1,091 research outputs found
How heavy can the Fermions in Split Susy be? A study on Gravitino and Extradimensional LSP
In recently introduced Split Susy theories, in which the scale of Susy
breaking is very high, the requirement that the relic abundance of the Lightest
SuperPartner (LSP) provides the Dark Matter of the Universe leads to the
prediction of fermionic superpartners around the weak scale. This is no longer
obviously the case if the LSP is a hidden sector field, such as a Gravitino or
an other hidden sector fermion, so, it is interesting to study this scenario.
We consider the case in which the Next-Lightest SuperPartner (NLSP) freezes out
with its thermal relic abundance, and then it decays to the LSP. We use the
constraints from BBN and CMB, together with the requirement of attaining Gauge
Coupling Unification and that the LSP abundance provides the Dark Matter of the
Universe, to infer the allowed superpartner spectrum. As very good news for a
possible detaction of Split Susy at LHC, we find that if the Gravitino is the
LSP, than the only allowed NLSP has to be very purely photino like. In this
case, a photino from 700 GeV to 5 TeV is allowed, which is difficult to test at
LHC. We also study the case where the LSP is given by a light fermion in the
hidden sector which is naturally present in Susy breaking in Extra Dimensions.
We find that, in this case, a generic NLSP is allowed to be in the range 1-20
TeV, while a Bino NLSP can be as light as tens of GeV.Comment: 29 pages, 12 figures. v2: modified conclusions for bino NLSP. v3:
corrected small mistake in Gauge Coupling Unification, conclusions unchange
Per un ritratto del buon ambasciatore. Regole di comportamento e profilo dell\u2019inviato negli scritti di Diomede Carafa, Nicol\uf2 Machiavelli e Francesco Guicciardini
Memoriali e ricordi nella tradizione italiana (F.S.) Nelle cancellerie italiane del tardo medioevo e della prima età moderna circolavano molti testi a corredo dell’attività diplomatica : avvisi, avvertimenti, diari, estratti, exempla, informazioni, istruzioni, memoriali, note, notule, ordini, rapporti, relazioni, ricordi, riporti, risposte, ritratti, sommari, un complesso di scritture destinate agli addetti ai lavori, cancellieri e ambasciatori. Tipologie testuali e definizioni sono fluide, a..
Electron Correlation and Charge Transfer Instability in Bilayered Two Dimensional Electron Gas
We prove that the predicted charge transfer state in symmetric bilayers of
two dimensional electron gases is always unstable at zero bias voltage, due to
interlayer correlation and/or tunneling. This is most easily seen by resorting
to a pseudospin formalism and considering coherent states obtained from the
charge transfer state through rotations of the pseudospins. Evidently, the
charge transfer state is stabilized by a sufficiently strong gate voltage, as
found in recent experiments. We show that a simple model, in which the layers
are strictly two dimensional, is able to account quantitatively for such
experimental findings, when correlation is properly included.Comment: 5 pages, 3 figures. Subm. to Europhys. Let
Dielectric matrix and plasmon dispersion in strongly coupled electronic bilayer liquids
We develop a dielectric matrix and analyze plasmon dispersion in strongly
coupled charged-particle bilayers in the quantum domain. The formulation is
based on the classical quasi-localized charge approximation (QLCA) and extends
the QLCA formalism into the quantum domain. Its development, which parallels
that of 2D companion paper [Phys. Rev. E 70, 026406 (2004)] by three of the
authors, generalizes the single-layer scalar formalism therein to a bilayer
matrix formalism. Using pair correlation function data generated from diffusion
Monte Carlo simulations, we calculate the dispersion of the in-phase and
out-of-phase plasmon modes over a wide range of in-layer coupling values and
layer spacings. The out-of-phase spectrum exhibits an exchange-correlation
induced long-wavelength energy gap in contrast to earlier predictions of
acoustic dispersion softened by exchange-correlations. The energy gap is
similar to what has been previously predicted for classical charged-particle
bilayers and subsequently confirmed by recent molecular dynamics computer
simulations.Comment: 53 pages including 15 Figures with their captions. Submitted to
Physical Review
Effects of thickness on the spin susceptibility of the 2D electron gas
Using available quantum Monte Carlo predictions for a strictly 2D electron
gas, we have estimated the spin susceptibility of electrons in actual devices
taking into account the effect of the finite transverse thickness and finding a
very good agreement with experiments. A weak disorder, as found in very clean
devices and/or at densities not too low, just brings about a minor enhancement
of the susceptibility.Comment: 4 pages, 3 figure
Spin-Polarization transition in the two dimensional electron gas
We present a numerical study of magnetic phases of the 2D electron gas near
freezing. The calculations are performed by diffusion Monte Carlo in the fixed
node approximation. At variance with the 3D case we find no evidence for the
stability of a partially polarized phase. With plane wave nodes in the trial
function, the polarization transition takes place at Rs=20, whereas the best
available estimates locate Wigner crystallization around Rs=35. Using an
improved nodal structure, featuring optimized backflow correlations, we confirm
the existence of a stability range for the polarized phase, although somewhat
shrunk, at densities achievable nowadays in 2 dimensional hole gases in
semiconductor heterostructures . The spin susceptibility of the unpolarized
phase at the magnetic transition is approximately 30 times the Pauli
susceptibility.Comment: 7 pages, 4 figure
Exchange and correlation effects on the plasmon dispersions and the Coulomb drag in low-density electron bilayers
We investigate the effect of exchange and correlation (xc) on the plasmon
spectrum and the Coulomb drag between spatially separated low-density
two-dimensional electron layers. We adopt a new approach, which employs dynamic
xc kernels in the calculation of the bi-layer plasmon spectra and of the
plasmon-mediated drag, and static many-body local field factors in the
calculation of the particle-hole contribution to the drag. The spectrum of
bi-layer plasmons and the drag resistivity are calculated in a broad range of
temperatures taking into account both intra- and inter-layer correlation
effects. We observe that both plasmon modes are strongly affected by xc
corrections. After the inclusion of the complex dynamic xc kernels, a decrease
of the electron density induces shifts of the plasmon branches in opposite
directions. And this is in stark contrast to the tendency obtained within the
RPA that both optical and acoustical plasmons move away from the boundary of
the particle-hole continuum with a decrease in the electron density. We find
that the introduction of xc corrections results in a significant enhancement of
the transresistivity and qualitative changes in its temperature dependence. In
particular, the large high-temperature plasmon peak that is present in the
random phase approximation is found to disappear when the xc corrections are
included. Our numerical results at low temperatures are in good agreement with
the results of recent experiments by M. Kellogg {\it et al.}, Solid State
Commun. \textbf{123}, 515 (2002).Comment: 28 pages, 15 figure
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