Impact of dark matter decays and annihilations on reionization

One of the possible methods to distinguish among various dark matter candidates is to study the effects of dark matter decays. We consider four different dark matter candidates (light dark matter, gravitinos, neutralinos and sterile neutrinos), for each of them deriving the decaying/annihilation rate, the influence on reionization, matter temperature and CMB spectra. We find that light dark matter particles (1-10 MeV) and sterile neutrinos (2-8 keV) can be sources of partial early reionization (z<~100). However, their integrated contribution to Thomson optical depth is small (<~0.01) with respect to the three year WMAP results (tau_e=0.09+/-0.03). Finally, they can significantly affect the behavior of matter temperature. On the contrary, effects of heavy dark matter candidates (gravitinos and neutralinos) on reionization and heating are minimal. All the considered dark matter particles have completely negligible effects on the CMB spectra.Comment: 6 pages, 5 figures; MNRAS, in pres

Isocurvature fluctuations in Affleck-Dine mechanism and constraints on inflation models

We reconsider the Affleck-Dine mechanism for baryogenesis and show that the baryonic isocurvature fluctuations are generated in many inflation models in supergravity. The inflationary scale and the reheating temperature must satisfy certain constraints to avoid too large baryonic isocurvature fluctuations.Comment: 18 pages, 1 figur

New Q-ball Solutions in Gauge-Mediation, Affleck-Dine Baryogenesis and Gravitino Dark Matter

Affleck-Dine (AD) baryogenesis along a d=6 flat direction in gauge-mediated supersymmetry-breaking (GMSB) models can produce unstable Q-balls which naturally have field strength similar to the messenger scale. In this case a new kind of Q-ball is formed, intermediate between gravity-mediated and gauge-mediated type. We study in detail these new Q-ball solutions, showing how their properties interpolate between standard gravity-mediated and gauge-mediated Q-balls as the AD field becomes larger than the messenger scale. It is shown that E/Q for the Q-balls can be greater than the nucleon mass but less than the MSSM-LSP mass, leading to Q-ball decay directly to Standard Model fermions with no MSSM-LSP production. More significantly, if E/Q is greater than the MSSM-LSP mass, decaying Q-balls can provide a natural source of non-thermal MSSM-LSPs, which can subsequently decay to gravitino dark matter without violating nucleosynthesis constraints. The model therefore provides a minimal scenario for baryogenesis and gravitino dark matter in the gauge-mediated MSSM, requiring no new fields.Comment: 13 pages, 9 figures. Some corrections and additional discussion. Version published in JCA

Optical RKKY Interaction between Charged Semiconductor Quantum Dots

We show how a spin interaction between electrons localized in neighboring quantum dots can be induced and controlled optically. The coupling is generated via virtual excitation of delocalized excitons and provides an efficient coherent control of the spins. This quantum manipulation can be realized in the adiabatic limit and is robust against decoherence by spontaneous emission. Applications to the realization of quantum gates, scalable quantum computers, and to the control of magnetization in an array of charged dots are proposed.Comment: 4 pages, 2 figure

Reheating as a surface effect

We describe a new mechanism for reheating the Universe through evaporation of a surface charge of a fragmented inflaton condensate. We show that for a range of Yukawa coupling of the inflaton to the matter sector evaporation gives rise to a much smaller reheat temperature compared to the standard perturbative decay. As a consequence, reheating through a surface effect could solve the gravitino and moduli over production problem in inflationary models without fine tuning the Yukawa sector.Comment: 4 page

The oscillation effects on thermalization of the neutrinos in the universe with low reheating temperature

We study how the oscillations of the neutrinos affect their thermalization process during the reheating period with temperature O(1) MeV in the early universe. We follow the evolution of the neutrino density matrices and investigate how the predictions of big bang nucleosynthesis vary with the reheating temperature. For the reheating temperature of several MeV, we find that including the oscillations makes different predictions, especially for $^4$He abundance. Also, the effects on the lower bound of the reheating temperature from cosmological observations are discussed.Comment: 24 pages, 8 figures; references and explanatory comments added, conclusion unchange

Polymorphism in the internal transcribed spacer (ITS) of the ribosomal DNA of 26 isolates of ectomycorrhizal fungi.

Inter- and intraspecific variation among 26 isolates of ectomycorrhizal fungi belonging to 8 genera and 19 species were evaluated by analysis of the internal transcribed sequence (ITS) of the rDNA region using restriction fragment length polymorphism (RFLP). The ITS region was first amplified by polymerase chain reaction (PCR) with specific primers and then cleaved with different restriction enzymes. Amplification products, which ranged between 560 and 750 base pairs (bp), were obtained for all the isolates analyzed. The degree of polymorphism observed did not allow proper identification of most of the isolates. Cleavage of amplified fragments with the restriction enzymes Alu I, Hae III, Hinf I, and Hpa II revealed extensive polymorphism. All eight genera and most species presented specific restriction patterns. Species not identifiable by a specific pattern belonged to two genera: Rhizopogon (R. nigrescens, R. reaii, R. roseolus, R. rubescens and Rhizopogon sp.), and Laccaria (L. bicolor and L. amethystea). Our data confirm the potential of ITS region PCR-RFLP for the molecular characterization of ectomycorrhizal fungi and their identification and monitoring in artificial inoculation programs

Sharp lines in the absorption edge of EuTe and Pb0.1_{0.1}Eu0.9_{0.9}Te in high magnetic fields

The optical absorption spectra in the region of the \fd transition energies of epitaxial layers of of EuTe and \PbEuTe, grown by molecular beam epitaxy, were studied using circularly polarized light, in the Faraday configuration. Under \sigmam polarization a sharp symmetric absorption line (full width at half-maximum 0.041 eV) emerges at the low energy side of the band-edge absorption, for magnetic fields intensities greater than 6 T. The absorption line shows a huge red shift (35 meV/T) with increasing magnetic fields. The peak position of the absorption line as a function of magnetic field is dominated by the {\em d-f} exchange interaction of the excited electron and the \Euion spins in the lattice. The {\em d-f} exchange interaction energy was estimated to be $J_{df}S=0.15\pm 0.01$ eV. In \PbEuTe the same absorption line is detected, but it is broader, due to alloy disorder, indicating that the excitation is localized within a finite radius. From a comparison of the absorption spectra in EuTe and \PbEuTe the characteristic radius of the excitation is estimated to be $\sim 10$\AA.Comment: Journal of Physics: Condensed Matter (2004, at press

The fate of the B ball

The gauge-mediated SUSY-breaking (GMSB) model needs entropy production at a relatively low temperature in the thermal history of the Universe for the unwanted relics to be diluted. This requires a mechanism for the baryogenesis after the entropy production, and the Affleck and Dine (AD) mechanism is a promising candidate for it. The AD baryogenesis in the GMSB model predicts the existence of the baryonic Q ball, that is the B ball, and this may work as the dark matter in the Universe. In this article, we discuss the stability of the B ball in th presence of baryon-number violating interactions. We find that the evaporation rate increases monotonically with the B-ball charge because the large field value inside the B ball enhances the effect of the baryon-number-violating operators. While there are some difficulties to evaluate the evaporation rate of the B ball, we derive the evaporation time (lifetime) of the B ball for the mass-to-charge ratio \omega_0\gsim 100 \MEV. The lifetime of the B ball and the distortion of the cosmic ray positron flux and the cosmic background radiation from the B ball evaporation give constraints on the baryon number of the B ball and the interaction, if the B ball is the dark matter. We also discuss some unresolved properties of the B ball.Comment: 27 pages incl 8 figs, LaTe

Low temperature resistivity in a nearly half-metallic ferromagnet

We consider electron transport in a nearly half-metallic ferromagnet, in which the minority spin electrons close to the band edge at the Fermi energy are Anderson-localized due to disorder. For the case of spin-flip scattering of the conduction electrons due to the absorption and emission of magnons, the Boltzmann equation is exactly soluble to the linear order. From this solution we calculate the temperature dependence of the resistivity due to single magnon processes at sufficiently low temperature, namely $k_BT\ll D/L^2$, where $L$ is the Anderson localization length and $D$ is the magnon stiffness. And depending on the details of the minority spin density of states at the Fermi level, we find a $T^{1.5}$ or $T^{2}$ scaling behavior for resistivity. Relevance to the doped perovskite manganite systems is discussed