In models with supersymmetry breaking by boundary conditions on an extra-dimension it is possible to relate in a quantitative natural way the Fermi scale to the size of the extra-dimension. We analyze in detail the compatibility of such models with ElectroWeak Precision Tests.

We have calculated the full one-loop electroweak (EW) and QCD corrections to the third generation scalar-fermion pair production processes $e^{+}{e}^{-}\to \gamma \gamma \to \widetilde{f_i}\overline{\widetilde{f_i}}(f=t,b,\tau )$ at an electron-positron linear collider(LC) in the minimal supersymmetric standard model (MSSM). We analyze the dependence of the radiative corrections on the parameters such as the colliding energy $\sqrt{\widehat{s}}$ and the SUSY fundamental parameters $A_f$, $\tan \beta$, $\mu$, $M_{SUSY}$ and so forth. The numerical results show that the EW corrections to the squark-, stau-pair production processes and QCD corrections to the squark-pair production processes give substantial contributions in some parameter space. The EW relative corrections to squark-pair production processes can be comparable with QCD corrections at high energies. Therefore, these EW and QCD corrections cannot be neglected in precise measurement of sfermion pair productions via $\gamma \gamma$ collision at future linear colliders.

The vortex free energy is studied in the random vortex world-surface model of the infrared sector of $SU(3)$ Yang-Mills theory. The free energy of a center vortex extending into two spatial directions, which is introduced into Yang-Mills configurations when acting with the ’t Hooft loop operator, is verified to furnish an order parameter for the deconfinement phase transition. It is shown to exhibit a weak discontinuity at the critical temperature, corresponding to the weak first-order character of the transition.

We demonstrate that the polarization fractions of most tree-dominated $B\to VV$ decays can be simply understood by means of kinematics in the heavy-quark or large-energy limit. For example, the longitudinal polarization fractions $R_L$ of the $B^0\to (D_s^{*+},D^{*+},{\rho }^{+})D^{*-}$ and $B^{+}\to (D_s^{*+},D^{*+},{\rho }^{+}){\rho }^0$ modes increase as the masses of the mesons $D_s^{*+},D^{*+},{\rho }^{+}$ emitted from the weak vertex decrease. The subleading finite-mass or finite-energy corrections modify these simple estimates only slightly. Our predictions for the $B\to D_{(s)}^{*}{D}^{*}$ polarization fractions derived in the perturbative QCD framework, especially $R_L\sim 1$ for $B^0\to {\overline{D}}^{*0}{D}^{*0}$ governed by nonfactorizable $W$-exchange amplitudes, can be confronted with future data. For penguin-dominated modes, such as $B\to \rho (\omega )K^{*}$, the polarization fractions can be understood by the annihilation effect from the $(S-P)(S+P)$ operators, plus the interference with a small tree amplitude. At last, we comment on the various mechanisms proposed in the literature to explain the abnormal $B\to \varphi K^{*}$ polarization data, none of which are satisfactory.

I investigate the relationship between the gluon distribution obtained using a dipole model fit to low-$x$ data on $F_2(x,Q^2)$ and standard gluons obtained from global fits with the collinear factorization theorem at fixed order. I stress the necessity to do fits of this type carefully, and, in particular, to include the contribution from heavy flavors to the inclusive structure function. I find that the dipole cross section must be rather steeper than the gluon distribution, which at least partially explains why dipole model fits produce dipole cross sections growing quite strongly at small $x$, while DGLAP (Dokshitzer-Gribov-Lipatov-Altarelli-Parisi) based fits have valencelike, or even negative, small-$x$ gluons as inputs. However, I also find that the gluon distributions obtained from the dipole fits are much too small to match onto the conventional DGLAP gluons at high $Q^2\sim 50\mathrm{Ge}{\mathrm{V}}^2$, where the two approaches should coincide. The main reason for this discrepancy is found to be the large approximations made in converting the dipole cross sections into structure functions using formulas which are designed only for asymptotically small $x$. The shortcomings in this step affect the accuracy of the extracted dipole cross sections in terms of size and shape, and hence also in terms of interpretation, at all scales.

We present a study of $s$-channel single top quark production at the upgraded Tevatron $p\overline{p}$ collider, including the next-to-leading order (NLO) QCD corrections to the production and decay of the top quark. The modified narrow width approximation was adopted to preserve the spin of the top quark in its production and decay. We discuss the effect of the different $O({\alpha }_s)$ contributions on the inclusive cross section as well as various kinematical distributions after imposing the relevant cuts to select $s$-channel single top signal events. In particular, the $O({\alpha }_s)$ decay contribution, while small in size, has a significant impact on several distributions. With the help of the best-jet algorithm to reconstruct the top quark, we demonstrate that it is possible to study kinematical and spin correlations in $s$-channel single top events. We furthermore compare top quark spin measurements in two different bases and show how NLO corrections have to be taken into consideration in searches for the Higgs boson through $W^{\pm }H$ associated production at the Tevatron.

We present a calculation of the next-to-leading-order QCD corrections, with the one-scale phase space slicing method, to single top quark production and decay process $p\overline{p},pp\to t\overline{b}+X\to b\ell \nu \overline{b}+X$ at hadron colliders. Using the helicity amplitude method, the angular correlation of the final state partons and the spin correlation of the top quark are preserved. The effect of the top quark width is also examined.

We present explicit numerical evidence of reflection-positivity violation for the lattice Landau gluon propagator in three-dimensional pure $SU(2)$ gauge theory. We use data obtained at very large lattice volumes ($V={80}^3,{140}^3$) and for three different lattice couplings in the scaling region ($\beta =4.2,5.0,6.0$). In particular, we observe a clear oscillatory pattern in the real-space propagator $C(t)$. We also verify that the (real-space) data show good scaling in the range $t\in [0,3]fm$ and can be fitted using a Gribov-like form. The violation of positivity is in contradiction with a stable-particle interpretation of the associated field theory and may be viewed as a manifestation of confinement.

We present a measurement of the mass dependence of the forward-backward charge asymmetry ($A_{FB}$) for $e^{+}{e}^{-}$ pairs produced via an intermediate $Z/{\gamma }^{*}$ with mass $M_{ee}>40\mathrm{G}\mathrm{e}\mathrm{V}/c^2$. We study the constraints on the $Z$-quark couplings imposed by our measurement. We analyze an integrated luminosity of $72{\mathrm{p}\mathrm{b}}^{-1}$ collected by the CDF-II detector in $\overline{p}p$ collisions at $\sqrt{s}=1.96\mathrm{T}\mathrm{e}\mathrm{V}$ at the Fermilab Tevatron. A comparison of the uncorrected $A_{FB}$ between data and standard model Monte Carlo gives good agreement with a ${\chi }^2/\mathrm{D}\mathrm{O}\mathrm{F}$ of 15.7/15. The couplings measurements are also consistent with standard model predictions.

The problem of finding supersymmetric brane configurations in the near-horizon attractor geometry of a Calabi-Yau black hole with magnetic-electric charges $(p^I,q_I)$ is considered. Half-BPS (Bogomol’nyi-Prasad-Sommerfield) configurations, which are static for some choice of global $Ad{S}_2$ coordinate, are found for wrapped brane configurations with essentially any four-dimensional charges $(u^I,v_I)$. Half-BPS multibrane configurations can also be found for any collection of wrapped branes provided they all have the same sign for the symplectic inner product $p^I{v}_I-u^I{q}_I$ of their charges with the black hole charges. This contrasts with the Minkowski problem for which a mutually preserved supersymmetry requires alignment of all the charge vectors. The radial position of the branes in global $Ad{S}_2$ is determined by the phase of their central charge.

A striking aspect of the recently proposed split supersymmetry is the existence of heavy gluinos which are metastable because of the very heavy squarks which mediate their decay. In this paper we correlate the expected flux of these particles with the accompanying neutrino flux produced in inelastic $pp$ collisions in distant astrophysical sources. We show that an event rate at the Pierre Auger Observatory of approximately $1{\mathrm{yr}}^{-1}$ for gluino masses of about 500 GeV is consistent with existing limits on neutrino fluxes. Such an event rate requires powerful cosmic ray engines able to accelerate particles up to extreme energies, somewhat above $5\times {10}^{13}\mathrm{GeV}$. The extremely low inelasticity of the gluino-containing hadrons in their collisions with the air molecules makes possible a distinct characterization of the showers induced in the atmosphere. Should such anomalous events be observed, we show that their cosmogenic origin, in concert with the requirement that they reach the Earth before decay, leads to a lower bound on their proper lifetime of the order of 100 years, and consequently, to a lower bound on the scale of supersymmetry breaking, ${\Lambda }_{\mathrm{SUSY}}>2.6\times {10}^{11}\mathrm{GeV}$. Obtaining such a bound is not possible in collider experiments.

We formulate $\mathcal{N}=1$ super Yang-Mills theory in $3\text{}+\text{}1$ dimensions on a two dimensional transverse lattice using supersymmetric discrete light-cone quantization in the large-$N_c$ limit. This formulation is free of fermion species doubling. We are able to preserve one supersymmetry. We find a rich, nontrivial behavior of the mass spectrum as a function of the coupling $g\sqrt{N_c}$, and see some sort of transition in the structure of a bound state as we go from the weak coupling to the strong coupling. Using a toy model we give an interpretation of the rich behavior of the mass spectrum. We present the mass spectrum as a function of the winding number for those states whose color flux winds all the way around in one of the transverse directions. We use two fits to the mass spectrum and the one that has a string theory justification appears preferable. For those states whose color flux is localized we present an extrapolated value for $m^2$ for some low-energy bound states in the limit where the numerical resolution goes to infinity.

We study the class of noncommutative theories in $d$ dimensions whose spatial coordinates $(x_i{)}_{i=1}^d$ can be obtained by performing a smooth change of variables on $(y_i{)}_{i=1}^d$, the coordinates of a standard noncommutative theory, which satisfy the relation $[y_i,y_j]=i{\theta }_{ij}$, with a constant ${\theta }_{ij}$ tensor. The $x_i$ variables verify a commutation relation which is, in general, space dependent. We study the main properties of this special kind of noncommutative theory and show explicitly that, in two dimensions, any theory with a space-dependent commutation relation can be mapped to another where that ${\theta }_{ij}$ is constant.

We present a new three-dimensional general relativistic hydrodynamics code which is intended for simulations of stellar core collapse to a neutron star, as well as pulsations and instabilities of rotating relativistic stars. Contrary to the common approach followed in most existing three-dimensional numerical relativity codes which are based in Cartesian coordinates, in this code both the metric and the hydrodynamics equations are formulated and solved numerically using spherical polar coordinates. A distinctive feature of this new code is the combination of two types of accurate numerical schemes specifically designed to solve each system of equations. More precisely, the code uses spectral methods for solving the gravitational field equations, which are formulated under the assumption of the conformal flatness condition (CFC) for the three-metric. Correspondingly, the hydrodynamics equations are solved by a class of finite difference methods called high-resolution shock-capturing schemes, based upon state-of-the-art Riemann solvers and third-order cell-reconstruction procedures. We demonstrate that the combination of a finite difference grid and a spectral grid, on which the hydrodynamics and metric equations are, respectively, solved, can be successfully accomplished. This approach, which we call Mariage des Maillages (French for grid wedding), results in high accuracy of the metric solver and, in practice, allows for fully three-dimensional applications using computationally affordable resources, along with ensuring long-term numerical stability of the evolution. We compare our new approach to two other, finite difference based, methods to solve the metric equations which we already employed in earlier axisymmetric simulations of core collapse. A variety of tests in two and three dimensions is presented, involving highly perturbed neutron star spacetimes and (axisymmetric) stellar core collapse, which demonstrate the ability of the code to handle spacetimes with and without symmetries in strong gravity. These tests are also employed to assess the gravitational waveform extraction capabilities of the code, which is based on the Newtonian quadrupole formula. The code presented here is not limited to approximations of the Einstein equations such as CFC, but it is also well suited, in principle, to recent constrained formulations of the metric equations where elliptic equations have a preeminence over hyperbolic equations.

We show that scalar as well as vector and tensor metric perturbations in the Randall-Sundrum II braneworld allow normalizable tachyonic modes, i.e., possible instabilities. These instabilities require nonvanishing initial anisotropic stresses on the brane. We show with a specific example that within the Randall-Sundrum II model, even though the tachyonic modes are excited, no instability develops. We argue, however, that in the cosmological context instabilities might in principle be present. We conjecture that the tachyonic modes are due to the singularity of the orbifold construction. We illustrate this with a simple but explicit toy model.

We consider wakelike density fluctuations produced by cosmic strings at the quark-hadron transition in the early universe. We show that low momentum axions which are produced through the radiation from the axionic string at an earlier stage, may get trapped inside these wakes due to delayed hadronization in these overdense regions. As the interfaces, bordering the wakes, collapse, the axions pick-up momentum from the walls and finally leave the wake regions. These axions thus can produce large scale isocurvature fluctuations. We have calculated the detailed profile of these axionic density fluctuations and discuss its astrophysical consequences.

In this work we show that the gravitational Chern-Simons term, aside from being a key ingredient in inflationary baryogenesis, modifies superhorizon gravitational waves produced during inflation. We compute the super-Hubble gravitational power spectrum in the slow-roll approximation and show that its overall amplitude is modified while its spectral index remains unchanged (at leading order in the slow-roll parameters). Then, we calculate the correction to the tensor to scalar ratio, $T/S$. We find a correction of $T/S$ which is dependent on $\mathcal{N}$ (more precisely quadratic in $\mathcal{N}$), the parameter characterizing the amplitude of the Chern-Simons terms. In a stringy embedding of the leptogenesis mechanism, $\mathcal{N}$ is the ratio between the Planck scale and the fundamental string scale. Thus, in principle, we provide a direct probe of leptogenesis due to stringy dynamics in the cosmic microwave background. However, we demonstrate that the corresponding correction of $T/S$ is in fact very small and not observable in the regime where our calculations are valid. To obtain a sizable effect, we argue that a nonlinear calculation is necessary.

We extend the theory of Kimberly and Magueijo for the spacetime variation of the electroweak couplings in the unified Glashow-Salam-Weinberg model of the electroweak interaction to include quantum corrections. We derive the effective quantum-corrected dilaton evolution equations in the presence of a background cosmological matter density that is composed of weakly interacting and non-weakly-interacting nonrelativistic dark-matter components.

We show that a supersymmetric standard model exhibiting anomaly mediated supersymmetry breaking can generate naturally the observed neutrino mass spectrum as well mixings when we include bilinear $R$-parity violation interactions. In this model, one of the neutrinos gets its mass due to the tree-level mixing with the neutralinos induced by the $R$-parity violating interactions while the other two neutrinos acquire their masses due to radiative corrections. One interesting feature of this scenario is that the lightest supersymmetric particle is unstable and its decay can be observed at high energy colliders, providing a falsifiable test of the model.

We discuss the weak coupling expansion of a one-plaquette $SU(2)$ lattice gauge theory. We show that the conventional perturbative series for the partition function has a zero radius of convergence and is asymptotic. The average plaquette is discontinuous at $g^2=0$. However, the fact that $SU(2)$ is compact provides a perturbative sum that converges toward the correct answer for positive $g^2$. This alternate method amounts to introducing a specific coupling-dependent field cut, that turns the coefficients into $g$-dependent quantities. Generalizing to an arbitrary field cut, we obtain a regular power series with a finite radius of convergence. At any order in the modified perturbative procedure, and for a given coupling, it is possible to find at least one (and sometimes two) values of the field cut that provide the exact answer. This optimal field cut can be determined approximately using the strong coupling expansion. This allows us to interpolate accurately between the weak and strong coupling regions. We discuss the extension of the method to lattice gauge theory on a $D$-dimensional cubic lattice.