1,598 research outputs found
Renormalization of vacuum expectation values in spontaneously broken gauge theories: Two-loop results
We complete the two-loop calculation of beta-functions for vacuum expectation
values (VEVs) in gauge theories by the missing O(g^4)-terms. The full two-loop
results are presented for generic and supersymmetric theories up to two-loop
level in arbitrary R_xi-gauge. The results are obtained by means of a scalar
background field, identical to our previous analysis. As a by-product, the
two-loop scalar anomalous dimension for generic supersymmetric theories is
presented. As an application we compute the beta-functions for VEVs and
tan(beta) in the MSSM, NMSSM, and E6SSM.Comment: 13 pages, 1 figur
Higgs mass prediction in the MSSM at three-loop level in a pure context
The impact of the three-loop effects of order on the
mass of the light CP-even Higgs boson in the MSSM is studied in a pure
context. For this purpose, we implement the results of
Kant et al. into the C++ module Himalaya and link it to FlexibleSUSY, a
Mathematica and C++ package to create spectrum generators for BSM models. The
three-loop result is compared to the fixed-order two-loop calculations of the
original FlexibleSUSY and of FeynHiggs, as well as to the result based on an
EFT approach. Aside from the expected reduction of the renormalization scale
dependence with respect to the lower order results, we find that the three-loop
contributions significantly reduce the difference from the EFT prediction in
the TeV-region of the SUSY scale . Himalaya can be linked also to other
two-loop codes, thus allowing for the elevation of these
codes to the three-loop level.Comment: 32 pages, 8 figures, 1 table [version submitted to EPJC
Mass spectrum prediction in non-minimal supersymmetric models
Supersymmetry is an attractive extension of the Standard Model (SM) of particle physics. The minimal supersymmetric extension (MSSM) provides gauge coupling unification, a dark matter candidate particle and can explain the breaking of the electroweak symmetry dynamically. However, it suffers from the little hierarchy and the mu-problem.
Non-minimal supersymmetric extensions of the SM with a larger particle content or a higher symmetry can evade the problems of the MSSM. Such models may be well-motivated by Grand Unified Theories (GUTs) and can provide a rich new phenomenology with an extended Higgs sector, exotic particles, additional interactions and a close connection to String Theory. Interesting examples are the Next-to Minimal Supersymmetric Standard Model (NMSSM), which is motivated by the mu-problem, and the Exceptional Supersymmetric Standard Model (E6SSM), which is inspired by E6 GUTs.
For phenomenological investigations of supersymmetric (SUSY) models the pole mass spectrum must be calculated from the fundamental model parameters. This task, however, is non-trivial as the spectrum must be consistent with measured low-energy observables (fine-structure constant, Z boson pole mass, muon decay etc.) as well as electroweak symmetry breaking and potential universality conditions on the soft supersymmetry breaking parameters at the GUT scale.
Programs, which calculate the SUSY mass spectrum consistent with constraints of this kind are called spectrum generators.
In this thesis four different contributions to the prediction of mass spectra and model parameters in non-minimal SUSY models are presented. (i) One-loop matching corrections of the E6SSM gauge and Yukawa couplings to the SM are calculated to increase the precision of the mass spectrum prediction in the constrained E6SSM. (ii) The beta-functions of vacuum expectation values (VEVs) are calculated in a general and supersymmetric gauge theory at the one- and two-loop level. The results enable an accurate calculation of the renormalization group running of the VEVs in non-minimal SUSY models. (iii) An NMSSM extension of Softsusy, a spectrum generator for the MSSM, is implemented. It represents a precise alternative to the already existing spectrum generator NMSPEC. (iv) FlexibleSUSY is presented, a general framework which creates a fast, modular and precise spectrum generator for any user-defined SUSY model. It represents a generalization of the hand-written SUSY spectrum generators and allows the study of a large variety of new SUSY models easily with high precision
An algorithm to approximate the real trilogarithm for a real argument
We present an algorithm to approximate the real trilogarithm for a real
argument with IEEE 754-1985 double precision accuracy. The approximation is
structured such that it can make use of instruction-level parallelism when
executed on appropriate CPUs.Comment: 4 pages, 3 tables, attached source cod
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
Two-loop results on the renormalization of vacuum expectation values and infrared divergences in the FDH scheme
Recent progress in the understanding of vacuum expectation values and of
infrared divergences in different regularization schemes is reviewed. Vacuum
expectation values are gauge and renormalization-scheme dependent quantities.
Using a method based on Slavnov-Taylor identities, the renormalization
properties could be better understood. The practical outcome is the computation
of the beta functions for vacuum expectation values in general gauge theories.
The infrared structure of gauge theory amplitudes depends on the regularization
scheme. The well-known prediction of the infrared structure in CDR can be
generalized to the FDH and DRED schemes and is in agreement with explicit
computations of the quark and gluon form factors. We discuss particularly the
correct renormalization procedure and the distinction between MSbar and DRbar
renormalization. An important practical outcome are transition rules between
CDR and FDH amplitudes.Comment: 8 pages, proceedings for Loops and Legs in Quantum Field Theory 2014,
Weimar, German
Vacuum stability and supersymmetry at high scales with two Higgs doublets
We investigate the stability of the electroweak vacuum for two-Higgs doublet
models with a supersymmetric UV completion. The supersymmetry breaking scale is
taken to be of the order of the grand unification scale. We first study the
case where all superpartners decouple at this scale. We show that contrary to
the Standard Model with one Higgs doublet, matching to the supersymmetric UV
completion is possible if the low-scale model contains two Higgs doublets. In
this case vacuum stability and experimental constraints point towards low
values of tan(beta) < 2 and pseudoscalar masses of at least about a TeV. If the
higgsino superpartners of the Higgs fields are also kept light, the conclusions
are similar and essentially independent of the higgsino mass. Finally, if all
gauginos are also given electroweak-scale masses (split supersymmetry with two
Higgs doublets), the model cannot be matched to supersymmetry at very high
scales when requiring a 125 GeV Higgs. Light neutral and charged higgsinos
therefore emerge as a promising signature of a supersymmetric UV completion of
the Standard Model at the grand unification scale.Comment: 27 pages, 4 figures; v2: minor changes in references and text,
results unchange
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
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