Supersymmetry offers a cold dark matter candidate, provided that lepton number is not violated by an odd number of units. On the other hand, lepton number violation by even (two) units gives us an attractive mechanism of neutrino mass generation. Here we offer an explanation of this, in a supergravity framework underlying a supersymmetric scenario, the essential feature being particles carrying lepton numbers, which interact only gravitationally with all other known particles. It is shown that one can have the right amount of $\Delta L=2$ effect giving rise to neutrino masses, whereas the lifetime for $\Delta L=1$ decays of the lightest supersymmetric particle can be prolonged beyond the present age of the Universe.

Using a general Ginzburg-Landau effective Lagrangian, we study the topological structure and low-lying collective modes of dense QCD having both chiral and diquark condensates, for two and three massless flavors. As we found earlier, the QCD axial anomaly acts as an external field applied to the chiral condensate in a color superconductor and, as a new critical point emerges, leads to a crossover between the broken chiral symmetry and color superconducting phases. At intermediate densities where both chiral and diquark condensates are present, we derive a generalized Gell-Mann–Oakes-Renner relation between the masses of pseudoscalar bosons and the magnitude of the chiral and diquark condensates. We show explicitly the continuity of the ordinary pion at low densities to a generalized pion at high densities.

We derive the perturbative four-dimensional effective theory describing heterotic M theory with branes and antibranes in the bulk space. The backreaction of both the branes and antibranes is explicitly included. To first order in the heterotic ${ϵ}_S$ expansion, we find that the forces on branes and antibranes vanish and that the Kachru-Kallosh-Linde-Trivedi (KKLT) procedure of simply adding to the supersymmetric theory the probe approximation to the energy density of the antibrane reproduces the correct potential. However, there are additional nonsupersymmetric corrections to the gauge-kinetic functions and matter terms. The new correction to the gauge-kinetic functions is important in a discussion of moduli stabilization. At second order in the ${ϵ}_S$ expansion, we find that the forces on the branes and antibranes become nonvanishing. These forces are not precisely in the naive form that one may have anticipated and, being second order in the small parameter ${ϵ}_S$, they are relatively weak. This suggests that moduli stabilization in heterotic models with antibranes is achievable.

We present details of the analytic computation of the spectrum of lowest spin glueballs in pure Yang-Mills theory in $2+1$ dimensions. The new ingredient is provided by the conjectured new nontrivial expression for the (quasi)Gaussian part of the ground state wave functional. We show that this wave functional can be derived by solving the Schrödinger equation under certain assumptions. The mass spectrum of the theory is determined by the zeros of Bessel functions, and the agreement with available lattice data is excellent.

Starting from quaternionic $N=8$ supersymmetric mechanics we perform a reduction over a bosonic radial variable, ending up with a nonlinear off-shell supermultiplet with three bosonic end eight fermionic physical degrees of freedom. The geometry of the bosonic sector of the most general sigma-model type action is described by an arbitrary function obeying the three dimensional Laplace equation on the sphere $S^3$. Among the bosonic components of this new supermultiplet there is a constant which gives rise to potential terms. After dualization of this constant one may come back to the supermultiplet with four physical bosons. However, this new supermultiplet is highly nonlinear. The geometry of the corresponding sigma-model action is briefly discussed.

An exhaustive classification of a certain class of static solutions for the five-dimensional Einstein-Gauss-Bonnet theory in vacuum is presented. The class of metrics under consideration is such that the spacelike section is a warped product of the real line with a nontrivial base manifold. It is shown that for generic values of the coupling constants the base manifold must be necessarily of constant curvature, and the solution reduces to the topological extension of the Boulware-Deser metric. It is also shown that the base manifold admits a wider class of geometries for the special case when the Gauss-Bonnet coupling is properly tuned in terms of the cosmological and Newton constants. This freedom in the metric at the boundary, which determines the base manifold, allows the existence of three main branches of geometries in the bulk. For the negative cosmological constant, if the boundary metric is such that the base manifold is arbitrary, but fixed, the solution describes black holes whose horizon geometry inherits the metric of the base manifold. If the base manifold possesses a negative constant Ricci scalar, two different kinds of wormholes in vacuum are obtained. For base manifolds with vanishing Ricci scalar, a different class of solutions appears resembling “spacetime horns.” There is also a special case for which, if the base manifold is of constant curvature, due to a certain class of degeneration of the field equations, the metric admits an arbitrary redshift function. For wormholes and spacetime horns, there are regions for which the gravitational and centrifugal forces point towards the same direction. All of these solutions have finite Euclidean action, which reduces to the free energy in the case of black holes, and vanishes in the other cases. The mass is also obtained from a surface integral.

We study the interior of distorted static axisymmetric black holes. We obtain a general interior solution and study its asymptotics both near the horizon and singularity. As a special example, we apply the obtained results to the case of the so-called “caged” black holes.

Models which accelerate the expansion of the universe through the addition of a function of the Ricci scalar $f(R)$ leave a characteristic signature in the large-scale structure of the universe at the Compton wavelength scale of the extra scalar degree of freedom. We search for such a signature in current cosmological data sets: the WMAP cosmic microwave background (CMB) power spectrum, Supernovae Legacy Survey supernovae distance measures, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and galaxy-CMB angular correlations. Because of theoretical uncertainties in the nonlinear evolution of $f(R)$ models, the galaxy power spectrum conservatively yields only weak constraints on the models despite the strong predicted signature in the linear matter power spectrum. Currently the tightest constraints involve the modification to the integrated Sachs-Wolfe effect from growth of gravitational potentials during the acceleration epoch. This effect is manifest for large Compton wavelengths in enhanced low multipole power in the CMB and anticorrelation between the CMB and tracers of the potential. They place a bound on the Compton wavelength of the field to be less than of order the Hubble scale.

An upper limit on the total annihilation cross section of dark matter (DM) has recently been derived from the observed atmospheric neutrino background. We show that comparable bounds are obtained for DM masses around the TeV scale by observations of the diffuse gamma-ray flux by EGRET, because electroweak bremsstrahlung leads to non-negligible electromagnetic branching ratios, even if DM particles only couple to neutrinos at tree level. A better mapping and the partial resolution of the diffuse gamma-ray background into astrophysical sources by the GLAST satellite will improve this bound in the near future.

We carry out numerical investigations of the perturbations in N-flation models where the mass spectrum is generated by random matrix theory. The tensor-to-scalar ratio and non-Gaussianity are already known to take the single-field values, and so the density perturbation spectral index is the main parameter of interest. We study several types of random field initial conditions and compute the spectral index as a function of mass spectrum parameters. Comparison with microwave anisotropy data from the Wilkinson Microwave Anisotropy Probe shows that the model is currently viable in the majority of its parameter space.

We study the possibility of experimentally testing the manifestations of the equivalence principle in spin-gravity interactions. We reconsider the earlier experimental data and get the first experimental bound on the anomalous gravitomagnetic moment. The spin coupling to the Earth’s rotation may also be explored at the extensions of neutron electric-dipole-moment and $g-2$ experiments. The spin coupling to terrestrial gravity produces a considerable effect which may be discovered at the planned deuteron electric-dipole-moment experiment. The Earth’s rotation should also be taken into account in optical experiments in search of axionlike particles.

Extensions of the standard model with $N$ Higgs doublets are simple extensions presenting a rich mathematical structure. An underlying Minkowski structure emerges from the study of both variable space and parameter space. The former can be completely parametrized in terms of two future lightlike Minkowski vectors with spatial parts forming an angle whose cosine is $-(N-1{)}^{-1}$. For the parameter space, the Minkowski parametrization enables one to impose sufficient conditions for bounded below potentials, characterize certain classes of local minima, and distinguish charge breaking vacua from neutral vacua. A particular class of neutral minima presents a degenerate mass spectrum for the physical charged Higgs bosons.

Within supersymmetric $SU(5)$ grand unified theory (GUT) we suggest mechanisms for suppression of baryon number violating dimension five and six operators. The mechanism is based on the idea of split multiplets (i.e. quarks and leptons are not coming from a single GUT state) which is realized by an extension with additional vectorlike matter. The construction naturally avoids wrong asymptotic relation ${\widehat{M}}_D={\widehat{M}}_E$. Thus, the long-standing problems of the minimal supersymmetric $SU(5)$ GUT can be resolved. In a particular example of flavor structure and with additional $\mathcal{U}(1)\times {\mathcal{Z}}_{3N}$ symmetry we demonstrate how the split multiplet mechanism works out. Namely, the considered model is compatible with successful gauge coupling unification and realistic fermion mass pattern. The nucleon decay rates are relatively suppressed and can be well compatible with current experimental bounds.

We study the spectrum of the even-parity excitations of the nucleon in quenched lattice QCD. We extend our earlier analysis by including an expanded basis of nucleon interpolating fields, increasing the physical size of the lattice, including more configurations to enhance statistics and probing closer to the chiral limit. With a review of world lattice data, we conclude that there is little evidence of the Roper resonance in quenched lattice QCD.

The $X(3872)$ seems to be a loosely-bound hadronic molecule whose constituents are two charm mesons. A novel feature of this molecule is that the mass difference of the constituents is close to the mass of a lighter meson that can be exchanged between them, namely, the pion. We analyze this feature in a simple model with spin-0 mesons only. Various observables are calculated to next-to-leading order in the interaction strength of the exchanged meson. Renormalization requires summing a geometric series of next-to-leading order corrections. The dependence of observables on the ultraviolet cutoff can be removed by renormalizations of the mass of the heaviest meson, the coupling constant for the contact interaction between the heavy mesons, and short-distance coefficients in the operator product expansion. The next-to-leading order correction has an unphysical infrared divergence at the threshold of the two heavier mesons that can be eliminated by a further resummation that takes into account the nonzero width of the heaviest meson.

We study the possible contributions of dimension six operators containing fermion fields to Higgs production at a 500 GeV or 1 TeV $e^{+}{e}^{-}$ linear collider. We show that—depending on the production mechanism—the effects of such operators can be kinematically enhanced relative to standard model (SM) contributions. We determine constraints on the operator coefficients implied by existing precision electroweak measurements and the scale of neutrino mass. We find that even in the presence of such constraints, substantial deviations from SM Higgs production cross sections are possible. We compare the effects of fermionic operators with those associated with purely bosonic operators that have been previously discussed in the literature.

We provide a framework for quasidegenerate neutrinos consistent with a successful leptogenesis, based on the $L_{\mu }-L_{\tau }$ flavor symmetry and its breaking pattern. In this scheme, a fine-tuning is needed to arrange the small solar neutrino mass splitting. Once it is ensured, the atmospheric neutrino mass splitting and the deviation from the maximal atmospheric mixing angle $\Delta {\theta }_{23}$ are driven by the same symmetry breaking parameter $\lambda \sim 0.1$, and the reactor angle ${\theta }_{13}$ is predicted to be slightly smaller than $\lambda$ while the Dirac $CP$ phase is generically of order one. Given that the pseudo-Dirac nature of right-handed neutrinos is protected from the flavor symmetry breaking, a small mass splitting can be generated radiatively. For moderate values of $\tan \beta \sim 10$, this allows for low-scale supersymmetric leptogenesis, overcoming a strong washout effect of the quasidegenerate light neutrinos and evading the gravitino overproduction.

We present results from an analysis of $B^0\to {\rho }^{+}{\rho }^{-}$ decays using $(383.6\pm 4.2)\times {10}^6$ $B\overline{B}$ pairs collected by the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC. The measurements of the $B^0\to {\rho }^{+}{\rho }^{-}$ branching fraction, longitudinal polarization fraction $f_L$, and the $CP$-violating parameters $S_{\mathrm{long}}$ and $C_{\mathrm{long}}$ are as follows: $\mathcal{B}(B^0\to {\rho }^{+}{\rho }^{-})=(25.5\pm 2.1(\mathrm{stat}{)}_{-3.9}^{+3.6}(\mathrm{syst}))\times {10}^{-6}$, $f_L=0.992\pm 0.024(\mathrm{stat}{)}_{-0.013}^{+0.026}(\mathrm{syst})$, $S_{\mathrm{long}}=-0.17\pm 0.20(\mathrm{stat}{)}_{-0.06}^{+0.05}(\mathrm{syst})$, $C_{\mathrm{long}}=0.01\pm 0.15(\mathrm{stat})\pm 0.06(\mathrm{syst})$. We determine the unitarity triangle angle $\alpha$, using an isospin analysis of $B\to \rho \rho$ decays. One of the two solutions, $\alpha =[73.1,117.0]°$ at 68% confidence level, is compatible with standard model-based fits of existing data. Constraints on the unitarity triangle are also evaluated using an $SU(3)$ symmetry-based approach.

We present a measurement of the $t\overline{t}$ pair production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ utilizing approximately $425{\mathrm{pb}}^{-1}$ of data collected with the D0 detector. We consider decay channels containing two high $p_T$ charged leptons (either $e$ or $\mu$) from leptonic decays of both top-daughter $W$ bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., $e\mu$, $ee$, or $\mu \mu$) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least one hadronic jet in each event be tagged as containing a $b$ quark. For a top quark mass of 175 GeV, the measured cross section is $7.4\pm 1.4(\mathrm{stat})\pm 1.0(\mathrm{syst})\mathrm{pb}$ and for the current Tevatron average top quark mass of 170.9 GeV, the resulting value of the cross section is $7.8\pm 1.8(\mathrm{stat}+\mathrm{syst})\mathrm{pb}$.

According to two-time physics, there is more to space and time than can be garnered with the ordinary formulation of physics. Two-time physics has shown that the standard model of particles and forces is successfully reproduced by a two-time field theory in four space and two time dimensions projected as a holographic image on an emergent space-time in $3+1$ dimensions. Among the successes of this approach is the resolution of the strong $CP$ problem of QCD as an outcome of the restrictions imposed by the higher symmetry structures in $4+2$ dimensions. In this paper we launch a program to construct the duals of the standard model as other holographic images of the same $4+2$ dimensional theory on a variety of emergent spacetimes in $3+1$ dimensions. These dual field theories are obtained as a family of gauge choices in the master $4+2$ field theory. In the present paper we deal with some of the simpler gauge choices which lead to interacting Klein-Gordon field theories for the conformal scalar with a predicted $\mathrm{SO}(d,2)$ symmetry in a variety of interesting curved spacetimes in $(d-1)+1$ dimensions. More challenging and more interesting gauge choices (including some that relate to mass) which are left to future work are also outlined. Through this approach we discover a new realm of previously unexplored dualities and hidden symmetries that exist both in the macroscopic and microscopic worlds, at the classical and quantum levels. Such phenomena predicted by Two time physics (2T-physics) can in principle be confirmed both by theory and experiment. One time physics (1T-physics) can be used to analyze the predictions but in most instances gives no clue that the predicted phenomena exist in the first place. This point of view suggests a new paradigm for the construction of a fundamental theory that is likely to impact on the quest for unification.