A detailed comparison of LEP data with the predictions of the minimal supersymmetric SU(5) GUT (original) (raw)
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Combined fit of low energy constraints to minimal supersymmetry and discovery potential at LEP II
Zeitschrift f�r Physik C Particles and Fields, 1996
Within the Constrained Minimal Supersymmetric Standard Model (CMSSM) it is possible to predict the low energy gauge couplings and masses of the 3. generation particles from a few parameters at the GUT scale. In addition the MSSM predicts electroweak symmetry breaking due to large radiative corrections from Yukawa couplings, thus relating the Z 0 boson mass to the top quark mass. From a χ 2 analysis, in which these constraints are considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. The recently measured top quark mass prefers two solutions for the mixing angle in the Higgs sector: tan β in the range between 1 and 3 or alternatively tan β ≈ 15 − 50. For both cases we find a unique χ 2 minimum in the parameter space. From the corresponding most probable parameters at the GUT scale, the masses of all predicted particles can be calculated at low energies using the RGE, albeit with rather large errors due to the logarithmic nature of the running of the masses and coupling constants. Our fits include full second order corrections for the gauge and Yukawa couplings, low energy threshold effects, contributions of all (s)particles to the Higgs potential and corrections to m b from gluinos and higgsinos, which exclude (in our notation) positive values of the mixing parameter in the Higgs potential µ for the large tan β region. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of the b-quark into sγ and the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Supersymmetric Particle (LSP) not to overclose the universe. For the low tan β solution these additional constraints can be fulfilled simultaneously for quite a large region of the parameter space. In contrast, for the high tan β solution the correct value for the b → sγ rate is obtained only for small values of the gaugino scale and electroweak symmetry breaking is difficult, unless one assumes the minimal SU(5) to be a subgroup of a larger symmetry group, which is broken between the Planck scale and the unification scale. In this case small splittings in the Yukawa couplings are expected at the unification scale and electroweak symmetry breaking is easily obtained, provided the Yukawa coupling for the top quark is slightly above the one for the bottom quark, as expected e.g. if the larger symmetry group would be SO(10). For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. The highest LEP II energies (205 GeV) are just high enough to cover a large region of the preferred parameter space, both for the low and high tan β solutions. For low tan β the production of the lightest Higgs boson, which is expected to have a mass below 115 GeV, is the most promising channel, while for large tan β the production of Higgses, charginos and/or neutralinos covers the preferred parameter space.
Precise Predictions for the Masses and Couplings in the Minimal Supersymmetric Standard Model
1995
We present selected results of our program to determine the masses, gauge couplings, and Yukawa couplings of the minimal supersymmetric model in a full oneloop calculation. We focus on the precise prediction of the strong coupling α s (M Z ) in the context of supersymmetric unification. We discuss the importance of including the finite corrections and demonstrate that the leading-logarithmic approximation can significantly underestimate α s (M Z ) when some superpartner masses are light. We show that if GUT thresholds are ignored, and the superpartner masses are less than about 500 GeV, the prediction for α s (M Z ) is quite large. We impose constraints from nucleon decay experiments and find that minimal SU(5) GUT threshold corrections increase α s (M Z ) over most of the parameter space. We also consider the missing-doublet SU(5) model and find that it predicts preferred values for the strong coupling, even for a very light superpartner spectrum. We briefly discuss predictions for the bottom-quark mass in the small tan β region. * M 0 is the universal scalar mass, M 1/2 is the universal gaugino mass, and A 0 is the universal A-term. † See Ref.
Physical Review D, 2002
The decoupling properties of the Higgs sector in the Minimal Supersymmetric Standard Model (MSSM) imply that a light CP-even Higgs boson discovered at the Tevatron or LHC may closely resemble the Standard Model (SM) Higgs boson. In this paper, we investigate how precision measurements of Higgs properties at a Linear Collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson. We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle α and tan β-enhanced vertex corrections. The general expectation is that the Higgs couplings to W + W − , ZZ, cc and tt should quickly approach their SM values for increasing CP-odd Higgs mass m A , while the couplings to bb and τ + τ − do so more slowly. Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit. For a wide range of MSSM parameters, the LC is sensitive to m A ∼ 600 GeV almost independently of tan β. For large values of tan β and some specific choices of MSSM parameters [e.g., A t µ < 0 and |A t | |µ| O(M S)], one of the CP-even Higgs bosons can be SM-like independent of the value of m A. In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.
Using gauge coupling unification and proton decay to test minimal supersymmetric SU (5)
Physics Letters B, 1995
We derive a one-loop expression, including all thresholds, for the mass of the proton decay mediating color triplets, M D c , in minimal supersymmetric SU(5). The result for M D c does not depend on other heavy thresholds or extra representations with SU(5) invariant masses which might be added to the minimal model. We numerically correct our result to two-loop accuracy. Choosing inputs to maximize M D c and τ P , within experimental limits on the inputs and a 1 T eV naturalness bound, we derive a strict bound α 3 > 0.117. We discuss how this bound will change as experimental limits improve. Measurements of α 3 from deep inelastic scattering and the charmonium spectrum are below the bound α 3 > 0.117 by more than 3σ. We briefly review several ideas of how to resolve the discrepancy between these low values of α 3 and the determinations of α 3 from LEP event shapes.
Effects of the Variation of SUSY Breaking Scale on Yukawa and Gauge Couplings Unification
Advances in High Energy Physics, 2015
The present analysis addresses an interesting primary question on how do the gauge and Yukawa couplings unification scales vary with varying SUSY breaking scalesms, assuming a single scale for all supersymmetric particles. It is observed that the gauge coupling unification scale increases withmswhereas third-generation Yukawa couplings unification scale decreases withms. The rising of the unification scale and also the mass of the color triplet multiplets is necessary to increase the proton decay lifetime; the analysis is carried out with two-loop RGEs for the gauge and Yukawa couplings within the minimal supersymmetric SU(5) model, while ignoring for simplicity the threshold effects of the heavy particles, which could be as large as a few percentages.
Physics impact of ILC Higgs coupling measurements: The effect of theory uncertainties
Physical Review D, 2007
We study the effect of theoretical and parametric uncertainties on the ability of future Higgs coupling measurements at the International Linear Collider (ILC) to reveal deviations from the Standard Model (SM). To quantify the impact of the experimental and theoretical uncertainties we plot ∆χ 2 = 25 contours for the deviations between the SM Higgs couplings and the light Higgs couplings in the m max h benchmark scenario of the Minimal Supersymmetric Standard Model (MSSM). We consider the theoretical uncertainties in the SM Higgs decay partial widths and production cross section and the parametric uncertainties in the bottom and charm masses and the strong coupling α s. We find that the impact of the theory and parametric uncertainties is negligible in the first phase of ILC data-taking (500 fb −1 at 350 GeV centre-of-mass energy), while in the second phase (1000 fb −1 at 1000 GeV) they reduce the "reach" in the CP-odd MSSM Higgs mass M A by about 15%. No single source of theoretical or parametric uncertainty dominates the effect, so that improving the situation will require advances in multiple theoretical calculations.
Advances in High Energy Physics, 2018
Nonsupersymmetric minimal SU(5) with Higgs representations 24 퐻 and 5 퐻 and standard fermions in 5 퐹 ⊕ 10 퐹 is well known for its failure in unification of gauge couplings and lack of predicting neutrino masses. Like standard model, it is also affected by the instability of the Higgs scalar potential. We note that extending the Higgs sector by 75 퐻 and 15 퐻 not only leads to the popular type-II seesaw ansatz for neutrino masses with a lower bound on the triplet mass Δ > 2 × 10 9 GeV, but also achieves precision unification of gauge couplings without proliferation of nonstandard light Higgs scalars or fermions near the TeV scale. Consistent with recent LUX-2016 lower bound, the model easily accommodates a singlet scalar WIMP dark matter near the TeV scale which resolves the vacuum stability issue even after inclusion of heavy triplet threshold effect. We estimate proton lifetime predictions for → + 0 including uncertainties due to input parameters and threshold effects due to superheavy Higgs scalars and superheavy ±4/3 , ±1/3 gauge bosons. The predicted lifetime is noted to be verifiable at Super Kamiokande and Hyper Kamiokande experiments.
The Higgs boson mass as a probe of the minimal supersymmetric standard model
Physics Letters B, 1998
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 GU T (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.
Higgs couplings at the end of 2012
Journal of High Energy Physics, 2013
Performing a fit to all publicly available data, we analyze the extent to which the latest results from the LHC and Tevatron constrain the couplings of the Higgs bosonlike state at ∼ 125 GeV. To this end we assume that only Standard Model (SM) particles appear in the Higgs decays, but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM are free parameters. We also assume that the leptonic couplings relative to the SM are the same as for the down-quark, and a custodial symmetry for the V = W, Z couplings. In the simplest approach, the effective Higgs couplings to gluons and photons are computed in terms of the previous parameters. This approach is also applied to Two-Higgs-Doublet Models of Type I and Type II. However, we also explore the possibility that the net Higgs to gg and γγ couplings have extra loop contributions coming from Beyond-the-Standard Model physics. We find that the SM pvalue ∼ 0.5 is more than 2σ away from fits in which: a) there is some non-SM contribution to the γγ coupling of the Higgs; or b) the sign of the top quark coupling to the Higgs is opposite that of the W coupling. In both these cases p-values ∼ 0.9 can be achieved. Since option b) is difficult to realize in realistic models, it would seem that new physics contributions to the effective couplings of the Higgs are preferred.