885 research outputs found
Dark Matter from Freeze-In via the Neutrino Portal
We investigate a minimal neutrino portal dark matter (DM) model where a
right-handed neutrino both generates the observed neutrino masses and mediates
between the SM and the dark sector, which consists of a fermion and a boson. In
contrast to earlier work, we explore regions of the parameter space where DM is
produced via freeze-in instead of freeze-out motivated by the small neutrino
Yukawa couplings in case of heavy
neutrinos. \\ For a non-resonant production of DM, its energy density is
independent of the DM mass. Assuming a democratic coupling structure we find
. For the resonant production of DM, we find
that it can be produced via freeze-in or freeze-out even with couplings of
. However, the measurement of the
Lyman- forest rules out the feeble coupled freeze-out case completely,
while the resonant freeze-in production is only viable for .Comment: 19 pages + appendices, 7 figure
Leptonic Flavor Structure in the Brane Shifted Extra Dimensional Seesaw Mechanism
We discuss the leptonic flavor structure generated by a brane shifted extra
dimensional seesaw model with a single right handed neutrino in the bulk. In
contrast to previous works, no unitarity approximation for the
submatrix has been employed. This allows to study phenomenological signatures
such as lepton flavor violating decays. A strong prediction of the model,
assuming CP conservation, are the ratios of flavor violating charged lepton
decay and Z decay branching ratios which are correlated with the neutrino
mixing angles and the neutrino mass hierarchy. Furthermore, it is possible to
obtain branching ratios for close to the
experimental bounds even with Yukawa couplings of order one.Comment: 13 pages plus appendix and references, 4 figures. v2: version
accepted by EPJ
International risk sharing in the short run and in the long run
Using a panel of 23 industrialised countries, the paper investigates how short-run and long-run income risks are shared and how the source of uncertainty matters for the way this risk gets insured. Surprisingly, short-term and long-term output risks are found to be equally well insured. Transitory shocks get smoothed almost completely whereas permanent shocks remain 80 percent uninsured. We find a somewhat more important role for international capital markets than earlier studies. Whereas our results tie in with some recent theoretical insights and are consistent with empirical findings on home bias in international portfolios, they raise the question why permanent shocks are so hard to insure internationally. Keywords; international consumption risk sharing, European integration, panel data, panel vector autoregressions
Intra-and International Risk-Sharing in the Short Run and the Long Run
We investigate empirically how industrialized countries and U.S. states share consumption risk at horizons between one and thirty years. U.S. federal states share about 50 percent of their permanent idiosyncratic risk through cross-state capital income flows. While insurance against transitory fluctuations in output is virtually complete, OECD countries do not share any of their permanent idiosyncratic risk. Our results suggest that purely transaction cost based theories cannot explain the home bias, since the potential welfare gains from insurance against permanent shocks would by far outweigh that of insuring against transitory variation. We conclude that permanent and transitory shocks constitute two qualitatively different kinds of risk and that various forms of endogenous market incompleteness may render permanent shocks a lot harder to insure, in particular at the international level.consumption risk sharing, home bias, international business cycles, panel vector autoregressions
Equity Fund Ownership and the Cross-Regional Diversification of Household Risk
We explore the link between portfolio home bias and consumption risk sharing among Italian regions using aggregated household level information on consumption, income and portfolio holdings. We propose to use data on equity fund ownership to proxy for regional home bias: equity funds are typically diversified at the national or international level and will therefore provide interregional diversification. In assessing the impact of equity fund ownership on interregional risk sharing we distinguish between two dimensions: variation in the share of equity funds in fund-holder's wealth (the intensive margin) and variation in the fraction of households that hold funds (the extensive margin). We find that equity fund ownership is an important determinant of interregional risk sharing. First, diversification incentives qualitatively line up with actually observed portfolio choices: fund holders in regions where households are particularly exposed to region-specific labor income risk hold a larger fraction of their wealth in (out-of-region) funds. Secondly, for a region as a whole, risk sharing increases in both the intensive and the extensive margins of diversification and the two margins reinforce each other. The marginal effect of wider equity fund participation seems particularly strong, suggesting that policies aimed at increasing equity market participation could help foster better interregional risk sharing.consumption risk sharing, regional home bias, survey of household income and wealth, labor income risk, portfolio choice, stock market participation
Dark matter models: the neutrino and flavor portals
In this thesis, we analyze several standard model extensions involving one or multiple dark matter candidates and link the dark matter problem to different other standard model shortcomings such as neutrino mass generation and flavor anomalies. First we discuss the leptonic flavor structure of an extra dimensional seesaw mechanism, which does not include a dark matter candidate. However, the mechanism suppresses couplings to the new right-handed neutrino state. This serves as a motivation to investigate a feebly coupled neutrino portal to dark matter model where the right-handed neutrino both generates the observed neutrino masses and mediates between the standard model and the dark sector. We classify the dark matter production regimes of the model and point out its phenomenological implications. Furthermore, we apply consistency conditions to strongly coupled versions of the neutrino portal to dark matter. We find that the consistency conditions induce an upper limit on the dark matter mass in such a scenario. We continue by discussing the effects of a bound state that can form in a heavy dark sector. We find that the bound state can facilitate particle number transfer from the dark sector to other sectors even if they are only feebly coupled. We also explore a class of models in this thesis that is dedicated to one-loop solutions to the R_K anomaly in the light of dark matter searches. We find that current dark matter direct detection experiments can test the one-loop solutions to the R_K anomaly
Ionization heating in rare-gas clusters under intense XUV laser pulses
The interaction of intense extreme ultraviolet (XUV) laser pulses
(, \,W/cm) with small rare-gas clusters
(Ar) is studied by quasi-classical molecular dynamics simulations. Our
analysis supports a very general picture of the charging and heating dynamics
in finite samples under short-wavelength radiation that is of relevance for
several applications of free-electron lasers. First, up to a certain photon
flux, ionization proceeds as a series of direct photoemission events producing
a jellium-like cluster potential and a characteristic plateau in the
photoelectron spectrum as observed in [Bostedt {\it et al.}, Phys. Rev. Lett.
{\bf 100}, 013401 (2008)]. Second, beyond the onset of photoelectron trapping,
nanoplasma formation leads to evaporative electron emission with a
characteristic thermal tail in the electron spectrum. A detailed analysis of
this transition is presented. Third, in contrast to the behavior in the
infrared or low vacuum ultraviolet range, the nanoplasma energy capture
proceeds via {\it ionization heating}, i.e., inner photoionization of localized
electrons, whereas collisional heating of conduction electrons is negligible up
to high laser intensities. A direct consequence of the latter is a surprising
evolution of the mean energy of emitted electrons as function of laser
intensity.Comment: figure problems resolve
STABILIZATION OF UPLAND RICE PRODUCTION UNDER SHORTENED FALLOW IN WEST AFRICA: RESEARCH PRIORITY SETTING IN A DYNAMIC ENVIRONMENTAL AND ECONOMIC CLIMATE
This paper presents a dynamic model of land resource degradation and shifting rice cultivation in West Africa based upon Boserup and Dvorak. The model indicates the ex ante impact of research strategies to maximize the economic benefits of host plant resistance and land resource management and thereby stabilize yield decline and reduce land degradation.Land Economics/Use, Resource /Energy Economics and Policy,
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