Neutrino Models and Leptogenesis

1.7 MB·English

by  Sandy S. C. Law

Neutrino Models
and
Leptogenesis
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Submitted in total ful(cid:28)lment of the requirements of the degree of

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tor of Philosophy
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1
v Sandy Sheung Che Law
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3
2
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1 S
hool of Physi
s
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9 The University of Melbourne
0
: AUSTRALIA
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X
r De
ember, 2008
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Abstract
e u t r i n o properties
an play a
ru
ial role in determining the matter-antimatter
asymmetry of the universe if thermal leptogenesis is the
orre
t solution to the
N baryogenesis problem. Owing to this, the study of neutrino models goes beyond
the mere purpose of generating tiny neutrino masses, and it is natural to in
orporate the
puzzle of the
osmi
baryon asymmetry. To this end, we have investigated several di(cid:27)erent
extensions of the neutrino model based on the type I seesaw me
hanism with parti
ular
emphasis on their leptogenesis impli
ations.
Inthe(cid:28)rstpartofourwork, wepresentathoroughanalysis,intheleptogenesis
ontext,
of
onstrainedneutrinomodelswhi
hhaveanabelianfamilysymmetryandoneextraHiggs
singlet. The general result is that although these models
ontain less free parameters than
thedefault typeIseesawsetup, they donot hinderthepossibility of su

essfulleptogenesis
in both the one-(cid:29)avor approximation and when (cid:29)avor e(cid:27)e
ts are in
luded. In fa
t, we
have dis
overed that they do not modify or provide signi(cid:28)
ant
onstraints on the typi
al
leptogenesis s
enario with hierar
hi
al heavy right-handed neutrinos.
We then explore how the seesaw se
tor in neutrino mass models may be
onstrained
throughsymmetriestobe
ompletelydeterminedintermsoflow-energymass,mixingangle
CP
and violating phase observables, with the subsequent aim to study their leptogenesis
impli
ations. The key ingredient in a
hieving this
onne
tion between the two distin
t
energy se
tors is to simultaneously employ intra- and inter-(cid:29)avor symmetries so that the
neutrino Dira
mass matrix is only given in terms of the
harged-lepton or quark mass
matri
es while all relevant diagonalization matri
es
an be fully predi
ted by the theory.
We have built illustrative models to demonstrate this and shown that leptogenesis
an
su

eed in small regions of parameter spa
e for the
ase where the neutrino Dira
and up-
quarkmassmatrixareidenti
al. Also,ithasbeenfoundthatwhentheneutrinoDira
mass
matrix is equal to its
harged-lepton
ounterpart, TeV s
ale heavy neutrinos are possible
although it is unlikely that they
an be dete
ted in
olliders.
Finally, we present a new leptogenesis s
enario, where the lepton asymmetry is gener-
CP
ated by violating de
ays of heavy right-handed neutrinos via ele
tromagneti
dipole
moment
ouplings to the ordinary light neutrinos. Akin to the usual s
enario where the
i
ii ABSTRACT
de
ays are mediated through Yukawa intera
tions, we have shown, by expli
it
al
ulations,
that the desired asymmetry
an be produ
ed through the interferen
e of the
orresponding
tree-level and one-loop de
ay amplitudes involving the e(cid:27)e
tive dipole moment operators.
Furthermore, we (cid:28)nd that the relationship of the leptogenesis s
ale to the light neutrino
masses is similar to that for the standard Yukawa-mediated me
hanism.
Declaration
This is to
ertify that
(i) the thesis
omprises only my original work towards the PhD ex
ept where indi
ated
in the Prefa
e,
(ii) due a
knowledgement has been made in the text to all other material used,
(iii) thethesisislessthan100,000wordsinlength,ex
lusiveoftable,maps,bibliographies,
appendi
es and footnotes.
...................................
Sandy S. C. Law
Date: / /
iii

Preface
The work presented here
omprises of (cid:28)ve main
hapters (ex
luding auxiliary materials
su
h as bibliography and appendi
es):
Chapter 1 is an original literature review on the various topi
s relating to neutrino prop-
erties, baryon asymmetry of the universe and thermal leptogenesis;
Chapter 2, 3 and 4 are based on the work presented in Publi
ations 1, 3 and 2 (see
page 157) respe
tively. They were done in
ollaboration with N. F. Bell (Chapter 4),
X. G. He (Chapter 3), B. J. Kayser (Chapter 4) and R. R. Volkas (Chapter 2 and 3).
Most of the initial ideas for these investigations are due to N. F. Bell (Chapter 4) and
R. R. Volkas (Chapter 2 and 3). But, all subsequent analyses and methods of presentation
are my own work with the ex
eptions of Se
. 3.4.4 where X. G. He has made a signi(cid:28)
ant

ontribution, and the proof in Se
. 4.3.1 whi
h is due to B. J. Kayser;
Chapter 5 is the
on
lusion.
v