598 research outputs found
Testing the Higgs boson gluonic couplings at LHC
We study Higgs + jet production at hadron colliders in order to look for new
physics residual effects possibly described by the operators
{\O}_{GG} and {\widetilde\O}_{GG} which induce anomalous and
couplings. Two ways for constraining these operators at LHC may be ~useful. The
first is based on the total Higgs boson production rate induced by gluon-gluon
fusion, in which the main cause of limitations are due to theoretical
uncertainties leading to sensitivities of and
for the corresponding anomalous
couplings, in the mass range 100 GeV \lsim \mh \lsim 2~00 GeV. These results
imply sensitivity to new physics scales of 51 and 24 TeV respectively. The
second way investigated here concerns the shape of the Higgs transverse
momentum; for which the theoretical uncertainties are less severe and the
limitations are mainly induced by statistics. A simple analysis, based on the
ratio of the number of events at large and low at LHC, leads to similar
sensitivities, if only the decay mode is used. But the
sensitivities can now be improved by a factor 2 to 10, depending on the Higgs
mass, if the Higgs decay modes to , , , are also used.Comment: 23 pages and 7 figures, version to appear in Phys.ReV.D. e-mail:
[email protected]
Of Higgs, Unitarity and other Questions
On the verge of conclusive checks on the Standard Model by the LHC, we
discuss some of the basic assumptions. The reason for this analysis stems from
a recent proposal of an Electroweak Model based on a nonlinearly realized gauge
group SU(2) X U(1), where, in the perturbative approximation, there is no Higgs
boson. The model enjoys the Slavnov-Taylor identities and therefore the
perturbative unitarity. On the other hand, it is commonly believed that the
existence of the Higgs boson is entangled with the property of unitarity, when
high energy processes are considered. The argument is based mostly on the
Froissart bound and on the Equivalence Theorem. In this talk we briefly review
some of our objections on the validity of such arguments. Some open questions
are pointed out, in particular on the limit of zero mass for the vector mesons
and on the fate of the longitudinal polarizations.Comment: 23 pages, 1 figure, presented by Ruggero Ferrari at the International
Conference "Gauge Fields. Yesterday, Today, Tomorrow" in honor of A.A.
Slavnov. Moscow, January 19-24 201
A FORTRAN code for in SM and MSSM
Through the present paper, the code gamgamZZ is presented, which may be used
to calculate all possible observables related to the process , in either the Standard Model (SM), or the minimal sypersymmetric standard
model (MSSM) with real parameters.Comment: 13 pages, 7 figures Revised according to the EPJC Referee suggestion
A note on the rare decay of a Higgs boson into photons and a boson
We have calculated the width of the rare decay at
one-loop level in the standard model for Higgs boson masses in the range . For this range of Higgs boson masses
we find that boson is predominantly longitudinally polarized, and the
photons have the same helicity. A comparison of the decay width to those of and shows that,
for the Higgs boson mass of , the ratios of the decay
widths are .Comment: 4 pages, 5 figures, RevTe
The processes in SM and MSSM
We present the results of a complete analysis of the one loop electroweak
corrections to in the Standard (SM) and
the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on
the high energy behaviour of the various helicity amplitudes and the way the
logarithmic structure is generated. The large magnitude of these effects, which
induce striking differences between the SM and MSSM cases at high energies,
offers the possibility of making global tests which could check the consistency
of these models, and even decide whether any additional new physics is
required.Comment: Short version (16 pages and 9 figures) of the paper hep-ph/0207273,
to appear in Phy.Rev.D. e-mail: [email protected]
Effects of genuine dimension-six Higgs operators
We systematically discuss the consequences of genuine dimension-six Higgs
operators. These operators are not subject to stringent constraints from
electroweak precision data. However, they can modify the couplings of the Higgs
boson to electroweak gauge bosons and, in particular, the Higgs
self-interactions. We study the sensitivity to which those couplings can be
probed at future \ee linear colliders in the sub-TeV and in the multi-TeV
range. We find that for GeV with a luminosity of 1 ab the
anomalous and couplings may be probed to about the 0.01 level, and
the anomalous coupling to about the 0.1 level.Comment: 21 pages, 17 figures; typos corrected and references adde
Hunting a light CP-violating Higgs via diffraction at the LHC
We study the central diffractive production of the (three neutral) Higgs
bosons, with a rapidity gap on either side, in an MSSM scenario with
CP-violation. We consider the bb-bar and tautau-bar decay for the light H_1
boson and the four b-jet final state for the heavy H_2 and H_3 bosons, and
discuss the corresponding backgrounds. A direct indication of the existence of
CP-violation can come from the observation of either an azimuthal asymmetry in
the angular distribution of the tagged forward protons (for the exclusive pp ->
p+H+p process) or of a sin(2phi) contribution in the azimuthal correlation
between the transverse energy flows in the proton fragmentation regions for the
process with the diffractive dissociation of both incoming protons (pp ->
X+H+Y). We emphasise the advantage of reactions with the rapidity gaps (that is
production by the pomeron-pomeron fusion) to probe CP parity and to determine
the quantum numbers of the produced central object.Comment: 11 pages, 3 figure
RacoonWW1.3: A Monte Carlo program for four-fermion production at e^+ e^- colliders
We present the Monte Carlo generator RacoonWW that computes cross sections to
all processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma and calculates the
complete O(alpha) electroweak radiative corrections to e^+ e^- -> W W -> 4f in
the electroweak Standard Model in double-pole approximation. The calculation of
the tree-level processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma is based on
the full matrix elements for massless (polarized) fermions. When calculating
radiative corrections to e^+ e^- -> W W -> 4f the complete virtual
doubly-resonant electroweak corrections are included, i.e. the factorizable and
non-factorizable virtual corrections in double-pole approximation, and the real
corrections are based on the full matrix elements for e^+ e^- -> 4f + gamma.
The matching of soft and collinear singularities between virtual and real
corrections is done alternatively in two different ways, namely by using a
subtraction method or by applying phase-space slicing. Higher-order
initial-state photon radiation and naive QCD corrections are taken into
account. RacoonWW also provides anomalous triple gauge-boson couplings for all
processes e^+ e^- -> 4f and anomalous quartic gauge-boson couplings for all
processes e^+ e^- -> 4f + gamma.Comment: 62 pages, LaTeX, elsart styl
Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables
We list all possible dimension-six CP-conserving invariant operators involving the third-family quarks which
could be generated by new physics at a higher scale. Expressions for these
operators after electroweak gauge symmetry breaking and the induced effective
couplings , and are
presented. Analytic expressions for the tree level contributions of all these
operators to the observables and at LEP I,
and at LEP II,
and at the NLC, as well as
at the Tevatron upgrade, are provided.
The effects of these operators on different electroweak observables are
discussed and numerical examples presented. Numerical analyses show that in the
coupling region allowed by and at LEP I, some of the new
physics operators can still have significant contributions at LEP II, the
Tevatron and the NLC.Comment: 25 page
Effective lagrangian description of top production and decay
We propose a rather general description of residual New Physics (NP) effects
on the top quark couplings. These effects are described in terms of 20 gauge
invariant operators involving gauge and Higgs bosons as well as quarks
of the third family. We compute their implications for the , and vertices and study their observability in the process
with . We present results for
the integrated cross section, the angular distribution and various decay
distribution and polarization asymmetries for NLC energies of .
Observability limits are discussed and interpreted in terms of the NP scales
associated to each operator through the unitarity constraints. The general
landscape of the residual NP effects in the heavy quark and bosonic sectors is
also presented.Comment: 36 pages (9 figures available through email in .uu form, e-mail:
[email protected]
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