73 research outputs found
Revisiting neutrino masses from Planck scale operators
Planck scale lepton number violation is an interesting and natural
possibility to explain non-zero neutrino masses. We consider such operators in
the context of Randall-Sundrum (RS1) scenarios. Implementation of this scenario
with a single Higgs localized on the IR brane (standard RS1) is not
phenomenologically viable as they lead to inconsistencies in the charged lepton
mass fits. In this work we propose a set-up with two Higgs doublets. We present
a detailed numerical analysis of the fits to fermion masses and mixing angles.
This model solves the issues regarding the fermion mass fits but solutions with
consistent electroweak symmetry breaking are highly fine tuned. A simple
resolution is to consider supersymmetry in the bulk and a detailed discussion
of which is provided. Constraints from flavour are found to be strong and
Minimal Flavour Violation (MFV) is imposed to alleviate them.Comment: 31 Pages, 12 Figures, Abstract reworded, Discussion modified and
improved, quark fits included, EWSB discussion expanded, examples of lepton
mass fits with MFV included, v
Bulk Majorana mass terms and Dirac neutrinos in Randall Sundrum Model
We present a novel scheme where Dirac neutrinos are realized even if lepton
number violating Majorana mass terms are present. The setup is the
Randall-Sundrum framework with bulk right handed neutrinos. Bulk mass terms of
both Majorana and Dirac type are considered. It is shown that massless zero
mode solutions exist when the bulk Dirac mass term is set to zero. In this
limit, it is found that the effective 4D small neutrino mass is primarily of
Dirac nature with the Majorana type contributions being negligible.
Interestingly, this scenario is very similar to the one known with flat extra
dimensions. Neutrino phenomenology is discussed by fitting both charged lepton
masses and neutrino masses simultaneously. A single Higgs localised on the IR
brane is highly constrained as unnaturally large Yukawa couplings are required
to fit charged lepton masses. A simple extension with two Higgs doublets is
presented which facilitates a proper fit for the lepton masses.Comment: 13 Pages, Few clarifications included and added references. Figure
removed. Published in PR
anomalies: From warped models to colliders
We address the anomalies in the semi leptonic decays of mesons in a
warped custodial framework. Two possible solutions of lepton non-universality
are discussed: A) The muon singlets couple non-universally to NP and B) The
non-universality is in the coupling of lepton doublets. Both these scenarios
are characterized by different predictions for rare Kaon decays. An essential
feature of these scenarios is that the electron contribution to the Wilson
coefficients (WC) is non-vanishing, thereby offering possibilities for
different patterns of solutions. Beginning with a generic model, we
demonstrate how the observation of the ratio can be mapped
to a given pattern of WC which satisfy the anomalies.Comment: 4 Pages, 2 Figures. Contributions to the proceedings for Rencontres
de Moriond, QCD and High energy interactions 201
A Framework for Finding Anomalous Objects at the LHC
Search for new physics events at the LHC mostly rely on the assumption that
the events are characterized in terms of standard-reconstructed objects such as
isolated photons, leptons, and jets initiated by QCD-partons. While such
strategy works for a vast majority of physics beyond the standard model
scenarios, there are examples aplenty where new physics give rise to anomalous
objects (such as collimated and equally energetic particles, decays due to long
lived particles etc.) in the detectors, which can not be classified as any of
the standard-objects. Varied methods and search strategies have been proposed,
each of which is trained and optimized for specific models, topologies, and
model parameters. Further, as LHC keeps excluding all expected candidates for
new physics, the need for a generic method/tool that is capable of finding the
unexpected can not be understated. In this paper, we propose one such method
that relies on the philosophy that all anomalous objects are
standard-objects. The anomaly finder, we suggest, simply is a collection of
vetoes that eliminate all standard-objects up to a pre-determined acceptance
rate. Any event containing at least one anomalous object (that passes all these
vetoes), can be identified as a candidate for new physics. Subsequent offline
analyses can determine the nature of the anomalous object as well as of the
event, paving a robust way to search for these new physics scenarios in a
model-independent fashion. Further, since the method relies on learning only
the standard-objects, for which control samples are readily available from
data, one can build the analysis in an entirely data-driven way.Comment: 32 pages, 5 tables and 12 figures; v2: references added; v3:
Practical guideline given for implementation at the LHC, comments added on
the possibility of inclusion of Muons and b-jets in the framework. Accepted
for publication in Nuclear Physics B; v4: Title fixed from v3 to match
journal version, funding information update
Gravitational rescue of minimal gauge mediation
Gravity mediation supersymmetry breaking become comparable to gauge mediated
supersymmetry breaking contributions when messenger masses are close to the GUT
scale. By suitably tuning the gravity contributions one can then modify the
soft supersymmetry breaking sector to generate a large stop mixing parameter
and a light higgs mass of 125 GeV. In this kind of hybrid models, however the
nice features of gauge mediation like flavour conservation etc, are lost. To
preserve the nice features, gravitational contributions should become important
for lighter messenger masses and should be important only for certain fields.
This is possible when the hidden sector contains multiple (at least two)
spurions with hierarchical vaccum expectation values. In this case, the
gravitational contribtutions can be organised to be `just right'. We present a
complete model with two spurion hidden sector where the gravitational
contribution is from a warped flavour model in a Randall-Sundrum setting. Along
the way, we present simple expressions to handle renormalisation group
equations when supersymmetry is broken by two different sectors at two
different scales.Comment: 24 Pages, 3 figures, Detailed discussions on flavour violation
included, added figure and references, Matches published versio
Warped Alternatives to Froggatt-Nielsen Models
We consider Randall-Sundrum set up (RS) to be a theory of flavour, as an
alternative to Froggatt-Nielsen models instead of as a solution to the
hierarchy problem. We consider a modified RS framework between the Planck scale
and the GUT scale. This also alleviates constraints from flavour physics.
Fermion masses and mixing angles are fit at the GUT scale. The ranges of the
bulk mass parameters are determined using a fit taking in to
consideration the variation in parameters. In the hadronic
sector, the heavy top quark requires large bulk mass parameters localising the
right handed top quark close to the IR brane. Two cases of neutrino masses are
considered (a) Planck scale lepton number violation and (b) Dirac neutrino
masses. Contrary to the case of weak scale RS models, both these cases give
reasonable fits to the data, with the Planck scale lepton number violation
fitting slightly better compared to the Dirac case. In the Supersymmetric
version, the fits are not significantly different except for the variation in
. If the Higgs superfield and the SUSY breaking spurion are
localized on the same brane then the structure of the sfermion masses are
determined by the profiles of the zero modes of the hypermultiplets in the
bulk. Trilinear terms have the same structure as the Yukawa matrices. The
resultant squark spectrum is around required by the light
Higgs mass to be around 125 GeV and to satisfy the flavour violating
constraints.Comment: 7 Figures, 34 pages. Minor modifications of the text mostly typos and
references added. A couple of typos fixed in the tables. Conclusions
unchange
Lepton Masses and Flavor Violation in Randall Sundrum Model
Lepton masses and mixing angles via localization of 5D fields in the bulk are
revisited in the context of Randall-Sundrum models. The Higgs is assumed to be
localized on the IR brane. Three cases for neutrino masses are considered: (a)
The higher dimensional LH.LH operator (b) Dirac masses (c) Type I see-saw with
bulk Majorana mass terms. Neutrino masses and mixing as well as charged lepton
masses are fit in the first two cases using minimisation for the bulk
mass parameters, while varying the Yukawa couplings between
0.1 and 4. Lepton flavour violation is studied for all the three cases. It is
shown that large negative bulk mass parameters are required for the right
handed fields to fit the data in the LH LH case. This case is characterized by
a very large Kaluza-Klein (KK) spectrum and relatively weak flavour violating
constraints at leading order. The zero modes for the charged singlets are
composite in this case and their corresponding effective 4-D Yukawa couplings
to the KK modes could be large. For the Dirac case, good fits can be obtained
for the bulk mass parameters, , lying between 0 and 1. However, most of
the `best fit regions' are ruled out from flavour violating constraints. In the
bulk Majorana terms case, we have solved the profile equations numerically. We
give example points for inverted hierarchy and normal hierarchy of neutrino
masses. Lepton flavor violating rates are large for these points. We then
discuss various minimal flavor violation (MFV) schemes for Dirac and bulk
Majorana cases. In the Dirac case with MFV hypothesis, it is possible to
simultaneously fit leptonic masses and mixing angles and alleviate lepton
flavor violating constraints for Kaluza-Klein modes with masses of around 3
TeV. Similar examples are also provided in the Majorana case.Comment: 43 pages, 20 figures, Revtex; version 2:a few clarified comments,
added references, Published in PRD versio
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