961 research outputs found
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
Electroweak corrections to W-boson pair production at the LHC
Vector-boson pair production ranks among the most important Standard-Model
benchmark processes at the LHC, not only in view of on-going Higgs analyses.
These processes may also help to gain a deeper understanding of the electroweak
interaction in general, and to test the validity of the Standard Model at
highest energies. In this work, the first calculation of the full one-loop
electroweak corrections to on-shell W-boson pair production at hadron colliders
is presented. We discuss the impact of the corrections on the total cross
section as well as on relevant differential distributions. We observe that
corrections due to photon-induced channels can be amazingly large at energies
accessible at the LHC, while radiation of additional massive vector bosons does
not influence the results significantly.Comment: 29 pages, 15 figures, 4 tables; some references and comments on
\gamma\gamma -> WW added; matches version published in JHE
A New Renormalization Scheme of Fermion Fields in Electroweak Standard Model
This paper has been withdrawn by the author,due a immature idea.Comment: 6 page
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
Radiative Corrections to in the Electroweak Standard Model
The cross-section for with arbitrary polarized
photons is calculated within the electroweak Standard Model including the
complete virtual and soft-photonic corrections. We present a
detailed numerical discussion of the radiative corrections with particular
emphasis on the purely weak corrections. These are usually of the order of
1--10\% for energies up to 1 TeV. For unpolarized or equally polarized photons
they reach almost 10\% close to threshold. The large corrections cannot be
traced back to a universal origin like the running of or the
-parameter. Apart from the energy region around the Higgs resonance
the weak corrections are widely independent
of the Higgs-boson mass.Comment: 22 pages, LaTeX (compressed, uuencoded), 20 figures as compressed
uuencoded ps-files, complete ps-file available via anonymous ftp from
ftp://ftp.physik.uni-wuerzburg.de/pub/preprint/WUE-ITP-95-017.p
Electroweak Sudakov Logarithms and Real Gauge-Boson Radiation in the TeV Region
Electroweak radiative corrections give rise to large negative,
double-logarithmically enhanced corrections in the TeV region. These are partly
compensated by real radiation and, moreover, affected by selecting
isospin-noninvariant external states. We investigate the impact of real gauge
boson radiation more quantitatively by considering different restricted final
state configurations. We consider successively a massive abelian gauge theory,
a spontaneously broken SU(2) theory and the electroweak Standard Model. We find
that details of the choice of the phase space cuts, in particular whether a
fraction of collinear and soft radiation is included, have a strong impact on
the relative amount of real and virtual corrections.Comment: 20 pages, 4 figure
Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies
We present precision calculations of the processes e+e- -> 4-fermions in
which the double resonant W+W- intermediate state occurs. Referring to this
latter intermediate state as the 'signal process', we show that, by using the
YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate
combination, we achieve a physical precision on the signal process, as isolated
with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge
invariance of our calculations and we compare our results with those of other
authors where appropriate. In particular, sample Monte Carlo data are
explicitly illustrated and compared with the results of the program RacoonWW of
Dittmaier {\it et al.}. In this way, we show that the total (physical plus
technical) precision tag for the WW signal process cross section is 0.4 per
cent for 200 GeV, for example. Results are also given for 500 GeV with an eye
toward the LC.Comment: 19 pages, 2 figs;corrected Tab. 3;improved refs.,figs.,text;improved
refs.,text;improved tex
Oblique Corrections To The W Width
The lowest-order expression for the partial width to , has no oblique radiative
corrections from new physics if the measured mass is used. Here GeV/ is the muon decay constant. For
the present value of GeV/, and with
GeV, one expects MeV. The total
width is also expected to lack oblique corrections from
new physics, so that . Present data are consistent with this prediction.Comment: 15 pages (LaTeX), one PostScript figure not included (available upon
request
The Phenomenology of a Top Quark Seesaw Model
The top quark seesaw mechanism offers a method for constructing a composite
Higgs field without the usual difficulties that accompany traditional
technicolor or topcolor theories. The focus of this article is to study the
phenomenology of the new physics required by this mechanism. After establishing
a set of criteria for a plausible top quark seesaw theory, we develop two
models, the first of which has a heavy weak singlet fermion with hypercharge
4/3 while the second has, in addition, a heavy weak singlet hypercharge -2/3
fermion. At low energies, these theories contain one or two Higgs doublets
respectively. We then derive the low energy effective Higgs potential in detail
for the two-doublet theory as well as study the likely experimental signatures
for both theories. A strong constraint on the one-doublet model is the measured
value of the rho parameter which permits the new heavy fermion to have a mass
of about 5-7 TeV, when the Higgs has a mass greater than 300 GeV. In the
two-doublet model, mixing of the new heavy Y=-2/3 fermion and the b quark
affects the prediction for R_b. In order to agree with the current limits on
R_b, the mass of this fermion should be at least 12 TeV. The mass of the heavy
Y=4/3 fermion in the two-doublet model is not as sharply constrained by
experiments and can be as light as 2.5 TeV.Comment: 33 pages, 12 figures, uses harvmac and picte
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