Neutrino unification Chankowski, P H; Ioannisian, A N; Pokorski, S ...
Physical review letters,
04/2001, Letnik:
86, Številka:
16
Journal Article
Recenzirano
Odprti dostop
Present neutrino data are consistent with neutrino masses arising from a common seed at some "neutrino unification" scale M(X). Such a simple theoretical ansatz naturally leads to quasidegenerate ...neutrinos that could lie in the electron-volt range with neutrino mass splittings induced by renormalization effects associated with supersymmetric thresholds. In such a scheme the leptonic analog of the Cabibbo angle straight theta(middle dot in circle) describing solar neutrino oscillations is nearly maximal. Its exact value is correlated with the smallness of straight theta(reactor). The two leading mass-eigenstate neutrinos present in nu(e) form a pseudo-Dirac neutrino, avoiding conflict with neutrinoless double beta decay.
We compute the low energy threshold corrections to neutrino masses and mixing in the standard model (SM) and its minimal supersymmetric version, using the effective theory technique. We demonstrate ...that they stabilize the results for neutrino masses and mixing with respect to the choice of the scale to which the renormalization group (RG) equation is integrated. (This confirms the correctness of the recent re-derivation of the RGE for the SM in hep-ph/0108005.) Since, as is known, those corrections are potentially very important for phenomenology we derive for them the explicit formulae that can be applied to specific models of neutrino masses and mixing.
We propose a novel mechanism of electroweak symmetry breaking in supersymmetric models, as the one recently discussed by Birkedal, Chacko and Gaillard, in which the Standard Model Higgs doublet is a ...pseudo-Goldstone boson of some global symmetry. The Higgs mass parameter is generated at one-loop level by two different, moderately fine-tuned sources of the global symmetry breaking. The mechanism works for scalar superpartner masses of order 10 TeV, but gauginos can be light. The scale at which supersymmetry breaking is mediated to the visible sector has to be low, of order 100 TeV. Fine-tuning in the scalar potential is at least two orders of magnitude smaller than in the MSSM with similar soft scalar masses. The physical Higgs boson mass is (for tanβ≫1) in the range 120–135 GeV.
Flavour violation in general supergravity Chankowski, Piotr H.; Lebedev, Oleg; Pokorski, Stefan
Nuclear physics. B,
06/2005, Letnik:
717, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We reappraise the flavour changing neutral currents (FCNC) problem in string-derived supergravity models. We overview and classify possible sources of flavour violation and find that the problem ...often does not arise in classes of models which generate hierarchical Yukawa matrices. In such models, constraints from the
K- and
D-meson systems leave room for substantial flavour non-universality of the soft terms. The current
B-physics experiments only begin to probe its natural range. Correlations among different observables can allow one to read off the chirality structure of flavour violating sources. We briefly discuss the lepton sector where the problem of FCNC is indeed serious and perhaps points at an additional symmetry or flavour universality.
We present an up-to-date analysis of the constraints the precision data impose on the (CP-conserving) Two Higgs Doublet Model of type II with emphasis on the possible existence of very light neutral ...(pseudo)scalar Higgs boson with mass below 20–30 GeV. We show that even in the presence of such light particles, the 2HDM(II) can describe the electroweak data with the precision comparable to that given by the SM. Particularly interesting lower limits on the mass of the lighter neutral CP-even scalar \(h^0\) are obtained in the scenario with light CP-odd Higgs boson \(A^0\) and large \(\tan\beta\).
Haggling over the fine-tuning price of LEP Chankowski, Piotr H.; Ellis, John; Olechowski, Marek ...
Nuclear physics. B,
04/1999, Letnik:
544, Številka:
1
Journal Article
Recenzirano
We amplify previous discussions of the fine-tuning price to be paid by supersymmetric models in the light of LEP data. The whole range of tan β is discussed, including large values. In the minimal ...supergravity model with universal gaugino and scalar masses, a small fine-tuning price is possible only for intermediate values of tan β and for a small range of superpartner masses. Moreover, the fine-tuning price in this region is significantly higher if we require β-τ Yukawacoupling unification. We interpret the significant increase after LEP of the fine-tuning price in the minimal supergravity model as a message for theory and not for the experiment. For possible choices of low-energy parameters in the MSSM consistent with present experimental constraints and, optionally, with some other theoretical assumptions such as ifb-τ Yukawa-coupling unification, a measure of the amount of fine tuning becomes an interesting criterion for the naturalness of various theoretical models for mass terms in the MSSM Lagrangian. In particular, we emphasize that the fine-tuning price will depend on the actual solution to the μ problem. We illustrate the relevance of this fact by considering a simple ansatz of linear dependence of μ on
M
1
2
or
A
0, showing that big price reductions are obtained in such cases. Significant price reductions are also obtained for large tan β if non-universal soft Higgs mass parameters are allowed. We also study input relations between MSSM parameters suggested in some interpretations of string theory: the price may depend significantly on these inputs, potentially providing guidance for building string models. However, in the available models the fine-tuning price may not be reduced significantly.
The fine-tuning price of LEP Chankowski, Piotr H; Ellis, John; Pokorski, Stefan
Physics letters. B,
03/1998, Letnik:
423, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We quantify the amount of fine tuning of input parameters of the Minimal Supersymmetric Extension of the Standard Model (MSSM) that is needed to respect the lower limits on sparticle and Higgs masses ...imposed by precision electroweak measurements at LEP, measurements of
b→
X
s
γ, and searches at LEP 2. If universal input scalar masses are assumed in a gravity-mediated scenario, a factor of ≳180 is required at tan
β∼1.65, decreasing to ∼20 at tan
β∼10. The amount of fine tuning is not greatly reduced if non-universal input scalar Higgs masses are allowed, but may be significantly reduced if some theoretical relations between MSSM parameters are assumed.
We present predictions for flavour-violating charged-lepton decays induced by the seesaw mechanism implemented within the constrained minimal supersymmetric standard model (CMSSM) with universal ...input soft supersymmetry breaking terms. We assume that one heavy singlet neutrino almost decouples from the seesaw mechanism, as suggested by the pattern of light neutrino masses and mixing angles. This is suggested independently by sneutrino inflation with a low reheating temperature,
T
RH
≲10
7
GeV
, so as to avoid overproducing gravitinos. This requirement further fixes the mass of the weakly-coupled sneutrino, whose decays may lead to leptogenesis. We find that
BR(
μ→
eγ)≳10
−13 but
BR(
τ→
μγ)≲10
−9 in the bulk of the acceptable parameter space, apart from a few isolated points. The ratio
BR(
μ→
eγ)/
BR(
τ→
eγ) depends on only one complex parameter, and is particularly interesting to compare with experiment.
Recently, the LEP collaborations have reported a lower bound on a Standard Model-like Higgs boson of order 89 GeV. We discuss the implications of this bound for the minimal supersymmetric extension ...of the Standard Model (MSSM). In particular, we show that the lower bound on tan
β, which can be obtained from the presently allowed Higgs boson mass value, becomes stronger than the one set by the requirement of perturbative consistency of the theory up to scales of order
M
GUT (associated with the infrared fixed-point solution of the top quark Yukawa coupling) in a large fraction of the allowed parameter space. The potentiality of future LEP2 searches to further probe the MSSM parameter space is also discussed.
We investigate the potential effects of the scalar flavor changing neutral currents that are generated e.g. in supersymmetry with \(\tan\beta\gg1\) in the \(b\rightarrow sl^ + l^-\) transitions. ...Using the experimental upper limit on \({\mathrm {BR}}(B^0_s\rightarrow\mu^ + \mu^-)\) we place stringent model independent constraints on the impact these currents may have on the rates \({\mathrm {BR}}(B\rightarrow X_s\mu^ + \mu^-)\) and \({\mathrm {BR}}(B\rightarrow K\mu^ + \mu^-)\). 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 form factors 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 flavor changing neutral currents are further constrained by the experimental lower limit on the B0s-\(\bar B^0_s\) mass difference, so that most likely no detectable signal of the supersymmetry generated scalar flavor changing neutral currents in the processes \(B\rightarrow X_s\mu^ + \mu^-\) and \(B\rightarrow K\mu^ + \mu^-\) is possible.
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