18 research outputs found
CP Violation In Single Top Production And Decay Via p p-bar -> t b-bar +X -> W^+ b b-bar +X Within The MSSM: A Possible Application For Measuring \arg(A_t) At Hadron Colliders
CP-nonconserving effects in the reaction p p-bar -> t b-bar +X -> W^+ b b-bar
+X, driven by the supersymmetric CP-odd phase of the stop trilinear soft
breaking term, \arg(A_t), are studied. We discuss the CP-nonconserving effects
in both production and the associated decay amplitudes of the top. We find
that, within a plausible low energy scenario of the MSSM and keeping the
neutron electric dipole moment below its current limit, a CP-violating
cross-section asymmetry as large as 2-3% can arise if some of the parameters
lie in a favorable range. A partial rate asymmetry originating only in the top
decay t -> W^+ b is found to be, in general, below the 0.1% level which is
somewhat smaller than previous claims. For a low \tan\beta of order one the
decay asymmetry can reach at the most ~0.3%. This (few) percent level overall
CP-violating signal in p p-bar -> t b-bar +X -> W^+ b b-bar +X might be within
the reach of the future 2(4) TeV pp-bar Tevatron collider that may be able to
produce ~10000(~30000) such tb-bar events with an integrated luminosity of 30
fb^{-1}. In particular, it may be used to place an upper bound on \arg(A_t) if
indeed \arg(\mu) -> 0, as implied from the present experimental limit on the
neutron electric dipole moment. The partial rate asymmetry in the top decay
(~few \times 10^{-3}) may also be within the reach of the LHC with ~10^7 pairs
of tt-bar produced, provided detector systematics are sufficiently small. We
also show that if the GUT-scale universality of the soft breaking trilinear
terms is relaxed, then the phases associated with \arg A_u and \arg A_d can
take values up to ~few \times 10^{-1} even with squarks and gluino masses of
several hundred GeV's without contradicting the experimental limit on the
neutron electric dipole moment.Comment: 39 pages, plain latex, 20 figures embadded in the text using epsfi
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric Model
We determine the neutralino and chargino masses in the MSSM at one-loop. We
perform a Feynman diagram calculation in the on-shell renormalization scheme,
including quark/squark and lepton/slepton loops. We find generically the
corrections are of order 6%. For a 20 GeV neutralino the corrections can be
larger than 20%. The corrections change the region of
parameter space which is ruled out by LEP data. We demonstrate that, e.g., for
a given and the lower limit on the parameter can shift
by 20 GeV.Comment: 11 pages, JHU-TIPAC-930030, PURD-TH-93-13, uses epsf.sty, 6 uuencoded
postscript figures, added one sentence and a referenc
Inverting the Supersymmetric Standard Model Spectrum: from Physical to Lagrangian Ino Parameters
We examine the possibility of recovering the supersymmetric (and soft
supersymmetry breaking) Lagrangian parameters as direct {\em analytical}
expressions of appropriate physical masses, for the unconstrained (but CP and
R-parity conserving) minimal supersymmetric standard model. We concentrate
mainly on the algebraically non-trivial "inversion" for the ino parameters, and
obtain, for given values of , simple analytical expressions for the
, and parameters in terms of three arbitrary input physical
masses, namely either two chargino and one neutralino masses, or alternatively
one chargino and two neutralino masses. We illustrate and discuss in detail the
possible occurrence of ambiguities in this reconstruction. The dependence of
the resulting ino Lagrangian parameters upon physical masses is illustrated,
and some simple generic behaviour uncovered in this way. We finally briefly
sketch generalizing such an inversion to the full set of MSSM Lagrangian
parameters.Comment: Latex, 28 pages, 6 figures, 1 table, some typos corrected, one
paragraph extended in section 4.2. Version to appear in Phys. Rev.
Loop induced Higgs and Z boson couplings to Neutralinos and implications for collider and Dark Matter searches
We calculate the one-loop induced couplings of two gaugino-like neutralinos
to the and Higgs bosons in the Minimal Supersymmetric Standard Model. These
couplings, which vanish at the tree level, can be generated through loops
involving fermions and sfermions. We show that, while the neutralino
contribution to the invisible boson decay width remains small, the loop
induced couplings to the lightest Higgs boson might be sufficiently large to
yield a rate of invisible decays of this Higgs boson that should be detectable
at future colliders. We also study the implications of these couplings
for direct searches of Dark Matter and show that they can modify appreciably
the neutralino-nucleon elastic cross section for some parameter range.Comment: LaTeX with 6 (e)ps and 2 axodraw figures, 25 pages in total;
axodraw.sty is included v.2: Added one figure and some discussions; version
to appear in PR
Supersymmetric Scenarios with Dominant Radiative Neutralino Decay
The radiative decay of the next-to-lightest neutralino into a lightest
neutralino and a photon is analyzed in the MSSM. We find that significant
regions of the supersymmetric parameter space with large radiative BR's (up to
about 100%) do exist. The radiative channel turns out to be enhanced when the
neutralino tree-level decays are suppressed either "kinematically" or
"dynamically". In general, in the regions allowed by LEP data and not
characterized by asymptotic values of the SuSy parameters, the radiative
enhancement requires tan beta ~= 1 and/or M_1 ~= M_2, and negative values of
\mu. We present typical specific scenarios where these "necessary" conditions
are fulfilled, relaxing the usual relation M_1=(5/3)*tan^2(th_W)*M_2. The
influence of varying the stop masses and mixing angle when the radiative decay
is enhanced is also considered. Some phenomenological consequences of the above
picture are discussed.Comment: 32 pages, LaTeX file + 23 figures embedded with epsf.sty. In this
revised version, Eq.(3) plus some related notations and text passages have
been changed. Minor error corrected in Fig.12(a). The numerical analysis and
the conclusions of the paper are not affected. (Includes the erratum to
appear in Phys. Rev. D.) Source and ps files are also available at
ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1148/ or at
http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1
The neutralino projector formalism for complex SUSY parameters
We present a new formalism describing the neutralino physics in the context
of the minimal supersymmetric model (MSSM), where CP violation induced by
complex and parameters is allowed. The formalism is based on the
construction of neutralino projectors, and can be directly generalized to
non-minimal SUSY models involving any number of neutralinos. It extends a
previous work applied to the real SUSY parameter case. In MSSM, the method
allows to describe all physical observables related to a specific neutralino,
in terms of its
CP eigenphase and three complex numbers called its "reduced projector
elements".
As the experimental knowledge on the neutralino-chargino sectors will be
being accumulated, the problem of extracting the various SUSY parameters will
arise. Motivated by this, we consider various scenarios concerning the
quantities that could be first measured. Analytical disentangled expressions
determining the related SUSY parameters from them, are then derived, which also
emphasize the efficiency of the formalism.Comment: Version accepted in Phys. Rev. D. e-mail: [email protected]
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]
Low energy supersymmetry with a neutralino LSP and the CDF ee\gamma\gamma + missing E_T event
We present a refined and expanded analysis of the CDF ee\gamma\gamma + \Et
event as superpartner production, assuming the lightest neutralino is the
lightest supersymmetric particle. A general low-energy Lagrangian is
constrained by a minimum cross section times branching ratio into two electrons
and two photons, kinematics consistent with the event, and LEP1-LEP130 data. We
examine how the supersymmetric parameters depend on the kinematics, branching
ratios and experimental predictions with a selectron interpretation of the
event, and discuss to what extent these are modified by other interpretations.
Predictions for imminent CERN LEP upgrades and the present and future Fermilab
Tevatron are presented. Finally, we briefly discuss the possible connection to
other phenomena including a light stop, the neutralino relic density, the shift
in and the associated shift in , and implications for the form
of the theory.Comment: 57 pages, LaTeX, uses epsf.sty, 19 figures. Version accepted for
publication in Phys. Rev. D, with minor changes and a few clarification
Higgs decay with monophoton + MET signature from low scale supersymmetry breaking
We study the decay of a standard model-like Higgs boson into a gravitino and
a neutralino, which subsequently decays promptly into another gravitino and a
photon. Such a decay can be important in scenarios where the supersymmetry
breaking scale is of the order of a few TeV, and in the region of low
transverse momenta of the photon, it may provide the dominant contribution to
the final state with a photon and two gravitinos. We estimate the relevant
standard model backgrounds and the prospects for discovering this Higgs decay
through a photon and missing transverse energy signal at the LHC in terms of a
simplified model. We also give an explicit model with manifest, but
spontaneously broken, supersymmetry in which the usual MSSM soft terms are
promoted to supersymmetric operators involving a dynamical goldstino
supermultiplet. This model can give rise to a SM-like CP-even neutral Higgs
particle with a mass of 125 GeV, without requiring substantial radiative
corrections, and with couplings sufficiently large for a signal discovery
through the above mentioned Higgs decay channel with the upcoming data from the
LHC.Comment: 28 pages, 5 figures, 4 tables; v2: updated to JHEP version,
references adde
Light Stop Decay in the MSSM with Minimal Flavour Violation
In supersymmetric scenarios with a light stop particle and a
small mass difference to the lightest supersymmetric particle (LSP) assumed to
be the lightest neutralino, the flavour changing neutral current decay
can be the dominant decay channel and can
exceed the four-body stop decay for certain parameter values. In the framework
of Minimal Flavour Violation (MFV) this decay is CKM-suppressed, thus inducing
long stop lifetimes. Stop decay length measurements at the LHC can then be
exploited to test models with minimal flavour breaking through Standard Model
Yukawa couplings. The decay width has been given some time ago by an
approximate formula, which takes into account the leading logarithms of the MFV
scale. In this paper we calculate the exact one-loop decay width in the
framework of MFV. The comparison with the approximate result exhibits
deviations of the order of 10% for large MFV scales due to the neglected
non-logarithmic terms in the approximate decay formula. The difference in the
branching ratios is negligible. The large logarithms have to be resummed. The
resummation is performed by the solution of the renormalization group
equations. The comparison of the exact one-loop result and the tree level
flavour changing neutral current decay, which incorporates the resummed
logarithms, demonstrates that the resummation effects are important and should
be taken into account.Comment: 29 page