keldysh effective action and a semiclassical Langevin equation that describes the motion of the mirror including noise and dissipative effects due to its coupling to the quantum fields.

We propose a quasilocal formula for the linear momentum of black-hole horizons inspired by the formalism of quasilocal horizons. We test this formula using two complementary configurations: (i) by calculating the large orbital linear momentum of the two black holes in an unequal-mass, zero-spin, quasicircular binary and (ii) by calculating the very small recoil momentum imparted to the remnant of the head-on collision of an equal-mass, anti-aligned-spin binary. We obtain results consistent with the horizon trajectory in the orbiting case, and consistent with the net radiated linear momentum for the much smaller head-on recoil velocity.

The unparticle stuff scenario related to the nontrivial IR fixed point in 4D-conformal field theory was recently suggested by Georgi. We illustrate its physical effects in the deep inelastic scattering (DIS) process. The possible signals of the unparticle related to parity violation asymmetry in DIS is investigated. It is found out that the behavior of this parity violation signal is sensitive to the value of the scale dimension $d_{\mathcal{U}}$ of the unparticle.

A numerical technique is proposed for an efficient numerical determination of the average phase factor of the fermionic determinant continued to imaginary values of the chemical potential. The method is tested in QCD with eight flavors of dynamical staggered fermions. A direct check of the validity of analytic continuation is made on small lattices and a study of the scaling with the lattice volume is performed.

We investigate the transition form factors between nucleon and $\Delta (1232)$ particles by using a covariant quark-spectator-diquark field theory model in $(3+1)$ dimensions. Performing a light-front calculation in parallel with the manifestly covariant calculation in the light-front helicity basis, we examine the light-front zero-mode contribution to the helicity components of light-front good (“$+$”) current matrix elements. Choosing the light-front gauge (${ϵ}_{h=\pm }^{+}=0$) with circular polarization in the Drell-Yan-West frame, we find that only the helicity components $(\frac{1}{2},\frac{1}{2})$ and $(\frac{1}{2},-\frac{1}{2})$ of the good current receive the zero-mode contribution. Taking into account the zero mode, we find the prescription independence in obtaining the light-front solution of form factors from any three helicity matrix elements with smeared light-front wave functions. The angular condition, which guarantees the full covariance of different schemes, is recovered.

Considering a general mass matrix for quasidegenerate neutrinos and treating the experimentally known oscillation parameters as inputs, we study the correlation between the degenerate mass scale $(m)$ and the mixing angle ${\theta }_{13}$. We find that, corresponding to different values of $m$, there exist upper bounds on ${\theta }_{13}$, so that a precise determination of the latter in the future may put an upper limit on the former, and vice versa. One can also find a possible correlation between $m$ and a lower bound of ${\theta }_{13}$, depending on the relative strength of the unperturbed degenerate mass matrix and the perturbation. The possible constraints on the parameters of a few models of quasidegenerate neutrinos are briefly discussed.

We examine the effects of new physics on the Higgs sector of the standard model, focusing on the effects on the Higgs self-couplings. We demonstrate that a low mass Higgs, $m_h<2m_t$, can have a strong effective self-coupling due to the effects of a new interaction at a TeV. We investigate the possibility that the first evidence of such an interaction could be a Higgs-Higgs bound state. To this end, we construct an effective field theory formalism to examine the physics of such a low mass Higgs boson. We explore the possibility of a nonrelativistic bound state of the Higgs field (Higgsium) at CERN’s Large Hadron Collider and construct a nonrelativistic effective field theory of the Higgs sector that is appropriate for such studies (NRHET).

We report on a search for the radiative decay of ${\rm Y}(1\mathrm{S})$ to the pseudoscalar mesons $\eta$ and ${\eta }^{\prime }$ in $(21.2\pm 0.2)\times {10}^6$ ${\rm Y}(1\mathrm{S})$ decays collected with the CLEO III detector at the Cornell Electron Storage Ring. The $\eta$ meson was reconstructed in the three modes $\eta \to \gamma \gamma$, $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, or $\eta \to {\pi }^0{\pi }^0{\pi }^0$. The ${\eta }^{\prime }$ meson was reconstructed in the mode ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\eta$ with $\eta$ decaying through any of the above three modes, and also ${\eta }^{\prime }\to \gamma {\rho }^0$, where ${\rho }^0\to {\pi }^{+}{\pi }^{-}$. Five out of the seven submodes are found to have very low backgrounds. In four of them we find no signal candidates and in one [${\rm Y}(1\mathrm{S})\to \gamma {\eta }^{\prime }$, ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\eta$, $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$] there are two good signal candidates, which is insufficient evidence to claim a signal. The other two submodes ($\eta \to \gamma \gamma$ and ${\eta }^{\prime }\to \gamma \rho$) are background limited, and show no excess of events in their signal regions. We combine the results from different channels and obtain upper limits at the 90% C.L. which are $\mathcal{B}({\rm Y}(1\mathrm{S})\to \gamma \eta )<1.0\times {10}^{-6}$ and $\mathcal{B}({\rm Y}(1\mathrm{S})\to \gamma {\eta }^{\prime })<1.9\times {10}^{-6}$. Our limits are an order of magnitude tighter than the previous ones and below the predictions made by some theoretical models.

In this paper we analyze a version of the $\mathrm{SU}(N)$ gauge theory on noncommutative space-time which is one-loop renormalizable to first order in the expansion in the noncommutativity parameter $\theta$. The one-loop renormalizability is obtained through the modification of the initial “minimal” action, with the gauge fields in the adjoint representation of $\mathrm{SU}(N)$, and by the renormalization of the noncommutativity parameter $\theta$.

We study the possibility of decoupling gravity from the vacuum energy. This is effectively equivalent to promoting Newton’s constant to a high-pass filter that degravitates sources of characteristic wavelength larger than a certain macroscopic (super) horizon scale $L$. We study the underlying physics and the consistency of this phenomenon. In particular, the absence of ghosts, already at the linear level, implies that in any such theory the graviton should either have a mass $1/L$, or be a resonance of similar width. This has profound physical implications for the degravitation idea.

We propose a retrofitted gravity-mediation model which alleviates the gravitino overproduction from decays of an inflaton and a supersymmetry breaking field. In the model, we introduce an approximate $U(1)$ symmetry under which the supersymmetry breaking field is charged, although it is broken by a mass term of messenger fields to generate gaugino masses of order the weak scale. In a low-scale inflation model, we find regions in which the gravitino-overproduction problem is avoided.

We consider the extension of the supersymmetric Pati-Salam model which solves the $b$-quark mass problem of supersymmetric grand unified models with exact Yukawa unification and universal boundary conditions and leads to the so-called new shifted hybrid inflationary scenario. We show that this model can also lead to a new version of smooth hybrid inflation based only on renormalizable interactions provided that a particular parameter of its superpotential is somewhat small. The potential possesses valleys of minima with classical inclination, which can be used as inflationary paths. The model is consistent with the fitting of the three-year Wilkinson microwave anisotropy probe data by the standard power-law cosmological model with cold dark matter and a cosmological constant. In particular, the spectral index turns out to be adequately small so that it is compatible with the data. Moreover, the Pati-Salam gauge group is broken to the standard model gauge group during inflation and, thus, no monopoles are formed at the end of inflation. Supergravity corrections based on a nonminimal Kähler potential with a convenient choice of a sign keep the spectral index comfortably within the allowed range without generating maxima and minima of the potential on the inflationary path. So, unnatural restrictions on the initial conditions for inflation can be avoided.

Cosmic structure formation leads to large-scale shocked baryonic flows which are expected to produce a cosmological population of structure-formation cosmic rays (SFCRs). Interactions between SFCRs and ambient baryons will produce lithium isotopes via $\alpha +\alpha \to {}^{6,7}\mathrm{Li}$. This pre-galactic (but nonprimordial) lithium should contribute to the primordial ${}^7\mathrm{Li}$ measured in halo stars and must be subtracted in order to arrive to the true observed primordial lithium abundance. In this paper we point out that the recent halo star ${}^6\mathrm{Li}$ measurements can be used to place a strong constraint to the level of such contamination, because the exclusive astrophysical production of ${}^6\mathrm{Li}$ is from cosmic-ray interactions. We find that the putative ${}^6\mathrm{Li}$ plateau, if due to pre-galactic cosmic-ray interactions, implies that SFCR-produced lithium represents ${\mathrm{Li}}_{\mathrm{SFCR}}/{\mathrm{Li}}_{\mathrm{plateau}}\approx 15\%$ of the observed elemental Li plateau. Taking the remaining plateau Li to be cosmological ${}^7\mathrm{Li}$, we find a revised (and slightly worsened) discrepancy between the Li observations and big bang nucleosynthesis predictions by a factor of ${}^7\mathrm{Li}_{\mathrm{BBN}}/{}^7\mathrm{Li}_{\mathrm{plateau}}\approx 3.7$. Moreover, SFCRs would also contribute to the extragalactic gamma-ray background (EGRB) through neutral pion production. This gamma-ray production is tightly related to the amount of lithium produced by the same cosmic rays; the ${}^6\mathrm{Li}$ plateau limits the pre-galactic (high-redshift) SFCR contribution to be at the level of $I_{{\gamma }_{\pi }\mathrm{SFCR}}/I_{\mathrm{EGRB}}\lesssim 5\%$ of the currently observed EGRB.

The thermodynamic properties of an $SU(3)$ gauge theory without quarks are calculated using a string formulation for $1.2T_c\le T\le 3T_c$. The results are in good agreement with the lattice data. We also comment on $SU(N)$ gauge theories.

In this paper, we explore the implications of a two-point discretization of an extra dimension in a five-dimensional quantum setup. We adopt a pragmatic attitude by considering the dynamics of spin-half particles through the simplest possible extension of the existing Dirac and Pauli equations. It is shown that the benefit of this approach is to predict new physical phenomena while maintaining the number of constitutive hypotheses at minimum. As the most striking feature of the model, we demonstrate the possibility of fermionic matter oscillations between the two four-dimensional sections and hyperfast displacements in case of asymmetric warping (without conflicting special relativity). This result, similar to previous reported ones in braneworld theories, is completely original as it is derived by using quantum mechanics only without recourse to general relativity and bulk geodesics calculation. The model allows causal contact between normally disconnected regions. If it proves to be physically founded, its practical aspects could have deep implications for the search of extra dimensions.

We analyze the stability of the Einstein static universe by considering homogeneous scalar perturbations in the context of $f(R)$ modified theories of gravity. By considering specific forms of $f(R)$, the stability regions of the solutions are parametrized by a linear equation of state parameter $w=p/\rho$. Contrary to classical general relativity, it is found that in $f(R)$ gravity a stable Einstein cosmos with a positive cosmological constant does indeed exist. Thus, we are lead to conclude that, in principle, modifications in $f(R)$ gravity stabilize solutions which are unstable in general relativity.

The annihilation of dark matter (DM) in the Galaxy could produce specific imprints on the spectra of antimatter species in Galactic cosmic rays, which could be detected by upcoming experiments such as PAMELA and AMS02. Recent studies show that the presence of substructures can enhance the annihilation signal by a “boost factor” that not only depends on energy, but that is intrinsically a statistical property of the distribution of DM substructures inside the Milky Way. We investigate a scenario in which substructures consist of $\sim 100$ “minispikes” around intermediate-mass black holes. Focusing on primary positrons and antiprotons, we find large boost factors, up to a few thousand, that exhibit a large variance at high energy in the case of positrons and at low energy in the case of antiprotons. As a consequence, an estimate of the DM particle mass based on the observed cutoff in the positron spectrum could lead to a substantial underestimate of its actual value.