Recently, the HERMES Collaboration at DESY, using a leading order QCD analysis of their data on semi-inclusive deep inelastic production of charged hadrons, reported a marginally positive polarization for the strange quarks in the proton. We argue that a non-negative polarization is almost impossible.

We investigate proton mass effects in the handbag approach to wide-angle Compton scattering. We find that theoretical uncertainties due to the proton mass are significant for photon energies presently studied at Jefferson Lab. With the proposed energy upgrade such uncertainties will be clearly reduced.

We compute the total cross section for direct production of the pseudoscalar Higgs boson in hadron collisions at next-to-next-to-leading order (NNLO) in perturbative QCD. The $\mathcal{O}\left({\alpha }_s^2\right)$ QCD corrections increase the NLO production cross section by approximately 20–30%.

The existing definitions of mixing angles (one-loop radiatively corrected and renormalization-scale independent) for scalar particles turn out to be gauge dependent when used in gauge theories. We show that a scale- and gauge-independent mixing angle can be obtained if the scalar self-energy is improved by the pinch technique, and give two relevant examples in the minimal supersymmetric standard model: the mixing of CP-even Higgs scalars and of top squarks. We also show that the recently proposed definition of a mixing angle that uses the (unpinched) scalar two-point function evaluated at a particular value of the external momentum $\left[p_{*}^2{=(M}_1^2{+M}_2^2\right)/2,$ where $M_{1,2}$ are the masses of the mixed particles] computed in the Feynman gauge coincides with the gauge-invariant pinched result. In alternative definitions (e.g., in the on-shell scheme), the improved Higgs mixing angle is different from that in the Feynman gauge. Some freedom in the pinch technique for scalar-scalar-gauge couplings is also discussed.

The observation of charged lepton flavor nonconservation would be a clear signature of physics beyond the standard model. In particular, supersymmetric (SUSY) models introduce mixings in the sneutrino and the charged slepton sectors which could imply flavor-changing processes at rates accessible to upcoming experiments. In this paper we analyze the possibility to observe $\overrightarrow{Z}{\mathcal{l}}_I{\mathcal{l}}_J$ in the GigaZ option of TESLA at DESY. We show that although models with SUSY masses above the current limits could predict a branching ratio $\mathrm{BR}\left(\overrightarrow{Z}\mu e\right)$ accessible to the experiment, they would imply an unobserved rate of $\overrightarrow{\mu }e\gamma$ and thus are excluded. In models with a small mixing angle between the first and the third (or the second and the third) slepton families GigaZ could observe $\overrightarrow{Z}\tau \mu$ (or $\overrightarrow{Z}\tau e)$ consistently with present bounds on ${\mathcal{l}}_J\to {\mathcal{l}}_I\gamma .$ In contrast, if the mixing angles between the three slepton families are large the bounds from $\overrightarrow{\mu }e\gamma$ push these processes below the reach of GigaZ. We show that in this case the masses of the three slepton families must be strongly degenerated (with mass differences of order ${10}^{-3}).\mathrm{}$ We update the limits on the slepton mass insertions ${\delta }_{LL,RR,LR}$ and discuss the correlation between flavor changing and $g_{\mu }-2$ in SUSY models.

Using renormalization-group methods, we derive differential equations for the all-orders summation of logarithmic corrections to the QCD series for $R\left(s\right)=\sigma {(e}^{+}{e}^{-}\to \mathrm{hadrons})/\sigma {(e}^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}),$ as obtained from the imaginary part of the purely perturbative vector-current correlation function. We present explicit solutions for the summation of leading and up to three subsequent subleading orders of logarithms. The summations accessible from the four-loop vector correlator not only lead to a substantial reduction in sensitivity to the renormalization scale, but necessarily impose a common infrared bound on perturbative approximations to $R\left(s\right),$ regardless of the infrared behavior of the true QCD couplant.

We study the contribution of gluon induced partonic subprocesses to $Z\gamma$ pair production at hadron colliders. These processes contribute only at next-to-next-to-leading order but are potentially enhanced by two factors of the gluon parton densities. However, we find that their contribution is modest and that next-to-leading order calculations give reliable predictions.

Inclusive standard model Higgs boson pair production at hadron colliders has the capability to determine the Higgs boson self-coupling $\lambda .$ We present a detailed analysis of the $g\overrightarrow{g}H\overrightarrow{H}{(W}^{+}{W}^{-}{\left)\right(W}^{+}{W}^{-})\to (jj{\mathcal{l}}^{\pm }\nu \left)\right(jj{\mathcal{l}}^{\prime \pm }\nu )$ and $g\overrightarrow{g}H\overrightarrow{H}{(W}^{+}{W}^{-}{\left)\right(W}^{+}{W}^{-})\to (jj{\mathcal{l}}^{\pm }\nu \left)\right({\mathcal{l}}^{\prime \pm }\nu {\mathcal{l}}^{″\mp }\nu )$ $(\mathcal{l},{\mathcal{l}}^{\prime },{\mathcal{l}}^{″}=e,\mu )$ signal channels, and the relevant background processes, for the CERN Large Hadron Collider, and a future Very Large Hadron Collider operating at a center-of-mass energy of 200 TeV. We also derive quantitative sensitivity limits for $\lambda .$ We find that it should be possible at the LHC with design luminosity to establish that the standard model Higgs boson has a nonzero self-coupling and that $\lambda /{\lambda }_{\mathrm{SM}}$ can be restricted to a range of 0–3.8 at $95\%$ confidence level (C.L.) if its mass is between 150 and 200 GeV. At a 200 TeV collider with an integrated luminosity of $300{\mathrm{fb}}^{-1},$ $\lambda$ can be determined with an accuracy of 8–25 % at $95\%$ C.L. in the same mass range.

A largely model-independent measurement of the inclusive electron momentum spectrum and branching fraction for semileptonic decays of B mesons is presented based on data recorded at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance with the BABAR detector. Backgrounds from secondary charm decays are separated from prompt B decays using charge and angular correlations between the electron from one B meson and a high momentum electron tag from the second B meson. The resulting branching fraction is $\mathcal{B}\left(\overrightarrow{B}\mathrm{Xe}\nu \right)=[10.87\pm 0.18(\mathrm{stat})\pm 0.30(\mathrm{syst}\left)\right]\%.\mathrm{}$ Based on this measurement we determine the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $|V_{\mathrm{cb}}|.$

We present a simple four-dimensional model in which anomaly mediated supersymmetry breaking naturally dominates. The central ingredient is that the hidden sector is near a strongly coupled infrared fixed point for several decades of energy below the Planck scale. Strong renormalization effects then sequester the hidden sector from the visible sector. Supersymmetry is broken dynamically and requires no small input parameters. The model provides a natural and economical explanation of the hierarchy between the supersymmetry-breaking scale and the Planck scale, while allowing anomaly mediation to address the phenomenological challenges posed by weak scale supersymmetry. In particular, flavor-changing neutral currents are naturally near their experimental limits.

The evolution of magnetic fields frozen to a perfectly conducting plasma fluid around a Kerr black hole is investigated. We focus on the plunging region between the black hole horizon and the marginally stable circular orbit in the equatorial plane, where the centrifugal force is unable to stably balance the gravitational force. Adopting the kinematic approximation where the dynamical effects of magnetic fields on the fluid motion are ignored, we exactly solve Maxwell’s equations with the assumptions that the geodesic motion of the fluid is stationary and axisymmetric, the magnetic field has only radial and azimuthal components and depends only on time and radial coordinates. We show that the stationary state of the magnetic field in the plunging region is uniquely determined by the boundary conditions at the marginally stable circular orbit. If the magnetic field at the marginally stable circular orbit is in a stationary state, the magnetic field in the plunging region will quickly settle into a stationary state if it is not so initially, in a time determined by the dynamical time scale in the plunging region. The radial component of the magnetic field at the marginally stable circular orbit is more important than the toroidal component in determining the structure and evolution of the magnetic field in the plunging region. Even if at the marginally stable circular orbit the toroidal component is zero, in the plunging region a toroidal component is quickly generated from the radial component by the shear motion of the fluid. Finally, we discuss the dynamical effects of magnetic fields on the motion of the fluid in the plunging region. We show that the dynamical effects of magnetic fields are unimportant in the plunging region if they are negligible on the marginally stable circular orbit. This supports the “no-torque inner boundary condition” of thin disks, contrary to the claim in the recent literature.

A reanalysis of data from a recent search for ultraheavy isotopes of gold and iron leads to new constraints on several classes of exotic objects. These include strangelets, MEMOs (metastable exotic multihypernuclear objects), and CHAMPs (charged massive particles) which may have been present in the data, but which could have nonetheless gone undetected due to the design of the original experiment. As a result of the new analysis we are able to greatly enlarge the exclusion regions for exotic particles of mass M and charge Z, and provide limits as low as ${10}^{-11}$ for small $M/Z,$ and ${10}^{-7}$ for $M/Z$ up to 120.

The mixing of the known quarks with new heavy singlets can modify significantly some observables with respect to the standard model predictions. We analyze the range of deviations permitted by the constraints from precision electroweak data and flavor-changing neutral processes at low energies. We study top charged current and neutral current couplings, which will be directly tested at top factories, such as the CERN LHC and the DESY TESLA. We discuss some examples of observables from K and B physics, such as the branching ratio of $K_L\to {\pi }^0\nu \overline{\nu },$ the $B_s^0$ mass difference, or the time-dependent $\mathrm{CP}$ asymmetry in $B_s^0\to D_s^{+}{D}_s^{-},$ which can also show large new effects.

It has been conjectured that the (weakly coupled) Randall-Sundrum (RS) model with gauge fields in the bulk is dual to a (strongly coupled) 4D conformal field theory (CFT) with an UV cutoff and in which global symmetries of the CFT are gauged. We elucidate features of this dual CFT which are crucial for a complete understanding of the proposed duality. We argue that the limit of no (or small) brane-localized kinetic term for bulk gauge field on the RS side (often studied in the literature) is dual to no bare kinetic term for the gauge field which is coupled to the CFT global current. In this limit, the kinetic term for this gauge field in the dual CFT is “induced” by CFT loops. Then, this CFT loop contribution to the gauge field 1PI two-point function is dual (on the RS side) to the full gauge propagator (i.e., including the contribution of Kaluza-Klein and zero modes) with both external points on the Planck brane. We also emphasize that loop corrections to the gauge coupling on the RS side are dual to subleading effects in a large-$N$ expansion on the CFT side; these subleading corrections to the gauge coupling in the dual CFT are (in general) sensitive to the strong dynamics of the CFT.

The methods of nonequilibrium quantum field theory are used to investigate the possibility of representing dissipation in the equation of motion for the expectation value of a scalar field by a friction term, such as is commonly included in phenomenological inflaton equations of motion. A sequence of approximations is exhibited which reduces the nonequilibrium theory to a set of local evolution equations. However, the adiabatic solution to these evolution equations which is needed to obtain a local equation of motion for the expectation value is not well defined; nor, therefore, is the friction coefficient. Thus, a nonequilibrium treatment is essential, even for a system that remains close to thermal equilibrium, and the formalism developed here provides one means of achieving this numerically.

We calculate the full 1-loop corrections to the low energy coupling of a bulk gauge boson in a slice of ${\mathrm{AdS}}_5$ which are induced by generic 5-dimensional scalar, Dirac fermion, and vector fields with arbitrary $Z_2\times Z_2^{\prime }$ orbifold boundary conditions. In the supersymmetric limit, our results correctly reproduce the results obtained by an independent method based on 4-dimensional effective supergravity. This provides a nontrivial check of our results and assures the regularization scheme independence of the results.

Possible single productions of fourth family $u_4$ and $d_4$ quarks via anomalous $q_4\mathrm{qV}$ interactions at the Fermilab Tevatron are studied. The signatures of such processes are discussed and compared with the recent results from Tevatron.

The initial conditions describing seed fluctuations for the formation of structure in standard cosmological models, i.e. the Harrison-Zeldovich distribution, have very characteristic “super-homogeneous” properties: they are statistically translation invariant and isotropic, and the variance of the mass fluctuations in a region of volume V grows more slowly than V. We discuss the geometrical construction of distributions of points in ${\mathbf{R}}^3$ with similar properties encountered in tiling and in statistical physics, e.g. the Gibbs distribution of a one-component system of charged particles in a uniform background [one-component plasma (OCP)]. Modifications of the OCP can produce equilibrium correlations of the kind assumed in the cosmological context. We then describe how such systems can be used for the generation of initial conditions in gravitational N-body simulations.