455 research outputs found
Update on an Electromagnetic Basis for Inertia, Gravitation, the Principle of Equivalence, Spin and Particle Mass Ratios
A possible connection between the electromagnetic quantum vacuum and inertia
was first published by Haisch, Rueda and Puthoff (1994). If correct, this would
imply that mass may be an electromagnetic phenomenon and thus in principle
subject to modification, with possible technological implications for
propulsion. A multiyear NASA-funded study at the Lockheed Martin Advanced
Technology Center further developed this concept, resulting in an independent
theoretical validation of the fundamental approach (Rueda and Haisch, 1998ab).
Distortion of the quantum vacuum in accelerated reference frames results in a
force that appears to account for inertia. We have now shown that the same
effect occurs in a region of curved spacetime, thus elucidating the origin of
the principle of equivalence (Rueda, Haisch and Tung, 2001). A further
connection with general relativity has been drawn by Nickisch and Mollere
(2002): zero-point fluctuations give rise to spacetime micro-curvature effects
yielding a complementary perspective on the origin of inertia. Numerical
simulations of this effect demonstrate the manner in which a massless
fundamental particle, e.g. an electron, acquires inertial properties; this also
shows the apparent origin of particle spin along lines originally proposed by
Schroedinger. Finally, we suggest that the heavier leptons (muon and tau) may
be explainable as spatial-harmonic resonances of the (fundamental) electron.
They would carry the same overall charge, but with the charge now having
spatially lobed structure, each lobe of which would respond to higher frequency
components of the electromagnetic quantum vacuum, thereby increasing the
inertia and thus manifesting a heavier mass.Comment: 10 pages, 4 figures, AIP Conf. Proc., Space Technology and
Applications International Forum (STAIF-2003
Lyman alpha initiated winds in late-type stars
The IUE survey of late-type stars revealed a sharp division in the HR diagram between stars with solar type spectra (chromosphere and transition region lines) and those with non-solar type spectra (only chromosphere lines). Models of both hot coronae and cool wind flows were calculated using stellar model chromospheres as starting points for stellar wind calculations in order to investigate the possibility of having a supersonic transition locus in the HR diagram dividing hot coronae from cool winds. From these models, it is concluded that the Lyman alpha flux may play an important role in determining the location of a stellar wind critical point. The interaction of Lyman alpha radiation pressure with Alfven waves in producing strong, low temperature stellar winds in the star Arcturus is examined
X-Ray Evidence for Flare Density Variations and Continual Chromospheric Evaporation in Proxima Centauri
Using the XMM-Newton X-ray observatory to monitor the nearest star to the
Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically
active star ever observed. Correlated X-ray and optical variability provide
strong support for coronal energy and mass supply by a nearly continuous
sequence of rapid explosive energy releases. Variable emission line fluxes were
observed in the He-like triplets of OVII and NeIX during a giant flare. They
give direct X-ray evidence for density variations, implying densities between
2x10^{10} - 4x10^{11} cm^{-3} and providing estimates of the mass and the
volume of the line-emitting plasma. We discuss the data in the context of the
chromospheric evaporation scenario.Comment: 10 pages, 2 figures, accepted by The Astrophysical Journal, Letters;
improved calculations of radiative loss of cool plasma (toward end of paper
Lepton-Quark Collisions at the Large Hadron Collider
Processes commonly studied at the Large Hadron Collider (LHC) are induced by quarks and gluons inside the protons of the LHC beams. In this Letter, we demonstrate that, since protons also contain leptons, it is possible to target lepton-induced processes at the LHC as well. In particular, by picking a lepton from one beam and a quark from the other beam, we present for the first time a comprehensive analysis of resonant single leptoquark (LQ) production at a hadron collider. In the case of minimal scalar LQs, we derive novel bounds that arise from the LHC Run II considering all possible flavor combinations of an electron or a muon and an up (u), a down (d), a strange, or a charm quark. For the flavor combinations with a u or a d quark, the obtained limits represent the most stringent constraints to date on LQs of this type. The prospects of our method at future LHC runs are also explored. Given the discovery reach of the proposed LQ signature, we argue that dedicated resonance searches in final states featuring a single light lepton and a single light-flavor jet should be added to the exotics search canon of both the ATLAS and the CMS Collaborations
Flares from small to large: X-ray spectroscopy of Proxima Centauri with XMM-Newton
(Abridged) We report results from a comprehensive study of the nearby M dwarf
Proxima Centauri with the XMM-Newton satellite. We find strongly variable
coronal X-ray emission, with flares ranging over a factor of 100 in peak flux.
The low-level emission is found to be continuously variable. Several weak
flares are characteristically preceded by an optical burst, compatible with
predictions from standard solar flare models. We propose that the U band bursts
are proxies for the elusive stellar non-thermal hard X-ray bursts suggested
from solar observations. A very large X-ray flare was observed in its entirety,
with a peak luminosity of 3.9E28 erg/s [0.15-10 keV] and a total X-ray energy
of 1.5E32 erg. This flare has allowed to measure significant density variations
from X-ray spectroscopy of the OVII He-like triplet; we find peak densities
reaching up to 4E11 cm^-3 for plasma of about 1-5 MK. Abundance ratios show
little variability in time, with a tendency of elements with a high first
ionization potential to be overabundant relative to solar photospheric values.
We do not find significant effects due to opacity during the flare, indicating
that large opacity increases are not the rule even in extreme flares. We model
the large flare in terms of an analytic 2-Ribbon flare model and find that the
flaring loop system should have large characteristic sizes (~1R*). These
results are supported by full hydrodynamic simulations. Comparing the large
flare to flares of similar size occurring much more frequently on more active
stars, we propose that the X-ray properties of active stars are a consequence
of superimposed flares such as the example analyzed in this paper. Such a model
also explains why, during episodes of low-level emission, more active stars
show hotter plasma than less active stars.Comment: Accepted for A&A, 20 pages, 11 figures, 2 tables, preprint also at
http://www.astro.phys.ethz.ch/papers/guedel/guedel_p_nf.htm
A new young stellar cluster embedded in a molecular cloud in the far outer Galaxy
We report the discovery of a new young stellar cluster and molecular cloud
located in the far outer Galaxy, seen towards IRAS 06361-0142, and we
characterise their properties. Near-infrared images were obtained with
VLT/ISAAC through JHKs filters, millimetre line observations of CO(1-0) were
obtained with SEST, and VLA 6 cm continuum maps obtained from archive data. The
cloud and cluster are located at a distance of 7 kpc and a Galactocentric
distance of 15 kpc, well in the far outer Galaxy. Morphologically, IRAS
06361-0142 appears as a cluster of several tens of stars surrounded by a nearly
spherical nebular cavity centred at the position of the IRAS source. The
cluster appears composed of low and intermediate-mass, young reddened stars
with a large fraction having cleared the inner regions of their circumstellar
discs responsible for (H - Ks) colour excess. The observations are compatible
with a 4 Myr cluster with variable spatial extinction between Av = 6 and Av =
13.Comment: 6 pages, 6 figure
Recent developments in radiative B decays
We report on recent theoretical progress in radiative B decays. We focus on a
calculation of logarithmically enhanced QED corrections to the branching ratio
and forward-backward asymmetry in the inclusive rare decay anti-B --> X(s) l+
l-, and present the results of a detailed phenomenological analysis. We also
report on the calculation of NNLO QCD corrections to the inclusive decay anti-B
--> X(s) gamma. As far as exclusive modes are concerned we consider
transversity amplitudes and the impact of right-handed currents in the
exclusive anti-B --> K^* l+ l- decay. Finally, we state results for exclusive B
--> V gamma decays, notably the time-dependent CP-asymmetry in the exclusive B
--> K^* gamma decay and its potential to serve as a so-called ``null test'' of
the Standard Model, and the extraction of CKM and unitarity triangle parameters
from B --> (rho,omega) gamma and B --> K^* gamma decays.Comment: 5 pages, 2 figures. Accepted for publication in the proceedings of
International Europhysics Conference on High Energy Physics (EPS-HEP2007),
Manchester, England, 19-25 Jul 200
The Extended Environment of M17: A Star Formation History
M17 is one of the youngest and most massive nearby star-formation regions in
the Galaxy. It features a bright H II region erupting as a blister from the
side of a giant molecular cloud (GMC). Combining photometry from the Spitzer
GLIMPSE survey with complementary infrared (IR) surveys, we identify candidate
young stellar objects (YSOs) throughout a 1.5 deg x 1 deg field that includes
the M17 complex. The long sightline through the Galaxy behind M17 creates
significant contamination in our YSO sample from unassociated sources with
similar IR colors. Removing contaminants, we produce a highly-reliable catalog
of 96 candidate YSOs with a high probability of association with the M17
complex. We fit model spectral energy distributions to these sources and
constrain their physical properties. Extrapolating the mass function of 62
intermediate-mass YSOs (M >3 Msun), we estimate that >1000 stars are in the
process of forming in the extended outer regions of M17.
From IR survey images from IRAS and GLIMPSE, we find that M17 lies on the rim
of a large shell structure ~0.5 deg in diameter (~20 pc at 2.1 kpc). We present
new maps of CO and 13CO (J=2-1) emission, which show that the shell is a
coherent, kinematic structure associated with M17 at v = 19 km/s. The shell is
an extended bubble outlining the photodissociation region of a faint, diffuse H
II region several Myr old. We provide evidence that massive star formation has
been triggered by the expansion of the bubble. The formation of the massive
cluster ionizing the M17 H II region itself may have been similarly triggered.
We conclude that the star formation history in the extended environment of M17
has been punctuated by successive waves of massive star formation propagating
through a GMC complex.Comment: 31 pages, 15 figures, accepted for publication in ApJ. For a version
with higher-quality figures, see
http://www.astro.wisc.edu/glimpse/Povich2009_M17.pd
A Search for Mid-Infrared Molecular Hydrogen Emission from Protoplanetary Disks
We observed the Herbig Ae/Be stars UX Ori, HD 34282, HD 100453, HD 101412, HD
104237 and HD 142666, and the T Tauri star HD 319139 and searched for H2 0-0
S(2) emission at 12.278 micron and H2 0-0 S(1) emission at 17.035 micron with
VISIR, ESO-VLT's high-resolution MIR spectrograph. None of the sources present
evidence for H2 emission. Stringent 3sigma upper limits to the integrated line
fluxes and the mass of optically thin warm gas in the disks are derived. The
disks contain less than a few tenths of Jupiter mass of optically thin H2 gas
at 150 K at most, and less than a few Earth masses of optically thin H2 gas at
300 K and higher temperatures. We compare our results to a Chiang and Goldreich
(1997, CG97) two-layer disk model. The upper limits to the disk's optically
thin warm gas mass are smaller than the amount of warm gas in the interior
layer of the disk, but they are much larger than the amount of molecular gas in
the surface layer. We present a calculation of the expected thermal H2 emission
from optically thick disks, assuming a CG97 disk structure, a gas-to-dust ratio
of 100 and Tgas = Tdust. The expected H2 thermal emission fluxes from typical
disks around Herbig Ae/Be stars (10^-16 to 10^-17 erg/s/cm2 at 140 pc) are much
lower than the detection limits of our observations (5*10^-15 erg/s/cm2). H2
emission levels are very sensitive to departures from the thermal coupling
between the molecular gas and dust. Additional sources of heating of gas in the
disk's surface layer could have a major impact on the expected H2 disk
emission. In the observed sources the molecular gas and dust in the surface
layer have not significantly departed from thermal coupling (Tgas/Tdust< 2) and
that the gas-to-dust ratio in the surface layer is very likely lower than 1000.Comment: 16 pages, 9 figures, accepted by A&A. v2: typo in footnote **
corrected, v3: corrections of the A&A language editor included, typo in title
of Fig. 1. correcte
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