4,201 research outputs found
Distances on the tropical line determined by two points
Let . Write if is a multiple of
. Two different points and in uniquely
determine a tropical line , passing through them, and stable under
small perturbations. This line is a balanced unrooted semi--labeled tree on
leaves. It is also a metric graph.
If some representatives and of and are the first and second
columns of some real normal idempotent order matrix , we prove that the
tree is described by a matrix , easily obtained from . We also
prove that is caterpillar. We prove that every vertex in
belongs to the tropical linear segment joining and . A vertex, denoted
, closest (w.r.t tropical distance) to exists in . Same for
. The distances between pairs of adjacent vertices in and the
distances \dd(p,pq), \dd(qp,q) and \dd(p,q) are certain entries of the
matrix . In addition, if and are generic, then the tree
is trivalent. The entries of are differences (i.e., sum of principal
diagonal minus sum of secondary diagonal) of order 2 minors of the first two
columns of .Comment: New corrected version. 31 pages and 9 figures. The main result is
theorem 13. This is a generalization of theorem 7 to arbitrary n. Theorem 7
was obtained with A. Jim\'enez; see Arxiv 1205.416
Electroweak Vacuum Stability and the Seesaw Mechanism Revisited
We study the electroweak vacuum stability in Type I seesaw models for 3
generations of neutrinos in scenarios where the right-handed neutrinos have
explicit bare mass terms in the Lagrangian and where these are dynamically
generated through the mechanism of spontaneous symmetry breaking. To best
highlight the difference of the two cases we concentrate on the absolute
stability of the scalar potential. We observe that for the first scenario, the
scale at which the scalar potential becomes unstable is lower from that within
the Standard Model. In addition the Yukawa couplings are
constrained such that \Tr{[\mathbf{Y}^{\dagger}_\nu \mathbf{Y}_{\nu}}]
\lesssim10^{-3}. In the second scenario the electroweak stability can be
improved in a large region of parameter space. However, we found that the
scalar used to break the lepton number symmetry cannot be too light and have a
large coupling to right-handed neutrinos in order for the seesaw mechanism to
be a valid mechanism for neutrino mass generation. In this case we have \Tr
[\mathbf{Y}^\dagger_{\nu} \mathbf{Y}_\nu]\lesssim 0.01
Long-lived Colored Scalars at the LHC
We study the collider signatures of a long-lived massive colored scalar
transforming trivially under the weak interaction and decaying within the inner
sections of a detector such as ATLAS or CMS. In our study, we assume that the
colored scalar couples at tree-level to a top quark and a stable fermion,
possibly arising from a dark sector or from supersymmetric extensions of the
Standard Model. After implementing the latest experimental searches for
long-lived colored scalars, we observe a region of parameter space consistent
with a colored electroweak-singlet scalar with mass between GeV
and a lifetime between together, with a nearly degenerate
dark fermion that may be probed at the TeV LHC. We show that a
search strategy using a combination of cuts on missing transverse energy and
impact parameters can exclude regions of parameter space not accessed by prompt
searches. We show that a region of parameter space within our simplified model
may naturally arise from the light-stop window regime of supersymmetric
extensions of the Standard Model, where a light mostly right-handed stop has a
mass slightly larger than the lightest neutralino and decays through a
four-body process
A Singlet Extension of the MSSM with a Dark Matter Portal
The minimal extension of the MSSM (NMSSM) has been widely studied in the
search for a natural solution to the problem. In this work, we consider a
variation of the NMSSM where an extra singlet is added and a Peccei-Quinn
symmetry is imposed. We study its neutralino sector and compute the
annihilation cross section of the lightest neutralino. We use existent
cosmological and collider data to constrain the parameter space and consider
the lightest neutralino, which is very light, as a dark matter candidate.Comment: 26 pages, 8 figures . v4: minor corrections; version accepted for
publicatio
Tropical conics for the layman
We present a simple and elementary procedure to sketch the tropical conic
given by a degree--two homogeneous tropical polynomial. These conics are trees
of a very particular kind. Given such a tree, we explain how to compute a
defining polynomial.
Finally, we characterize those degree--two tropical polynomials which are
reducible and factorize them. We show that there exist irreducible degree--two
tropical polynomials giving rise to pairs of tropical lines.Comment: 19 pages, 4 figures. Major rewriting of formerly entitled paper
"Metric invariants of tropical conics and factorization of degree--two
homogeneous tropical polynomials in three variables". To appear in Idempotent
and tropical mathematics and problems of mathematical physics (vol. II), G.
Litvinov, V. Maslov, S. Sergeev (eds.), Proceedings Workshop, Moscow, 200
Top Quark as a Dark Portal and Neutrino Mass Generation
We present a new model for radiatively generating Majorana active neutrino
masses while incorporating a viable dark matter candidate. This is possible by
extending the Standard Model with a single Majorana neutrino endowed with a
dark parity, a colour electroweak singlet scalar, as well as a colour
electroweak triplet scalar. Within this framework, the -type quarks play a
special role, serving as a portal for dark matter, and a messenger for neutrino
mass generation. We consider three benchmark scenarios where the abundance of
dark matter can match the latest experimental results, while generating
neutrino masses in the milli-electronvolt range. We show how constraints from
lepton flavour violation, in particular the branching fraction of , can place lower bounds on the coupling between our dark matter
candidate and top quarks. Furthermore, we show that this coupling can also be
constrained using collider data from the Tevatron and the LHC.Comment: 8 captions, 10 figure
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