School of Physics
http://hdl.handle.net/10539/1059
Research Content for the School of Physics2015-11-30T08:01:36ZNatural supersymmetry and dynamical flavour with meta-stable vacua
http://hdl.handle.net/10539/18156
Natural supersymmetry and dynamical flavour with meta-stable vacua
Abela, Steven; McGarrie, Moritz
We show how gauged flavour breaking and N = 1 supersymmetry breaking can be dynamically aligned to produce natural models. Supersymmetry is broken in a metastable vacuum, while a weakly gauged flavour symmetry is identified with an SU (3) F subgroup of the global symmetry of the SQCD model. We find that alignment can easily occur either through strongly coupled flavour models, with SQCD bound states playing the role of flavons, or entirely weakly coupled and renormalizable models with elementary SU (3) F adjoint flavons. In both cases it is essential that the SU (3) F breaking, and hence all the flavour structure, is driven dynamically by the SUSY breaking. The resulting flavour gauge mediation in conjunction with the usual gauge mediation contribution leads to naturally light third generations squarks, with first and second generations above.
2014-07-29T00:00:00ZLight third-generation squarks from flavour gauge messengers
http://hdl.handle.net/10539/18155
Light third-generation squarks from flavour gauge messengers
Brummer, Felix; McGarrie, Moritz; Weiler, Andreas
We study models of gauge-mediated supersymmetry breaking with a gauged horizontal SU(3)F symmetry acting on the quark superfields. If SU(3)F is broken nonsupersymmetrically by F -term vacuum expectation values, the massive gauge bosons and gauginos become messengers for SUSY breaking mediation. These gauge messenger fields induce a flavour-dependent, negative contribution to the soft masses of the squarks at one loop. In combination with the soft terms from standard gauge mediation, one obtains large and degenerate first- and second-generation squark masses, while the stops and sbottoms are light. We discuss the implications of this mechanism for the superparticle spectrum and for flavour precision observables. We also provide an explicit realization in a model with simultaneous SUSY and SU(3)F breaking.
2014-04-10T00:00:00ZLarge A without the desert
http://hdl.handle.net/10539/18154
Large A without the desert
Abdalgabar, Ammar; Cornell, Alan S.; Deandrea, Aldo; McGarrie, Moritz
Even if the unification and supersymmetry breaking scales are around 106 to 109 TeV, a large A t coupling may be entirely generated at low energies through RGE evolution in the 5D MSSM. Independent of the precise details of supersymmetry breaking, we take advantage of power law running in five dimensions and a compactification scale in the 10 − 103 TeV range to show how the gluino mass may drive a large enough A t to achieve the required 125.5 GeV Higgs mass. This also allows for sub-TeV stops, possibly observable at the LHC, and preserving GUT unification, thereby resulting in improved naturalness properties with respect to the four dimensional MSSM. The results apply also to models of “split families” in which the first and second generation matter fields are in the bulk and the third is on the boundary, which may assist in the generation of light stops whilst satisfying collider constraints on the first two generations of squarks.
2014-07-31T00:00:00ZIndefinite theta functions for counting attractor backgrounds
http://hdl.handle.net/10539/18153
Indefinite theta functions for counting attractor backgrounds
Cardoso, Gabriel Lopes; Ciraficia, Michele; Nampurib, Suresh
In this note, we employ indefinite theta functions to regularize canonical partition functions for single-center dyonic BPS black holes. These partition functions count dyonic degeneracies in the Hilbert space of four-dimensional toroidally compactified heterotic string theory, graded by electric and magnetic charges. The regularization is achieved by viewing the weighted sums of degeneracies as sums over charge excitations in the near-horizon attractor geometry of an arbitrarily chosen black hole background, and eliminating the unstable modes. This enables us to rewrite these sums in terms of indefinite theta functions. Background independence is then implemented by using the transformation property of indefinite theta functions under elliptic transformations, while modular transformations are used to make contact with semi-classical results in supergravity.
2014-10-03T00:00:00Z