1,805 research outputs found
Charge centers in CaF: Ab initio calculation of elementary physical properties
Charge centers in ionic crystals provide a channel for elementary interaction
between electromagnetic radiation and the lattice. We calculate the electronic
ground state energies which are needed to create a charge center -- namely a
- and a -center. In well agreement with common understanding the
-center results in being accompanied by a small lattice distortion whereas
the -center is accompanied by a very large lattice deformation. Opposite to
the common understanding the additional positive charge in the charge center
results rather to be localized on a F complex than on a
F-complex. From the ground states of the charge centers we derive binding
energies, diffusion barriers and agglomeration energies for -center
formation. These microscopic quantities are of fundamental interest to
understand the dynamic processes which are initiated if the crystals interact
with extreme intense deep ultra violet radiation. We further derive the
equilibrium concentrations of charge centers in grown crystals.Comment: to appear in Phys. Rev. B in Aug. 2006, 11 Fig
Reconstruction of Fundamental SUSY Parameters
We summarize methods and expected accuracies in determining the basic
low-energy SUSY parameters from experiments at future ee linear
colliders in the TeV energy range, combined with results from LHC. In a second
step we demonstrate how, based on this set of parameters, the fundamental
supersymmetric theory can be reconstructed at high scales near the grand
unification or Planck scale. These analyses have been carried out for minimal
supergravity [confronted with GMSB for comparison], and for a string effective
theory.Comment: 8 pages, latex, 7 figures, expanded version of contributions to the
proceedings of ICHEP.2002 (Amstersdam) and LCWS.2002 (Jeju Island
Interference Effects, Time Reversal Violation and Search for New Physics in Hadronic Weak Decays
We propose some methods for studying hadronic sequential two-body decays
involving more spinning particles. It relies on the analysis of T-odd and
T-even asymmetries, which are related to interference terms. The latter
asymmetries turn out to be as useful as the former ones in inferring time
reversal violating observables; these in turn may be sensitive, under some
particular conditions, to possible contributions beyond the standard model. Our
main result is that one can extract such observables even after integrating the
differential decay width over almost all of the available angles. Moreover we
find that the correlations based exclusively on momenta are quite general,
since they provide as much information as those involving one or more spins. We
generalize some methods already proposed in the literature for particular decay
channels, but we also pick out a new kind of time reversal violating
observables. Our analysis could be applied, for example, to data of LHCb
experiment.Comment: 35 page
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
Physics Opportunities at mu+mu- Higgs Factories
We update theoretical studies of the physics opportunities presented by
mu+mu- Higgs factories. Interesting measurements of the Standard Model Higgs
decays into {\bar b}b, tau+tau- and WW* may be possible if the Higgs mass is
less than about 160 GeV, as preferred by the precision electroweak data, the
mass range being extended by varying appropriately the beam energy resolution.
A suitable value of the beam energy resolution would also enable the
uncertainty in the b-quark mass to be minimized, facilitating measurements of
parameters in the MSSM at such a first mu+mu- Higgs factory. These measurements
would be sensitive to radiative corrections to the Higgs-fermion-antifermion
decay vertices, which may violate CP. Radiative corrections in the MSSM may
also induce CP violation in Higgs-mass mixing, which can be probed via various
asymmetries measurable using polarized mu+mu- beams. In addition,
Higgs-chargino couplings may be probed at a second mu+mu- Higgs factory.Comment: Report of the Higgs factory working group of the ECFA-CERN study on
Neutrino Factory & Muon Storage Rings at CERN. 28 p
The effects of interface morphology on Schottky barrier heights: a case study on Al/GaAs(001)
The problem of Fermi-level pinning at semiconductor-metal contacts is
readdressed starting from first-principles calculations for Al/GaAs. We give
quantitative evidence that the Schottky barrier height is very little affected
by any structural distortions on the metal side---including elongations of the
metal-semiconductor bond (i.e. interface strain)---whereas it strongly depends
on the interface structure on the semiconductor side. A rationale for these
findings is given in terms of the interface dipole generated by the ionic
effective charges.Comment: 5 pages, latex file, 2 postscript figures automatically include
The long-wavelength behaviour of the exchange-correlation kernel in the Kohn-Sham theory of periodic systems
The polarization-dependence of the exchange-correlation (XC) energy functional of periodic insulators within Kohn-Sham (KS) density-functional theory requires a divergence in the XC kernel for small vectors q. This behaviour, exemplified for a one-dimensional model semiconductor, is also observed when an insulator happens to be described as a KS metal, or vice-versa. Although it can occur in the exchange-only kernel, it is not found in the usual local, semi-local or even non-local approximations to KS theory. We also show that the test-charge and electronic definitions of the macroscopic dielectric constant differ from one another in exact KS theory, but are equivalent in the above-mentioned approximations
One-loop corrections to the chargino and neutralino mass matrices in the on-shell scheme
We present a consistent procedure for the calculation of the one-loop
corrections to the charginos and neutralinos by using their on-shell mass
matrices. The on-shell gaugino mass parameters M and M', and the Higgsino mass
parameter \mu are defined by the elements of these on-shell mass matrices. The
on-shell mass matrices are different by finite one-loop corrections from the
tree-level ones given in terms of the on-shell parameters. When the on-shell M
and \mu are determined by the chargino sector, the neutralino masses receive
corrections up to 4%. This must be taken into account in precision measurements
at future e^+ e^- linear colliders.Comment: One reference added, typo in eq. (20) correcte
A new CP violating observable for the LHC
We study a new type of CP violating observable that arises in three body
decays that are dominated by an intermediate resonance. If two interfering
diagrams exist with different orderings of final state particles, the required
CP-even phase arises due to the different virtualities of the resonance in each
of the two diagrams. This method can be an important tool for accessing new CP
phases at the LHC and future colliders.Comment: 22 pages, v2: discussion of charged particle decays and a few
references added v3: typos corrected, matches published versio
Transverse Polarization Signatures of Extra Dimensions at Linear Colliders
If significant longitudinal polarization of both the electrons and positrons
becomes feasible at a future linear collider(LC), it may be possible to use
spin rotators to produce transversely polarized beams. Using the transverse
polarization of both beams, new azimuthal spin asymmetries can be formed which
will be sensitive probes for new physics beyond the Standard Model. Here we
demonstrate that these asymmetries are particularly sensitive to the exchange
of Kaluza-Klein towers of gravitons, or other spin-2 fields, that are predicted
to exist in higher dimensional theories which address the hierarchy problem.
These new asymmetries are shown to be able to extend the search reach for such
new physics by more than a factor of two, provide an additional tool for
isolating the signatures for spin-2 exchange up to mass scales in excess of
, and can be used to help differentiate among the proposed solutions
to the hierarchy problem below the production threshold for new particles.Comment: 22 pages, 6 figs. LaTe
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