Charge centers in CaF2_2: Ab initio calculation of elementary physical properties

Charge centers in ionic crystals provide a channel for elementary interaction between electromagnetic radiation and the lattice. We calculate the electronic ground state energies which are needed to create a charge center -- namely a $F$- and a $H$-center. In well agreement with common understanding the $F$-center results in being accompanied by a small lattice distortion whereas the $H$-center is accompanied by a very large lattice deformation. Opposite to the common understanding the additional positive charge in the charge center results rather to be localized on a F$_4^{3-}$ complex than on a F$_2^-$-complex. From the ground states of the charge centers we derive binding energies, diffusion barriers and agglomeration energies for $M$-center formation. These microscopic quantities are of fundamental interest to understand the dynamic processes which are initiated if the crystals interact with extreme intense deep ultra violet radiation. We further derive the equilibrium concentrations of charge centers in grown crystals.Comment: to appear in Phys. Rev. B in Aug. 2006, 11 Fig

How Can Active Region Plasma Escape into the Solar Wind from below a Closed Helmet Streamer?

Recent studies show that active-region (AR) upflowing plasma, observed by the EUV-Imaging Spectrometer (EIS), onboard Hinode, can gain access to open field-lines and be released into the solar wind (SW) via magnetic-interchange reconnection at magnetic null-points in pseudo-streamer configurations. When only one bipolar AR is present on the Sun and it is fully covered by the separatrix of a streamer, such as AR 10978 in December 2007, it seems unlikely that the upflowing AR plasma can find its way into the slow SW. However, signatures of plasma with AR composition have been found at 1 AU by Culhane et al. (2014) apparently originating from the West of AR 10978. We present a detailed topology analysis of AR 10978 and the surrounding large-scale corona based on a potential-field source-surface (PFSS) model. Our study shows that it is possible for the AR plasma to get around the streamer separatrix and be released into the SW via magnetic reconnection, occurring in at least two main steps. We analyse data from the Nan\c{c}ay Radioheliograph (NRH) searching for evidence of the chain of magnetic reconnections proposed. We find a noise storm above the AR and several varying sources at 150.9 MHz. Their locations suggest that they could be associated with particles accelerated during the first-step reconnection process and at a null point well outside of the AR. However, we find no evidence of the second-step reconnection in the radio data. Our results demonstrate that even when it appears highly improbable for the AR plasma to reach the SW, indirect channels involving a sequence of reconnections can make it possible.Comment: 26 pages, 10 figures. appears in Solar Physics, 201

Combined LHC/ILC analysis of a SUSY scenario with heavy sfermions

We discuss the potential of combined analyses at the Large Hadron Collider and the planned International Linear Collider to explore low-energy supersymmetry in a difficult region of the parameter space characterized by masses of the scalar SUSY particles around 2 TeV. Precision analyses of cross sections for light chargino production and forward--backward asymmetries of decay leptons and hadrons at the ILC, together with mass information on chi^0_2 and squarks from the LHC, allow us to determine the underlying fundamental gaugino/higgsino MSSM parameters and to constrain the masses of the heavy, kinematically inaccessible sparticles. No assumptions on a specific SUSY-breaking mechanism are imposed. For this analysis the complete spin correlations between production and decay processes are taken into account.Comment: new figure added, updated to match the published versio

Neutralino Pair Production and 3-Body Decays at e+e−e^+e^- Linear Colliders as Probes of CP Violation in the Neutralino System

In the CP-invariant supersymmetric theories, the steep S-wave (slow P-wave) rise of the cross section for any non-diagonal neutralino pair production in $e^+ e^-$ annihilation, $e^+e^- \to \tilde{\chi}^0_i \tilde{\chi}^0_j$ ($i \neq j$), near threshold is accompanied by the slow P-wave (steep S-wave) decrease of the fermion invariant mass distribution of the 3-body neutralino decay, $\tilde{\chi}^0_i \to \tilde{\chi}^0_j f\bar{f}$ ($f=l$ or $q$), near the end point. These selection rules, unique to the neutralino system due to its Majorana nature, guarantee that the observation of simultaneous sharp S-wave excitations of the production cross section near threshold and the lepton and quark invariant mass distribution near the end point is a qualitative, unambiguous evidence for CP violation in the neutralino system.Comment: 11 pages, 1 eps figure, a reference adde

Width of Radio-Loud and Radio-Quiet CMEs

In the present paper we report on the difference in angular sizes between radio-loud and radio-quiet CMEs. For this purpose we compiled these two samples of events using Wind/WAVES and SOHO/LASCO observations obtained during 1996-2005. It is shown that the radio-loud CMEs are almost two times wider than the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore we show that the radio-quiet CMEs have a narrow expanding bright part with a large extended diffusive structure. These results were obtained by measuring the CME widths in three different ways.Comment: Solar Physic, in pres

Parallel Evolution of Quasi-separatrix Layers and Active Region Upflows

Persistent plasma upflows were observed with Hinode's EUV Imaging Spectrometer (EIS) at the edges of active region (AR) 10978 as it crossed the solar disk. We analyze the evolution of the photospheric magnetic and velocity fields of the AR, model its coronal magnetic field, and compute the location of magnetic null-points and quasi-sepratrix layers (QSLs) searching for the origin of EIS upflows. Magnetic reconnection at the computed null points cannot explain all of the observed EIS upflow regions. However, EIS upflows and QSLs are found to evolve in parallel, both temporarily and spatially. Sections of two sets of QSLs, called outer and inner, are found associated to EIS upflow streams having different characteristics. The reconnection process in the outer QSLs is forced by a large-scale photospheric flow pattern which is present in the AR for several days. We propose a scenario in which upflows are observed provided a large enough asymmetry in plasma pressure exists between the pre-reconnection loops and for as long as a photospheric forcing is at work. A similar mechanism operates in the inner QSLs, in this case, it is forced by the emergence and evolution of the bipoles between the two main AR polarities. Our findings provide strong support to the results from previous individual case studies investigating the role of magnetic reconnection at QSLs as the origin of the upflowing plasma. Furthermore, we propose that persistent reconnection along QSLs does not only drive the EIS upflows, but it is also responsible for a continuous metric radio noise-storm observed in AR 10978 along its disk transit by the Nan\c{c}ay Radio Heliograph.Comment: 29 pages, 10 figure

One-loop corrections to the chargino and neutralino mass matrices in the on-shell scheme

We present a consistent procedure for the calculation of the one-loop corrections to the charginos and neutralinos by using their on-shell mass matrices. The on-shell gaugino mass parameters M and M', and the Higgsino mass parameter \mu are defined by the elements of these on-shell mass matrices. The on-shell mass matrices are different by finite one-loop corrections from the tree-level ones given in terms of the on-shell parameters. When the on-shell M and \mu are determined by the chargino sector, the neutralino masses receive corrections up to 4%. This must be taken into account in precision measurements at future e^+ e^- linear colliders.Comment: One reference added, typo in eq. (20) correcte

Polynomials, Riemann surfaces, and reconstructing missing-energy events

We consider the problem of reconstructing energies, momenta, and masses in collider events with missing energy, along with the complications introduced by combinatorial ambiguities and measurement errors. Typically, one reconstructs more than one value and we show how the wrong values may be correlated with the right ones. The problem has a natural formulation in terms of the theory of Riemann surfaces. We discuss examples including top quark decays in the Standard Model (relevant for top quark mass measurements and tests of spin correlation), cascade decays in models of new physics containing dark matter candidates, decays of third-generation leptoquarks in composite models of electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with discussion of Higgs to tau tau deca

Ice: a strongly correlated proton system

We discuss the problem of proton motion in Hydrogen bond materials with special focus on ice. We show that phenomenological models proposed in the past for the study of ice can be recast in terms of microscopic models in close relationship to the ones used to study the physics of Mott-Hubbard insulators. We discuss the physics of the paramagnetic phase of ice at 1/4 filling (neutral ice) and its mapping to a transverse field Ising model and also to a gauge theory in two and three dimensions. We show that H3O+ and HO- ions can be either in a confined or deconfined phase. We obtain the phase diagram of the problem as a function of temperature T and proton hopping energy t and find that there are two phases: an ordered insulating phase which results from an order-by-disorder mechanism induced by quantum fluctuations, and a disordered incoherent metallic phase (or plasma). We also discuss the problem of decoherence in the proton motion introduced by the lattice vibrations (phonons) and its effect on the phase diagram. Finally, we suggest that the transition from ice-Ih to ice-XI observed experimentally in doped ice is the confining-deconfining transition of our phase diagram.Comment: 12 pages, 9 figure