Brane World Cosmology with Gauss-Bonnet Interaction

We study a Randall-Sundrum model modified by a Gauss-Bonnet interaction term. We consider, in particular, a Friedmann-Robertson-Walker metric on the brane and analyse the resulting cosmological scenario. It is shown that the usual Friedmann equations are recovered on the brane. The equation of state relating the enery density and the pressure is uniquely determined by the matching conditions. A cosmological solution with negative pressure is found.Comment: 9 pages, revtex styl

Braneworld dynamics with the BraneCode

We give a full nonlinear numerical treatment of time-dependent 5d braneworld geometry, which is determined self-consistently by potentials for the scalar field in the bulk and at two orbifold branes, supplemented by boundary conditions at the branes. We describe the BraneCode, an algorithm which we designed to solve the dynamical equations numerically. We applied the BraneCode to braneworld models and found several novel phenomena of the brane dynamics. Starting with static warped geometry with de Sitter branes, we found numerically that this configuration is often unstable due to a tachyonic mass of the radion during inflation. If the model admits other static configurations with lower values of de Sitter curvature, this effect causes a violent re-structuring towards them, flattening the branes, which appears as a lowering of the 4d effective cosmological constant. Braneworld dynamics can often lead to brane collisions. We found that in the presence of the bulk scalar field, the 5d geometry between colliding branes approaches a universal, homogeneous, anisotropic strong gravity Kasner-like asymptotic, irrespective of the bulk/brane potentials. The Kasner indices of the brane directions are equal to each other but different from that of the extra dimension.Comment: 38 pages, 10 figure

An amplitude analysis of the N‾N→π−π+\overline{N}N \to \pi^- \pi^+ reaction

A simple partial wave amplitude analysis of $\overline{p}p \rightarrow \pi^- \pi^+$ has been performed for data in the range p_{\sl lab} = 360 -- 1000 MeV/c. Remarkably few partial waves are required to fit the data, while the number of required $J$ values barely changes over this energy range. However, the resulting set of partial wave amplitudes is not unique. We discuss possible measurements with polarized beam and target which will severely restrict and help resolve the present analysis ambiguities. New data from the reaction $\overline{p}p \rightarrow \pi^0 \pi^0$ alone, are insufficient for that purpose.Comment: 16 pages (revtex), 8 figures available on request, submitted to Phys. Rev.

Stable, Time-Dependent, Exact Solutions for Brane Models with a Bulk Scalar Field

We derive two classes of brane-world solutions arising in the presence of a bulk scalar field. For static field configurations, we adopt a time-dependent, factorizable metric ansatz that allows for radion stabilization. The solutions are characterized by a non-trivial warping along the extra dimension, even in the case of a vanishing bulk cosmological constant, and lead to a variety of inflationary, time-dependent solutions of the 3D scale factor on the brane. We also derive the constraints necessary for the stability of these solutions under time-dependent perturbations of the radion field, and we demonstrate the existence of phenomenologically interesting, stable solutions with a positive cosmological constant on the brane.Comment: 24 pages, latex, 4 eps figur

Measurements of the Sigma_c^0 and Sigma_c^{++} Mass Splittings

Using a high statistics sample of photoproduced charmed particles from the FOCUS experiment at Fermilab (FNAL-E831), we measure the mass splittings of the charmed baryons Sigma_c^0 and Sigma_c^{++}. We find M(Sigma_c^0 - Lambda_c^+) = 167.38 +/- 0.21 +/- 0.13 MeV/c^2 and M(Sigma_c^++ - Lambda_c^+) = 167.35 +/- 0.19 +/- 0.12 MeV/c^2 with samples of 362 +/- 36 and 461 +/- 39 events, respectively. We measure the isospin mass splitting M(Sigma_c^++ - Sigma_c^0) to be -0.03 +/- 0.28 +/- 0.11 Mev/c^2. The first errors are statistical and the second are systematic.Comment: 10 pages, 2 figure

Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton

Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb^{-1}. The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.

Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0

Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/- 0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included in the Monte Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8), which is similar in strength to the anomalous soft photon signal observed in fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.

Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector

Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an integrated luminosity of 617 pb^{-1}, yielding a cross-section of sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the event shapes of different types of gamma gamma processes in the PYTHIA program, we conclude that (74 +/- 22)% of the observed J/psi events are due to `resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.Comment: 13 pages, 8 figures, Accepted by Phys. Lett.

CP asymmetry in B→ϕKSB \to \phi K_S in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of decay $B \to \phi K_S$ in an extension of the Standard Model with both two Higgs doublets and additional fourth-generation quarks. We show that although the Standard Model with two-Higgs-doublet and the Standard model with fourth generation quarks alone are not likely to largely change the effective $\sin 2 \beta$ from the decay of $B \to \phi K_S$, the model with both additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of $\sin 2 \beta$ without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor changing Yukawa interactions between neutral Higgs bosons and the heavy fourth generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from $b \to s \bar{s} s$ processes such as $B \to X_s \gamma$ and $\Delta m_{B_s^0}$, this model can lead to the effective $\sin 2 \beta$ to be as large as $- 0.4$ in the CP asymmetry of $B \to \phi K_S$.Comment: 13 pages, 5 figures, references added, to appear in Eur.Phys.J.

Energy dependence of Cronin momentum in saturation model for p+Ap+A and A+AA+A collisions

We calculate $\sqrt{s}$ dependence of Cronin momentum for $p+A$ and $A+A$ collisions in saturation model. We show that this dependence is consistent with expectation from formula which was obtained using simple dimentional consideration. This can be used to test validity of saturation model (and distinguish among its variants) and measure $x$ dependence of saturation momentum from experimental data.Comment: LaTeX2e, 12 pages, 8 figure