2,107 research outputs found
Dirac Neutrino Masses from Generalized Supersymmetry Breaking
We demonstrate that Dirac neutrino masses in the experimentally preferred
range are generated within supersymmetric gauge extensions of the Standard
Model with a generalized supersymmetry breaking sector. If the usual
superpotential Yukawa couplings are forbidden by the additional gauge symmetry
(such as a U(1)'), effective Dirac mass terms involving the "wrong Higgs" field
can arise either at tree level due to hard supersymmetry breaking fermion
Yukawa couplings, or at one-loop due to nonanalytic or "nonholomorphic" soft
supersymmetry breaking trilinear scalar couplings. As both of these operators
are naturally suppressed in generic models of supersymmetry breaking, the
resulting neutrino masses are naturally in the sub-eV range. The neutrino
magnetic and electric dipole moments resulting from the radiative mechanism
also vanish at one-loop order.Comment: 5 pages, 1 figure, references added, note added on effective
superpotential mass terms generated upon U(1)' breakin
The Properties of Brightest Cluster Galaxies in X-Ray Selected Clusters
We present the K-band Hubble diagram for 162 brightest cluster galaxies
(BCGs) in X-ray selected clusters, 0.01<z<0.83. The sample incorporates that of
Burke, Collins, & Mann (2000) and includes additional infrared data from the
2MASS extended source catalogue. We show that below z=0.1 the BCGs show no
correlation with their environment, however, above z=0.1 BCGs in more X-ray
luminous clusters are more uniform in their photometric properties. This
suggests that there may be two populations of BCGs which have different
evolutionary histories.Comment: 2 pages, to appear in the proceedings of the Sesto 2001 conference on
tracing cosmic evolution with galaxy cluster
The Establishment of International Mechanisms for Enforcing Provisional Orders and Final Judgments Arising From Securities Law Violations
In the 1980s and early 1990s, securities regulators have made substantial progress in developing cooperative relationships to reduce the value of international borders as barriers to the detection and prosecution of securities fraud, but there needs to be an establishment of international mechanisms for enforcing provisional orders and final judgments. The development of mechanisms pursuant to which regulators can assist each other in freezing assets and recovering illicit profits is discussed
Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta
The detection of olivine on Vesta is interesting because it may provide
critical insights into planetary differentiation early in our Solar System's
history. Ground-based and Hubble Space Telescope (HST) observations of asteroid
(4) Vesta have suggested the presence of olivine on the surface. These
observations were reinforced by the discovery of olivine-rich HED meteorites
from Vesta in recent years. However, analysis of data from NASA's Dawn
spacecraft has shown that this olivine-bearing unit is actually impact melt in
the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed
during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole,
further complicated this picture. Ammannito et al., (2013a) reported the
discovery of local scale olivine-rich units in the form of excavated material
from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here
we explore alternative sources for the olivine in the northern hemisphere of
Vesta by reanalyzing the data from the VIR instrument using laboratory spectral
measurements of meteorites. We suggest that these olivine exposures could be
explained by the delivery of olivine-rich exogenic material. Based on our
spectral band parameters analysis, the lack of correlation between the location
of these olivine-rich terrains and possible mantle-excavating events, and
supported by observations of HED meteorites, we propose that a probable source
for olivine seen in the northern hemisphere are remnants of impactors made of
olivine-rich meteorites. Best match suggests these units are HED material mixed
with either ordinary chondrites, or with some olivine-dominated meteorites such
as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January
2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01
Chiral Fermions and Quadratic Divergences
In an approach towards naturalness without supersymmetry, renormalization
properties of nonsupersymmetric abelian quiver gauge theories are studied. In
the construction based on cyclic groups Z_p the gauge group is U(N)^p, the
fermions are all in bifundamentals and the construction allows scalars in
adjoints and bifundamentals. Only models without adjoint scalars, however,
exhibit both chiral fermions and the absence of one-loop quadratic divergences
in the scalar propagator.Comment: 11 page
Massive Neutrinos and (Heterotic) String Theory
String theories in principle address the origin and values of the quark and
lepton masses. Perhaps the small values of neutrino masses could be explained
generically in string theory even if it is more difficult to calculate
individual values, or perhaps some string constructions could be favored by
generating small neutrino masses. We examine this issue in the context of the
well-known three-family standard-like Z_3 heterotic orbifolds, where the theory
is well enough known to construct the corresponding operators allowed by string
selection rules, and analyze the D- and F-flatness conditions. Surprisingly, we
find that a simple see-saw mechanism does not arise. It is not clear whether
this is a property of this construction, or of orbifolds more generally, or of
string theory itself. Extended see-saw mechanisms may be allowed; more analysis
will be needed to settle that issue. We briefly speculate on their form if
allowed and on the possibility of alternatives, such as small Dirac masses and
triplet see-saws. The smallness of neutrino masses may be a powerful probe of
string constructions in general. We also find further evidence that there are
only 20 inequivalent models in this class, which affects the counting of string
vacua.Comment: 18 pages in RevTeX format. Single-column postscript version available
at http://sage.hep.upenn.edu/~bnelson/singpre.p
Evolution of the Cluster Correlation Function
We study the evolution of the cluster correlation function and its
richness-dependence from z = 0 to z = 3 using large-scale cosmological
simulations. A standard flat LCDM model with \Omega_m = 0.3 and, for
comparison, a tilted \Omega_m = 1 model, TSCDM, are used. The evolutionary
predictions are presented in a format suitable for direct comparisons with
observations. We find that the cluster correlation strength increases with
redshift: high redshift clusters are clustered more strongly (in comoving
scale) than low redshift clusters of the same mass. The increased correlations
with redshift, in spite of the decreasing mass correlation strength, is caused
by the strong increase in cluster bias with redshift: clusters represent higher
density peaks of the mass distribution as the redshift increases. The
richness-dependent cluster correlation function, presented as the
correlation-scale versus cluster mean separation relation, R_0 - d, is found to
be, remarkably, independent of redshift to z <~ 2 for LCDM and z <~ 1 for TCDM
(for a fixed correlation function slope and cluster mass within a fixed
comoving radius). The non-evolving R_0 - d relation implies that both the
comoving clustering scale and the cluster mean separation increase with
redshift for the same mass clusters so that the R_0 - d relation remains
essentially unchanged. The evolution of the R_0 - d relation from z ~ 0 to z ~
3 provides an important new tool in cosmology; it can be used to break
degeneracies that exist at z ~ 0 and provide precise determination of
cosmological parameters.Comment: AASTeX, 15 pages, including 5 figures, accepted version for
publication in ApJ, vol.603, March 200
Up-beat UK: a programme of research into the relationship between coronary heart disease and depression in primary care patients.
Coronary heart disease and depression are both common health problems and by 2020 will be the two leading causes of disability worldwide. Depression has been found to be more common in patients with coronary heart disease but the nature of this relationship is uncertain. In the United Kingdom general practitioners are now being remunerated for case-finding for depression in patients with coronary heart disease, however it is unclear how general practitioners should manage these patients. We aim to explore the relationship between coronary heart disease and depression in a primary care population and to develop an intervention for patients with coronary heart disease and depression
A survey of energy loss calculations for heavy ions between 1 and 100 keV
The original Lindhard-Scharff-Schi{\o}tt (LSS) theory and the more recent
Tilinin theory for calculating the nuclear and electronic stopping powers of
slow heavy ions are compared with predictions from the SRIM code by Ziegler.
While little discrepancies are present for the nuclear contribution to the
energy loss, large differences are found in the electronic one. When full ion
recoil cascade simulations are tested against the elastic neutron scattering
data available in the literature, it can be concluded that the LSS theory is
the more accurate.Comment: Presented at the 10th International Symposium on Radiation Physics,
17-22 September, 2006, Coimbra, Portugal; style corrections, small change to
fig.
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