Grand unification with local supersymmetry

We study general conditions for obtaining spontaneous breaking of local supersymmetry in N = 1 supergravity coupled to supersymmetric matter. We consider in particular the coupling of N = 1 supergravity to grand unified theories like SU(5) and study the conditions which must be met in order to obtain a realistic model. Specific models are built in which local supersymmetry is broken at a scale √M_Wm_p ～ 10¹⁰ GeV. This breaking of supersymmetry is only detected at low energies through soft terms breaking explicitly the global supersymmetry. These soft terms (scalar masses, gaugino masses and trilinear scalar couplings) are renormalized at low energies according to the renormalization group. The (mass)² of the Higgs doublet evolve towards negative values at low energies giving rise to SU(2) × U(1) breaking as a radiative effect of local supersymmetry breaking. We finally point out the possible relevance of non-renormalizable superpotentials for the problem of fermion masses.     

A grand unified theory based onSU(n, 1)-minimal supergravity

We discuss a grand unified theory in the framework ofSU(n, 1) minimal supergravity with the Planck mass as the only input mass scale.M _W ≈m _3/2 is fixed by radiative corrections to be naturally ?M _P1. Due to the particular form of explicit soft supersymmetry breaking a light singlet can be used to obtain naturally light Higgs doublets and for a new mechanism for radiativeSU (2)×U(1) breaking. The low energy particle spectrum is very restricted withm _3/2≈10⁴ GeV.     

Radiative gauge symmetry breaking in supersymmetric flipped SU(5)

The radiative breaking of the SU(5)×U(1) symmetry in the flipped SU(5) model recently proposed by Antoniadis et al. is studied using renormalization group techniques. It is shown that gaugino masses can only be the dominant source of supersymmetry breaking at the Planck scale if the U(1) gaugino mass M₁ is at least 10 times larger than the SU(5) gaugino mass M₅. If M₁≅M₅ at the Planck scale, non-vanishing trilinear soft breaking terms (“A-terms”) are needed already at the Planck scale. In both cases consequences for the sparticle spectrum at the weak scale are discussed.     

Low-energy dilation

We study consequences of scale symmetry breaking in the QCD effective SU(2)×SU(2) chiral model. The mass of a pseudo-Goldstone boson dilation is estimated to be M_σ≅1 GeV and the upper bound to its lifetime τ_σ⩽4×10⁻²⁸ s. We also show that the dilation gives a considerable contribution to the pion scalar radius.     

Models for inflation with a low supersymmetry-breaking scale

We present models where the same scalar field is responsible for inflation and for the breaking of supersymmetry. The scale of supersymmetry breaking is related to the slope of the potential in the plateau region described by the scalar field during the slow rollover, and the gravitino mass can therefore be kept as small as M_W, the mass of the weak gauge boson. We show that such a result is stable under radiative corrections. We describe the inflationary scenario corresponding to the simplest of these models and show that no major problem arises, except for a violation of the thermal constraint (stabilization of the field in the plateau region at high temperature). We discuss the possibility of introducing a second scalar field to satisfy this constraint.     

Astrophysical constraints on broken supersymmetry

Arguments on the evolution of stars at an advanced stage constrain the interaction strength of light neutral fermions appearing in broken supersymmetric theories. In particular a consideration of white dwarfs leads to a bound on the fundamental scale of supersymmetry breaking d > 2.6 × 10³GeV², an order of magnitude improvement compared to the existing bound. A new bound on the scalar electron mass is obtained also.     

Limits on the top quark mass within the frame of the minimal superstrings inspired model

We study the process of spontaneous R parity breaking in minimal stringy models. In these models the top quark mass is bounded from below to allow the spontaneous breaking of SU (2)_L × U (1)_Y. On the other hand the requirement of stability for the neutral potential which is sufficient to avoid R parity breaking, gives us an upper bound. Allowed values for the top quark mass remain between 70 and 95 GeV, if supersymmetry breaking is triggered by gaugino masses.     

RG-invariant sum rule in a generalization of anomaly-mediated SUSY-breaking models

We study a generalization of anomaly-mediated supersymmetry-breaking (AMSB) scenarios, under the assumption that the effects of the high-scale theory do not completely decouple and that D-term type contributions can therefore be present. We investigate the effect of such possible D-term additional contributions to soft scalar masses by requiring that, for non-vanishing, renormalizable Yukawa couplings Y^ijk, the sum of squared soft supersymmetry breaking mass parameters, M²_ijk≡m_i²+m_j²+m_k², is RG-invariant, in the sense that it becomes independent of the specific ultraviolet boundary conditions as it occurs in the AMSB models. This type of models can avoid the problem of tachyonic solutions for the slepton mass spectrum present in AMSB scenarios. We implement the electroweak symmetry breaking condition and explore the sparticle spectrum associated with this framework. To show the possible diversity of the sparticle spectrum, we consider two examples, one in which the D-terms induce a common soft supersymmetry breaking mass term for all sfermion masses, and another one in which a light stop can be present in the spectrum.     

Threshold and compactification effects in GUTS

We review general results on threshold effects and their implications on GUTs in the context of LEP data. Among the blooming grand-desert models, threshold effects are computed in the presence of a single real scalar ζ (3, 0, 8) with M_ζ?10¹⁰ GeV leading to experimentally testable predictions on the proton lifetimeτ _p in SU (5) and, in addition, small neutrino masses in SO (10) needed for the solar neutrino flux and the dark matter of the universe. The fine structure constant matching at M_Z is ensured by including threshold effects on the unification coupling. In the minimal SUSY SU (5) such effects at the GUT scale modify the prediction of the supersymmetric mass threshold near the TeV scale and the precision measurments of the Standard Model couplings at M_Z probe into the superheavy mass spectrum. Consequences of theorems proved very useful for threshold, compactification and multiloop effects are discussed. It is noted that in a class of GUTs the highest intermediate scale M_I above which G_224P becomes a good symmetry is not affected by the GUT threshold or compactification effects or multiloop contributions in the range M_I-M_U. But spontaneous compatification effects can decrease the intermediate scale drastically in models where parity and SU(2)_R breakings are decoupled. Low mass W_R-bsosns are permitted in models with decoupled parity and SU (2)_R breakings.     

Radiative corrections in compactified superstring models

One-loop corrections to the effective potential in models obtained from compactification of ten-dimensional superstring theories are calculated. It is found that no masses are generated for gauge non-singlet scalars even in the presence of supersymmetry breaking terms induced by gauge and gaugino condensation, but that the gravitino mass is determined at one loop. The scales of grand unification, supersymmetry breaking and condensation are fixed by the gauge singlet scalars and are found to be close to Planck scale. Requiring M_GUT<M_Planck restricts the other parameters of the theory. The one-loop effective potential at scales between the condensate and compactification scales is also discussed, with possible implications for the allowed particle content of the effective theory.     

Prospects for supersymmetric SO(10) models with an intermediate mass scale

We investigate possible patterns of SO(10) gauge symmetry breaking compatible with supersymmetry, limiting ourselves to the cases with one intermediate breaking scale. It is found that the one where a 54 representation breaks SO(10) into a Pati-Salam group SU(4)_C×SU(2)_L×SU(2)_R and the one where a 210 breaks it into SU(3)_C× U(1)_C×SU(2)_L×SU(2)_R are the most preferable patterns when supersymmetry is taken into account. Two models with the Pati-Salam intermediate symmetry are studied in more detail.     

Proton decay in locally supersymmetric GUT

Proton decay is studied in the supergravity model with “the hidden sector” as the source of supersymmetry breaking. Each dimension-five operator is found to accompany ΔB ≠ 0 four-scalar interactions. The Higgs fermion exchange for loop diagrams at low energies can be as important as the gauge fermion exchange, if the associated Yukawa coupling is significant as suggested by the radiatively induced SU(2) × U(1) breaking mechanism. The experimental bound for p → K⁰μ⁺ gives the lower bound of the order of 10¹⁶ GeV for the mass of the baryon-number violating Higgs particle.     

Renormalization of the electroweak ϱ-parameter from supersymmetric particles

We compute the renormalization of the neutral-to-charged current Fermi constant ratio, arising from the new particles required in supersymmetric scheme?.We find that ? is insensitive to the scale of the supersymmetry mass-splitting. For a t-quark mass m_t greater than this scale, the scalar-t and scalar-b contribution increases proportionally to m_t² and it is essentially equal, in sign and magnitude, to the t-, b-quark contribution.Contributions from the gaugino-higgsino-Higgs boson sector are generally of the order of a few parts in 10^?3.For a class of models under consideration these results can be traced back to an approximate SU(2) symmetry which is also useful in the classification of the new particle spectrum.     

A low right-handed scale in a supersymmetric context

We investigate the prospects for a low right-handed scale M_R in the context of locally supersymmetric O(10), limiting ourselves to the most interesting case of a single breaking scale between the grand unified scale M_X and the W-mass. It is found that supersymmetry seems to imply a unique solution as regards the Higgs content and the intermediate symmetry group if a low right-handed scale (less than 10⁴ GeV) exist at all. Apart from a minimal set of representations providing the symmetry battern, the Higgs sector consist of a pair of 16 and $\text{16}$ spinor representations ying at scale M_R and the residual symmetry is SU(3)_c × U(1)_B?L × SU(2)_L × U(1)_R.     

Symmetry breaking in a supersymmetric model of strong and electroweak interactions

We describe a supersymmetric model of strong and electroweak interactions based on the gauge groupSU(3)×SU(2)×U(1)×?(1). We concentrate on the pattern of the spontaneous symmetry breaking by the tree level scalar potential. It is possible to break the?(1) factor at superlarge energies relative to the simultaneous breaking scale ofSU(2)×U(1) and supersymmetry. The model has?(1) anomalies. Attempts to make an anomaly-free model based on the groupE ₆ are described. We also comment on possible modifications of the?(1) anomaly problem due to gravitational effects.     

The weak mixing angle and unification mass in supersymmetric SU(5)

We consider the predictions for the weak mixing angle θ_W and the scale M of unification in a supersymmetric extension of SU(5), with particular emphasis on the sensitivity to the number of Higgs multiplets. In the one-loop approximation, we also calculate the ratio m_b/m_τ. We discuss generally the effects of an intermediate threshold between the weak interaction scale and M and estimate the sensitivity of θ_W and M to the scale of supersymmetry breaking.The evolution of the coupling constants of the supersymmetric SU(3) ? SU(2) ? U(1) effective gauge theory is described and the two-loop corrections to θ_{W and M} are calculated.     

Threshold and compactification effects in GUTS

We review general results on threshold effects and their implications on GUTs in the context of LEP data. Among the blooming grand-desert models, threshold effects are computed in the presence of a single real scalar ζ (3, 0, 8) with M_ζ≃10¹⁰ GeV leading to experimentally testable predictions on the proton lifetimeτ _p in SU (5) and, in addition, small neutrino masses in SO (10) needed for the solar neutrino flux and the dark matter of the universe. The fine structure constant matching at M_Z is ensured by including threshold effects on the unification coupling. In the minimal SUSY SU (5) such effects at the GUT scale modify the prediction of the supersymmetric mass threshold near the TeV scale and the precision measurments of the Standard Model couplings at M_Z probe into the superheavy mass spectrum. Consequences of theorems proved very useful for threshold, compactification and multiloop effects are discussed. It is noted that in a class of GUTs the highest intermediate scale M_I above which G_224P becomes a good symmetry is not affected by the GUT threshold or compactification effects or multiloop contributions in the range M_I-M_U. But spontaneous compatification effects can decrease the intermediate scale drastically in models where parity and SU(2)_R breakings are decoupled. Low mass W_R-bsosns are permitted in models with decoupled parity and SU (2)_R breakings.     

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_WR < 10⁹ GeV. The unification scale lies within an order of magnitude below the Planck mass.     

Effective lagrangian for supersymmetric theories with intermediate breaking scale

We investigate effective lagrangians in supersymmetric models broken spontaneously at an intermediate energy (～ μ ? M_GUT). It is shown to all orders in perturbation theory that the low-energy interactions of light particles are described by an effective lagrangian with explicit but soft supersymmetry breaking of order μ² / M_GUT.     

Can the superstring inspire the standard model?

We discuss general features of models in which the E₈ × E′₈ heterotic superstring is compactified on a specific Calabi-Yau manifold. The gauge group of rank-6 in four dimensions is supposed to be broken down at an intermediate scale m_I to the standard model group SU(3)_C × SU(2)_L × U(1)_Y, as a result of two neutral scalar fields acquiring large vacuum expectations (vev's) in one of many flat directions of the effective potential. We find that it is difficult to generate such an intermediate scale by radiative symmetry breaking, whilst such models have prima facie problems with baryon decay mediated by massive particles and with non-perturbative behaviour of the gauge couplings, unless m_I ≳ 10¹⁶ GeV. Rapid baryon decay mediated by light particles, large neutrino masses, other Δ L ≠ 0 processes and flavour-changing neutral currents are generic features of these models. We illustrate these observations with explicit calculations in a number of different models given by vev's in different flat directions.