24,280 research outputs found
Exact eigenvalue assignment of linear scalar systems with single delay using Lambert W function
Eigenvalue assignment problem of a linear scalar system with a single
discrete delay is analytically and exactly solved. The existence condition of
the desired eigenvalue is established when the current and delay states are
present in the feedback loop. Design of the feedback controller is then
followed. Furthermore, eigenvalue assignment for the input-delay system is also
obtained as well. Numerical examples illustrate the procedure of assigning the
desired eigenvalue
Beyond Minimal Lepton Flavored Dark Matter
We consider a class of flavored dark matter (DM) theories where dark matter
interacts with the Standard Model lepton fields at the renormalizable level. We
allow for a general coupling matrix between the dark matter and leptons whose
structure is beyond the one permitted by the minimal flavor violation (MFV)
assumption. It is assumed that this is the only new source of flavor violation
in addition to the Standard Model (SM) Yukawa interactions. The setup can be
described by augmenting the SM flavor symmetry by an additional
, under which the dark matter transforms. This
framework is especially phenomenologically rich, due to possible novel
flavor-changing interactions which are not present within the more restrictive
MFV framework. As a representative case study of this setting, which we call
"beyond MFV" (BMFV), we consider Dirac fermion dark matter which transforms as
a singlet under the SM gauge group and a triplet under .
The DM fermion couples to the SM lepton sector through a scalar mediator
. Unlike the case of quark-flavored DM, we show that there is no
symmetry within either the MFV or BMFV settings which
automatically stabilizes the lepton-flavored DM. We discuss constraints on this
setup from flavor-changing processes, DM relic abundance as well as direct and
indirect detections. We find that relatively large flavor-changing couplings
are possible, while the dark matter mass is still within the phenomenologically
interesting region below the TeV scale. Collider signatures which can be
potentially searched for at the lepton and hadron colliders are discussed.
Finally, we discuss the implications for decaying dark matter, which can appear
if an additional stabilizing symmetry is not imposed.Comment: 30 pages, 12 figures; minor corrections, added references and
discussion on decaying dark matter, matches published versio
Thermodynamic properties and bulk viscosity near phase transition in the Z(2) and O(4) models
We investigate the thermodynamic properties including equation of state, the
trace anomaly, the sound velocity and the specific heat, as well as transport
properties like bulk viscosity in the Z(2) and O(4) models in the Hartree
approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism. We study these
properties in different cases, e.g. first order phase transition, second order
phase transition, crossover and the case without phase transition, and discuss
the correlation between the bulk viscosity and the thermodynamic properties of
the system. We find that the bulk viscosity over entropy density ratio exhibits
an upward cusp at the second order phase transition, and a sharp peak at the
1st order phase transition. However, this peak becomes smooth or disappears in
the case of crossover. This indicates that at RHIC, where there is no real
phase transition and the system experiences a crossover, the bulk viscosity
over entropy density might be small, and it will not affect too much on
hadronization. We also suggest that the bulk viscosity over entropy density
ratio is a better quantity than the shear viscosity over entropy density ratio
to locate the critical endpoint.Comment: 19 pages, 30 figures, 1 tabl
- …