We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector “aether” fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model $({\partial }_{\mu }{A}_{\nu }{)}^2$, the Maxwell Lagrangian $F_{\mu \nu }{F}^{\mu \nu }$, and a scalar Lagrangian $({\partial }_{\mu }{A}^{\mu }{)}^2$. The timelike sigma-model case is well defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.

In this paper, we introduce the $n$-dimensional Lorentzian wormhole solutions of third order Lovelock gravity. In contrast to Einstein gravity and as in the case of Gauss-Bonnet gravity, we find that the wormhole throat radius $r_0$ has a lower limit that depends on the Lovelock coefficients, the dimensionality of the spacetime, and the shape function. We study the conditions of having normal matter near the throat, and find that the matter near the throat can be normal for the region $r_0\le r\le r_{\max }$, where $r_{\max }$ depends on the Lovelock coefficients and the shape function. We also find that the third order Lovelock term with negative coupling constant enlarges the radius of the region of normal matter, and conclude that the higher order Lovelock terms with negative coupling constants enlarge the region of normal matter near the throat.

We study Einstein static universes in the context of generic $f(R)$ models. It is shown that Einstein static solutions exist for a wide variety of modified gravity models sourced by a barotropic perfect fluid with equation of state $w=p/\rho$, but these solutions are always unstable to either homogeneous or inhomogeneous perturbations. Our general results are in agreement with specific models investigated in that past. We also discuss how our techniques can be applied to other scenarios in $f(R)$ gravity.

It has been argued that a Universe governed by Eddington-Born-Infeld gravity can be compatible with current cosmological constraints. The extra fields introduced in this theory can behave as both dark matter and dark energy, unifying the dark sector in one coherent framework. We show the various roles the extra fields can play in the expansion of the Universe and study the evolution of linear perturbations in the various regimes. We find that, as a unified theory of the dark sector, Eddington-Born-Infeld gravity will lead to excessive fluctuations in the cosmic microwave background on large scales. In the presence of a cosmological constant, however, the extra fields can behave as a form of nonparticulate dark matter and can lead to a cosmology which is entirely compatible with current observations of large scale structure. We discuss the interpretation of this form of dark matter and how it can differ from standard, particulate dark matter.

A well-motivated extension of higher order holonomy corrections in loop quantum cosmology (LQC) for the $k=0$ Friedmann-Robertson-Walker model is investigated at the level of heuristic effective dynamics. It reveals that the quantum bounce is generic, regardless of the order of corrections, and the matter density remains finite, bounded from above by an upper bound in the regime of the Planckian density, even if all orders of corrections are included. This observation provides further evidence that the quantum bounce is essentially a consequence of the loopy nature (i.e. intrinsic discreteness) of LQC and LQC is fundamentally different from the Wheeler-DeWitt theory; it also encourages one to construct the quantum theory of LQC with the higher order holonomy corrections, which might be understood as related to the higher $j$ representations in the Hamiltonian operator of loop quantum gravity.

The recent positron excess observed in the PAMELA satellite experiment strengthens previous experimental findings. We give here an analysis of this excess in the framework of the Stueckelberg extension of the standard model which includes an extra $U(1{)}_X$ gauge field and matter in the hidden sector. Such matter can produce the right amount of dark matter consistent with the Wilkinson Microwave Anisotropy Probe (WMAP) constraints. Assuming the hidden sector matter to be Dirac fermions it is shown that their annihilation can produce the positron excess with the right positron energy dependence seen in the HEAT, AMS, and the PAMELA experiments. The predictions of the $\overline{p}/p$ flux ratio also fit the data.

We try to constrain the noncommutativity length scale of the theoretical model given in [E. Akofor, A. P. Balachandran, S. G. Jo, A. Joseph, and B. A. Qureshi, J. High Energy Phys. 05 (2008) 092.] using the observational data from ACBAR, CBI and 5 yr WMAP. ACBAR and CBI data restrict the lower bound of the noncommutativity energy scale to be around 10 TeV. We also derive an expression for the amount of noncausality coming from spacetime noncommutativity for the fields of primordial scalar perturbations that are spacelike separated.

We show that in (anomalous) $U(1)$ gauge theories with the Fayet-Iliopoulos term and with generic interactions, there are metastable vacua in which supersymmetry (SUSY) is spontaneously broken even without $U(1{)}_R$ symmetry. In this vacua, various hierarchical structures such as Yukawa hierarchy can be explained by the smallness of the Fayet-Iliopoulos parameter. It is shown that, by adding just one positively charged field to phenomenologically viable models, spontaneous SUSY breaking is realized. Moreover, we propose a new scenario for the stabilization of the moduli in the SUSY breaking models. It is a new feature that the moduli can be stabilized without the superpotential being dependent on them.

Supersymmetric theories with bilinear $R$-parity violation can give rise to the observed neutrino masses and mixings. One important feature of such models is that the lightest supersymmetric particle might have a sufficiently large lifetime to produce detached vertices. Working in the framework of supergravity models, we analyze the potential of the LHCb experiment to search for supersymmetric models exhibiting bilinear $R$-parity violation. We show that the LHCb experiment can probe a large fraction of the $m_0\otimes m_{1/2}$, being able to explore gluino masses up to 1.3 TeV. The LHCb discover potential for these kinds of models is similar to the ATLAS and CMS ones in the low luminosity phase of operation of the LHC.

We propose a new lattice framework to extract the relevant gluonic energy scale of QCD phenomena which is based on a “cut” on link variables in momentum space. This framework is expected to be broadly applicable to all lattice QCD calculations. Using this framework, we quantitatively determine the relevant energy scale of color confinement, through the analyses of the quark-antiquark potential and meson masses. The relevant energy scale of color confinement is found to be below 1.5 GeV in the Landau gauge. In fact, the string tension is almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV. When the relevant low-energy region is cut, the quark-antiquark potential is approximately reduced to a Coulomb-like potential, and each meson becomes a quasifree quark pair. As an analytical model calculation, we also investigate the dependence of the Richardson potential on the cut, and find the consistent behavior with the lattice result.

Lattice QCD with two flavors of Wilson fermions can exhibit spontaneous breaking of flavor and parity, with the resulting “Aoki phase” characterized by the nonzero expectation value $⟨\overline{\psi }{\gamma }_5{\tau }_3\psi ⟩\ne 0$. This phenomenon can be understood using the chiral effective theory appropriate to the Symanzik effective action. Within this standard analysis, the flavor-singlet pseudoscalar expectation value vanishes: $⟨i\overline{\psi }{\gamma }_5\psi ⟩=0$. A recent reanalysis has questioned this understanding, arguing that either the Aoki phase is unphysical, or that there are additional phases in which $⟨i\overline{\psi }{\gamma }_5\psi ⟩\ne 0$. The reanalysis uses the properties of probability distribution functions for observables built of fermion fields and expansions in terms of the eigenvalues of the Hermitian Wilson-Dirac operator. Here I show that the standard understanding of the Aoki phase can, in fact, be consistent with the approach used in the reanalysis. Furthermore, if one assumes that the standard understanding is correct, one can use the methods of the reanalysis to derive lattice generalizations of the continuum sum rules of Leutwyler and Smilga.

We present a general framework for analyzing inhomogeneous (color-)superconducting phases in the mean-field approximation without restriction to the Ginzburg-Landau approach. As a first application, we calculate real gap functions with general one-dimensional periodic structures for a $3+1$-dimensional toy model having two fermion species. The resulting solutions are energetically favored against homogeneous superconducting (BCS) and normal conducting phases in a window for the chemical potential difference $\delta \mu$ which is about twice as wide as that for the most simple plane-wave ansatz (“Fulde-Ferrell phase”). At the lower end of this window, we observe the formation of a soliton lattice and a continuous phase transition to the BCS phase. At the higher end of the window the gap functions are sinusoidal, and the transition to the normal conducting phase is of first order. We also discuss the quasiparticle excitation spectrum in the inhomogeneous phase. Finally, we compare the gap functions with the known analytical solutions of the $1+1$-dimensional theory.

We present measurements of the time-dependent $CP$-violation parameters $S$ and $C$ in the decays $B^0\to \omega K_S^0$, $B^0\to {\eta }^{\prime }{K}^0$, reconstructed as ${\eta }^{\prime }{K}_S^0$ and ${\eta }^{\prime }{K}_L^0$, and $B^0\to {\pi }^0{K}_S^0$. The data sample corresponds to the full BABAR dataset of $467\times {10}^6$ $B\overline{B}$ pairs produced at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at the Stanford Linear Accelerator Center. The results are $S_{\omega K_S^0}={0.55}_{-0.29}^{+0.26}\pm 0.02$, $C_{\omega K_S^0}=-{0.52}_{-0.20}^{+0.22}\pm 0.03$, $S_{{\eta }^{\prime }{K}^0}=0.57\pm 0.08\pm 0.02$, $C_{{\eta }^{\prime }{K}^0}=-0.08\pm 0.06\pm 0.02$, $S_{{\pi }^0{K}_S^0}=0.55\pm 0.20\pm 0.03$, and $C_{{\pi }^0{K}_S^0}=0.13\pm 0.13\pm 0.03$, where the first errors are statistical and the second systematic. These results are consistent with our previous measurements and the world average of $\sin 2\beta$ measured in $B^0\to J/\psi K_S^0$.

The periodic standing-wave method studies circular orbits of compact objects coupled to helically symmetric standing-wave gravitational fields. From this solution an approximation is extracted for the strong field, slowly inspiralling motion of binary black holes and binary neutron stars. Previous work on this project has developed a method using a few multipoles of specially adapted coordinates well suited both to the radiation and the source regions. This method had previously been applied to linear and nonlinear scalar field models, to linearized gravity, and to a post-Minkowski approximation. Here we present the culmination of this approach: the application of the method in full general relativity. The fundamental equations had previously been developed and the challenge presented by this step is primarily a computational one which was approached with an innovative technique. The numerical results of these computations are compared with the corresponding results from linearized and post-Minkowksi computations.

An energy threshold of $(220\pm 10)\mathrm{eV}$ was achieved at an efficiency of 50% with a four-channel ultralow-energy germanium detector, each with an active mass of 5 g. This provides a unique probe to weakly interacting massive particles (WIMP) dark matter with mass below 10 GeV. With a data acquisition live time of 0.338 kg-day at the Kuo-Sheng Laboratory, constraints on WIMPs in the galactic halo were derived. The limits improve over previous results on both spin-independent WIMP-nucleon and spin-dependent WIMP-neutron cross-sections for WIMP mass between 3 and 6 GeV. Sensitivities for full-scale experiments are projected. This detector technique makes the unexplored sub-keV energy window accessible for new neutrino and dark matter experiments.

A Faraday rotation experiment can set limits on the magnetic moment of a electrically-neutral, dark-matter particle, and the limits increase in stringency as the candidate-particle mass decreases. Consequently, if we assume the dark-matter particle to be a thermal relic, our most stringent constraints emerge at the keV mass scale. We discuss how such an experiment could be realized and determine the limits on the magnetic moment as a function of mass which follow given demonstrated experimental capacities.

During the last few years the Tevatron has dramatically improved the bounds on rare $B$-meson decays into two leptons. In the case of $B_s^0\to {\mu }^{+}{\mu }^{-}$, the current bound is only 10 times greater than the standard model expectation. Sensitivity to this decay is one of the benchmark goals for LHCb performance and physics. The Higgs penguin dominates this rate in the region of large $\tan \beta$ of the minimal supersymmetric standard model. This is not necessarily the case in the region of low $\tan \beta$, since box and $Z$-penguin diagrams may contribute at a comparable rate. In this article, we compute the complete one-loop minimal supersymmetric standard model contribution to $B_{s,d}^0\to {\ell }^{+}{\ell }^{\prime -}$ for $\ell$, ${\ell }^{\prime }=e$, $\mu$. We study the predictions for general values of $\tan \beta$ with arbitrary flavor mixing parameters. We discuss the possibility of both enhancing and suppressing the branching ratios relative to their standard model expectations. In particular, we find that there are “cancellation regions” in parameter space where the branching ratio is suppressed well below the standard model expectation, making it effectively invisible to the LHC.

We calculate the pretzelosity distribution ($h_{1T}^{\perp }$), which is one of the eight leading twist transverse momentum dependent parton distributions (TMDs), in the light-cone formalism. We find that this quantity has a simple relation with the quark orbital angular momentum distribution, thus it may provide a new possibility to access the quark orbital angular momentum inside the nucleon. The pretzelosity distribution can manifest itself through the $\sin (3{\varphi }_h-{\varphi }_S)$ asymmetry in semi-inclusive deep inelastic scattering process. We calculate the $\sin (3{\varphi }_h-{\varphi }_S)$ asymmetry at HERMES, COMPASS, and JLab kinematics and present our prediction on different targets including the proton, deuteron, and neutron targets. Inclusion of transverse momentum cut in data analysis could significantly enhance the $\sin (3{\varphi }_h-{\varphi }_S)$ asymmetry for future measurements.

We discuss the possible extension of the bosonic classical field theory simulations to include fermions. This problem has been addressed in terms of the inhomogeneous mean-field approximation by Aarts and Smit. By performing a stochastic integration of an equivalent set of equations we can extend the original $1+1$ dimensional calculations so that they become feasible in higher dimensions. We test the scheme in $2+1$ dimensions and discuss some classical applications with fermions for the first time, such as the decay of oscillons.

We study the gravity duals of symmetry-breaking deformations of superconformal field theories, AdS/CFT dual to Type IIB string theory on ${\mathrm{AdS}}_5\times Y$ where $Y$ is a Sasaki-Einstein manifold. In these vacua both conformal invariance and baryonic symmetries are spontaneously broken. We present a detailed discussion of the supergravity moduli space, which involves flat form fields on asymptotically conical Calabi-Yau manifolds and match this to the gauge theory vacuum moduli space. We discuss certain linearized fluctuations of the moduli, identifying the Goldstone bosons associated with spontaneous breaking of nonanomalous baryonic symmetries. The remaining moduli fields are related to spontaneous breaking of anomalous baryonic symmetries. We also elaborate on the proposal that computing condensates of baryon operators is equivalent to computing the partition function of a noncompact Euclidean D3-brane in the background supergravity solution, with fixed boundary conditions at infinity.