295 research outputs found
One-loop Electroweak and QCD corrections to vector boson scattering into top pairs and application to ILC
We calculate the electroweak and QCD corrections to W-W+ -> tt and ZZ -> tt.
We also consider the interplay of these corrections with the effect of
anomalous interactions that affect the massive weak bosons and the top. The
results at the VV level fusion are convoluted with the help of the effective
vector boson approximation to give predictions for a high energy e+e- collider.Comment: 19 pages, 27 figure
Methanol diffusion and dynamics in zeolite H-ZSM-5 probed by quasi-elastic neutron scattering and classical molecular dynamics simulations
Zeolite ZSM-5 is a key catalyst in commercially relevant processes including the widely studied methanol to hydrocarbon reaction, and molecular diffusion in zeolite pores is known to be a crucial factor in controlling catalytic reactions. Here, we present critical analyses of recent quasi-elastic neutron scattering (QENS) data and complementary molecular dynamics (MD) simulations. The QENS experiments show that the nature of methanol diffusion dynamics in ZSM-5 pores is dependent both on the Si/Al ratio (11, 25, 36, 40 and 140), which determines the Brønsted acid site density of the zeolite, and that the nature of the type of motion observed may vary qualitatively over a relatively small temperature range. At 373 K, on increasing the ratio from 11 to 140, the observed mobile methanol fraction increases and the nature of methanol dynamics changes from rotational (in ZSM-5 with Si/Al of 11) to translational diffusion. The latter is either confined localized diffusion within a pore in zeolites with ratios up to 40 or non-localized, longer-range diffusion in zeolite samples with the ratio of 140. The complementary MD simulations conducted over long time scales (1 ns), which are longer than those measured in the present study by QENS (≈1-440 ps), at 373 K predict the occurrence of long-range translational diffusion of methanol in ZSM-5, independent of the Si/Al ratios (15, 47, 95, 191 and siliceous MFI). The rate of diffusion increases slightly by increasing the ratio from 15 to 95 and thereafter does not depend on zeolite composition. Discrepancies in the observed mobile methanol fraction between the MD simulations (100% methanol mobility in ZSM-5 pores across all Si/Al ratios) and QENS experiments (for example, ≈80% immobile methanol in ZSM-5 with Si/Al of 11) are attributed to the differences in time resolutions of the techniques. This perspective provides comprehensive information on the effect of acid site density on methanol dynamics in ZSM-5 pores and highlights the complementarity of QENS and MD, and their advantages and limitations. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'
Static quantities of a neutral bilepton in the 331 model with right-handed neutrinos
A neutral vector boson can possess static electromagnetic properties provided
that the associated field is no self-conjugate. This possibility is explored in
the model with right-handed neutrinos, which
predicts a complex neutral gauge boson in a nontrivial representation of
the electroweak group. In this model the only nonvanishing form factors are the
CP-even ones, which arise from both the quark and gauge sectors, and contribute
to the magnetic dipole and the electric quadrupole moments of this neutral
particle.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Loop-induced photon spectral lines from neutralino annihilation in the NMSSM
We have computed the loop-induced processes of neutralino annihilation into
two photons and, for the first time, into a photon and a Z boson in the
framework of the NMSSM. The photons produced from these radiative modes are
monochromatic and possess a clear "smoking gun" experimental signature. This
numerical analysis has been done with the help of the SloopS code, initially
developed for automatic one-loop calculation in the MSSM. We have computed the
rates for different benchmark points coming from SUGRA and GMSB soft SUSY
breaking scenarios and compared them with the MSSM. We comment on how this
signal can be enhanced, with respect to the MSSM, especially in the low mass
region of the neutralino. We also discuss the possibility of this observable to
constrain the NMSSM parameter space, taking into account the latest limits from
the FERMI collaboration on these two modes.Comment: 18 pages, 3 figures. Minor clarifications added in the text. Typing
mistakes and references corrected. Matches published versio
Fermion contribution to the static quantities of arbitrarily charged vector bosons
We present an analysis of the one-loop contribution from left- and
right-handed fermions to the static electromagnetic properties of an
arbitrarily charged no self-conjugate vector boson . Particular emphasis is
given to the case of a no self-conjugate neutral boson . Regardless the
electric charge of the boson, a fermionic loop can induce the two CP-even
form factors but only one CP-odd. As a result the corresponding electric dipole
moment is directly proportional to the magnetic quadrupole moment. The CP-odd
form factor might be severely suppressed since it requires the presence of both
left- and right-handed fermions. The behavior of the form factors is analyzed
for several scenarios of the fermion masses in the context of the decoupling
theorem.Comment: 12 pages, 3 figures, submitted to Journal of Physics
New Precision Electroweak Tests of SU(5) x U(1) Supergravity
We explore the one-loop electroweak radiative corrections in supergravity via explicit calculation of vacuum-polarization and
vertex-correction contributions to the and
parameters. Experimentally, these parameters are obtained from a global fit to
the set of observables , and . We
include -dependent effects, which induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The
(non-oblique) supersymmetric vertex corrections to \Zbb, which define the
parameter, show a significant positive shift for light chargino
masses, which for can be nearly compensated by a negative
shift from the charged Higgs contribution. We conclude that at the 90\%CL, for
m_t\lsim160\GeV the present experimental values of and
do not constrain in any way supergravity in
both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV
the constraints on the parameter space become increasingly stricter. We
demonstrate this trend with a study of the m_t=170\GeV case, where only a
small region of parameter space, with \tan\beta\gsim4, remains allowed and
corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus
supergravity combined with high-precision LEP data would
suggest the presence of light charginos if the top quark is not detected at the
Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon
request as an uuencoded file(0.4MB) or 4 PS files from [email protected],
CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9
How Big Can Anomalous W Couplings Be?
Conventional wisdom has it that anomalous gauge-boson self-couplings can be
at most a percent or so in size. We test this wisdom by computing these
couplings at one loop in a generic renormalizable model of new physics. (For
technical reasons we consider the CP-violating couplings here, but our results
apply more generally.) By surveying the parameter space we find that the
largest couplings (several percent) are obtained when the new particles are at
the weak scale. For heavy new physics we compare our findings with expectations
based on an effective-lagrangian analysis. We find general patterns of induced
couplings which robustly reflect the nature of the underlying physics. We build
representative models for which the new physics could be first detected in the
anomalous gauge couplings.Comment: 40 pages, 11 figures, (dvi file and figures combined into a uuencoded
compressed file), (We correct an error in eq. 39 and its associated figure
(9). No changes at all to the text.), McGill-93/40, UQAM-PHE-93/03,
NEIPH-93-00
Spin Discrimination in Three-Body Decays
The identification of the correct model for physics beyond the Standard Model
requires the determination of the spin of new particles. We investigate to
which extent the spin of a new particle can be identified in scenarios
where it decays dominantly in three-body decays . Here we
assume that is a candidate for dark matter and escapes direct detection at
a high energy collider such as the LHC. We show that in the case that all
intermediate particles are heavy, one can get information on the spins of
and at the LHC by exploiting the invariant mass distribution of the two
standard model fermions. We develop a model-independent strategy to determine
the spins without prior knowledge of the unknown couplings and test it in a
series of Monte Carlo studies.Comment: 31+1 pages, 4 figures, 8 tables, JHEP.cls include
Long-lived Charginos in the Focus-point Region of the MSSM Parameter Space
We analyse the possibility to get light long-lived charginos within the
framework of the MSSM with gravity mediated SUSY breaking. We find out that
this possibility can be realized in the so-called focus-point region of
parameter space. The mass degeneracy of higgsino-like chargino and two
higgsino-like neutralinos is the necessary condition for a long lifetime. It
requires the fine-tuning of parameters, but being a single additional
constraint in the whole parameter space it can be fulfilled in the Constrained
MSSM along the border line where radiative electroweak symmetry breaking fails.
In a narrow band close to the border line the charginos are long-lived
particles. The cross-sections of their production and co-production at the LHC
via electroweak interaction reach a few tenth of pb.Comment: LaTeX, 11 pages, 11 eps figure
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