6,770 research outputs found
Learning Behavioural Context
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New scalar resonances from sneutrino-Higgs mixing in supersymmetry with small lepton number (R-parity) violation
We consider new s-channel scalar exchanges in top quark and massive
gauge-bosons pair production in e+e- collisions, in supersymmetry with a small
lepton number violation. We show that a soft bilinear lepton number violating
term in the scalar potential which mixes the Higgs and the slepton fields can
give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and
in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming
light leptons through its sneutrino component and to either the top quark or
the massive gauge bosons through its Higgs component. Such a scalar resonance
in these specific production channels cannot result from trilinear Yukawa-like
R-parity violation alone, and may, therefore, stand as strong evidence for the
existence of R-parity violating bilinears in the supersymmetric scalar
potential. We use the LEP2 measurements of the WW and ZZ cross-sections to
place useful constrains on this scenario, and investigate the expectations for
the sensitivity of a future linear collider to these signals. We find that
signals of these scalar resonances, in particular in top-pair production, are
well within the reach of linear colliders in the small lepton number violation
scenario.Comment: 22 pages in revtex, 10 figures embadded in the text using epsfi
R-parity violation and uses of the rare decay sneutrino-->gamma+gamma in hadron and photon colliders
We consider implications of the loop process sneutrino -> gamma gamma in the
MSSM with R-parity violation for future experiments, where the sneutrino is
produced as the only supersymmetric particle. We present a scenario for the
R-parity violating couplings, where this clean decay, although rare with
Br(sneutrino -> gamma gamma) ~ 10^{-6}, may be useful for sneutrino detection
over a range of sneutrino masses at the LHC. Furthermore, the new
sneutrino-gamma-gamma effective coupling may induce detectable sneutrino
resonant production in gamma gamma collisions, over a considerably wide mass
range. We compare sneutrino -> gamma gamma, gg throughout the paper with the
analogous yet quantitatively very different, Higgs -> gamma gamma, gg decays
and comment on the loop processes sneutrino -> WW, ZZ.Comment: 19 pages using REVTEX, 3 figures embadded in the text using epsfi
The flavor changing top decay t-->c+sneutrino or sneutrino-->t+c(bar) in the MSSM without R-parity
Widths for the new flavor changing top quark decay t-->c+sneutrino or for the
reversed sneutrino decay sneutrino-->t+c(bar) are calculated in the MSSM
without R-parity conservation. For large \tan\beta, e.g., \tan\beta ~ m_t/m_b ~
40, Br(t-->c+sneutrino) > 10^{-5} or Br(sneutrino-->t+c(bar)) > 10^{-6} in a
relatively wide range of the supersymmetric parameter space as long as there is
more than one non-zero R-parity violating coupling. In the best cases, with a
typical squark mass around 100 GeV, we find that Br(t-->c+sneutrino) ~ 10^{-4}
- 10^{-3} or Br(sneutrino-->t+c(bar)) ~ 10^{-5} - 10^{-4}. For \tan\beta ~ O(1)
the corresponding branching ratios for both top or sneutrino decays are too
small to be measured at the LHC. Therefore, the decays t-->c+sneutrino or
sneutrino-->t+c(bar) appear to be sensitive to \tan\beta and may be detected at
the LHC. The branching ratios of the corresponding decays to an up quark
instead of a charm quark, e.g., t-->u+sneutrino or sneutrino-->t+u(bar), may
also be similar.Comment: 23 pages, plain latex, 8 figures embadded in the text using epsfi
Absorption in the fractional quantum Hall regime: trion dichroism and spin polarization
We present measurements of optical interband absorption in the fractional
quantum Hall regime in a GaAs quantum well in the range 0 < nu < 1. We
investigate the mechanism of singlet trion absorption, and show that its
circular dichroism can be used as a probe of the spin polarization of the
ground state of the two-dimensional electron system (2DES). We find that at nu
= 1/3 the 2DES is fully spin-polarized. Increasing the filling factor results
in a gradual depolarization, with a sharp minimum in the dichroism near nu =
2/3. We find that in the range 0.5 < nu < 0.85 the 2DES remains partially
polarized for the broad range of magnetic fields from 2.75 to 11 Tesla. This is
consistent with the presence of a mixture of polarized and depolarized regions.Comment: 4 pages, 4 figures (Fig 4 is in color
Renormalization Ambiguities in Chern-Simons Theory
We introduce a new family of gauge invariant regularizations of Chern-Simons
theories which generate one-loop renormalizations of the coupling constant of
the form where can take any arbitrary integer value. In
the particular case we get an explicit example of a gauge invariant
regularization which does not generate radiative corrections to the bare
coupling constant. This ambiguity in the radiative corrections to is
reminiscent of the Coste-L\"uscher results for the parity anomaly in (2+1)
fermionic effective actions.Comment: 10 pages, harvmac, no changes, 1 Postscript figure (now included
Production and decay of the neutral top-pion in high energy colliders
We study the production and decay of the neutral top-pion
predicted by topcolor-assisted technicolor(TC2) theory. Our results show that,
except the dominant decay modes , and , the
can also decay into and modes. It can
be significantly produced at high energy collider(LC) experiments
via the processes and . We further calculate the production cross sections of the
processes and . We find that the signatures of the neutral top-pion
can be detected via these processes.Comment: Latex file, 13 Pages, 6 eps figures. to be published in Phys.Rev.
Electronic structure of and Quantum size effect in III-V and II-VI semiconducting nanocrystals using a realistic tight binding approach
We analyze the electronic structure of group III-V semiconductors obtained
within full potential linearized augmented plane wave (FP-LAPW) method and
arrive at a realistic and minimal tight-binding model, parameterized to provide
an accurate description of both valence and conduction bands. It is shown that
cation sp3 - anion sp3d5 basis along with the next nearest neighbor model for
hopping interactions is sufficient to describe the electronic structure of
these systems over a wide energy range, obviating the use of any fictitious s*
orbital, employed previously. Similar analyses were also performed for the
II-VI semiconductors, using the more accurate FP-LAPW method compared to
previous approaches, in order to enhance reliability of the parameter values.
Using these parameters, we calculate the electronic structure of III-V and
II-VI nanocrystals in real space with sizes ranging upto about 7 nm in
diameter, establishing a quantitatively accurate description of the band-gap
variation with sizes for the various nanocrystals by comparing with available
experimental results from the literature.Comment: 28 pages, 8 figures, Accepted for publication in Phys. Rev.
Broken R Parity Contributions to Flavor Changing Rates and CP Asymmetries in Fermion Pair Production at Leptonic Colliders
We examine the effects of the R parity odd renormalizable interactions on
flavor changing rates and CP violation asymmetries in the production of
fermion-antifermion pairs at leptonic colliders. The produced
fermions may be leptons, down-quarks or up-quarks, and the center of mass
energies may range from the Z-boson pole up to GeV. Off the Z-boson
pole, the flavor changing rates are controlled by tree level amplitudes and the
CP asymmetries by interference terms between tree and loop level amplitudes. At
the Z-boson pole, both observables involve loop amplitudes. The lepton number
violating interactions, associated with the coupling constants, \l_{ijk},
\l'_{ijk}, are only taken into account. The consideration of loop amplitudes
is restricted to the photon and Z-boson vertex corrections. We briefly review
flavor violation physics at colliders. We present numerical results using a
single, species and family independent, mass parameter, , for all the
scalar superpartners and considering simple assumptions for the family
dependence of the R parity odd coupling constants.Comment: Latex File. 23 pages. 4 postscript figures. 1 table. Revised version
with new results and several corrections in numerical result
Charged exctions in the fractional quantum Hall regime
We study the photoluminescence spectrum of a low density ()
two-dimensional electron gas at high magnetic fields and low temperatures. We
find that the spectrum in the fractional quantum Hall regime can be understood
in terms of singlet and triplet charged-excitons. We show that these spectral
lines are sensitive probes for the electrons compressibility. We identify the
dark triplet charged-exciton and show that it is visible at the spectrum at
K. We find that its binding energy scales like , where is
the magnetic length, and it crosses the singlet slightly above 15 T.Comment: 10 pages, 5 figure
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