4,073 research outputs found
The decays "neutrino{heavy} -> neutrino{light} + photon" and "neutrino{heavy} -> neutrino{light} e+ e-" of massive neutrinos
If, as recently reported by the Super-Kamiokande collaboration, the neutrinos
are massive, the heaviest one would not be stable and, though chargeless, could
in particular decay into a lighter neutrino and a photon by quantum loop
effects. The corresponding rate is computed in the standard model with massive
Dirac neutrinos as a function of the neutrino masses and mixing angles. The
lifetime of the decaying neutrino is estimated to be approximately 10^44 years
for a mass 5 10^{-2} eV. If kinematically possible, the decay of a heavy
neutrino into a lighter one plus an e+ e- pair occurs at tree level and its
one-loop radiative corrections get enhanced by a large logarithm of the
electron mass acting as an infrared cutoff. It then largely dominates the
photonic mode by several orders of magnitude, corresponding to a lifetime
approximately equal to 10^{-2} year for a mass 1.1 MeV.Comment: 12 pages, LaTeX 2e (epsf) with 9 postscript figures and one logo.
Some comments and references adde
Charge carrier localization induced by excess Fe in the Fe1+y(Te,Se) superconductor system
We have investigated the effect of Fe nonstoichiometry on properties of the
Fe1+y(Te, Se) superconductor system by means of resistivity, Hall coefficient,
magnetic susceptibility, and specific heat measurements. We find that the
excess Fe at interstitial sites of the (Te, Se) layers not only suppresses
superconductivity, but also results in a weakly localized electronic state. We
argue that these effects originate from the magnetic coupling between the
excess Fe and the adjacent Fe square planar sheets, which favors a short-range
magnetic order.Comment: 15 pages, 6 figures accepted for publication in PR
One-loop flavor changing electromagnetic transitions
We discuss the effect of the external fermion masses in the flavor-changing
radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion
at the one-loop level, and point out an often overlooked crucial difference in
the sign of a charge factor between transitions of the down type
and the up type . We give formulas for the
effective vertex in various approximations and the exact formula for and .Comment: LaTeX 16 pages + 4 postscript figures. Misprints corrected, some
Comments adde
QFlip: An Adaptive Reinforcement Learning Strategy for the FlipIt Security Game
A rise in Advanced Persistent Threats (APTs) has introduced a need for
robustness against long-running, stealthy attacks which circumvent existing
cryptographic security guarantees. FlipIt is a security game that models
attacker-defender interactions in advanced scenarios such as APTs. Previous
work analyzed extensively non-adaptive strategies in FlipIt, but adaptive
strategies rise naturally in practical interactions as players receive feedback
during the game. We model the FlipIt game as a Markov Decision Process and
introduce QFlip, an adaptive strategy for FlipIt based on temporal difference
reinforcement learning. We prove theoretical results on the convergence of our
new strategy against an opponent playing with a Periodic strategy. We confirm
our analysis experimentally by extensive evaluation of QFlip against specific
opponents. QFlip converges to the optimal adaptive strategy for Periodic and
Exponential opponents using associated state spaces. Finally, we introduce a
generalized QFlip strategy with composite state space that outperforms a Greedy
strategy for several distributions including Periodic and Uniform, without
prior knowledge of the opponent's strategy. We also release an OpenAI Gym
environment for FlipIt to facilitate future research.Comment: Outstanding Student Paper awar
Hidden attractors in fundamental problems and engineering models
Recently a concept of self-excited and hidden attractors was suggested: an
attractor is called a self-excited attractor if its basin of attraction
overlaps with neighborhood of an equilibrium, otherwise it is called a hidden
attractor. For example, hidden attractors are attractors in systems with no
equilibria or with only one stable equilibrium (a special case of
multistability and coexistence of attractors). While coexisting self-excited
attractors can be found using the standard computational procedure, there is no
standard way of predicting the existence or coexistence of hidden attractors in
a system. In this plenary survey lecture the concept of self-excited and hidden
attractors is discussed, and various corresponding examples of self-excited and
hidden attractors are considered
Charge-carrier localization induced by excess Fe in the superconductor Fe1+yTe1−xSex
We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te,Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific-heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square-planar sheets, which favors a short-range magnetic order
Charge-carrier localization induced by excess Fe in the superconductor Fe1+yTe1−xSex
We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te,Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific-heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square-planar sheets, which favors a short-range magnetic order
Extreme temperature impairs growth and productivity in a common tropical marine copepod
Abstract Shallow, tropical marine ecosystems provide essential ecosystem goods and services, but it is unknown how these ecosystems will respond to the increased exposure to the temperature extremes that are likely to become more common as climate change progresses. To address this issue, we tracked the fitness and productivity of a key zooplankton species, the copepod Pseudodiaptomus annandalei, acclimated at two temperatures (30 and 34 °C) over three generations. 30 °C is the mean temperature in the shallow water of the coastal regions in Southeast Asia, while 34 °C simulated a temperature extreme that occurs frequently during the summer period. For each generation, we measured the size at maturity and reproductive success of individuals. In all three generations, we found strong negative effects of warming on all measured fitness-related parameters, including prolonged development time, reduced size at maturity, smaller clutch sizes, lower hatching success, and reduced naupliar production. Our results suggest that P. annandalei are already exposed to temperatures that exceed their upper thermal optimum. Increased exposure to extreme temperatures may reduce the abundance of these tropical marine copepods, and thus reduce the availability of resources to higher trophic levels
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