447 research outputs found
On the Smallness of the Cosmological Constant in SUGRA Models Inspired by Degenerate Vacua
In the no-scale supergravity global symmetries protect local supersymmetry
and a zero value for the cosmological constant. The breakdown of these
symmetries, which ensures the vanishing of the vacuum energy density, results
in a set of degenerate vacua with broken and unbroken supersymmetry leading to
the natural realisation of the multiple point principle (MPP). In the MPP
inspired SUGRA models the cosmological constant is naturally tiny.Comment: Parallel talk at SUSY09, Boston, USA, June 2009, 5 page
SSX MHD Plasma Wind Tunnel
A new turbulent plasma source at the Swarthmore Spheromak Experiment (SSX) facility is described. The MHD wind tunnel configuration employs a magnetized plasma gun to inject high-beta plasma into a large, well-instrumented, vacuum drift region. This provides unique laboratory conditions approaching that in the solar wind: there is no applied background magnetic field in the drift region and has no net axial magnetic flux; the plasma flow speed is on the order of the local sound speed (M ~ 1), so flow energy density is comparable to thermal energy density; and the ratio of thermal to magnetic pressure is of order unity (plasma β ~ 1) so thermal energy density is also comparable to magnetic energy density. Results presented here and referenced within demonstrate the new capabilities and show how the new platform is proving useful for fundamental plasma turbulence studies
Tools for computing the AGN feedback: radio-loudness distribution and the kinetic luminosity function
We studied the Active Galactic Nuclei (AGN) radio emission from a compilation
of hard X-ray selected samples, all observed in the 1.4 GHz band. A total of
more than 1600 AGN with 2-10 keV de-absorbed luminosities higher than 10^42
erg/s were used. For a sub-sample of about 50 z\lsim 0.1 AGN it was possible to
reach a ~80% fraction of radio detections and therefore, for the first time, it
was possible to almost completely measure the probability distribution function
of the ratio between the radio and the X-ray luminosity Rx=log[L(1.4)/Lx]. The
probability distribution function of Rx was functionally fitted as dependent on
the X-ray luminosity and redshift, P(Rx|Lx,z). It roughly spans over 6 decades
(-7<Rx<-1), and does not show any sign of bi-modality. It resulted that the
probability of finding large values of the Rx ratio increases with decreasing
X-ray luminosities and (possibly) with increasing redshift. No statistical
significant difference was found between the radio properties of the X-ray
absorbed and unabsorbed AGN. The measure of the probability distribution
function of Rx allowed us to compute the kinetic luminosity function and the
kinetic energy density which, at variance with what assumed in many galaxy
evolution models, is observed to decrease of about a factor of five at redshift
below 0.5. About half of the kinetic energy density results to be produced by
the more radio quiet (Rx<-4) AGN. In agreement with previous estimates, the AGN
efficiency in converting the accreted mass energy into kinetic power is, on
average, ~5x10-3.Comment: 13 pages, ApJsty; ApJ in pres
Effects of the QCD phase transition on hadronic observables in relativistic hydrodynamic simulations of heavy-ion reactions in the FAIR/NICA energy regime
We investigate hadronic particle spectra and flow characteristics of
heavy-ion reactions in the FAIR/NICA energy range of within a relativistic ideal hydrodynamic one-fluid
approach. The particlization is realized by sampling the Cooper-Frye
distribution for a grand canonical hadron gas on a hypersurface of constant
energy density. Results of the hydrodynamic calculations for different
underlying equations of state are presented and compared with experimental data
and microscopic transport simulations. The sensitivity of the approach to
physical model inputs concerning the initial state and the particlization is
studied.Comment: Submitted to EPJ S
Variational Approach to Yang--Mills Theory with non-Gaussian Wave Functionals
A general method for treating non-Gaussian wave functionals in quantum field
theory is presented and applied to the Hamiltonian approach to Yang-Mills
theory in Coulomb gauge in order to include a three-gluon kernel in the
exponential of the vacuum wave functional. The three-gluon vertex is calculated
using the propagators found in the variational approach with a Gaussian trial
wave functional as input.Comment: 3 pages, 4 figures, talk presented at "Quark Confinement and the
Hadron Spectrum IX", Madrid, August 30-September 3, 2010, to appear in the
proceeding
Quarkonium at T>0
We report recent progress on theoretical investigations of quarkonia at
finite temperature. We discuss medium modification of charmonia and bottomonia
from a viewpoint of local operators and point out that while charmonia are
sensitive to the deconfinement transition bottomonia will be modified at much
higher temperatures.Comment: Talk given at XLI International Symposium of Multiparticle Dynamics
(ISMD 2011), 26-30, September 2011, Miyajima-Island, Hiroshima, Japan. 6
pages, 4 figures. To be published in Prog. Theor. Phys. Supp
The influence of strange quarks on QCD phase diagram and chemical freeze-out: Results from the hadron resonance gas model
We confront the lattice results on QCD phase diagram for two and three
flavors with the hadron resonance gas model. Taking into account the
truncations in the Taylor-expansion of energy density done on the
lattice at finite chemical potential , we find that the hadron resonance
gas model under the condition of constant describes very well the
lattice phase diagram. We also calculate the chemical freeze-out curve
according to the entropy density . The -values are taken from lattice QCD
simulations with two and three flavors. We find that this condition is
excellent in reproducing the experimentally estimated parameters of the
chemical freeze-out.Comment: 5 pages, 3 figures and 1 table Talk given at VIIIth international
conference on ''Strangeness in Quark Matter'' (SQM 2004), Cape Town, South
Africa, Sep. 15-20 200
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