771 research outputs found
VERITAS Very High Energy Observations of the Distant Blazar 1ES 0647+250
We perform an analysis of the long- and short-term variability of the very high energy (VHE; above 100 GeV) gamma-ray emission from the newly-detected distant blazar 1ES 0647+250. Both new and archival data from the VERITAS telescope were examined, and no strong evidence for integral flux variability on any timescale was found. This lack of variability is consistent with the application of current ultra-high energy cosmic ray (UHECR) models, which can produce secondary gamma-ray emission along the line of sight from the blazar; it also allows averaging over multiyear timescales without bias, aiding in the construction of spectral energy distribution plots (SEDs) for 1ES 0647+250. Because of its distance, 1ES 0647+250 is an object of interest for further study, particularly in efforts to constrain models of the extragalactic background light (EBL) and intergalactic magnetic field strength (IGMFs)
Constraints on economical 331 models from mixing of K, Bd and Bs neutral mesons
We analyze the effect of flavor changing neutral currents within 331 models.
In particular, we concentrate in the so-called "economical" models, which have
a minimal scalar sector. Taking into account the experimental measurements of
observables related to neutral K and B meson mixing, we study the resulting
bounds for angles and phases in the mixing matrix for the down quark sector,
and the mass and mixing parameters related to the new Z' gauge boson.Comment: 11 pages, 3 figures. Eqs. (8) and (9) corrected, to be published in
Phys. Rev.
Hadron structure in tau -> KKpi nu_tau decays
We analyse the hadronization structure of both vector and axial-vector
currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc
expansion, and considering only the contribution of the lightest resonances, we
work out, within the framework of the resonance chiral Lagrangian, the
structure of the local vertices involved in those processes. The couplings in
the resonance theory are constrained by imposing the asymptotic behaviour of
vector and axial-vector spectral functions ruled by QCD. In this way we predict
the hadron spectra and conclude that, contrarily to previous assertions, the
vector contribution dominates by far over the axial-vector one in all KKpi
charge channels.Comment: 32 pages, 7 figure
3D simulations of RS Oph: from accretion to nova blast
RS Ophiuchi is a recurrent nova with a period of about 22 years, consisting
of a wind accreting binary system with a white dwarf (WD) very close to the
Chandrasekhar limit and a red giant star (RG). The system is considered a prime
candidate to evolve into an SNIa. We present a 3D hydrodynamic simulation of
the quiescent accretion and the subsequent explosive phase. The computed
circumstellar mass distribution in the quiescent phase is highly structured
with a mass enhancement in the orbital plane of about a factor of 2 as compared
to the poleward directions. The simulated nova remnant evolves aspherically,
propagating faster toward the poles. The shock velocities derived from the
simulations are in agreement with those derived from observations. For v_RG =
20 km/s and for nearly isothermal flows, we derive a mass transfer rate to the
WD of 10% of the mass loss of the RG. For an RG mass loss of 10^{-7} solar
masses per year, we found the orbit of the system to decay by 3% per million
years. With the derived mass transfer rate, multi-cycle nova models provide a
qualitatively correct recurrence time, amplitude, and fastness of the nova. Our
simulations provide, along with the observations and nova models, the third
ingredient for a deeper understanding of the recurrent novae of the RS Oph
type. In combination with recent multi-cycle nova models, our results suggests
that the WD in RS Oph will increase in mass. Several speculative outcomes then
seem plausible. The WD may reach the Chandrasekhar limit and explode as an SN
Ia. Alternatively, the mass loss of the RG could result in a smaller Roche
volume, a common envelope phase, and a narrow WD+WD system. Angular momentum
loss due to graviational wave emission could trigger the merger of the two WDs
and - perhaps - an SN Ia via the double degenerate scenario.Comment: Accepted by Astronomy & Astrophysics Letters, 4 pages, 5 figures;
Version with high resolution figures and movie can be found at
http://www.astro.phys.ethz.ch/staff/folini/private/research/rsoph/rsoph.htm
Band and filling controlled transitions in exactly solved electronic models
We describe a general method to study the ground state phase diagram of
electronic models on chains whose extended Hubbard hamiltonian is formed by a
generalized permutator plus a band-controlling term. The method, based on the
appropriate interpretation of Sutherland's species, yields under described
conditions a reduction of the effective Hilbert space. In particular, we derive
the phase diagrams of two new models; the first one exhibits a band-controlled
insulator-superconductor transition at half-filling for the unusually high
value ; the second one is characterized by a filling-controlled
metal-insulator transition between two finite regions of the diagram.Comment: 5 pages, REVTEX, 2 eps figure
Disentangling the conductivity spectra of two-dimensional organic conductors
The optical spectrum of a κ -phase organic conductor is thoroughly analyzed for the example of κ -(BEDT-TTF) 2 Cu [ N(CN) 2 ] Br 0.85 Cl 0.15 in order to identify its various contributions. It is shown how the complex spectra can be decomposed using different approaches; the intradimer and interdimer contributions are discussed. In particular the fingerprints of electronic correlations in these spectra are considered
- …