1,099 research outputs found
On spin-1 massive particles coupled to a Chern-Simons field
We study spin one particles interacting through a Chern-Simons field. In the
Born approximation, we calculate the two body scattering amplitude considering
three possible ways to introduce the interaction: (a) a Proca like model
minimally coupled to a Chern-Simons field, (b) the model obtained from (a) by
replacing the Proca's mass by a Chern-Simons term and (c) a complex
Maxwell-Chern-Simons model minimally coupled to a Chern-Simons field. In the
low energy regime the results show similarities with the Aharonov-Bohm
scattering for spin 1/2 particles. We discuss the one loop renormalization
program for the Proca's model. In spite of the bad ultraviolet behavior of the
matter field propagator, we show that, up to one loop the model is power
counting renormalizable thanks to the Ward identities satisfied by the
interaction vertices.Comment: 14 pages, 5 figures, revte
The Casimir force and the quantum theory of lossy optical cavities
We present a new derivation of the Casimir force between two parallel plane
mirrors at zero temperature. The two mirrors and the cavity they enclose are
treated as quantum optical networks. They are in general lossy and
characterized by frequency dependent reflection amplitudes. The additional
fluctuations accompanying losses are deduced from expressions of the optical
theorem. A general proof is given for the theorem relating the spectral density
inside the cavity to the reflection amplitudes seen by the inner fields. This
density determines the vacuum radiation pressure and, therefore, the Casimir
force. The force is obtained as an integral over the real frequencies,
including the contribution of evanescent waves besides that of ordinary waves,
and, then, as an integral over imaginary frequencies. The demonstration relies
only on general properties obeyed by real mirrors which also enforce general
constraints for the variation of the Casimir force.Comment: 18 pages, 6 figures, minor amendment
Low energy electron/recoil discrimination for directional Dark Matter detection
Directional detection is a promising Dark Matter search strategy. Even though
it could accommodate to a sizeable background contamination, electron/recoil
discrimination remains a key and challenging issue as for direction-insensitive
detectors. The measurement of the 3D track may be used to discriminate
electrons from nuclear recoils. While a high rejection power is expected above
20 keV ionization, a dedicated data analysis is needed at low energy. After
identifying discriminant observables, a multivariate analysis, namely a Boosted
Decision Tree, is proposed, enabling an efficient event tagging for Dark Matter
search. We show that it allows us to optimize rejection while keeping a rather
high efficiency which is compulsory for rare event search.With respect to a
sequential analysis, the rejection is about 20 times higher with a multivariate
analysis, for the same Dark Matter exclusion limit.Comment: 20 pages, 20 figure
Exchange Bias and Vertical Shift in CoFe2O4 nanoparticles
Magnetic properties of core-shell cobalt ferrite nanoparticles 15 to 48nm
prepared by a sol-gel route have been studied. It is shown that the coercivity
follows non-monotonic size dependence varying as 1/d above the maximum (d is
the particle size). Field cooled magnetization exhibited both horizontal
(exchange bias) and vertical shifts. The exchange bias is understood as
originating at the interface between a surface region with structural and spin
disorder and a core ferrimagnetic region. The dependence of the exchange bias
and vertical shifts on the particle sizes and cooling fields are found to have
significant differences and the differences are explained in the light of
recent results which suggest that both weakly and strongly pinned spins are
present at the interface. It is suggested that the exchange bias is dominated
by the weakly pinned spins while the vertical shift is affected by the strongly
pinned ones.Comment: 2
Nitriding using cathodic cage technique of martensitic stainless steel AISI 420 with addition of CH4
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
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