1,345 research outputs found
Electroweak corrections and anomalous triple gauge-boson couplings in WW and WZ production at the LHC
We have analysed the production of WW and WZ vector-boson pairs at the LHC.
These processes give rise to four-fermion final states, and are particularly
sensitive to possible non-standard trilinear gauge-boson couplings. We have
studied the interplay between the influence of these anomalous couplings and
the effect of the complete logarithmic electroweak O(\alpha) corrections.
Radiative corrections to the Standard Model processes in double-pole
approximation and non-standard terms due to trilinear couplings are implemented
into a Monte Carlo program for p p -> 4f (+\gamma) with final states involving
four or two charged leptons. We numerically investigate purely leptonic final
states and find that electroweak corrections can fake new-physics signals,
modifying the observables by the same amount and shape, in kinematical regions
of statistical significance.Comment: 19 pages, LaTex, 12 eps figure
Logarithmic electroweak corrections to gauge-boson pair production at the LHC
We have studied the effects of the complete logarithmic electroweak O(alpha)
corrections on the production of vector-boson pairs WZ, ZZ, and WW at the LHC.
These corrections are implemented into a Monte Carlo program for pp -> 4f
(+\gamma) with final states involving four or two leptons using the double-pole
approximation. We numerically investigate purely leptonic final states and find
that electroweak corrections lower the predictions by 5-30% in the physically
interesting region of large di-boson invariant mass and large angle of the
produced vector bosons.Comment: 47 pages, LaTeX, 18 eps figure
Golem95C: A library for one-loop integrals with complex masses
We present a program for the numerical evaluation of scalar integrals and
tensor form factors entering the calculation of one-loop amplitudes which
supports the use of complex masses in the loop integrals. The program is built
on an earlier version of the golem95 library, which performs the reduction to a
certain set of basis integrals using a formalism where inverse Gram
determinants can be avoided. It can be used to calculate one-loop amplitudes
with arbitrary masses in an algebraic approach as well as in the context of a
unitarity-inspired numerical reconstruction of the integrand.Comment: 22 pages, 3 figure
Quadratic electroweak corrections for polarized Moller scattering
The paper discusses the two-loop (NNLO) electroweak radiative corrections to
the parity violating electron-electron scattering asymmetry induced by squaring
one-loop diagrams. The calculations are relevant for the ultra-precise 11 GeV
MOLLER experiment planned at Jefferson Laboratory and experiments at
high-energy future electron colliders. The imaginary parts of the amplitudes
are taken into consideration consistently in both the infrared-finite and
divergent terms. The size of the obtained partial correction is significant,
which indicates a need for a complete study of the two-loop electroweak
radiative corrections in order to meet the precision goals of future
experiments
Electroweak corrections to Higgs-strahlung off W/Z bosons at the Tevatron and the LHC with HAWK
The associate production of Higgs bosons with W or Z bosons, known as
Higgs-strahlung, is an important search channel for Higgs bosons at the hadron
colliders Tevatron and LHC for low Higgs-boson masses. We refine a previous
calculation of next-to-leading-order electroweak corrections (and recalculate
the QCD corrections) upon including the leptonic decay of the W/Z bosons,
thereby keeping the fully differential information of the 2-lepton + Higgs
final state. The gauge invariance of the W/Z-resonance treatment is ensured by
the use of the complex-mass scheme. The electroweak corrections, which are at
the level of -(5-10)% for total cross sections, further increase in size with
increasing transverse momenta p_T in differential cross sections. For instance,
for p_T,H >~ 200GeV, which is the interesting range at the LHC, the electroweak
corrections to WH production reach about -14% for M_H = 120GeV. The described
corrections are implemented in the HAWK Monte Carlo program, which was
initially designed for the vector-boson-fusion channel, and are discussed for
various distributions in the production channels pp / p \bar p -> H + l nu_l /
l^-l^+ / nu_l \bar nu_l + X.Comment: 22 p
A closed expression for the UV-divergent parts of one-loop tensor integrals in dimensional regularization
Starting from the general definition of a one-loop tensor N-point function,
we use its Feynman parametrization to calculate the UV-divergent part of an
arbitrary tensor coefficient in the framework of dimensional regularization. In
contrast to existing recursion schemes, we are able to present a general
analytic result in closed form that enables direct determination of the
UV-divergent part of any one-loop tensor N-point coefficient independent from
UV-divergent parts of other one-loop tensor N-point coefficients. Simplified
formulas and explicit expressions are presented for A-, B-, C-, D-, E-, and
F-functions.Comment: 19 pages (single column), the result of previous versions is further
evaluated leading to a closed analytic expression for the UV-divergent part
of an arbitrary one-loop tensor coefficient, title is modified accordingly, a
sign error in the appendix (C_{00000000}) has been corrected, a mathematica
notebook containing an implementation of the newly derived formula is
attache
Mixing of fermion fields of opposite parities and baryon resonances
We consider a loop mixing of two fermion fields of opposite parities whereas
the parity is conserved in a Lagrangian. Such kind of mixing is specific for
fermions and has no analogy in boson case. Possible applications of this effect
may be related with physics of baryon resonances. The obtained matrix
propagator defines a pair of unitary partial amplitudes which describe the
production of resonances of spin and different parity or
. The use of our amplitudes for joint description of
partial waves and shows that the discussed effect is clearly
seen in these partial waves as the specific form of interference between
resonance and background. Another interesting application of this effect may be
a pair of partial waves and where the picture is more
complicated due to presence of several resonance states.Comment: 22 pages, 6 figures, more detailed comparison with \pi N PW
Observation of lobes near the X-point in resonant magnetic perturbation experiments on MAST
The application of non-axisymmetric resonant magnetic perturbations (RMPs)
with a toroidal mode number n=6 in the MAST tokamak produces a significant
reduction in plasma energy loss associated with type-I Edge Localized Modes
(ELMs), the first such observation with n>3. During the ELM mitigated stage
clear lobe structures are observed in visible-light imaging of the X-point
region. These lobes or manifold structures, that were predicted previously,
have been observed for the first time in a range of discharges and their
appearance is correlated with the effect of RMPs on the plasma i.e. they only
appear above a threshold when a density pump out is observed or when the ELM
frequency is increased. They appear to be correlated with the RMPs penetrating
the plasma and may be important in explaining why the ELM frequency increases.
The number and location of the structures observed can be well described using
vacuum modelling. Differences in radial extent and poloidal width from vacuum
modelling are likely to be due to a combination of transport effects and plasma
screening.Comment: 15 pages, 5 figure
Electroweak-correction effects in gauge-boson pair production at the LHC
We have studied the effect of one-loop logarithmic electroweak radiative
corrections on WZ and production processes at the LHC. We present
analytical results for the leading-logarithmic electroweak corrections to the
corresponding partonic processes du -> WZ, Wgamma. Using the leading-pole
approximation we implement these corrections into Monte Carlo programs for
. We find that electroweak corrections
lower the predictions by 5-20% in the physically interesting region of large
transverse momentum and small rapidity separation of the gauge bosons.Comment: 28 pages, LaTex, 13 eps figures included; references added and
corrected typo
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