A Way to Reopen the Window for Electroweak Baryogenesis

We reanalyse the sphaleron bound of electroweak baryogenesis when allowing deviations to the Friedmann equation. These modifications are well motivated in the context of brane cosmology where they appear without being in conflict with major experimental constraints on four-dimensional gravity. While suppressed at the time of nucleosynthesis, these corrections can dominate at the time of the electroweak phase transition and in certain cases provide the amount of expansion needed to freeze out the baryon asymmetry without requiring a strongly first order phase transition. The sphaleron bound is substantially weakened and can even disappear so that the constraints on the higgs and stop masses do not apply anymore. Such modification of cosmology at early times therefore reopens the parameter space allowing electroweak baryogenesis which had been reduced substantially given the new bound on the higgs mass imposed by LEP. In contrast with previous attempts to turn around the sphaleron bound using alternative cosmologies, we are still considering that the electroweak phase transition takes place in a radiation dominated universe. The universe is expanding fast because of the modification of the Friedmann equation itself without the need for a scalar field and therefore evading the problem of the decay of this scalar field after the completion of the phase transition and the risk that its release of entropy dilutes the baryon asymmetry produced at the transition.Comment: 19 pages, 3 figures; v2: minor changes, remark added at end of section 5 and in caption of figure 1; v3: references added, version to be publishe

Measurement of the H(n=2) density matrix for 20–100-keV collisions of H+ on He

Density matrices are experimentally determined which describe H(n=2) atoms produced in electron-transfer collisions between 20-100-keV protons and helium. The density matrix contains the electron-transfer cross sections σ2s, σ2p0, and σ2p+/-1, as well as the real and imaginary parts of the s0p0 coherence. Experimentally, a monoenergetic proton beam traverses a helium gas cell producing hydrogen atoms H(n) via electron transfer. Within the gas cell an electric field is applied either axial or transverse to the proton beam. The Stokes parameters describing the intensity and linear polarization of Lyman-α radiation (122 nm) emitted by H(n=2) atoms are determined as a function of applied electric-field strength. The density-matrix elements are determined from a linear least-squares fit of the Stokes parameters to the set of five fitting functions which represent the contributions from individual density-matrix elements. The density-matrix results are self-consistent. Separate determinations using axial or transverse electric fields agree with each other. The general results indicate σ2s>σ2p0>σ2p+/-1 between 20 and 100 keV. The electric dipole moment z has a value near zero at 20 keV rising to a maximum of about 1.3 a.u. near 40 keV and remaining nearly constant through 100 keV. The z,s moment has a maximum of about 0.5 a.u. at 25 keV, passing through zero near 70 keV. These results compare favorably with available experimental results and are qualitatively predicted by present theoretical models. Comparison with previous H(n=3) results indicates that the Runge-Lenz vector z is larger for n=3 than for n=2 and that z,s has the same values for both n

Measurement of the H(n=2) density matrix for 20–100-keV collisions of H+ on He

Density matrices are experimentally determined which describe H(n=2) atoms produced in electron-transfer collisions between 20-100-keV protons and helium. The density matrix contains the electron-transfer cross sections σ2s, σ2p0, and σ2p+/-1, as well as the real and imaginary parts of the s0p0 coherence. Experimentally, a monoenergetic proton beam traverses a helium gas cell producing hydrogen atoms H(n) via electron transfer. Within the gas cell an electric field is applied either axial or transverse to the proton beam. The Stokes parameters describing the intensity and linear polarization of Lyman-α radiation (122 nm) emitted by H(n=2) atoms are determined as a function of applied electric-field strength. The density-matrix elements are determined from a linear least-squares fit of the Stokes parameters to the set of five fitting functions which represent the contributions from individual density-matrix elements. The density-matrix results are self-consistent. Separate determinations using axial or transverse electric fields agree with each other. The general results indicate σ2s>σ2p0>σ2p+/-1 between 20 and 100 keV. The electric dipole moment z has a value near zero at 20 keV rising to a maximum of about 1.3 a.u. near 40 keV and remaining nearly constant through 100 keV. The z,s moment has a maximum of about 0.5 a.u. at 25 keV, passing through zero near 70 keV. These results compare favorably with available experimental results and are qualitatively predicted by present theoretical models. Comparison with previous H(n=3) results indicates that the Runge-Lenz vector z is larger for n=3 than for n=2 and that z,s has the same values for both n

The nil Hecke ring and singularity of Schubert varieties

We give a criterion for smoothness of a point in any Schubert variety in any G/B in terms of the nil Hecke ring.Comment: AMSTE

Experimental determination of the H(n=3) density matrix for 80-keV H+ on He

The density matrix is determined for H(n=3) atoms produced in axially symmetric electron-transfer collisions of 80-keV protons on helium. In the experiment axial or transverse electric fields with respect to the proton beam are applied to the collision region. The intensity and polarization of Balmer-α radiation emitted by the H(n=3) atoms are measured as a function of the strength of the external electric field. Detailed analysis of the measured optical signals, taking into account the time evolution of the H(n=3) atoms in the applied electric field, makes it possible to extract the complete density matrix of the H(n=3) atoms at the moment of their formation, averaged over all impact parameters. Significant improvements in the experimental technique and in the data analysis associated with the fit of the density matrix to the optical signals have eliminated systematic effects that were present in our previous work [Phys. Rev. A 33, 276 (1986)]. The improvements in the apparatus are as follows: application of electric fields using electrodes with a simple geometry for the axial and transverse orientations that allows accurate calculation of the spatial variation of the electric field inside the collision chamber; use of high-quality optical elements and a rotatable, single-unit design for the polarimeter; automated gas handling for background subtraction; and full computer control of the electric fields, polarimeter, gas handling, and data acquisition. The analysis incorporates the following improvements: hyperfine structure of the H(n=3) manifold; cascade from the H(n=4) manifold; nonuniform detection efficiency over the viewing region; and modeling of the nonuniform electric fields, the nonuniform gas density, and the exponential decrease of the proton beam current in the gas cell due to electron transfer. With these improvements the results from axial electric field measurements are in good agreement with results obtained independently from transverse electric fields. Moreover, the extracted density-matrix elements are found to be within their physically meaningful bounds. The major results from 80-keV collisions are that the H(n=3) density matrix has an average coherence of 81%±1%, an electric dipole moment of 3.50±0.09 a.u., and a first-order moment of the electron current density distribution 〈(L×A)z,s〉 of -0.13±0.02 a.u. Results from a recent calculation show qualitative agreement with the experiment

Electromagnetic String Fluid in Rolling Tachyon

We study Born-Infeld type effective action for unstable D3-brane system including a tachyon and an Abelian gauge field, and find the rolling tachyon with constant electric and magnetic fields as the most general homogeneous solution. Tachyonic vacua are characterized by magnitudes of the electric and magnetic fields and the angle between them. Analysis of small fluctuations in this background shows that the obtained configuration may be interpreted as a fluid consisting of string-like objects carrying electric and magnetic fields. They are stretched along one direction and the rolling tachyon move in a perpendicular direction to the strings. Direction of the propagating waves coincides with that of strings with velocity equal to electric field.Comment: LaTeX, 18 pages, 1 figure, minor correction

MSSM Higgs sector CP violation at photon colliders: Revisited

We present a comprehensive analysis on the MSSM Higgs sector CP violation at photon colliders including the chargino contributions as well as the contributions of other charged particles. The chargino loop contributions can be important for the would-be CP odd Higgs production at photon colliders. Polarization asymmetries are indispensable in determining the CP properties of neutral Higgs bosons.Comment: 24 pages, 40 figure

Bounds from Primordial Black Holes with a Near Critical Collapse Initial Mass Function

Recent numerical evidence suggests that a mass spectrum of primordial black holes (PBHs) is produced as a consequence of near critical gravitational collapse. Assuming that these holes formed from the initial density perturbations seeded by inflation, we calculate model independent upper bounds on the mass variance at the reheating temperature by requiring the mass density not exceed the critical density and the photon emission not exceed current diffuse gamma-ray measurements. We then translate these results into bounds on the spectral index n by utilizing the COBE data to normalize the mass variance at large scales, assuming a constant power law, then scaling this result to the reheating temperature. We find that our bounds on n differ substantially (\delta n > 0.05) from those calculated using initial mass functions derived under the assumption that the black hole mass is proportional to the horizon mass at the collapse epoch. We also find a change in the shape of the diffuse gamma-ray spectrum which results from the Hawking radiation. Finally, we study the impact of a nonzero cosmological constant and find that the bounds on n are strengthened considerably if the universe is indeed vacuum-energy dominated today.Comment: 24 pages, REVTeX, 5 figures; minor typos fixed, two refs added, version to be published in PR

Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials

We investigate the cosmological evolution of the tachyon and phantom-tachyon scalar field by considering the potential parameter $\Gamma$($=\frac{V V"}{V'^2}$) as a function of another potential parameter $\lambda$($=\frac{V'}{\kappa V^{3/2}}$), which correspondingly extends the analysis of the evolution of our universe from two-dimensional autonomous dynamical system to the three-dimension. It allows us to investigate the more general situation where the potential is not restricted to inverse square potential and .One result is that, apart from the inverse square potential, there are a large number of potentials which can give the scaling and dominant solution when the function $\Gamma(\lambda)$ equals $3/2$ for one or some values of $\lambda_{*}$ as well as the parameter $\lambda_{*}$ satisfies condition Eq.(18) or Eq.(19). We also find that for a class of different potentials the dynamics evolution of the universe are actually the same and therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal C(2010), online first, http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=

Off-shell extension of S-matrix elements and tachyonic effective actions

We show that the on-shell S-matrix elements of four open string massless scalars, two scalars and two tachyons, and four open string tachyons in the super string theory can be written in a unique form. We then propose an off-shell extension for the S-matrix element of four scalars which is consistent, in the low energy limit, with the Dirac-Born-Infeld effective action. Using a similar off-shell extension for the S-matrix element of two scalars and two tachyons and for the S-matrix element of four tachyons, we show that they are fully consistent with the tachyonic DBI action.Comment: Latex, 17 pages, v3:a paragraph comparing off-shell and on- shell amplitudes added, reference adde