8,714 research outputs found
Revisiting LHC gluino mass bounds through radiative decays using MadAnalysis 5
The ATLAS and CMS experiments at the CERN LHC have collected about 25 inverse
femtobarns (fb) of data each at the end of their 8 TeV run, and ruled out a
huge swath of parameter space in the context of Minimally Supersymmetric
Standard Model (MSSM). Limits on masses of the gluino have been pushed to above
1 TeV. These limits are however extremely model dependent and do not always
reflect the level of exclusion. So far the limits on the gluino mass using the
simplified model approach only constrained its value using its three-body
decays. We show in this work that already existing ATLAS and CMS analysis can
also constrain the radiative gluino decay mode and we derived improved mass
limits in particular when the mass difference between the LSP and the gluino is
small.Comment: 4 pages, 3 figures. To appear in the proceedings of the 27th
Rencontres the Blois on Particle Physics and Cosmology, May 31 - June 05,
201
A Unified Model of Codon Reassignment in Alternative Genetic Codes
Many modified genetic codes are found in specific genomes in which one or
more codons have been reassigned to a different amino acid from that in the
canonical code. We present a model that unifies four possible mechanisms for
reassignment, based on the observation that reassignment involves a gain and a
loss. The loss could be the deletion or loss of function of a tRNA or release
factor. The gain could be the gain of a new type of tRNA for the reassigned
codon, or the gain of function of an existing tRNA due to a mutation or a base
modification. In the codon disappearance mechanism, the codon disappears from
the genome during the period of reassignment. In the other mechanisms, the
codon does not disappear. In the ambiguous intermediate mechanism, the gain
precedes the loss; in the unassigned codon mechanism, the loss precedes the
gain; and in the compensatory change mechanism, the loss and gain spread
through the population simultaneously. We present simulations of the gain-loss
model and demonstrate that all four mechanisms are possible. The frequencies of
the different mechanisms are influenced by selection strengths, number of
codons undergoing reassignment, directional mutation pressure and the
possibility of selection for reduced genome size.Comment: Latex file, 11 pages including 5 ps figures; revised version; to
appear in 'Genetics
Did Prepayments Sustain the Subprime Market?
This paper demonstrates that the reason for widespread default of mortgages in the subprime market was a sudden reversal in the house price appreciation of the early 2000's. Using loan-level data on subprime mortgages, we observe that the majority of subprime loans were hybrid adjustable rate mortgages, designed to impose substantial financial burden on reset to the fully indexed rate. In a regime of rising house prices, a financially distressed borrower could avoid default by prepaying the loan and our results indicate that subprime mortgages originated between 1998 and 2005 had extremely high prepayment rates. Most important, prepayment rates on subprime mortgages were extremely high (i) not just for ARMs but FRMs as well, (ii) even before the reset dates on hybrid-ARMs and (iii) despite prepayment penalties on the contract. However, a sudden reversal in house price appreciation increased default in this market because it made this prepayment exit option cost-prohibitive. In short, prepayments sustained the subprime boom and the extremely high default rates on 2006-2007 vintages were largely due to the inability of these mortgages to prepay (an option that was available for mortgages of earlier vintages).mortgages;subprime;refinance;prepayment;crisis
Fock spaces corresponding to positive definite linear transformations
Suppose is a positive real linear transformation on a finite dimensional
complex inner product space . The reproducing kernel for the Fock space of
square integrable holomorphic functions on relative to the Gaussian measure
is described
in terms of the holomorphic--antiholomorphic decomposition of the linear
operator . Moreover, if commutes with a conjugation on , then a
restriction mapping to the real vectors in is polarized to obtain a
Segal--Bargmann transform, which we also study in the Gaussian-measure setting
Knowing one's place: a free-energy approach to pattern regulation.
Understanding how organisms establish their form during embryogenesis and regeneration represents a major knowledge gap in biological pattern formation. It has been recently suggested that morphogenesis could be understood in terms of cellular information processing and the ability of cell groups to model shape. Here, we offer a proof of principle that self-assembly is an emergent property of cells that share a common (genetic and epigenetic) model of organismal form. This behaviour is formulated in terms of variational free-energy minimization-of the sort that has been used to explain action and perception in neuroscience. In brief, casting the minimization of thermodynamic free energy in terms of variational free energy allows one to interpret (the dynamics of) a system as inferring the causes of its inputs-and acting to resolve uncertainty about those causes. This novel perspective on the coordination of migration and differentiation of cells suggests an interpretation of genetic codes as parametrizing a generative model-predicting the signals sensed by cells in the target morphology-and epigenetic processes as the subsequent inversion of that model. This theoretical formulation may complement bottom-up strategies-that currently focus on molecular pathways-with (constructivist) top-down approaches that have proved themselves in neuroscience and cybernetics
An anomalous magnetic phase transition at 10 K in Nd7Rh3
The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has
been shown recently by us to exhibit a signature of magnetic phase-coexistence
phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric
intermetallic compounds, bearing a relevance to the trends in the field of
electronic phase-separation. In order to characterize this compound further, we
have carried out dc magnetic susceptibility (chi), electrical resistivity,
magnetoresistance and heat-capacity measurements as a function temperature (T=
1.8 to 300 K). The results reveal that this compound exhibits another unusual
finding at the 10K-transition in the sense that the plot of chi(T) shows a
sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve
shows a downturn below the transition. In addition, the sign of
magnetoresistance is negative and the magnitude is large over a wide
temperature range in the vicinity of magnetic ordering temperature, with a
sharp variation at 10 K. The results indicate that the transition below 10 K is
first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40
Unconventional scanning tunneling conductance spectra for graphene
We compute the tunneling conductance of graphene as measured by a scanning
tunneling microscope (STM) with a normal/superconducting tip. We demonstrate
that for undoped graphene with zero Fermi energy, the first derivative of the
tunneling conductance with respect to the applied voltage is proportional to
the density of states of the STM tip. We also show that the shape of the STM
spectra for graphene doped with impurities depends qualitatively on the
position of the impurity atom in the graphene matrix and relate this
unconventional phenomenon to the pseudopsin symmetry of the Dirac
quasiparticles in graphene. We suggest experiments to test our theory.Comment: 6 pages, 3 figure
Evolution of Crustal Magnetic Fields in Isolated Neutron Stars : Combined Effects of Cooling and Curvature of Space-time
The ohmic decay of magnetic fields confined within the crust of neutron stars
is considered by incorporating both the effect of neutron star cooling and the
effect of space-time curvature produced by the intense gravitational field of
the star. For this purpose a stationary and static gravitational field has been
considered with the standard as well as the accelerated cooling models of
neutron stars. It is shown that general relativistic effect reduces the
magnetic field decay rate substantially. At the late stage of evolution when
the field decay is mainly determined by the impurity-electron scattering, the
effect of space-time curvature suppresses the role of the impurity content
significantly and reduces the decay rate by more than an order of magnitude.
Even with a high impurity content the decay rate is too low to be of
observational interest if the accelerated cooling model along with the effect
of space-time curvature is taken into account. It is, therefore, pointed out
that if a decrease in the magnetic field strength by more than two orders of
magnitude from its initial value is detected by observation then the existence
of quark in the core of the neutron star would possibly be ruled out.Comment: 15 pages, AAS LATEX macros v4.0, 5 postscript figures, Accepted for
publication in the Astrophysical Journal (Part I
Time of flight observables and the formation of Mott domains of fermions and bosons on optical lattices
We study, using quantum Monte Carlo simulations, the energetics of the
formation of Mott domains of fermions and bosons trapped on one-dimensional
lattices. We show that, in both cases, the sum of kinetic and interaction
energies exhibits minima when Mott domains appear in the trap. In addition, we
examine the derivatives of the kinetic and interaction energies, and of their
sum, which display clear signatures of the Mott transition. We discuss the
relevance of these findings to time-of-flight experiments that could allow the
detection of the metal--Mott-insulator transition in confined fermions on
optical lattices, and support established results on the
superfluid--Mott-insulator transition in confined bosons on optical lattices.Comment: 5 pages, 6 figures, published versio
- …