82 research outputs found
Fine Tuning in Supersymmetric Models
The solution of a fine tuning problem is one of the principal motivations of
Supersymmetry. However experimental constraints indicate that many
Supersymmetric models are also fine tuned (although to a much lesser extent).
We review the traditional measure of this fine tuning used in the literature
and propose an alternative. We apply this to the MSSM and show the
implications.Comment: Included in proceedings of The 14th International Conference on
Supersymmetry and the Unification of Fundamental Interaction
Measuring Fine Tuning In Supersymmetry
The solution to fine tuning is one of the principal motivations for
supersymmetry. However constraints on the parameter space of the Minimal
Supersymmetric Standard Model (MSSM) suggest it may also require fine tuning
(although to a much lesser extent). To compare this tuning with different
extensions of the Standard Model (including other supersymmetric models) it is
essential that we have a reliable, quantitative measure of tuning. We review
the measures of tuning used in the literature and propose an alternative
measure. We apply this measure to several toy models and the MSSM with some
intriguing results.Comment: Submitted for the SUSY07 proceeding
Aspects of electroweak symmetry breaking in physics beyond the standard model
Fine tuning in the Standard Model (SM) is the basis for a widespread expectation that the minimal model for electroweak symmetry breaking, with a single Higgs boson, is
not realised in nature and that new physics, in addition to (or instead of) the Higgs, will be discovered at the Large Hadron Collider (LHC). However constraints on new physics indicate that many models which go beyond the SM (BSM) may also be fine tuned (although to a much lesser extent). To test this a reliable, quantitative measure of tuning is required. We review the measures of tuning used in the literature and propose an alternative measure. We apply this measure to several toy models and a constrained version of the Minimal Supersymmetric Standard Model.
The Exceptional Supersymmetric Standard Model (E6SSM) is another BSM motivated by naturalness. As a supersymmetric theory it solves the SM hierarchy problem and by breaking a new gauged U(1) symmetry it also solves the μ-problem of the
MSSM. We investigate the Renormalisation Group Evolution of the model and test for radiative electroweak symmetry breaking in two versions of the model with different high scale constraints. First we briefly look at scenarios with non-universal Higgs masses at the GUT scale and present a particle spectrum that could be observed at
the LHC. Secondly we study the constrained E6SSM (CE6SSM), with universal scalar (m0), trilinear (A0) and gaugino (M) masses. We reveal a large volume of CE6SSM
parameter space where the correct breakdown of the gauge symmetry can be achieved and all experimental constraints can be satisfied. We present benchmark points corresponding to different patterns of the particle spectrum. A general feature of the benchmark spectra is a light sector of SUSY particles consisting of a light gluino, two light neutralinos and a light chargino. Although the squarks, sleptons and Z′ boson are typically much heavier, the exotic color triplet charge 1/3 fermions as well as the
lightest stop can be also relatively light leading to spectacular new physics signals at the LHC
Model-independent analysis of the DAMPE excess
The Dark Matter Particle Explorer (DAMPE) recently released measurements of
the electron spectrum with a hint of a narrow peak at about 1.4 TeV. We
investigate dark matter (DM) models that could produce such a signal by
annihilation in a nearby subhalo whilst simultaneously satisfying constraints
from DM searches. In our model-independent approach, we consider all
renormalizable interactions via a spin 0 or 1 mediator between spin 0 or 1/2 DM
particles and the Standard Model leptons. We find that of the 20 combinations,
10 are ruled out by velocity or helicity suppression of the annihilation cross
section to fermions. The remaining 10 models, though, evade constraints from
the relic density, collider and direct detection searches, and include models
of spin 0 and 1/2 DM coupling to a spin 0 or 1 mediator. We delineate the
regions of mediator mass and couplings that could explain the DAMPE excess. In
all cases the mediator is required to be heaver than about 2 TeV by LEP limits.Comment: 28 pages, 5 figures and 2 tables. v2: references added. v3: minor
changes, matches published versio
FlexibleSUSY -- A spectrum generator generator for supersymmetric models
We introduce FlexibleSUSY, a Mathematica and C++ package, which generates a
fast, precise C++ spectrum generator for any SUSY model specified by the user.
The generated code is designed with both speed and modularity in mind, making
it easy to adapt and extend with new features. The model is specified by
supplying the superpotential, gauge structure and particle content in a SARAH
model file; specific boundary conditions e.g. at the GUT, weak or intermediate
scales are defined in a separate FlexibleSUSY model file. From these model
files, FlexibleSUSY generates C++ code for self-energies, tadpole corrections,
renormalization group equations (RGEs) and electroweak symmetry breaking (EWSB)
conditions and combines them with numerical routines for solving the RGEs and
EWSB conditions simultaneously. The resulting spectrum generator is then able
to solve for the spectrum of the model, including loop-corrected pole masses,
consistent with user specified boundary conditions. The modular structure of
the generated code allows for individual components to be replaced with an
alternative if available. FlexibleSUSY has been carefully designed to grow as
alternative solvers and calculators are added. Predefined models include the
MSSM, NMSSM, ESSM, USSM, R-symmetric models and models with right-handed
neutrinos.Comment: 56 pages, 3 figures, 3 tables; v3: correcting typos, matches version
accepted for publication by CP
Threshold Corrections in the Exceptional Supersymmetric Standard Model
We calculate threshold corrections to the running gauge and Yukawa couplings
in the Exceptional Supersymmetric Standard Model (E6SSM) and analyse the more
precise and reliable mass spectra in a constrained model (CE6SSM). Full
expressions for the corrections are provided and the implementation into a
spectrum generator is described. We find a dramatic reduction in the matching
scale dependency of the masses of many states and observe a significant
adjustment of the correlation of low-scale physical masses and high-scale
parameters. Still, in substantial regions of parameter space the mass of the
lightest Higgs is compatible with the new boson discovered at the LHC and the
model satisfies limits from collider searches for squark, gluinos and Z'
bosons. We study the implications for gauge coupling unification from a new
dependency of the spectrum on so-called survival Higgs fields which cannot be
addressed without the inclusion of the threshold corrections.Comment: 59 pages, 25 figures, v2 fixed typo and rephrased parts of section
5.3.1, v2 accepted for publication in Physical Review
- …