Flavour-Dependent Type II Leptogenesis

We reanalyse leptogenesis via the out-of-equilibrium decay of the lightest right-handed neutrino in type II seesaw scenarios, taking into account flavour-dependent effects. In the type II seesaw mechanism, in addition to the type I seesaw contribution, an additional direct mass term for the light neutrinos is present. We consider type II seesaw scenarios where this additional contribution arises from the vacuum expectation value of a Higgs triplet, and furthermore an effective model-independent approach. We investigate bounds on the flavour-specific decay asymmetries, on the mass of the lightest right-handed neutrino and on the reheat temperature of the early universe, and compare them to the corresponding bounds in the type I seesaw framework. We show that while flavour-dependent thermal type II leptogenesis becomes more efficient for larger mass scale of the light neutrinos, and the bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more constrained. We also argue that in general, flavour-dependent effects cannot be ignored when dealing with leptogenesis in type II seesaw models.Comment: 19 pages, 8 figures; v3: minor additions, typos corrected, results and conclusions unchange

Facile synthesis of mesoporous N doped zirconium titanium mixed oxide nanomaterial with enhanced photocatalytic activity under visible light

The present paper deals with a hydrazine mediated synthesis of high surface area and thermally stable N-doped zirconium titanium mixed oxide with enhanced photocatalytic activity towards reduction of selenium (VI) to metallic Se0 under visible light. Materials were synthesized at pH ¼ 2 by varying the hydrazine concentration and characterized by XRD, TEM, BET method, XPS, Raman spectroscopy and UV-vis solid state spectra. Presence of low amount of zirconium oxide (10 wt%) helps in phase stabilization and maintains the porous structure even at higher calcinations temperature in comparison to that of pure titania. XPS spectrum justifies the presence of nitrogen and Ti3+ in the material due to the decomposition reaction of hydrazine. Hydrazine controls the nitrogen content, surface area and the formation of oxygen vacancy in the material. Investigation of metal oxide to hydrazine ratio on the overall surface properties and photocatalytic activity indicates that the 1 : 6 ratio is the optimum composition for the best result. Surface area and pore volume increases to 298 m2/g and 0.323 cm3/g. The obtained material (TiZr-6N-400) is found to reduce selenium (VI) to selenium (0) under visible light within only 45 min of reaction. Increased photocatalytic activity under visible light is mostly due to the synergistic effect of substantial nitrogen doping, high surface area and presence of oxygen vacancy

Leptogenesis and low energy CP phases with two heavy neutrinos

An attractive explanation for non-zero neutrino masses and small matter antimatter asymmetry of the present Universe lies in "leptogenesis". At present the {\it size} of the lepton asymmetry is precisely known, while the {\it sign} is not known yet. In this work we determine the sign of this asymmetry in the framework of two right handed neutrino models by relating the leptogenesis phase(s) with the low energy CP violating phases appearing in the leptonic mixing matrix. It is shown that the knowledge of low energy lepton number violating re-phasing invariants can indeed determine the sign of the present matter antimatter asymmetry of the Universe and hence indirectly probing the light physical neutrinos to be Majorana type.Comment: 26 pages (revtex), 8 eps figures, Typos corrected and one reference is added, Section VI is expanded, Two new figures are added, Journal version, To appear in PR

Bivariate tt-distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems

Interacting many-particle systems with a mean-field one body part plus a chaos generating random two-body interaction having strength $\lambda$, exhibit Poisson to GOE and Breit-Wigner (BW) to Gaussian transitions in level fluctuations and strength functions with transition points marked by $\lambda=\lambda_c$ and $\lambda=\lambda_F$, respectively; $\lambda_F >> \lambda_c$. For these systems theory for matrix elements of one-body transition operators is available, as valid in the Gaussian domain, with $\lambda > \lambda_F$, in terms of orbitals occupation numbers, level densities and an integral involving a bivariate Gaussian in the initial and final energies. Here we show that, using bivariate $t$-distribution, the theory extends below from the Gaussian regime to the BW regime up to $\lambda=\lambda_c$. This is well tested in numerical calculations for six spinless fermions in twelve single particle states.Comment: 7 pages, 2 figure

Long-term stability test of a triple GEM detector

The main aim of the study is to perform the long-term stability test of gain of the single mask triple GEM detector. A simple method is used for this long- term stability test using a radioactive X-ray source with high activity. The test is continued till accumulation of charge per unit area > 12.0 mC/mm2. The details of the chamber fabrication, the test set-up, the method of measurement and the test results are presented in this paper.Comment: 8 pages, 5 figure

Re-Hardening of Hadron Transverse Mass Spectra in Relativistic Heavy-Ion Collisions

We analyze the spectra of pions and protons in heavy-ion collisions at relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented hadron-string cascade model. In this energy region, hadron transverse mass spectra first show softening until SPS energies, and re-hardening may emerge at RHIC energies. Since hadronic matter is expected to show only softening at higher energy densities, this re-hardening of spectra can be interpreted as a good signature of the quark-gluon plasma formation.Comment: 10 pages, 3 figures, 1 table, Poster presentation at QM2001, Revised to correct latex error in citation on April 6, 200