Evidence For SUSY from GUTS? Evidence For GUTS From SUSY!

Physical Review D, 1998

The significant heavy threshold effect is found in the minimal supersymmetric SU(5) model with two adjoint scalars, one of which is interpreted as a massive string mode largely decoupled from the lower-energy particle spectra. This threshold related with the generic mass splitting of the basic adjoint moduli is shown to alter properly the running of gauge couplings, thus giving a natural solution to the string-scale grand unification. The further symmetry condition of the ͑top-bottom͒ Yukawa and gauge coupling superunification at a string scale results in the perfectly working predictions for the top and bottom quark masses in the absence of any large supersymmetric threshold corrections. ͓S0556-2821͑98͒06617-X͔ PACS number͑s͒: 12.60. Jv, 11.30.Qc, 12.10.Dm Some of the euphoria caused by the first indication ͓1͔ of unification of gauge couplings extrapolated from their lowenergy values under the assumption of the simplest particle content corresponding to the minimal supersymmetric SU(5) model ͓2͔ seems to be over. In recent years many thorough tests of the standard model ͑SM͒ have been performed ͓3͔ and new precision measurement data for the strong coupling ␣ s (M Z ), weak mixing angle W ͓modified minimal subtraction scheme ͑MS͒ values͔ ␣ s ͑ M Z ͒ϭ0.119Ϯ0.004, sin 2 W ϭ0.2313Ϯ0.0003, ͑1͒

Physical Review D, 1996

The consequences of assuming the third-generation Yukawa couplings are all large and comparable are studied in the context of the minimal supersymmetric extension of the standard model. General aspects of the RG evolution of the parameters, theoretical constraints needed to ensure proper electroweak symmetry breaking, and experimental and cosmological bounds on low-energy parameters are presented. We also present complete and exact semi-analytic solutions to the 1-loop RG equations. Focusing on SU(5) or SO(10) unification, we analyze the relationship between the top and bottom masses and the superspectrum, and the phenomenological implications of the GUT conditions on scalar masses. Future experimental measurements of the superspectrum and of the strong coupling will distinguish between various GUT-scale scenarios. And if present experimental knowledge is to be accounted for most naturally, a particular set of predictions is singled out.

Progress of Theoretical and Experimental Physics, 2013

Nuclear Physics B, 2006

We construct realistic supersymmetric theories in which the correct scale for electroweak symmetry breaking is obtained without significant fine-tuning. We consider two classes of models. In one class supersymmetry breaking is transmitted to the supersymmetric standard model sector through Dirac gaugino mass terms generated by a D-term vacuum expectation value of a U (1) gauge field. In the other class the supersymmetry breaking sector is separated from the supersymmetric standard model sector in an extra dimension, and the transmission of supersymmetry breaking occurs through gauge mediation. In both these theories the Higgs sector contains two Higgs doublets and a singlet, but unlike the case for the next-to-minimal supersymmetric standard model the singlet field is not responsible for generating the supersymmetric or supersymmetry breaking mass for the Higgs doublets. These masses, as well as the mass for the singlet, are generated through gravitational-strength interactions. The scale at which the squark and slepton masses are generated is of order (1 ∼ 100) TeV, and the generated masses do not respect the unified mass relations. We find that electroweak symmetry breaking in these theories is caused by an interplay between the top-stop radiative correction and the holomorphic supersymmetry breaking mass for the Higgs doublets and that the fine-tuning can be reduced to the level of 20%. The theories have rich phenomenology, including a variety of possibilities for the lightest supersymmetric particle.

Nuclear Physics B, 1996

In the context of the standard SUSY GUT scenario, we present a detailed analysis of the softly broken finite supersymmetric grand unified theory. The model, albeit non-minimal, remains very rigid due to the requirement of finiteness. It is based on the SU (5) gauge group and is UV finite to all orders of perturbation theory. It contains three generations of the matter fields together with four pairs of Higgses. The requirement of UV finiteness fixes all the Yukawa couplings at the GUT scale. Imposing the condition of universality on the soft couplings at the Planck scale and then extending the condition of finiteness to them, one gets a completely finite unified theory above M GU T. This makes the fine-tuning procedure more meaningful and leads to the usual Minimal Supersymmetric Standard Model below M GU T. All the masses of the ordinary particles including Higgses are obtained due to the Higgs mechanism at the electro-weak scale. The hierarchy of quark and lepton masses is related to that of v.e.v.'s of the Higgs fields and is governed by the Higgs mixing matrix in the generation space. Superpartners develop their masses according to the RG equations starting from the soft terms at the Planck scale. The suggestion of complete finiteness and maximal simplicity of the unified theory leads to the connection between the initial values of soft SUSY breaking parameters, namely m 2 0 = 1/3m 2 1/2 , A t = A b = A τ = −m 1/2 , B = −m 1/2 , so that the number of free parameters is less than that of the MSSM.

The Albuquerque Meeting Vol 2, 1995

We explore the possibility of a fourth generation in the gauge-coupling-unied, minimal supersymmetric (MSSM) framework. We nd that a sequential fourth generation (with a heavy neutrino 0 ) can still t, surviving all present experimental constraints, provided b (M U ) = ( M U ) Y ukawa unication is relaxed. For the theory to remain perturbative u p t o M U , the new leptonic generation must lie within reach of LEP-II and the new b 0 ; t 0 m ust have masses within the reach o f t h e T evatron. For example, for m t > 150 GeV we nd m 0 ; m 0 < 86 GeV, m t 0 < 178, and m b 0 < 156 GeV. Experiments at Fermilab are already sensitive to the latter mass regions; we comment on direct b 0 searches and on the m t 0 ' m t case in light of new CDF data. Discovery may i n v olve n o v el decay signatures; however, CDF and LEP-II will conrm or exclude an MSSM fourth generation in the near future. ? Permanent Address. y We identify the fourth generation by the CKM matrix hierarchy: V tb ' V t 0 b 0 > V t 0 b V tb 0 . z We note that in the minimal SU(5) model, adding a R would lead to a Dirac mass that would naturally be of the order of the quarks or leptons due to the 5 f 5 H R coupling.

2012

Supersymmetric grand unified models based on the gauge group SU (5) often require in addition to gauge coupling unification, the unification of b-quark and τ-lepton Yukawa couplings. We examine SU (5) SUSY GUT parameter space under the condition of b − τ Yukawa coupling unification using 2-loop MSSM RGEs including full 1-loop threshold effects. The Yukawa-unified solutions break down into two classes. Solutions with low tan β ∼ 3 − 11 are characterized by mg ∼ 1 − 4 TeV and mq ∼ 1 − 5 TeV. Many of these solutions would be beyond LHC reach, although they contain a light Higgs scalar with m h < 123 GeV and so may be excluded should the LHC Higgs hint persist. The second class of solutions occurs at large tan β ∼ 35 − 60, and are a subset of t − b − τ unified solutions. Constraining only b − τ unification to ∼ 5% favors a rather light gluino with mg ∼ 0.5−2 TeV, which should ultimately be accessible to LHC searches. While our b − τ unified solutions can be consistent with a picture of neutralino-only cold dark matter, invoking additional moduli or Peccei-Quinn superfields can allow for all of our Yukawa-unified solutions to be consistent with the measured dark matter abundance.

Physical Review D, 2002

We make explicit the statement that Minimal Supersymmetric SU(5) has been excluded by the Super-Kamiokande search for the process p-+ [(+IJ. This exclusion is made by first placing limits on the colored Higgs triplet mass, by forcing the gauge couplings to unify. We also show that taking the superpartners of the first two generations to be very heavy in order to avoid flavor changing neutral currents, the so-called "decoupling" idea, is insufficient to resurrect the Minimal SUSY SU(5). We comment on various mechanisms to further suppress proton decay in SUSY SU(5). Finally, we address the contributions to proton decay from gauge boson exchange in the Minimal SUSY SU(5) and flipped SU(5) models.

Physics Letters B, 2004

We show that the minimal renormalizable supersymmetric SO(10) GUT with the usual three generations of spinors has a Higgs sector consisting only of a "light" 10-dimensional and "heavy" 126, 126 and 210 supermultiplets. The theory has only two sets of Yukawa couplings with fifteen real parameters and ten real parameters in the Higgs superpotential. It accounts correctly for all the fermion masses and mixings. The theory predicts at low energies the MSSM with exact R-parity. It is arguably the minimal consistent supersymmetric grand unified theory.

Physics Letters B, 1994

We explore the possibility of a fourth generation in the gauge-coupling-unied, minimal supersymmetric (MSSM) framework. We nd that a sequential fourth generation (with a heavy neutrino 0 ) can still t, surviving all present experimental constraints, provided b (M U ) = ( M U ) Y ukawa unication is relaxed. For the theory to remain perturbative u p t o M U , the new leptonic generation must lie within reach of LEP-II and the new b 0 ; t 0 m ust have masses within the reach o f t h e T evatron. For example, for m t > 150 GeV we nd m 0 ; m 0 < 86 GeV, m t 0 < 178, and m b 0 < 156 GeV. Experiments at Fermilab are already sensitive to the latter mass regions; we comment on direct b 0 searches and on the m t 0 ' m t case in light of new CDF data. Discovery may i n v olve n o v el decay signatures; however, CDF and LEP-II will conrm or exclude an MSSM fourth generation in the near future.