84 research outputs found
Higgs production and decay: Analytic results at next-to-leading order QCD
The virtual two-loop corrections for Higgs production in gluon fusion are
calculated analytically in QCD for arbitrary Higgs and quark masses. Both
scalar and pseudo-scalar Higgs bosons are considered. The results are obtained
by expanding the known one-dimensional integral representation in terms of
m_H/m_q, and matching it with a suitably chosen ansatz of Harmonic
Polylogarithms. This ansatz is motivated by the known analytic result for the
Higgs decay rate into two photons. The method also allows us to check this
result and to extend it to the pseudo-scalar decay rate.Comment: LaTeX, 16 pages, 5 figures (8 eps-files
Analytic Results for Virtual QCD Corrections to Higgs Production and Decay
We consider the production of a Higgs boson via gluon-fusion and its decay
into two photons. We compute the NLO virtual QCD corrections to these processes
in a general framework in which the coupling of the Higgs boson to the external
particles is mediated by a colored fermion and a colored scalar. We present
compact analytic results for these two-loop corrections that are expressed in
terms of Harmonic Polylogarithms. The expansion of these corrections in the low
and high Higgs mass regimes, as well as the expression of the new Master
Integrals which appear in the reduction of the two-loop amplitudes, are also
provided. For the fermionic contribution, we provide an independent check of
the results already present in the literature concerning the Higgs boson and
the production and decay of a pseudoscalar particle.Comment: 19 pages, 3 figures, version accepted by JHE
Radiative Neutralino Decay in Split Supersymmetry
Radiative neutralino decay is studied in a Split
Supersymmetric scenario, and compared with mSUGRA and MSSM. This 1-loop process
has a transition amplitude which is often quite small, but has the advantage of
providing a very clear and distinct signature: electromagnetic radiation plus
missing energy. In Split Supersymmetry this radiative decay is in direct
competition with the tree-level three-body decay , and we obtain large values for the branching ratio which can be close to unity in the region .
Furthermore, the value for the radiative neutralino decay branching ratio has a
strong dependence on the split supersymmetric scale , which is
otherwise very difficult to infer from experimental observables.Comment: 15 pages and 10 figure
Implications of the Higgs Discovery in the MSSM Golden Region
If the lightest CP-even Higgs boson in the MSSM is discovered at the LHC, two
measurements could be made simultaneously: the Higgs mass m_h and the event
rate Bs(gg -> h -> gamma gamma). We study to what extent the combination of
these two measurements would allow us to extract parameters in the stop mass
matrix, including the off-diagonal mixing term, with a focus on the MSSM golden
region where the stops are light and the mixing is large. Even though both the
production cross-section and the decay amplitude are not sensitive to
supersymmetric parameters outside of the stop sector, the branching ratio
depends on the total decay width, which is dominated by the Higgs decay to b
quarks and sensitive to both the pseudo-scalar mass m_A and the supersymmetric
Higgs mass \mu. In the end we find m_A is an important input in extracting the
stop mass parameters, while a fair estimate of the off-diagonal mixing term
could be obtained without prior knowledge of \mu.Comment: 17 pages and 6 figures; v2: minor revision and added references to
match JHEP versio
On the possibility of a very light A^0 at low \tan\beta
The searches at LEP II for the processes e^+e^-\to h^0Z and e^+e^-\to h^0A^0
in the Minimal Supersymmetric Standard Model (MSSM) fail to exclude regions of
the m_h,m_A plane where \tan\beta <1, thus allowing a very light A^0 (m_A< 20
GeV). Such a parameter choice would predict a light H^\pm with m_{H^\pm}< m_W.
Although the potentially large branching ratio for H^\pm \to A^0 W^* would
ensure that H^\pm also escaped detection in direct searches at LEP II and the
Tevatron Run I, we show that this elusive parameter space is overwhelmingly
disfavoured by electroweak precision measurements.Comment: 11 pages, 2 figures, Revtex, references added, minor additions to
tex
Seesaw Majoron Model of Neutrino Mass and Novel Signals in Higgs Boson Production at LEP
We perform a careful study of the neutral scalar sector of a model which
includes a singlet, a doublet, and a triplet scalar field under . This
model is motivated by neutrino physics, since it is simply the most general
version of the seesaw model of neutrino mass generation through spontaneous
violation of lepton number. The neutral Higgs sector contains three CP-even and
one massive CP-odd Higgs boson , in addition to the massless CP-odd majoron
. The weakly interacting majoron remains massless if the breaking of lepton
number symmetry is purely spontaneous. We show that the massive CP-odd Higgs
boson may invisibly decay to three majorons, as well as to a CP-even Higgs
boson plus a majoron. We consider the associated Higgs production followed by invisible decays and and derive the
corresponding limits on masses and coupling that follow from LEP I precision
measurements of the invisible Z width. We also study a novel signal predicted by the model, analyse the background and
perform a Monte-Carlo simulation of the signal in order to illustrate the
limits on Higgs boson mass, couplings and branching ratios that follow from
that.Comment: 21 pages, 7 figures, late
Including R-parity violation in the numerical computation of the spectrum of the minimal supersymmetric standard model: SOFTSUSY
Current publicly available computer programs calculate the spectrum and
couplings of the minimal supersymmetric standard model under the assumption of
R-parity conservation. Here, we describe an extension to the SOFTSUSY program
which includes R-parity violating effects. The user provides a theoretical
boundary condition upon the high-scale supersymmetry breaking R-parity
violating couplings. Successful radiative electroweak symmetry breaking,
electroweak and CKM matrix data are used as weak-scale boundary conditions. The
renormalisation group equations are solved numerically between the weak scale
and a high energy scale using a nested iterative algorithm. This paper serves
as a manual to the R-parity violating mode of the program, detailing the
approximations and conventions used.Comment: Updated to SOFTSUSY3.3.3. Program may be downloaded from
http://projects.hepforge.org/softsusy/ and future manuals will be distributed
with the cod
Neutrino properties and the decay of the lightest supersymmetric particle
Supersymmetry with broken R-parity can explain the neutrino mass squared
differences and mixing angles observed in neutrino oscillation experiments. In
the minimal model, where R-parity is broken only by bilinear terms, certain
decay properties of the lightest supersymmetric particle (LSP) are correlated
with neutrino mixing angles. Here we consider charginos, squarks, gluinos and
sneutrinos being the LSP and calculate their decay properties in bilinear
R-parity breaking supersymmetry. Together with the decays of charged scalars
and neutralinos calculated previously this completes the proof that bilinear
R-parity breaking as the source of neutrino masses will be testable at future
colliders. Moreover, we argue that in case of GMSB, the decays of the NLSP can
be used to test the model.Comment: 15 pages, 8 figure
Two-Loop O(alpha_s G_F M_Q^2) Heavy-Quark Corrections to the Interactions between Higgs and Intermediate Bosons
By means of a low-energy theorem, we analyze at O(alpha_s G_F M_Q^2) the
shifts in the Standard-Model W^+W^-H and ZZH couplings induced by virtual
high-mass quarks, Q, with M_Q >> M_Z, M_H, which includes the top quark.
Invoking the improved Born approximation, we then find the corresponding
corrections to various four- and five-point Higgs-boson production and decay
processes which involve the W^+W^-H and ZZH vertices with one or both of the
gauge bosons being connected to light-fermion currents, respectively. This
includes e^+e^- -> f anti-f H via Higgs-strahlung, via W^+W^- fusion (with f =
nu_e), and via ZZ fusion (with f = e), as well as H -> 2V -> 4f (with V = W,
Z).Comment: 20 pages (Latex); Physical Review D (to appear
KK Parity in Warped Extra Dimension
We construct models with a Kaluza-Klein (KK) parity in a five- dimensional
warped geometry, in an attempt to address the little hierarchy problem present
in setups with bulk Standard Model fields. The lightest KK particle (LKP) is
stable and can play the role of dark matter. We consider the possibilities of
gluing two identical slices of 5D AdS in either the UV (IR-UV-IR model) or the
IR region (UV-IR-UV model) and discuss the model-building issues as well as
phenomenological properties in both cases. In particular, we find that the
UV-IR-UV model is not gravitationally stable and that additional mechanisms
might be required in the IR-UV-IR model in order to address flavor issues.
Collider signals of the warped KK parity are different from either the
conventional warped extra dimension without KK parity, in which the new
particles are not necessarily pair-produced, or the KK parity in flat universal
extra dimensions, where each KK level is nearly degenerate in mass. Dark matter
and collider properties of a TeV mass KK Z gauge boson as the LKP are
discussed.Comment: 35 pages, 11 figure
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