Supersymmetric Grand Unified Models Research Articles

The Georgi-Jarlskog Mass Relation in a Supersymmetric Grand Unified Model

We construct a supersymmetric grand unified (GUT) model in which the Georgi-Jarlskog mass relation at the GUT scale (∼1016GeV), mb ≃mτ, ms ≃mµ/3 and md ≃3me can be naturally realized within the context of the missing-partner mechanism. Our model assumes the existence of a pair of superheavy families at the GUT scale.

Peccei-Quinn symmetry and suppression of nucleon-decay rates in SUSY-GUTs

We construct a supersymmetric grand unified model with a Peccei-Quinn symmetry. The dimension-five operators for baryon-number violation are suppressed by the Peccei-Quinn symmetry. We show that the dimension-five operators can be made much below the upper bound from the present nucleon-decay experiments, keeping superparticles at ⪷ 1 TeV which may be necessity for the supersymmetry to be a solution to the mass hierarchy problem. However, the dimension-five operators cannot be arbitrarily small due to the requirement of the unification of gauge coupling constants.

Probing the desert using gauge coupling unification

Abstract We present analytic one-loop expressions for sin 2 θ w , the unification scale M x , and the coupling at the unification scale α ( M x ), in supersymmetric grand-unified models with arbitrary intermediate scales. We correct these expressions to agree with a two-loop calculation for central values of the inputs. Our general results quickly determine whether a particular model has hope of compatibility with the low energy couplings. We then apply these results to traditional supersymmetric SU (5) and to supersymmetric flipped SU (5) × U (1). These results translate into a narrow bound on a function of the extra intermediate scales. In particular, we conclude that even allowing for the experimental uncertainties in low-energy couplings and effects of supersymmetric and Higgs thresholds, traditional supersymmetric SU (5) grand unification without extra thresholds is about one standard deviation away from the measured value of sin 2 θ w . We also calculate the range of proton decay in minimal flipped SU (5) × U (1) allowing for uncertainties in the low-energy couplings and the effects of supersymmetric and Higgs thresholds. Non-observation of proton decay gives a bound on another function of additional intermediate scales beyond the minimal model.

Determination Of Gut Scale And A Class Of No Scale Susy Guts

The GUT scale is determined in supersymmetric grand unified models. It is obtained naturally that there is only one heavy scale. So we can construct a class of no scale SUSY GUTs in which the gravitino mass and is determined by radiative corrections.

Left-right symmetry breaking scale and supersymmetry in unified theories

We propose a class of supersymmetric grand unified models where parity and SU(2) R breaking scales are widely separated and compatible with a low-lying mass for the right-handed gauge boson W R. The intermediate symmetry SU(4) c ×SU(2) L×SU(2) R and Higgs content are uniquely fixed if m W R < 10 9 GeV. The unification scale lies within an order of magnitude below the Planck mass.

Transition from weak to strong coupling in QCD and in grand unified models at high temperature

We investigate the weak-coupling expansion at high temperature for relativistic quantum field theories. Boson self-energies generally acquire a non-analytic dependence on the coupling due to the infrared plasmon effect. We show how to sum loops within loops for such thermodynamic quantities as pressure and energy density. Recent high-precision Monte Carlo simulations of quarkless SU(3) gauge theory are compared to the weak-coupling expansion and an excellent agreement is obtained for the high-temperature phase. Weak-coupling calculations are also carried out for supersymmetric grand unified models. We find indications that such models are often strongly coupled already at the unification temperature. This may have a significant effect on models of the early universe.

Strong coupling phase transitions in supersymmetric grand unified models

The determination of the temperature at which a grand unified model becomes strongly coupled should be based upon a physical quantity such as the screening lenght rather than the ad hoc condition that the opening becomes O(1). I use a recent calculation of this screening length (the inverse electric mass) to discuss some aspects of strong coupling behavior in the cosmology of supersymmetric grand unified models. Significant effects may occur in a variety of cases. An interesting possibilit is that there may be a pair of confining and deconfining phase transitions at a temperature as low as the supersymmetry breaking scale (O(TeV)). I present illustrative examples for these effects.

Possible candidates for finite supersymmetric grand unified theories

A realistic finite grand unified model has to accomodate at least three generations of ordinary fermions. When this criterion is imposed, we found that only a few models of the SU( N), SO(2 N), SO(2 N+1) and exceptional groups can survive as candidates for possible realistic finite supersymmetric grand unified models. All possible solutions are obtained, but the SU(5) model is excluded.

Possible Candidates for Finite Supersymmetric Grand Unified Theories

A realistic finite grand unified model has to accommodate at least three generations of ordinary fermions. When this criterion is imposed, we found that only few models of and exceptional groups can survive as candidates for possible realistic finite supersymmetric grand unified models. All possible solutions are obtianed, but the model is excluded.

Constraints on a system of two neutral fermions from cosmology

Using the standard model of cosmology we study the evolution of the population of a coupled system of two neutral fermions in which the lighter one is stable. During the expansion their population can be frozen at a certain level which makes them contribute to the mass density of the universe. The details of the freezing depend crucially on the couplings and on the masses of these two fermions, so that, comparison with the measured mass density in the universe gives constraints on the parameters of the physical system we examine. We discuss in detail different configurations for the couplings among these fermions; in particular in the case of large mixing we obtain restrictive bounds on both masses. Our study is relevant to supersymmetric grand unified models which predict the occurance of light interacting neutral fermions, particularly higgsinos.

The sliding singlet

Supersymmetric grand unified models with a sliding singlet are considered. We review the argument that the sliding does not work in models with large supersymmetry breaking. Then we consider the possibility of using a sliding singlet with low-energy supersymmetry breaking. A number of problems with such a program are noted and illustrated in simple examples. Using the experience gained from these examples a realistic model is constructed and analyzed.

Supergravity and upper bound on scale of supersymmetry breaking

In locally supersymmetric grand unified models we show a rather model-independent upper bound 3·1011 GeV for the scale of supersymmetry breaking, which is derived by consideringSU2×U1 breaking at electroweak mass scale. This bound necessarily implies the existence of new particles (superpartners) below 104 GeV.

Quantum versus gravitational effects in supersymmetric theories

We consider what happens when certain globally supersymmetric grand unified models are coupled to N = 1 supergravity. Treating only leading (i.e. tree level) gravitational effects while treating non-gravitational effects to all orders, we show how the original globally supersymmetric theory is recovered as M p → ∞. This allows us to compare the importance of various gravitational and non-gravitational effects. A potentially realistic model is presented and analyzed. Possible quantum gravitational effects are mentioned.

Constraints on the stability of mass hierarchies in supergravity

We study supersymmetric grand unified models coupled to N = 1 supergravity with a gauge hierarchy induced by the breakdown of local supersymmetry, and a low energy scale given by the gravitino mass. Certain conditions must be fulfilled for this hierarchy to remain stable in perturbation theory. We discuss these constraints and show that most presently available models do not have a stable hierarchy.

SuperB production, matter stability and gauge hierarchy in SUSY GUTs

We analyze the connections between the problems of the cosmological baryon asymmetry (CBA), matter stability and mass hierarchy in supersymmetric Grand Unified models. We show that the typical delay of the phase transition in supersymmetric theories as well as a natural solution to the triplet-doublet Higgs hierarchy problem imply baryon production after the Grand Unification phase transition which in a wide class of SUSY GUTs takes place atT∼109–1010 GeV. Light Higgs colour triplets as a means of producing the CBA are discussed in detail. An alternative mechanism involving a singlet superfield is proposed leading to striking consequences in proton decay with the appearance of (B+L) conserving modes with a muon and a kaon in the final state:n→μ− K +,p μ 2212;π+ K + and a lifetime of 1031 years.

Phenomenological predictions of the SO(10) supersymmetric grand unified model

The phenomenological predictions of the SO(10) supersymmetric grand unified model (SO(10) SGUM) for the mass scales M 1, M 2, weak angle ifsin 2 θ w, quark-leptons mass ratios m b m τ , m t m b , m τ m ν τ and proton lifetime τ p are estimated by using renormalization group analysis at one-loop level. In contrast with SU(5) SGUM, we find that the SO(10) SGUM still has problems with τ p but not with sin 2 θ w and m b m τ , which may suggest that supersymmetry would be bro at a mass scale ⪆10 7 GeV .

Fractionally Charged Particles as Evidence for Supersymmetry

Supersymmetric grand unified models with fractionally charged color singlets ("fractons") are considered. It is shown that the minimal supersymmetrized fracton model, which occurs in SU(7), gives a value of ${sin}^{2}\ensuremath{\theta}({m}_{W})$ that is naturally lower than the minimal SU(5) supersymmetric grand unified theory prediction, and can be in agreement with experiment for fracton charge $q=\frac{e}{3}$.

Monopole supression and baryon production in cosmologies based on Witten's upside down hierarchy model

Abstract We demonstrate that the supersymmetric grand unified models proposed by Witten do not lead to an overproduction of superheavy monopoles at the SU(5) phase transition. The causal bound in these theories is consistent with standard cosmology. We discuss baryon production in these theories and argue that in order to produce a sufficient number of baryons, the color triplet Higgs mass must be much lighter than the grand unification scale. This leads to unacceptably large proton decay rates via Weinberg's dimension-5 operator.

Gauge hierarchy in an SO(10) supersymmetric grand unified model

Constructs an SO(10) supersymmetric grand unified model in which the gauge hierarchy problem may be solved. Using Higgs superfields belonging to the SO(10) representations 16, 10 and 54, it is found that if SO(10) is broken down to SU(3)c*SU(2)L*U(1) via SO(6)*SO(4) approximately SU(4)c*SU(2)L*SU(2)R at unification mass scales without supersymmetry breaking, the gauge hierarchy puzzle might be carried away. It is also shown that the colour-triplet Higgs, which mediates proton decay, is superheavy by an incredibly accurate, but 'natural' adjustment of parameters in the potential.

Low Energy Parameters and Particle Masses in a Supersymmetric Grand Unified Model

Low Energy Parameters and Particle Masses in a Supersymmetric Grand Unified Model