UHE neutrino damping in a thermal gas of relic neutrinos

We present a calculation of the damping of an ultra-energetic (UHE) cosmic neutrino travelling through the thermal gas of relic neutrinos, using the formalism of finite-temperature field theory. From the self-energy diagram due to Z exchange, we obtain the annihilation cross section for an UHE neutrino interacting with an antineutrino from the background. This method allows us to derive the full expressions for the UHE neutrino transmission probability, taking into account the momentum of relic neutrinos. We compare our results with the approximations in use in the literature. We discuss the effect of thermal motion on the shape of the absorption dips for different UHE neutrino fluxes as well as in the context of relic neutrino clustering. We find that for ratios of the neutrino mass to the relic background temperature $10^2$ or smaller, the thermal broadening of the absorption lines could significantly affect the determination of the neutrino mass and of the characteristics of the population of UHE sources.Comment: 18 pages, 6 figures. Typos corrected. More accurate treatment of the interaction with relic neutrino clusters. Accepted for publication in Astroparticle Physic

The PPARγ Agonist Rosiglitazone Suppresses Syngeneic Mouse SCC (Squamous Cell Carcinoma) Tumor Growth through an Immune-Mediated Mechanism

Recent evidence suggests that PPARγ agonists may promote anti-tumor immunity. We show that immunogenic PDV cutaneous squamous cell carcinoma (CSCC) tumors are rejected when injected intradermally at a low cell number (1 × 106) into immune competent syngeneic hosts, but not immune deficient mice. At higher cell numbers (5 × 106 PDV cells), progressively growing tumors were established in 14 of 15 vehicle treated mice while treatment of mice with the PPARγ agonist rosiglitazone resulted in increased tumor rejection (5 of 14 tumors), a significant decrease in PDV tumor size, and a significant decrease in tumor cell Ki67 labeling. Rosiglitazone treatment had no effect on tumor rejection, tumor volume or PDV tumor cell proliferation in immune deficient NOD.CB17-PrkdcSCID/J mice. Rosiglitazone treatment also promoted an increase in tumor infiltrating CD3+ T-cells at both early and late time points. In contrast, rosiglitazone treatment had no significant effect on myeloid cells expressing either CD11b or Gr-1 but suppressed a late accumulation of myeloid cells expressing both CD11b and Gr-1, suggesting a potential role for CD11b+Gr-1+ myeloid cells in the late anti-tumor immune response. Overall, our data provides evidence that the PPARγ agonist rosiglitazone promotes immune-mediated anti-neoplastic activity against tumors derived from this immunogenic CSCC cell line

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

Thermal effects on the absorption of ultra-high energy neutrinos by the cosmic neutrino background

We use the formalism of finite-temperature field theory to study the interactions of ultra-high energy (UHE) cosmic neutrinos with the background of relic neutrinos and to derive general expressions for the UHE neutrino transmission probability. This approach allows us to take into account the thermal effects introduced by the momentum distribution of the relic neutrinos. We compare our results with the approximate expressions existing in the literature and discuss the influence of thermal effects on the absorption dips in the context of favoured neutrino mass schemes, as well as in the case of clustered relic neutrinos.Comment: 3 pages, 2 figures. Prepared for the Proceedings of the 9th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2005), Zaragoza (Spain), September 10-14, 200

Vrsta nehomogenih mezonskih modela s perfektnom tekućinom i vremenski-ovisnim članom Λ

A class of non-static inhomogeneous cosmological models are investigated with cosmological term Λ(t) when source of the gravitational field is generated by a mixture of meson field and perfect fluid. Using gamma law equation of state, Einstein’s field equations are solved for two particular cases which are physically important. The cosmological term Λ(t) is found to be a decreasing function of time, which is supported by results found from recent type Ia supernovae observations. Some physical and geometrical aspects of the models are also discussed.Proučavamo vrstu nestatičkih i nehomogenih kozmoloških modela s kozmološkim članom Λ(t) kada je izvor gravitacijskog polja mješavina mezonskog polja i perfektne tekućine. Primjenom zakona za γ za jednadžbu stanja rješavamo za Einsteinove jednadžbe polja za dva posebna slučaja koji su važni za fiziku. Nalazimo kozmološki član Λ(t) kao opadajuću funkciju vremena, što je u skladu s opažanjima supernova Ia. Raspravljaju se neka fizička i geometrijska svojstva modela