664 research outputs found
Effects of Relativistic Dynamics in near Threshold
The cross-section for threshold production in proton-proton
collisions is evaluated in the framework of the covariant spectator
description. The negative energy intermediate states are included
non-perturbatively and seen to yield a considerably smaller contribution, when
compared to perturbative treatments. A family of OBE-models with different
off-shell scalar coupling is considered.Comment: 10 pages, 3 figures, 1 tabl
Two-pion exchange and strong form-factors in covariant field theories
In this work improvements to the application of the Gross equation to nuclear
systems are tested. In particular we evaluate the two pion exchange diagrams,
including the crossed-box diagram, using models developed within the
spectator-on-mass-shell covariant formalism. We found that the form factors
used in these models induce spurious contributions that violate the unitary cut
requirement. We tested then some alternative form-factors in order to preserve
the unitarity condition. With this new choice, the difference between the exact
and the spectator-on-mass-shell amplitudes is of the order of the one boson
scalar exchange, supporting the idea that this difference may be parameterized
by this type of terms.Comment: RevTeX, 21 pages, 19 figures (PostScript
QualitÀtssicherung interdisziplinÀrer Polytraumaversorgung: Möglichkeiten und Grenzen retrospektiver Standarderfassung
Zusammenfassung: Hintergrund: Inwieweit kann die Auswertung standardmĂ€Ăig erhobener Patienten- und Krankenhausdaten einen Behandlungsvergleich mit anderen Erhebungen gestatten? Material und Methoden: Es wurde eine retrospektive Analyse epidemiologischer und klinisch-technischer Parameter aller Mehrfachverletzten [Injury Severity Score (ISS)>15] einer Zentrumsklinik (n=172; Zeitraum: 01.01.1997-31.12.1999) bezĂŒglich der Ablauforganisation und des Outcome (p74Jahre, Hypotension, initial verminderte HĂ€moglobin- und Quick-Werte, verminderte Glasgow Coma Scale (GCS) sowie Anzahl erhaltener Blutkonzentrate. Eine GegenĂŒberstellung der erhobenen Daten mit der zeitgleichen prospektiven Multizenterstudie der Deutschen Gesellschaft fĂŒr Unfallchirurgie (DGU) bestĂ€tigte die Ergebnisse bezĂŒglich des Ablaufs und des Outcome. Schlussfolgerung: Die interdisziplinĂ€re retrospektive Datenauswertung ist unter Fokussierung auf prognoserelevante und routinemĂ€Ăig erhobene Parameter eine praktikable sowie aussagefĂ€hige Alternative zu prospektiven Erfassungen und ermöglicht eine erste qualitative Standortbestimmun
Four dimensional "old minimal" N=2 supersymmetrization of R^4
We write in superspace the lagrangian containing the fourth power of the Weyl
tensor in the "old minimal" d=4, N=2 supergravity, without local SO(2)
symmetry. Using gauge completion, we analyze the lagrangian in components. We
find out that the auxiliary fields which belong to the Weyl and compensating
vector multiplets have derivative terms and therefore cannot be eliminated
on-shell. Only the auxiliary fields which belong to the compensating nonlinear
multiplet do not get derivatives and could still be eliminated; we check that
this is possible in the leading terms of the lagrangian. We compare this result
to the similar one of "old minimal" N=1 supergravity and we comment on possible
generalizations to other versions of N=1,2 supergravity.Comment: 31 pages, no figures. Minor corrections. Details of the full
calculation included as an appendix. Reference adde
Deformed Superspace, N=1/2 Supersymmetry and (Non)Renormalization Theorems
We consider a deformed superspace in which the coordinates \theta do not
anticommute, but satisfy a Clifford algebra. We present results on the
properties of N=1/2 supersymmetric theories of chiral superfields in deformed
superspace, taking the Wess-Zumino model as the prototype. We prove new
(non)renormalization theorems: the F-term is radiatively corrected and becomes
indistinguishable from the D-term, while the Fbar-term is not renormalized.
Supersymmetric vacua are critical points of the antiholomorphic superpotential.
The vacuum energy is zero to all orders in perturbation theory. We illustrate
these results with several examples.Comment: 21 pages, 5 figures and one table; V2: references adde
Finite gravitational action for higher derivative and stringy gravities
We generalize the local surface counterterm prescription suggested in
Einstein gravity for higher derivative (HD) and Weyl gravities. Explicitly, the
surface counterterm is found for three- and five-dimensional HD gravities. As a
result, the gravitational action for asymptotically AdS spaces is finite and
gravitational energy-momentum tensor is well-defined. The holographic trace
anomaly for d2 and d4 boundary (gauge) QFT dual to above HD gravity is
calculated from gravitational energy-momentum tensor. The calculation of AdS
black hole mass in HD gravity is presented within above prescrition. The
comparison with the standard prescription (using reference spacetime) is done.Comment: LaTeX file, 21 page
Efimov Trimers near the Zero-crossing of a Feshbach Resonance
Near a Feshbach resonance, the two-body scattering length can assume any
value. When it approaches zero, the next-order term given by the effective
range is known to diverge. We consider the question of whether this divergence
(and the vanishing of the scattering length) is accompanied by an anomalous
solution of the three-boson Schr\"odinger equation similar to the one found at
infinite scattering length by Efimov. Within a simple zero-range model, we find
no such solutions, and conclude that higher-order terms do not support Efimov
physics.Comment: 8 pages, no figures, final versio
4-point effective actions in open and closed superstring theory
Recently the effective action for the 4-point functions in abelian open
superstring theory has been derived, giving an explicit construction of the
bosonic and fermionic terms of this infinite series. In the present
work we generalize this result to the nonabelian case. We test our result, at
and order, with several existing versions for these
terms, finding agreement in most of the cases. We also apply these ideas to
derive the effective action for the 4-point functions of the NS-NS sector of
closed superstring theory, to all order in .Comment: 26 pages, 1 figure. To appear in JHE
There is no "Theory of Everything" inside E8
We analyze certain subgroups of real and complex forms of the Lie group E8,
and deduce that any "Theory of Everything" obtained by embedding the gauge
groups of gravity and the Standard Model into a real or complex form of E8
lacks certain representation-theoretic properties required by physical reality.
The arguments themselves amount to representation theory of Lie algebras in the
spirit of Dynkin's classic papers and are written for mathematicians.Comment: Final version, to appear in Communications in Mathematical Physics.
The main difference, from the previous version, is the creation of a new
section, containing a response to Lisi's objections to our wor
The modulation effect for supersymmetric dark matter detection with asymmetric velocity dispersion
The detection of the theoretically expected dark matter is central to
particle physics cosmology. Current fashionable supersymmetric models provide a
natural dark matter candidate which is the lightest supersymmetric particle
(LSP). Such models combined with fairly well understood physics like the quark
substructure of the nucleon and the nuclear form factor and the spin response
function of the nucleus, permit the evaluation of the event rate for
LSP-nucleus elastic scattering. The thus obtained event rates are, however,
very low or even undetectable. So it is imperative to exploit the modulation
effect, i.e. the dependence of the event rate on the earth's annual motion. In
this review we study such a modulation effect in directional and undirectional
experiments. We calculate both the differential and the total rates using
symmetric as well as asymmetric velocity distributions. We find that in the
symmetric case the modulation amplitude is small, less than 0.07. There exist,
however, regions of the phase space and experimental conditions such that the
effect can become larger. The inclusion of asymmetry, with a realistic enhanced
velocity dispersion in the galactocentric direction, yields the bonus of an
enhanced modulation effect, with an amplitude which for certain parameters can
become as large as 0.46.Comment: 35 LATEX pages, 7 Tables, 8 PostScript Figures include
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