arXiv subjects

G. G. Ross

Publications and source records attributed to G. G. Ross.

At least 37 records · Page 2Linked to original sources

arXiv2006

Neutrino tri-bi-maximal mixing from a non-Abelian discrete family symmetry

The observed neutrino mixing, having a near maximal atmospheric neutrino mixing angle and a large solar mixing angle, is close to tri-bi-maximal. We argue that this structure suggests a family symmetric origin in which the magnitude of the mixing angles are related to the existence of a discrete non-Abelian family symmetry. We construct a model in which the family symmetry is the non-Abelian discrete group $Δ(27)$, a subgroup of SU(3) in which the tri-bi-maximal mixing directly follows from the vacuum structure enforced by the discrete symmetry. In addition to the lepton mixing angles, the model accounts for the observed quark and lepton masses and the CKM matrix. The structure is also consistent with an underlying stage of Grand Unification.

hep-ph↗

arXiv2006

Anomaly Mediation and Dimensional Transmutation

We show how a sparticle spectrum characteristic of anomaly mediation can arise from a theory whose Lagrangian contains no explicit mass scale. The scale of supersymmetry breaking is governed by the gravitino mass, which is the vacuum expectation value of the F-term of the conformal compensator field, and the tachyonic slepton problem is resolved by the breaking of a U(1) gauge symmetry at a scale determined by dimensional transmutation.

hep-ph↗

arXiv2006

Probing neutrino oscillations from supernovae shock waves via the IceCube detector

The time dependent neutrino oscillation signals due to the passage of a shock wave through the supernovae are analyzed for the case of three active neutrinos and also for the case that there are two additional sterile neutrinos. It is shown that, even without flavour identification and energy measurement, detailed information about the masses and mixing angles of the neutrinos may be obtained with a detector with excellent time resolution such as IceCube. Such a signal would also give important information about the nature of the shock wave within the supernovae.

hep-ph↗

arXiv2005

Tri-bimaximal neutrino mixing from discrete subgroups of SU(3) and SO(3) family symmetry

It has recently been shown how tri-bimaximal neutrino mixing can be achieved, using the see-saw mechanism with constrained sequential dominance, through the vacuum alignment of a broken non-Abelian gauged family symmetry such as SO(3) or SU(3). Generalising the approach of Altarelli and Feruglio developed for an $A_4$ model we show how the reduction of the underlying symmetry to a discrete subgroup of SO(3) or SU(3) renders this alignment a generic property of such models. This means near tri-bimaximal mixing can be quite naturally accommodated in a complete unified theory of quark and lepton masses.

hep-ph↗

arXiv2005

Anomaly Mediation, Fayet-Iliopoulos D-terms and precision sparticle spectra

We consider the sparticle spectra that arise when anomaly mediation is the source of supersymmetry-breaking and the tachyonic slepton problem is solved by a Fayet-Iliopoulos D-term. We also show how this can lead to a minimal viable extension of anomaly mediation, in which the gauge symmetry associated with this D-term is broken at very high energies, leaving as its footprint in the low energy theory only the required D-terms and seesaw neutrino masses.

hep-ph↗

arXiv2005

Soft SUSY breaking and family symmetry

A spontaneously broken non-Abelian SU(3) family symmetry can generate a realistic form for quark, charged lepton and neutrino masses and mixing angles. It also gives a new solution to the SUSY flavour problem by ensuring near family degeneracy of the soft mass SUSY breaking terms. However the need to generate large third generation fermion masses means that the group must be strongly broken to SU(2) giving significant corrections to the third family squark and slepton masses. We investigate the phenomenological implications of such breaking and show that it leads to new solutions capable of fitting all present experimental measurements and bounds as well as the dark matter abundance.

hep-ph↗

arXiv2004

Wilson line breaking and gauge coupling unification

We estimate the effect of threshold corrections coming from Wilson lines to gauge coupling unification in the weakly coupled heterotic string with orbifold compactification. By expressing the corrections in terms of an effective field theory calculation we are able to estimate the minimal threshold corrections in a realistic model without constructing the full string theory. Using this we show that the effect of the gauge boson Kaluza Klein excitations is systematically to reduce the string prediction for the unification scale. In the case of discrete Wilson lines the effect of the Wilson lines on both the gauge and matter sectors is fixed. We show that the combined effect of the gauge and matter threshold corrections of the Kaluza Klein excitations of the MSSM states can readily bring both the prediction for the unification scale and for the strong coupling constant into good agreement with experiment.

hep-ph↗

arXiv2004

Neutrino Phenomenology -- the case of two right handed neutrinos

We make a general analysis of neutrino phenomenology for the case neutrino masses are generated by the see-saw mechanism with just two right handed neutrinos. We find general constraints on leptogenesis and lepton flavour violating processes. We also analyse the predictions following from a nontrivial texture zero structure.

hep-ph↗

arXiv2003

Neutrino properties from Yukawa structure

We discuss the implications for lepton mixing and CP violation of structure in the lepton mass matrices, for the case that neutrino masses are generated by the see-saw mechanism with an hierarchical structure for the Majorana masses. For a particularly interesting case with enhanced symmetry in which the lepton Dirac mass matrices are related to those in the quark sector, the CHOOZ angle is near the present limit and the CP violating phase relevant to thermal leptogenesis and to $ν0 ββ$ decay is near maximal.

hep-ph↗

arXiv2003

Fermion Masses and Mixing Angles from SU(3) Family Symmetry and Unification

We develop a bottom-up approach to constructing a theory of fermion masses and mixing angles based on the gauge group $SU(3)\times G$ where SU(3) is a family symmetry and $G$ contains a unified group such as SO(10) or its Pati-Salam subgroup, together with other discrete symmetries. We construct a realistic model and show that it can provide an excellent description of quark and lepton masses and mixing angles, including almost maximal atmospheric mixing and the LMA MSW solar neutrino solution. We predict a neutrino mixing angle $θ_{13}$ near the current limit. The model provides the basis for a new solution to the flavour problem with a characteristic soft SUSY breaking mass spectrum.

hep-ph↗

arXiv2003

Yukawa structure, flavour and CP violation in Supergravity

The hierarchical structure of fermion masses and mixings strongly suggests an underlying family symmetry. In supergravity any familon field spontaneously breaking this symmetry necessarily acquires an F-term which contributes to the soft trilinear couplings. We show, as a result, mu -> e gamma decay can receive large contributions from this source at the level of current experimental bounds and thus this channel may provide the first indication of supersymmetry and a clue to the structure of the soft breaking sector. Using the mercury EDM bounds we find strong bounds on the right handed down quark mixing angles that are inconsistent with models relating them to neutrino mixing angles and favour a near-symmetric form for the magnitude of the down quark mass matrix.

hep-ph↗

arXiv2002

Symmetries and fermion masses

We discuss whether quark, charged lepton and neutrino masses and mixing angles may be related by an extended flavour and family symmetry group. We show that current measurements of all fermion masses and mixing angles are consistent with a combination of an underlying SU(3) family symmetry together with a GUT symmetry such as SO(10). In this the near bi-maximal mixing observed in the neutrino sector is directly related to the small mixing observed in the quark sector, the difference between quark and lepton mixing angles being due to the see-saw mechanism. Using this connection we make a detailed prediction for the lepton mixing angles determining neutrino oscillation phenomena.

hep-ph↗

arXiv2001

Fermion Masses and Mixing Angles from SU(3) Family Symmetry

We propose a model based on SU(3) family symmetry which leads to a successful description of quark and lepton masses and mixing angles including approximate bi-maximal mixing in the neutrino sector suitable for the LOW or quasi-vacuum solar solutions, with the atmospheric angle predicted to be accurately maximal due to the SU(3) symmetry. The model predicts a CHOOZ angle $θ_{13}\sim |V_{ub}|.$ The SU(3) symmetry can also ensure the near degeneracy of squarks and sleptons needed to avoid large flavour changing neutral currents.

hep-ph↗

arXiv2001

Precision test of a Fermion mass texture

Texture zeros in the quark Yukawa matrices generally lead to precise and simple expressions for CKM matrix elements in terms of ratios of quark masses. Using the new data on $b-$decays we test a particularly promising texture zero solution and show that it is at best approximate. We analyse the approximate texture zero structure and show it is consistent with experiment. We investigate the implications for the CKM unitarity triangle, measurements at $BaBar$ and $BELLE$ as well as for the theories which invoke family symmetries.

hep-ph↗

arXiv2000

Report of the Beyond the Standard Model Working Group of the 1999 UK Phenomenology Workshop on Collider Physics (Durham)

The Beyond the Standard Model Working Group discussed a variety of topics relating to exotic searches at current and future colliders, and the phenomenology of current models beyond the Standard Model. For example, various supersymmetric (SUSY) and extra dimensions search possibilities and constraints are presented. Fine-tuning implications of SUSY searches are derived. The implications of Higgs (non)-discovery are discussed, as well as the program HDECAY. The individual contributions are included seperately. Much of the enclosed work is original, although some is reviewed.

hep-ph↗

arXiv2000

A Three three-brane Universe:New Phenomenology for the New Millennium?

We consider an extension of the Randall-Sundrum model with three parallel 3-branes in a 5-dimensional spacetime. This new construction, apart from providing a solution to the Planck hierarchy problem, has the advantage that the SM fields are confined on a positive tension brane. The study of the phenomenology of this model reveals an anomalous first KK state which is generally much lighter than the remaining tower and also much more strongly coupled to matter. Bounds on the parameter space of the model can be placed by comparison of specific processes with the SM background as well as by the latest Cavendish experiments. The model suggests a further exotic possibility if one drops the requirement of solving the hierarchy problem. In this case gravity may result from the exchange of the ordinary graviton plus an ultralight KK state and modifications of gravity may occur at both small and extremely large scales.

hep-ph↗

arXiv1998

Probing the Structure of the Pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark--pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron.

hep-ph↗

arXiv1998

Unification and Extra Space-Time Dimensions

We analyse the phenomenological implications of a particular class of supersymmetric models with additional space-time dimensions below the unification scale. Assuming the unification of the gauge couplings and using a two-loop calculation below the scale of the additional space-time dimensions, we show that the value of $α_3(M_z)$ is further increased from the two-loop Minimal Supersymmetric Standard Model prediction. We consider whether decompactification threshold effects could bring $α_3(M_z)$ into agreement with experiment and discuss the associated level of fine tuning needed.

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