36 research outputs found
Neutrino Mixing from SUSY breaking
We propose a mechanism to generate the neutrino mixing matrix from
supersymmetric threshold corrections. Flavor violating soft breaking terms
induce flavor changing self-energies that give a finite renormalization to the
mixing matrix. The described threshold corrections get enhanced in case of
quasi-degenerate neutrino masses. In this scenario, we adjust potentially
arbitrary soft breaking parameters in a way to reproduce the observed neutrino
mixing at one loop working with non-minimal flavor violating soft parameters.
To incorporate small neutrino masses already at tree-level via a type I seesaw
mechanism, we extend the Minimal Supersymmetric Standard Model with singlet
Majorana neutrinos. The radiative corrections do not decouple with the scale of
Supersymmetry and persist when the spectrum is shifted to higher values.
Moreover, the mixing matrix renormalization with flavor-changing self-energies
is not restricted to supersymmetric theories and give similar results in any
theory with new flavor structures.Comment: 11 pages. Talk given at the Summer School and Workshop on the
Standard Model and Beyond 2013; to appear in the Proceedings of the Corfu
Summer Institute 2014 "School and Workshops on Elementary Particle Physics
and Gravity
Texture zeros and hierarchical masses from flavour (mis)alignment
We introduce an unconventional interpretation of the fermion mass matrix
elements. As the full rotational freedom of the gauge-kinetic terms renders a
set of infinite bases called weak bases, basis-dependent structures as mass
matrices are unphysical. Matrix invariants, on the other hand, provide a set of
basis-independent objects which are of more relevance. We employ one of these
invariants to give a new parametrization of the mass matrices. By virtue of it,
one gains control over its implicit implications on several mass matrix
structures. The key element is the trace invariant which resembles the equation
of a hypersphere with a radius equal to the Frobenius norm of the mass matrix.
With the concepts of alignment or misalignment we can identify texture zeros
with certain alignments whereas Froggatt-Nielsen structures in the matrix
elements are governed by misalignment. This method allows further insights of
traditional approaches to the underlying flavour geometry.Comment: 27 pages; v2 matches version accepted by NPB, discussion on Dirac CP
phase for neutrinos adde
Vacuum stability of the effective Higgs potential in the Minimal Supersymmetric Standard Model
The parameters of the Higgs potential of the Minimal Supersymmetric Standard
Model (MSSM) receive large radiative corrections which lift the mass of the
lightest Higgs boson to the measured value of 126 GeV. Depending on the MSSM
parameters, these radiative corrections may also lead to the situation that the
local minimum corresponding to the electroweak vacuum state is not the global
minimum of the Higgs potential. We analyze the stability of the vacuum for the
case of heavy squark masses as favored by current LHC data. To this end we
first consider an effective Lagrangian obtained by integrating out the heavy
squarks and then study the MSSM one-loop effective potential V_eff, which
comprises all higher-dimensional Higgs couplings of the effective Lagrangian.
We find that only the second method gives correct results and argue that the
criterion of vacuum stability should be included in phenomenological analyses
of the allowed MSSM parameter space. Discussing the cases of squark masses of 1
and 2 TeV we show that the criterion of vacuum stability excludes a portion of
the MSSM parameter space in which (mu tanbeta) and A_t are large.Comment: minor changes in text and list of references, figures in eps format,
matches published version; Erratum added and sent to PR
The electroweak contribution to the top quark forward-backward asymmetry at the Tevatron
The electroweak contributions to the forward-backward asymmetry in the
production of top-quark pairs at the Tevatron are evaluated at O(alpha^2) and
O(alpha*alphas^2). We perform a detailed analysis of all partonic channels that
produce an asymmetry and combine them with the QCD contributions. They provide
a non-negligible fraction of the QCD-induced asymmetry with the same overall
sign, thus enlarging the Standard Model prediction and diminishing the observed
deviation. For the observed mass-dependent forward-backward asymmetry a 3-sigma
deviation still remains at an invariant-mass cut of M_(t-tbar) > 450 GeV.Comment: 14 pages, 8 figure
Hadronic production of squark-squark pairs: The electroweak contributions
We compute the electroweak (EW) contributions to squark--squark pair
production processes at the LHC within the framework of the Minimal
Supersymmetric Standard Model (MSSM). Both tree-level EW contributions, of
O(alpha_s alpha + alpha^2), and next-to-leading order (NLO) EW corrections, of
O(alpha_s^2 alpha), are calculated. Depending on the flavor and chirality of
the produced quarks, many interferences between EW-mediated and QCD-mediated
diagrams give non-zero contributions at tree-level and NLO. We discuss the
computational techniques and present an extensive numerical analysis for
inclusive squark--squark production as well as for subsets and single
processes. While the tree-level EW contributions to the integrated cross
sections can reach the 20% level, the NLO EW corrections typically lower the LO
prediction by a few percent.Comment: 36 pages, 18 figure
Hadronic production of bottom-squark pairs with electroweak contributions
We present the complete computation of the tree-level and the next-to-leading
order electroweak contributions to bottom-squark pair production at the LHC.
The computation is performed within the minimal supersymmetric extension of the
Standard Model. We discuss the numerical impact of these contributions in
several supersymmetric scenarios.Comment: 33 pages, v2: preprint numbers correcte
The MSSM prediction for W+/- H-/+ production by gluon fusion
We discuss the associated W+/- H-/+ production in p p collision for the Large
Hadron Collider. A complete one-loop calculation of the loop-induced subprocess
g g -> W+/- H-/+ is presented in the framework of the Minimal Supersymmetric
Standard Model (MSSM), and the possible enhancement of the hadronic cross
section is investigated under the constraint from the squark direct-search
results and the low-energy precision data. Because of the large destructive
interplay in the quark-loop contributions between triangle-type and box-type
diagrams, the squark-loop contributions turn out to be comparable with the
quark-loop ones. In particular, the hadronic cross section via gluon fusion can
be extensively enhanced by squark-pair threshold effects in the box-type
diagrams, so that it can be as large as the hadronic cross section via the b
b-bar -> W+/- H-/+ subprocess which appears at tree level.Comment: 35 pages, 7 figures, version to appear in Physical Review
Precise Prediction for M_W in the MSSM
We present the currently most accurate evaluation of the W boson mass, M_W,
in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase
dependence at the one-loop level, all available MSSM two-loop corrections as
well as the full Standard Model result have been included. We analyse the
impact of the different sectors of the MSSM at the one-loop level with a
particular emphasis on the effect of the complex phases. We discuss the
prediction for M_W based on all known higher-order contributions in
representative MSSM scenarios. Furthermore we obtain an estimate of the
remaining theoretical uncertainty from unknown higher-order corrections.Comment: 38 pages, 25 figures. Minor corrections, additional reference
Top quark physics in hadron collisions
The top quark is the heaviest elementary particle observed to date. Its large
mass makes the top quark an ideal laboratory to test predictions of
perturbation theory concerning heavy quark production at hadron colliders. The
top quark is also a powerful probe for new phenomena beyond the Standard Model
of particle physics. In addition, the top quark mass is a crucial parameter for
scrutinizing the Standard Model in electroweak precision tests and for
predicting the mass of the yet unobserved Higgs boson. Ten years after the
discovery of the top quark at the Fermilab Tevatron top quark physics has
entered an era where detailed measurements of top quark properties are
undertaken. In this review article an introduction to the phenomenology of top
quark production in hadron collisions is given, the lessons learned in Tevatron
Run I are summarized, and first Run II results are discussed. A brief outlook
to the possibilities of top quark research a the Large Hadron Collider,
currently under construction at CERN, is included.Comment: 84 pages, 32 figures, accepted for publication by Reports on Progress
in Physic