252 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
Z' mass limits and the naturalness of supersymmetry
The discovery of a 125 GeV Higgs boson and rising lower bounds on the masses
of superpartners have lead to concerns that supersymmetric models are now fine
tuned. Large stop masses, required for a 125 GeV Higgs, feed into the
electroweak symmetry breaking conditions through renormalisation group
equations forcing one to fine tune these parameters to obtain the correct
electroweak vacuum expectation value. Nonetheless this fine tuning depends
crucially on our assumptions about the supersymmetry breaking scale. At the
same time extensions provide the most compelling solution to the
-problem, which is also a naturalness issue, and allow the tree level
Higgs mass to be raised substantially above . These very well motivated
supersymmetric models predict a new boson which could be discovered at the
LHC and the naturalness of the model requires that the boson mass should
not be too far above the TeV scale. Moreover this fine tuning appears at the
tree level, making it less dependent on assumptions about the supersymmetry
breaking mechanism. Here we study this fine tuning for several
supersymmetric extensions of the Standard Model and compare it to the situation
in the MSSM where the most direct tree level fine tuning can be probed through
chargino mass limits. We show that future LHC searches are extremely
important for challenging the most natural scenarios in these models.Comment: 58 pages, 5 figures; typos corrected, references added; matches
version to be published in Phys. Rev.
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
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
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
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