144 research outputs found
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.
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
Phenomenological Consequences of the Constrained Exceptional Supersymmetric Standard Model
The Exceptional Supersymmetric Standard Model (ESSM) provides a low
energy alternative to the MSSM, with an extra gauged U(1) symmetry, solving
the -problem of the MSSM. Inspired by the possible embedding into an E
GUT, the matter content fills three generations of E multiplets, thus
predicting exciting exotic matter such as diquarks or leptoquarks. We present
predictions from a constrained version of the model (cESSM), with a
universal scalar mass , trilinear mass and gaugino mass . We
reveal a large volume of the cESSM parameter space where the correct
breakdown of the gauge symmetry is achieved and all experimental constraints
satisfied. We predict a hierarchical particle spectrum with heavy scalars and
light gauginos, while the new exotic matter can be light or heavy depending on
parameters. We present representative cESSM scenarios, demonstrating that
there could be light exotic particles, like leptoquarks and a U(1) Z'
boson, with spectacular signals at the LHC.Comment: Contribution to the proceedings of SUSY 09, Boston, USA, June 2009, 4
page
LHC Signatures of the Constrained Exceptional Supersymmetric Standard Model
We discuss two striking Large Hadron Collider (LHC) signatures of the
constrained version of the exceptional supersymmetric standard model (cE6SSM),
based on a universal high energy soft scalar mass m_0, soft trilinear coupling
A_0 and soft gaugino mass M_{1/2}. The first signature we discuss is that of
light exotic colour triplet charge 1/3 fermions, which we refer to as
D-fermions. We calculate the LHC production cross section of D-fermions, and
discuss their decay patterns. Secondly we discuss the E6 type U(1)_N spin-1 Z'
gauge boson and show how it may decay into exotic states, increasing its width
and modifying the line shape of the dilepton final state. We illustrate these
features using two representative cE6SSM benchmark points, including an "early
LHC discovery" point, giving the Feynman rules and numerical values for the
relevant couplings in order to facilitate further studies.Comment: 30 pages, 5 figures, corrections to figure caption
Next-to-minimal SOFTSUSY
We describe an extension to the SOFTSUSY program that provides for the
calculation of the sparticle spectrum in the Next-to-Minimal Supersymmetric
Standard Model (NMSSM), where a chiral superfield that is a singlet of the
Standard Model gauge group is added to the Minimal Supersymmetric Standard
Model (MSSM) fields. Often, a symmetry is imposed upon the
model. SOFTSUSY can calculate the spectrum in this case as well as the case
where general violating (denoted as
) terms are added to the
soft supersymmetry breaking terms and the superpotential. The user provides a
theoretical boundary condition for the couplings and mass terms of the singlet.
Radiative electroweak symmetry breaking data along with electroweak and CKM
matrix data are used as weak-scale boundary conditions. The renormalisation
group equations are solved numerically between the weak scale and a high energy
scale using a nested iterative algorithm. This paper serves as a manual to the
NMSSM mode of the program, detailing the approximations and conventions used
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