Block-Transitive Designs in Affine Spaces

This paper deals with block-transitive $t$-$(v,k,\lambda)$ designs in affine spaces for large $t$, with a focus on the important index $\lambda=1$ case. We prove that there are no non-trivial 5-$(v,k,1)$ designs admitting a block-transitive group of automorphisms that is of affine type. Moreover, we show that the corresponding non-existence result holds for 4-$(v,k,1)$ designs, except possibly when the group is one-dimensional affine. Our approach involves a consideration of the finite 2-homogeneous affine permutation groups.Comment: 10 pages; to appear in: "Designs, Codes and Cryptography

A strong electroweak phase transition in the 2HDM after LHC8

The nature of the electroweak phase transition in two-Higgs-doublet models is revisited in light of the recent LHC results. A scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar (m_A^0 > 400 GeV) and a mass hierarchy in the scalar sector, m_H^+ gamma gamma decay channel and find that an enhancement in the branching ratio is allowed, and in some cases even preferred, when a strongly first-order phase transition is required

Discovery of the secondary eclipse of HAT-P-11 b

We report the detection of the secondary eclipse of HAT-P-11 b, a Neptune-sized planet orbiting an active K4 dwarf. Using all available short-cadence data of the Kepler mission, we derive refined planetary ephemeris increasing their precision by more than an order of magnitude. Our simultaneous primary and secondary transit modeling results in improved transit and orbital parameters. In particular, the precise timing of the secondary eclipse allows to pin down the orbital eccentricity to $0.26459_{-0.00048}^{+0.00069}$. The secondary eclipse depth of $6.09_{-1.11}^{+1.12}$ ppm corresponds to a $5.5\sigma$ detection and results in a geometric albedo of $0.39\pm0.07$ for HAT-P-11 b, close to Neptune's value, which may indicate further resemblances between these two bodies. Due to the substantial orbital eccentricity, the planetary equilibrium temperature is expected to change significantly with orbital position and ought to vary between $630^\circ$ K and $950^\circ$ K, depending on the details of heat redistribution in the atmosphere of HAT-P-11 b.Comment: Accepted by A&A, 27/10/201

Echoes of the electroweak phase transition: discovering a second Higgs doublet through A0 → ZH0

The existence of a second Higgs doublet in nature could lead to a cosmological first-order electroweak phase transition and explain the origin of the matter-antimatter asymmetry in the Universe. We obtain the spectrum and properties of the new scalars H0, A0, and H� that signal such a phase transition and show that the observation of the decay A0 → ZH0 at LHC would be a “smoking gun” signature of these scenarios. We analyze the LHC search prospects for this decay in the llbb¯ and llWþW− final states, arguing that current data may be sensitive to this signature in the former channel as well as there being great potential for a discovery in either channel at the very early stages of the 14 TeV run

Optimization of a neutrino factory oscillation experiment

We discuss the optimization of a neutrino factory experiment for neutrino oscillation physics in terms of muon energy, baselines, and oscillation channels (gold, silver, platinum). In addition, we study the impact and requirements for detector technology improvements, and we compare the results to beta beams. We find that the optimized neutrino factory has two baselines, one at about 3000 to 5000km, the other at about 7500km (``magic'' baseline). The threshold and energy resolution of the golden channel detector have the most promising optimization potential. This, in turn, could be used to lower the muon energy from about 50GeV to about 20GeV. Furthermore, the inclusion of electron neutrino appearance with charge identification (platinum channel) could help for large values of \sin^2 2 \theta_{13}. Though tau neutrino appearance with charge identification (silver channel) helps, in principle, to resolve degeneracies for intermediate \sin^2 2 \theta_{13}, we find that alternative strategies may be more feasible in this parameter range. As far as matter density uncertainties are concerned, we demonstrate that their impact can be reduced by the combination of different baselines and channels. Finally, in comparison to beta beams and other alternative technologies, we clearly can establish a superior performance for a neutrino factory in the case \sin^2 2 \theta_{13} < 0.01.Comment: 51 pages, 25 figures, 6 tables, references corrected, final version to appear in Phys. Rev.

Top transport in electroweak baryogenesis

In non-supersymmetric models of electroweak baryogenesis the top quark plays a crucial role. Its CP-violating source term can be calculated in the WKB approximation. We point out how to resolve certain discrepancies between computations starting from the Dirac equation and the Schwinger--Keldysh formalism. We also improve on the transport equations, keeping the W-scatterings at finite rate. We apply these results to a model with one Higgs doublet, augmented by dimension-6 operators, where our refinements lead to an increase in the baryon asymmetry by a factor of up to about 5.Comment: 17 pages, 3 figures, references adde

Spin dynamics in a superconductor / ferromagnet proximity system

The ferromagnetic resonance of thin sputtered Ni80Fe20 films grown on Nb is measured. By varying the temperature and thickness of the Nb the role of the superconductivity on the whole ferromagnetic layer in these heterostructures is explored. The change in the spin transport properties below the superconducting transition of the Nb is found to manifest itself in the Ni80Fe20 layer by a sharpening in the resonance of the ferromagnet, or a decrease in the effective Gilbert damping co-efficient. This dynamic proximity effect is in contrast to low frequency studies in these systems, where the effect of the superconductor is confined to a small region in the ferromagnet. We interpret this in terms of the spin pumping model.Comment: 4 pages, 4 figures, to be submitted for publicatio

A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits

We analyze the surface structure of the planet host star CoRoT-2a using a consistent model for both the `global' (i.e., rotationally modulated) lightcurve and the transit lightcurves, using data provided by the CoRoT mission. Selecting a time interval covering two stellar rotations and six transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the surface to reproduce the photometric modulation inside and outside the transits simultaneously. Our reconstructions show that it is possible to achieve appropriate fits for the entire sub-interval using a low-resolution surface model with 36 strips. The surface reconstructions indicate that the brightness on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the average brightness of the remaining surface. This result suggests a concentration of stellar activity in a band around the stellar equator similar to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200