630 research outputs found
The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding
rocket payload built to study the crucial interface between the solar
chromosphere and the corona by observing the strongest line in the solar
spectrum, the Ly-a line at 1216 {\AA}. In two flights, VAULT succeeded in
obtaining the first ever sub-arcsecond (0.5") images of this region with high
sensitivity and cadence. Detailed analyses of those observations have
contributed significantly to new ideas about the nature of the transition
region. Here, we present a broad overview of the Ly-a atmosphere as revealed by
the VAULT observations, and bring together past results and new analyses from
the second VAULT flight to create a synthesis of our current knowledge of the
high-resolution Ly-a Sun. We hope that this work will serve as a good reference
for the design of upcoming Ly-a telescopes and observing plans.Comment: 28 pages, 11 figure
Quasi-long-range order in the random anisotropy Heisenberg model: functional renormalization group in 4-\epsilon dimensions
The large distance behaviors of the random field and random anisotropy O(N)
models are studied with the functional renormalization group in 4-\epsilon
dimensions. The random anisotropy Heisenberg (N=3) model is found to have a
phase with the infinite correlation radius at low temperatures and weak
disorder. The correlation function of the magnetization obeys a power law <
m(x) m(y) >\sim |x-y|^{-0.62\epsilon}. The magnetic susceptibility diverges at
low fields as \chi \sim H^{-1+0.15\epsilon}. In the random field O(N) model the
correlation radius is found to be finite at the arbitrarily weak disorder for
any N>3. The random field case is studied with a new simple method, based on a
rigorous inequality. This approach allows one to avoid the integration of the
functional renormalization group equations.Comment: 12 pages, RevTeX; a minor change in the list of reference
Bounds on the dipole moments of the tau-neutrino via the process in a 331 model
We obtain limits on the anomalous magnetic and electric dipole moments of the
through the reaction
and in the framework of a 331 model. We consider initial-state radiation, and
neglect and photon exchange diagrams. The results are based on the data
reported by the L3 Collaboration at LEP, and compare favorably with the limits
obtained in other models, complementing previous studies on the dipole moments.Comment: 13 pages, 4 figures, to be published in The European Physical J C.
arXiv admin note: substantial text overlap with arXiv:hep-ph/060527
Parity Violation in Proton-Proton Scattering
Measurements of parity-violating longitudinal analyzing powers (normalized
asymmetries) in polarized proton-proton scattering provide a unique window on
the interplay between the weak and strong interactions between and within
hadrons. Several new proton-proton parity violation experiments are presently
either being performed or are being prepared for execution in the near future:
at TRIUMF at 221 MeV and 450 MeV and at COSY (Kernforschungsanlage Juelich) at
230 MeV and near 1.3 GeV. These experiments are intended to provide stringent
constraints on the set of six effective weak meson-nucleon coupling constants,
which characterize the weak interaction between hadrons in the energy domain
where meson exchange models provide an appropriate description. The 221 MeV is
unique in that it selects a single transition amplitude (3P2-1D2) and
consequently constrains the weak meson-nucleon coupling constant h_rho{pp}. The
TRIUMF 221 MeV proton-proton parity violation experiment is described in some
detail. A preliminary result for the longitudinal analyzing power is Az = (1.1
+/-0.4 +/-0.4) x 10^-7. Further proton-proton parity violation experiments are
commented on. The anomaly at 6 GeV/c requires that a new multi-GeV
proton-proton parity violation experiment be performed.Comment: 13 Pages LaTeX, 5 PostScript figures, uses espcrc1.sty. Invited talk
at QULEN97, International Conference on Quark Lepton Nuclear Physics --
Nonperturbative QCD Hadron Physics & Electroweak Nuclear Processes --, Osaka,
Japan May 20--23, 199
Nucleon Spin-Polarisabilities from Polarisation Observables in Low-Energy Deuteron Compton Scattering
We investigate the dependence of polarisation observables in elastic deuteron
Compton scattering below the pion production threshold on the spin-independent
and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The
calculation uses Chiral Effective Field Theory with dynamical Delta(1232)
degrees of freedom in the Small Scale Expansion at next-to-leading order.
Resummation of the NN intermediate rescattering states and including the Delta
induces sizeable effects. The analysis considers cross-sections and the
analysing power of linearly polarised photons on an unpolarised target, and
cross-section differences and asymmetries of linearly and circularly polarised
beams on a vector-polarised deuteron. An intuitive argument helps one to
identify kinematics in which one or several polarisabilities do not contribute.
Some double-polarised observables are only sensitive to linear combinations of
two of the spin-polarisabilities, simplifying a multipole-analysis of the data.
Spin-polarisabilities can be extracted at photon energies \gtrsim 100 MeV,
after measurements at lower energies of \lesssim 70 MeV provide high-accuracy
determinations of the spin-independent ones. An interactive Mathematica 7.0
notebook of our findings is available from [email protected]: 30 pages LaTeX2e, including 22 figures as 66 .eps file embedded with
includegraphicx; three errors in initial submission corrected. This
submission includes ot the erratum to be published in EPJA (2012) and the
corrections in the tex
Coronal Diagnostics from Narrowband Images around 30.4 nm
Images taken in the band centered at 30.4 nm are routinely used to map the
radiance of the He II Ly alpha line on the solar disk. That line is one of the
strongest, if not the strongest, line in the EUV observed in the solar
spectrum, and one of the few lines in that wavelength range providing
information on the upper chromosphere or lower transition region. However, when
observing the off-limb corona the contribution from the nearby Si XI 30.3 nm
line can become significant. In this work we aim at estimating the relative
contribution of those two lines in the solar corona around the minimum of solar
activity. We combine measurements from CDS taken in August 2008 with
temperature and density profiles from semiempirical models of the corona to
compute the radiances of the two lines, and of other representative coronal
lines (e.g., Mg X 62.5 nm, Si XII 52.1 nm). Considering both diagnosed
quantities from line ratios (temperatures and densities) and line radiances in
absolute units, we obtain a good overall match between observations and models.
We find that the Si XI line dominates the He II line from just above the limb
up to ~2 R_Sun in streamers, while its contribution to narrowband imaging in
the 30.4 nm band is expected to become smaller, even negligible in the corona
beyond ~2 - 3 R_Sun, the precise value being strongly dependent on the coronal
temperature profile.Comment: 26 pages, 11 figures; to be published in: Solar Physic
What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models
One of the major discoveries of the Extreme ultraviolet Imaging Telescope
(EIT) on SOHO were intensity enhancements propagating over a large fraction of
the solar surface. The physical origin(s) of the so-called `EIT' waves is still
strongly debated. They are considered to be either wave (primarily fast-mode
MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in
understanding the nature of EUV waves lies with the limitations of the EIT
observations which have been used almost exclusively for their study. Their
limitations are largely overcome by the SECCHI/EUVI observations on-board the
STEREO mission. The EUVI telescopes provide high cadence, simultaneous
multi-temperature coverage, and two well-separated viewpoints. We present here
the first detailed analysis of an EUV wave observed by the EUVI disk imagers on
December 07, 2007 when the STEREO spacecraft separation was .
Both a small flare and a CME were associated with the wave cadence, and single
temperature and viewpoint coverage. These limitations are largely overcome by
the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes
provide high cadence, simultaneous multi-temperature coverage, and two
well-separated viewpoints. Our findings give significant support for a
fast-mode interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.Comment: Solar Physics, 2009, Special STEREO Issue, in pres
Hubble expansion and structure formation in the "running FLRW model" of the cosmic evolution
A new class of FLRW cosmological models with time-evolving fundamental
parameters should emerge naturally from a description of the expansion of the
universe based on the first principles of quantum field theory and string
theory. Within this general paradigm, one expects that both the gravitational
Newton's coupling, G, and the cosmological term, Lambda, should not be strictly
constant but appear rather as smooth functions of the Hubble rate. This
scenario ("running FLRW model") predicts, in a natural way, the existence of
dynamical dark energy without invoking the participation of extraneous scalar
fields. In this paper, we perform a detailed study of these models in the light
of the latest cosmological data, which serves to illustrate the
phenomenological viability of the new dark energy paradigm as a serious
alternative to the traditional scalar field approaches. By performing a joint
likelihood analysis of the recent SNIa data, the CMB shift parameter, and the
BAOs traced by the Sloan Digital Sky Survey, we put tight constraints on the
main cosmological parameters. Furthermore, we derive the theoretically
predicted dark-matter halo mass function and the corresponding redshift
distribution of cluster-size halos for the "running" models studied. Despite
the fact that these models closely reproduce the standard LCDM Hubble
expansion, their normalization of the perturbation's power-spectrum varies,
imposing, in many cases, a significantly different cluster-size halo redshift
distribution. This fact indicates that it should be relatively easy to
distinguish between the "running" models and the LCDM cosmology using realistic
future X-ray and Sunyaev-Zeldovich cluster surveys.Comment: Version published in JCAP 08 (2011) 007: 1+41 pages, 6 Figures, 1
Table. Typos corrected. Extended discussion on the computation of the
linearly extrapolated density threshold above which structures collapse in
time-varying vacuum models. One appendix, a few references and one figure
adde
Calculating exclusion limits for Weakly Interacting Massive Particle direct detection experiments without background subtraction
Competitive limits on the weakly interacting massive particle (WIMP)
spin-independent scattering cross section are currently being produced by 76Ge
detectors originally designed to search for neutrinoless double beta decay,
such as the Heidelberg-Moscow and IGEX experiments. In the absence of
background subtraction, limits on the WIMP interaction cross section are set by
calculating the upper confidence limit on the theoretical event rate, given the
observed event rate. The standard analysis technique involves calculating the
90% upper confidence limit on the number of events in each bin, and excluding
any set of parameters (WIMP mass and cross-section) which produces a
theoretical event rate for any bin which exceeds the 90% upper confidence limit
on the event rate for that bin. We show that, if there is more than one energy
bin, this produces exclusion limits that are actually at a lower degree of
confidence than 90%, and are hence erroneously tight. We formulate criteria
which produce true 90% confidence exclusion limits in these circumstances,
including calculating the individual bin confidence limit for which the overall
probability that no bins exceeds this confidence limit is 90% and calculating
the 90% minimum confidence limit on the number of bins which exceed their
individual bin 90% confidence limits. We then compare the limits on the WIMP
cross-section produced by these criteria with those found using the standard
technique, using data from the Heidelberg-Moscow and IGEX experiments.Comment: 6 pages, 3 figures, 3 tables, shortened version to appear in Phys.
Rev. D, contents otherwise unchange
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