21 research outputs found
Note on gauge and gravitational anomalies of discrete symmetries
In this note, we discuss the consistency conditions which a discrete
symmetry should satisfy in order that it is not violated by gauge and
gravitational instantons. As examples, we enlist all the -symmetries as well as non- symmetries (N=2,3,4) in the
minimally supersymmetric standard model (MSSM) that are free from gauge and
gravitational anomalies. We show that there exists non-anomalous discrete
symmetries that forbid Baryon number violation up to dimension 6 level (in
superspace). We also observe that there exists no non-anomalous -symmetry in the MSSM. Furthermore, we point out that in a theory with one
Majorana spin 3/2 gravitino, a large class of -symmetries are
violated in the presence of Eguchi-Hanson (EH) gravitational instanton. This is
also in general true for higher -symmetries. We also notice
that in 4 dimensional supergravity, the global -symmetry is always violated by the EH instanton irrespective of the matter
content of the theory.Comment: Version to appear in JHE
Role of Tensor operators in and
The recent LHCb measurement of in two bins, when combined
with the earlier measurement of , strongly suggests lepton flavour
non-universal new physics in semi-leptonic meson decays. Motivated by these
intriguing hints of new physics, several authors have considered vector, axial
vector, scalar and pseudo scalar operators as possible explanations of these
measurements. However, tensor operators have widely been neglected in this
context. In this paper, we consider the effect of tensor operators in and
. We find that, unlike other local operators, tensor operators can
comfortably produce both of and
close to their experimental central values. However, a simultaneous explanation
of is not possible with only Tensor operators, and other vector or axial
vector operators are needed. In fact, we find that combination of vector and
tensor operators can provide simultaneous explanations of all the anomalies
comfortably at the level, a scenario which is hard to achieve with
only vector or axial vector operators. We also comment on the compatibility of
the various new physics solutions with the measurements of the inclusive decay
.Comment: Version to appear in PL
Unification with Vector-like fermions and signals at LHC
We look for minimal extensions of Standard Model with vector like fermions
leading to precision unification of gauge couplings. Constraints from proton
decay, Higgs stability and perturbativity are considered. The simplest models
contain several copies of vector fermions in two different (incomplete)
representations. Some of these models encompass Type III seesaw mechanism for
neutrino masses whereas some others have a dark matter candidate. In all the
models, at least one of the candidates has non-trivial representation under
. In the limit of vanishing Yukawa couplings, new QCD bound
states are formed, which can be probed at LHC. The present limits based on
results from 13 TeV already probe these particles for masses around a TeV.
Similar models can be constructed with three or four vector representations,
examples of which are presented.Comment: 48 pages; v3:major corrections with discussion on threshold
corrections, version accepted for publication in JHE