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.     

Neutrino mass and new light gauge boson in superstring models

The proposal that the neutrino owes the smallness of its mass to the spontaneous breaking of R parity in superstring models with an additional gauge boson coupled to the right-handed neutrino is analysed. The right-handed neutrino can not in general decouple from the low-energy theory in models with supersymmetry at the TeV scale and which possess the light Higgs doublets necessary for generating fermion masses. Experimental limits on neutrino mass then imply an upper limit on the new gauge boson mass m_Zr ⪅ 220 GeV.     

Spontaneous symmetry breaking in annealed and quenched gauge field models

The structure of annealed and quenched models with localU(1) gauge invariance is studied in terms of the Helmholtz free energy. The first non-trivial, or one-loop, account of fluctuations in the annealed model suggests that spontaneous symmetry breaking occurs in two and three dimensions, through a first-order phase transition. Within the same approximation scheme, the quenched model displays a continuous phase transition. A more complete account of the fluctuations in the annealed model changes the nature of the transition to a continuous one, whereas spontaneous symmetry breaking is then absent with quenched disorder.     

Spontaneous symmetry breaking in annealed and quenched gauge field models

The structure of annealed and quenched models with localU(1) gauge invariance is studied in terms of the Helmholtz free energy. The first non-trivial, or one-loop, account of fluctuations in the annealed model suggests that spontaneous symmetry breaking occurs in two and three dimensions, through a first-order phase transition. Within the same approximation scheme, the quenched model displays a continuous phase transition. A more complete account of the fluctuations in the annealed model changes the nature of the transition to a continuous one, whereas spontaneous symmetry breaking is then absent with quenched disorder.     

Spontaneous dynamical breaking of gauge symmetry in dual models

The consequences of gauge invariance are re-examined in dual models with unit intercept when the dimension of space-time has the maximum value compatible with the absence of ghosts. In that case, reggeon-reggeon bound states of zero mass are formed already at second order of perturbation theory. Gauge invariance no longer guarantees that the initially massless SU(3) singlet vector meson remains massless, and the mixing between the reggeon and pomeron sectors of the model yields a massive unitary singlet vector meson already at order g². A Lagrangian model which exhibits similar features to the dual situation is discussed.     

E7(7) symmetry and dual gauge algebra of M-theory on a twisted seven-torus

We consider M-theory compactified on a twisted 7-torus with fluxes when all the seven antisymmetric tensor fields in four dimensions have been dualized into scalars and thus the ${\mathrm{E}}_{7(7)}$ symmetry is recovered. We find that the Scherk–Schwarz and flux gaugings define a “dual” gauge algebra, subalgbra of ${\mathrm{E}}_{7(7)}$, where some of the generators are associated with vector fields which are dual to part of the original vector fields (deriving from the 3-form). In particular they are dual to those vector fields which have been “eaten” by the antisymmetric tensors in the original theory by the (anti-)Higgs mechanism. The dual gauge algebra coincides with the original gauge structure when the quotient with respect to these dual (broken) gauge generators is taken. The particular example of the S–S twist corresponding to a “flat group” is considered.     

Anomalies and gauge symmetry

Anomalies are known to have an intrinsic geometrical meaning. Using a formalism where the gauge condition is never made explicit we reanalyze the gauge theory anomaly problem. By requiring simultaneously the BRS and anti-BRS invariances, we do not need to use in our study the gauge dependent anti-ghost equation of motion. Then all equations definining the anomaly are independent of all parameters specifying the lagrangian. Not only does this stress explicitly the geometrical nature of the anomaly problem, but it allows for a single analysis for all possible BRS and anti-BRS invariant gauges, including those with four-ghost interactions. Our method for solving the anomaly equations is as a new sign of the relevance of the formalism in which the ghost components are unified with those of the classical gauge field, the ghost fields playing the role of a “connection” along unphysical directions. We recover the ABJ anomaly directly from the structure of BRS equations, as a straightforward application of the Chern-Weil theorem in some enlarged space. The method can be formally extended to higher space-time dimensions, and a general formula for “anomalies” in any even dimension is given.     

One-loop gauge anomaly in type-1 superstring theory

The vanishing of the hexagon gauge anomaly of type-I superstring was shown previously by Green and Schwarz in the case that the gauge group is SO(32). The result, as well as the finiteness f the one-loop amplitude, makes the superstring theory a candidate for the unified theory including gravity. The vanishing of the gauge anomaly can be established for all N-point functions. The one-loop gauge anomaly is shown to be absent if the gauge group is SO(32).     

E6 symmetry breaking in the superstring theory

We derive two methods for determining the symmetry breaking of E₆ in the low energy superstring theory, and classify all breaking patterns. A method for calculating the effective Higgs vacuum expectation values is presented. We show that there are theories with naturally light SU₂^w Higgs doublets, and classify all theories in which this occurs. The phenomenology of spontaneously broken E₆ theories is discussed, emphasizing the issues of nucleon decay and neutrino masses.     

有势力和规范对称性

介绍了有势力的一般性质,针对一般非惯性系中的惯性力引入其矢势和标势,并分析了其中的规范对称性与电磁学的形式类比.     

Discrete gauge symmetry anomalies

It has been recently argued that quantum gravity effects strongly violate all non-gauge symmetries. This would suggest that all low energy discrete symmetries should be gauge symmetries, either continuous or discrete. Acceptable continuous gauge symmetries are constrained by the condition they should be anomaly free. We show here that any discrete gauge symmetry should also obey certain “discrete anomaly cancellation” conditions. These conditions strongly constrains the massles fermion content of the theory and follow from the “parent” cancellation of the usual continuous gauge anomalies. They have interesting applications in model building. As an example we consider the constraints on the Z_N “generalized matter parities” of the supersymmetric standard model. We show that only a few (including the standard R-parity) are “discrete anomaly free” unless the fermion content of the minimal supersymmetric standard model is enlarged.     

Ultra-light neutrinos and R-parity in superstring models

A mechanism is suggested for generating ultra-light neutrinos in intermediate scale superstring models as a consequence of R-parity conservation. Neutrino masses are suppressed by four powers of the intermediate scale and could be appropriate to explain the reduced solar neutrino flux in terms of resonant oscillations of the electron- to the muon-neutrino.     

Absence of hexagon gauge anomalies in higher loop superstring amplitudes

It is shown that there are no gravitational, Yang-Mills, local supersymmetry hexagon anomalies in higher genus amplitudes of type II superstring and heterotic string theory in ten dimensions. The nonrenormalization theorem for massless parity-violating higher genus amplitudes is also proved.     

Radiative neutrino decay in superstring models

The rate for the radiative decay of neutrinos is calculated in E₆ superstring models with light colour triplet isosinglets h and h. In contrast to the standard model, the rate is not suppressed either by the GIM mechanism or by helicity matching. Comparison with astrophysical data allows one to set an upper limit on the Yukawa couplings QL and λd^cv^ch. Taking it is found that , compatible with m_vc, m_vμ in the range 10–100 eV. From the cosmological requirement of not photo-ionizing light elements after nucleosynthesis, it follows that the v_τ must lie in the same mass range and consequently .     

The electroweak sector in superstring models

Phenomenological constraints on the extra low-mass neutral gauge boson Z′ of present superstring models are presented and shown to imply a very fine tuning of the parameters involved in the Higgs potential.