We review the available constraints on the low energy supersymmetry. The bulk
of the electroweak data is well screened from supersymmetric loop effects, due
to the structure of the theory, even with ...superpartners generically light,
${\cal O}(M_Z)$. The only exception are the left-handed squarks of the third
generation which have to be $\simgt {\cal O}(300$ GeV) to maintain the success
of the SM in describing the precision data. The other superpartners can still
be light, at their present experimental mass limits. As an application of the
derived constraints (supplemented by the requirement of ``naturalness'') we
discuss the predictions for the mass of the lighter MSSM Higgs boson in
specific scanarios of supersymmetry breaking.
After reviewing briefly the upper bounds on the mass of the lightest Higgs
boson in the most general unconstrained minimal supersymmetric extension of the
Standard Model, we discuss various arguments ...which reduce the parameter space
of the model and give stronger predictions for $M_{h^0}$. First, the
constraints from the presently available experimental data are summarized.
Next, the role of of several additional theoretical assumptions is studied,
after extrapolating the model to high energy scales. The most important ones
are: perturbative validity up to the GUT scale and the electroweak symmetry
breaking. A Higgs boson with $M_{h^0}<$100 GeV is predicted in several
scenarios. Its absence in that mass range will have important implications for
the parameter space of the model.
Phys.Rev.D63:054012,2001 We present the results of the complete one-loop computation of the
$B^0_{d,s}\to l^+l^-$ decay rate in the MSSM. Both sources of the FCNC, the CKM
matrix and off-diagonal ...entries of the sfermion mass matrices are considered.
Strong enhancement of the branching ratio (compared to the SM prediction) can
be obtained in the large $\tan\beta\sim m_t/m_b$ regime in which the neutral
Higgs boson ``penguin'' diagrams dominate. We make explicit the strong
dependence of this enhancement on the top squarks mixing angle in the case of
the chargino contribution and on the $\mu$ parameter in the case of the gluino
contribution. We show that, in some regions of the MSSM parametre space, the
branching ratio for this process can be as large as $10^{-(5-4)}$ respecting
all existing constraints, including the CLEO measurement of $BR(B\to
X_s\gamma)$. We also estimate, that for chargino and stop masses $\sim{\cal
O}(100$ GeV) $BR(B^0_s\to l^+l^{\prime -})$ with $ll^\prime=e\tau$ or $\mu\tau$
can be of the order of $10^{-11}$ for the still allowed values of the
off-diagonal entries in the slepton mass matrix.
We investigate the potential effects of the scalar flavour changing neutral currents that are generated e.g. in supersymmetry with \(\tan\beta\gg1\) in the \(b\to sl^+l^-\) transitions. Using the ...experimental upper limit on \(BR(B^0_s\to\mu^+\mu^-)\) we place stringent model independent constraints on the impact these currents may have on the rates \(BR(B\to X_s\mu^+\mu^-)\) and \(BR(B\to K\mu^+\mu^-)\). We find that in the first case, contrary to the claim made recently in the literature, the maximal potential effects are always smaller than the uncertainty of the Standard Model NNLO prediction, that is of order 5-15%. In the second case, the effects can be large but the experimental errors combined with the unsettled problems associated with the relevant formfactors do not allow for any firm conclusion about the detectability of a new physics signal in this process. In supersymmetry the effects of the scalar flavour changing neutral currents are further constrained by the experimental lower limit on the \(B^0_s\)-\(\bar B^0_s\) mass difference, so that most likely no detectable signal of the supersymmetry generated scalar flavour changing neutral currents in processes \(B\to X_s\mu^+\mu^-\) and \(B\to K\mu^+\mu^-\) is possible.
Acta Phys.Polon. B36 (2005) 3463-3475 In supersymmetry with large tan(beta) the decays B0(B0bar) -> l+l- are
dominated by the scalar and pseudoscalar Higgs penguin diagrams leading to
strong ...enhancement of leptonic decay rates with potentially large CP
asymmetries in the tau+tau- decay modes measurable in BELLE or BaBar
experiments. The TAUOLA tau-lepton decay library supplemented by its universal
interface can efficiently be used to search for B0(B0bar) -> tau+tau- decays,
and to investigate how the CP asymmetry is reflected in realistic experimental
observables.
We make a simple observation that if one of the right-chiral neutrinos is very heavy or its Yukawa couplings to the standard lepton doublets are negligible, so that it effectively decouples from the ...see-saw mechanism, the prediction for the baryon asymmetry of the Universe resulting from leptogenesis depends, apart from the masses \(M_1\) and \(M_2\) of the remaining two right-chiral neutrinos, only on the element \(\YY{22}\) of the neutrino Yukawa coupling. For \(M_2\simgt10M_1\) the lower bound on \(M_1\) and also on \(T_{\rm reh}\), resulting from the requirement of 'successful leptogenesis' is then significantly increased compared to the one computed recently by Buchm\"uller {\it et al.} in the most general case. Within the framework of thermal leptogenesis, the only way to lower this limit is then to allow for sufficiently small mass difference \(M_2-M_1\).
We study the contraints on non-flavour-blind soft supersymmetry breaking
terms coming from flavour and CP violating processes in the presence of
hierarchical Yukawa couplings, and quantify how much ...these constraints are
weakened in the regions of the MSSM parameter space characterized by heavy
gauginos and multi-TeV sfermion masses, respectively. We also study the
inverted sfermion mass hierarchy scenario in the context of D-term
supersymmetry breaking, and show that generic hierarchical Yukawa couplings
with arbitrary phases require first generation squarks in the few 10 TeV range.
We consider the electroweak theory with an additional Higgs triplet at one loop using the hybrid renormalization scheme based on \(\alpha_{\rm EM}\), \(G_F\) and \(M_Z\) as input observables. We show ...that in this scheme loop corrections can be naturally split into the Standard Model part and corrections due to ``new physics''. The latter, however do not decouple in the limit of infinite triplet mass parameter, if the triplet trilinear coupling to SM Higgs doublets grows along with the the triplet mass. In electroweak observables computed at one loop this effect can be attributed to radiative generation in this limit of a nonvanishing vacuum expectation value of the triplet. We also point out that whenever tree level expressions for the electroweak observables depend on vacuum expectation values of scalar fields other than the Standard Model Higgs doublet, tadpole contribution to the ``oblique'' parameter \(T\) should in principle be included. In the Appendix the origin of nondecoupling is discussed on the basis of symmetry principles in a simple scalar field theory.
Phys.Rev.D71:055004,2005 We reconsider models of fermion masses and mixings based on a gauge anomalous
horizontal U(1) symmetry. In the simplest model with a single flavon field and
horizontal ...charges of the same sign for all Standard Model fields, only very
few charge assignements are allowed when all experimental data, including
neutrino oscillation data, is taken into account. We show that a precise
description of the observed fermion masses and mixing angles can easily be
obtained by generating sets of the order one parameters left unconstrained by
the U(1) symmetry. The corresponding Yukawa matrices show several interesting
features which may be important for flavour changing neutral currents and CP
violation effects in supersymmetric models.
