Returning magnetic flux in sunspot penumbrae

We study the presence of reversed polarity magnetic flux in sunspot penumbra. We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resulting Stokes profiles were inverted to infer the magnetic field vector using SIR. We find, for the first time, reversed polarity fields at the border of many bright penumbral filaments in the whole penumbra.Comment: 5 pages, 5 figures, accepted for publication in A&A Letter

Asymmetric effects of oil price fluctuations in international stock markets

New evidence on the way oil price fluctuations affect international stock markets is provided in analysis of the exposure of 43 stock markets. Oil price spikes depress international stock markets, but oil price drops do not necessarily increase stock market returns. Moreover, the volatility of oil prices has a negative impact on international stock market returns. Both these effects apply only to stock markets of developed countries. Emerging market returns are not sensitive to oil price variations. In addition, the asymmetry of oil price changes impacts oil volatility; i.e., when oil prices soar, oil volatility also increases, while negative oil price changes dampen volatility. Finally, oil price fluctuations are a factor in creating downside risk for international country investment.Asymmetry, Multifactor asset pricing Models, Oil prices, Panel data, Quantile regression, Volatility

Geographical versus Industrial Diversification: A Mean Variance Spanning Approach

This paper addresses whether country allocation provides benefits over industry allocation in a sample of European country and industry indexes. Strategy performance is compared using a mean-variance spanning test. We find that, for investors with low risk aversion, industry allocation is as good as investing in the complete set of assets. Moreover, in the most recent subperiod coinciding with the inception of the Euro, country and industry diversification are both effective. By contrast, investors with high risk aversion should always mix country and industry portfolios. A striking aspect of our analysis is that we do not find empirical evidence to support the argument that country diversification is a superior approach.Diversification gains, EMU, mean-variance spanning, portfolio allocation strategies

Risk factors in oil and gas industry returns: international evidence

This paper analyzes the exposure of the oil and gas industry of 34 countries to oil prices. Using a multifactor panel model to estimate the oil and gas excess stock returns, our results strongly support the view that oil price is a globally priced factor for the oil industry. In particular, the response of the oil and gas sector to changes oil prices is positive and larger for developed countries than for emerging markets. The industry response is asymmetric, with positive oil price changes having a greater impact on the oil sector returns than negative changes. Furthermore, local market index returns, currency rates and oil price volatility also have a significant impact on oil industry's excess returns. Finally, industry local sensitivities seem to vary with stock market activity and with levels of appropriation of industry revenues by governments. Results are robust to a battery of tests.Multifactor asset pricing models, Panel Data, Oil industry

D Mesons in Nuclear Matter: A DN Coupled-Channel Equations Approach

A set of coupled two-body scattering equations is solved for the DN system embedded in an iso-symmetric nuclear matter. The in-medium behavior of charmed D mesons: (D^+,D^0), is investigated from the self-consistent solution within this scheme. The effective meson-baryon Lagrangian in charm quantum number one sector, the key ingredient in the present study, is adopted from a recent model by Hofmann and Lutz which has aimed at combining the charmed meson degree of freedom in a consistent manner with chiral unitary models. After a critical examination, the original model is modified in several important aspects, such as the method of regularization, in order to be more consistent and practical for our objective. The resultant interaction is used to reproduce the position and width of the s-wave \Lambda_c(2593) resonance in the isospin zero DN channel. In the isospin one channel, it generates a rather wide resonance at \~2770 MeV. The corresponding in-medium solution is then sought by incorporating Pauli blocking and the D- and \pi-meson dressing self-consistently. At normal nuclear matter density, the resultant \Lambda_c (2593) is found to stay narrow and shifted at a lower energy, while the I=1 resonance is lowered in position as well and broadened considerably. The possible implication of our findings on the J/\Psi suppression, etc. in relativistic heavy ion collisions is briefly discussed.Comment: 30 pages, 8 eps figures, some typos and coefficients corrected, published in Phys. Rev.

Clear detection of dusty torus signatures in a Weak-Line Radio Galaxy: the case of PKS 0043-42

We report the clearest detection to date of dusty torus signatures in a Weak-Line Radio Galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS) rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42 (z=0.116) shows a clear spectral turnover at wavelengths longer than ~20 micron suggestive of warm dust, as well as a 9.7 micron silicate absorption feature. In addition, the hard X-ray results, based on Chandra data, strongly support a picture in which PKS 0043-42 has a torus and accretion disc more typical of Strong-Line Radio Galaxies (SLRGs). The MIR and X-ray spectra are markedly different from those of other WLRGs at similar redshifts, and here we show that the former can be successfully fitted with clumpy torus models with parameters characteristic of Type-2 AGN tori: close to edge-on (i=74 deg) and relatively broad (torus angular width=60 deg), with an outer radius of 2 pc, hydrogen column density ~1.6x10^(23) cm^(-2), and AGN bolometric luminosity ~1.6x10^(44) erg s^(-1). The presence of a compact torus in PKS 0043-42 provides evidence that this WLRG is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a diverse population, and PKS 0043-42 may represent a type of radio galaxy in which the AGN activity has been recently re-triggered as a consequence of intermittent gas supply, or in which the covering factor of the Narrow-Line Region (NLR) clouds is relatively low.Comment: 7 pages, 6 figures, 1 table. Accepted by MNRA

Quantum spin circulator in Y junctions of Heisenberg chains

We show that a quantum spin circulator, a nonreciprocal device that routes spin currents without any charge transport, can be achieved in Y junctions of identical spin-$1/2$ Heisenberg chains coupled by a chiral three-spin interaction. Using bosonization, boundary conformal field theory, and density-matrix renormalization group simulations, we find that a chiral fixed point with maximally asymmetric spin conductance arises at a critical point separating a regime of disconnected chains from a spin-only version of the three-channel Kondo effect. We argue that networks of spin-chain Y junctions provide a controllable approach to construct long-sought chiral spin liquid phases.Comment: 9 pages, 3 figure