6,059 research outputs found
The minimal scenario of leptogenesis
We review the main features and results of thermal leptogenesis within the
type I seesaw mechanism, the minimal extension of the Standard Model explaining
neutrino masses and mixing. After presenting the simplest approach, the vanilla
scenario, we discuss various important developments in recent years, such as
the inclusion of lepton and heavy neutrino flavour effects, a description
beyond a hierarchical heavy neutrino mass spectrum and an improved kinetic
description within the density matrix and the closed-time-path formalisms. We
also discuss how leptogenesis can ultimately represent an important
phenomenological tool to test the seesaw mechanism and the underlying model of
new physics.Comment: 37 pages, 4 figures; invited review chapter for the "Focus on the
Origin of Matter" issue published in the New Journal of Physic
Jet substructure shedding light on heavy Majorana neutrinos at the LHC
The existence of tiny neutrino masses and flavor mixings can be explained
naturally in various seesaw models, many of which typically having additional
Majorana type SM gauge singlet right handed neutrinos (). If they are at
around the electroweak scale and furnished with sizeable mixings with light
active neutrinos, they can be produced at high energy colliders, such as the
Large Hadron Collider (LHC). A characteristic signature would be same sign
lepton pairs, violating lepton number, together with light jets -- . We propose a new
search strategy utilising jet substructure techniques, observing that for a
heavy right handed neutrino mass much above , the two jets
coming out of the boosted may be interpreted as a single fat-jet ().
Hence, the distinguishing signal topology will be .
Performing a comprehensive study of the different signal regions along with
complete background analysis, in tandem with detector level simulations, we
compute statistical significance limits. We find that heavy neutrinos can be
explored effectively for mass ranges GeV GeV and
different light-heavy neutrino mixing . At the 13 TeV LHC with
3000 integrated luminosity one can competently explore
mixing angles much below present LHC limits, and moreover exceed bounds from
electroweak precision data.Comment: Accepted for publication in JHEP. 25 pages, 8 figures, 1 tabl
Disambiguating Seesaw Models using Invariant Mass Variables at Hadron Colliders
We propose ways to distinguish between different mechanisms behind the
collider signals of TeV-scale seesaw models for neutrino masses using kinematic
endpoints of invariant mass variables. We particularly focus on two classes of
such models widely discussed in literature: (i) Standard Model extended by the
addition of singlet neutrinos and (ii) Left-Right Symmetric Models. Relevant
scenarios involving the same "smoking-gun" collider signature of dilepton plus
dijet with no missing transverse energy differ from one another by their event
topology, resulting in distinctive relationships among the kinematic endpoints
to be used for discerning them at hadron colliders. These kinematic endpoints
are readily translated to the mass parameters of the on-shell particles through
simple analytic expressions which can be used for measuring the masses of the
new particles. A Monte Carlo simulation with detector effects is conducted to
test the viability of the proposed strategy in a realistic environment.
Finally, we discuss the future prospects of testing these scenarios at the
and 100 TeV hadron colliders.Comment: 35 pages, 12 figures, 2 tables; minor changes, accepted for
publication in JHE
Sterile Neutrinos and B-L Symmetry
We revisit the relation between the neutrino masses and the spontaneous
breaking of the B-L gauge symmetry. We discuss the main scenarios for Dirac and
Majorana neutrinos and point out two simple mechanisms for neutrino masses. In
this context the neutrino masses can be generated either at tree level or at
quantum level and one predicts the existence of very light sterile neutrinos
with masses below the eV scale. The predictions for lepton number violating
processes such as mu to e and mu to e gamma are discussed in detail. The impact
from the cosmological constraints on the effective number of relativistic
degree of freedom is investigated.Comment: v2 new section for the LFV processes, minor corrections, main
conclusion unchanged, version to appear in Physics Letters
Phenomenology of Light Sneutrino Dark Matter in cMSSM/mSUGRA with Inverse Seesaw
We study the possibility of a light Dark Matter (DM) within a constrained
Minimal Supersymmetric Standard Model (cMSSM) framework augmented by a SM
singlet-pair sector to account for the non-zero neutrino masses by inverse
seesaw mechanism. Working within a 'hybrid' scenario with the MSSM sector fixed
at high scale and the singlet neutrino sector at low scale, we find that,
contrary to the case of the usual cMSSM where the neutralino DM cannot be very
light, we can have a light sneutrino DM with mass below 100 GeV satisfying all
the current experimental constraints from cosmology, collider as well as
low-energy experiments. We also note that the supersymmetric inverse seesaw
mechanism with sneutrino as the lightest supersymmetric partner can have
enhanced same-sign dilepton final states with large missing transverse energy
(mET) coming from the gluino- and squark-pair as well as the squark-gluino
associated productions and their cascade decay through charginos. We present a
collider study for the same-sign dilepton+jets+mET signal in this scenario and
propose some distinctions with the usual cMSSM. We also comment on the
implications of such a light DM scenario on the invisible decay width of an 125
GeV Higgs boson.Comment: 24 pages, 4 figures, 7 tables; matches published versio
Reconciling the 2 TeV Excesses at the LHC in a Linear Seesaw Left-Right Model
We interpret the 2 TeV excesses at the LHC in a left-right symmetric model
with Higgs doublets and spontaneous -parity violation. The light neutrino
masses are understood via a linear seesaw, suppressed by a high -parity
breaking scale, and the heavy neutrinos have a pseudo-Dirac character. In
addition, with a suppressed right-handed gauge coupling
in an embedding, we can thereby interpret the observed excess
at CMS. We show that it can be reconciled with the diboson and dijet excesses
within a simplified scenario based on our model. Moreover, we find that the
mixing between the light and heavy neutrinos can be potentially large which
would induce dominant non-standard contributions to neutrinoless double beta
decay via long-range and neutrino exchange.Comment: References added, typos fixed, matches published version, 12 pages, 4
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