Aspects of Bottom-up Hidden Sector Models


First Edition

The standard model (SM) of particle physics is a hugely successful theory of nature, but it is incomplete. E.g., it cannot explain finite SM neutrino masses or the origin of the primordial baryon asymmetry (BAU). One way to address such problems is to postulate the existence of new but hidden particles... Read More

The standard model (SM) of particle physics is a hugely successful theory of nature, but it is incomplete. E.g., it cannot explain finite SM neutrino masses or the origin of the primordial baryon asymmetry (BAU). One way to address such problems is to postulate the existence of new but hidden particles. This thesis studies such "hidden sectors" in two ways: 1) An effective theory approach, where electroweak (EW) and GeV scale portal effective theories (PETs) are constructed that couple the SM to a generic light hidden mediator of spin 0, ½, or 1. The EW scale PETs include all portal operators of dimension d≤5. The GeV scale PETs additionally include all leading order (LO) flavour changing portal operators of dimension d≤6,7. They are used to derive a LO PET chiral perturbation theory Lagrangian that describes hidden sector induced light meson transitions in fixed target experiments like NA62 or SHiP. 2) An investigation of the type-I seesaw model, which couples the SM to n≥2 sterile neutrinos that can generate a BAU via “leptogenesis”. It is shown that thermal and spectator effects can result in a sign-flip and strong relative enhancement of the BAU in high-scale leptogenesis with two hierarchical sterile neutrinos of vanishing initial abundance. Much lighter sterile neutrinos may be detected via lepton number violating (LNV) decays at colliders, but LNV decays could be suppressed relative to lepton number conserving decays for 't Hooft natural parameter choices. It is shown that the corresponding parameter space consists of three regions: (a)with unsuppressed LNV decays, (b)with suppressed LNV decays, (c)with suppressed and unsuppressed LNV decays.


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Specifications


Publisher
Presses universitaires de Louvain
Author
Philipp Klose,
Set
Language
English
BISAC Subject Heading
SCI055000 SCIENCE / Physics > SCI074000 SCIENCE / Physics / Atomic & Molecular
BIC subject category (UK)
PH Physics > PHN Nuclear structure physics > PHP Particle & high-energy physics
Onix Audience Codes
06 Professional and scholarly
CLIL (Version 2013-2019)
3058 Physique
Title First Published
26 November 2020
Subject Scheme Identifier Code
: Physique atomique et moléculaire
: Sciences exactes
: Physique

Paperback


Publication Date
26 November 2020
ISBN-13
9782390610021
Extent
Main content page count : 216
Code
101032
Dimensions
16 x 24 cm
Weight
352 grams
Packaging Type
No outer packaging
List Price
21.00 €
ONIX XML
Version 2.1, Version 3

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Contents


1 Introduction 7
2 The Portal Effective Theory Framework 11
2.1 Philosophy and Limitations . . . . . . . . . . . . . . . . . 11
2.2 The Construction of General PET Lagrangians . . . . . . 14
2.2.1 General Approach . . . . . . . . . . . . . . . . . . 14
2.2.2 Power Counting and Naive Dimensional Analysis . 15
2.2.3 Elimination of Redundant Operators . . . . . . . . 17
2.2.4 Should one Diagonalize Quadratic Portal Interactions? 21
2.3 General Electroweak Scale PETs . . . . . . . . . . . . . . 23
2.3.1 Constructing a Minimal Basis of Portal Operators 23
2.3.2 The Full Portal Lagrangian . . . . . . . . . . . . . 29
2.3.3 Modifications after Electroweak Symmetry Breaking . . . . . . . . . . . . . . . . . . . . . . . 32
2.4 General GeV Scale PETs . . . . . . . . . . . . . . . . . . . 36
2.4.1 General Considerations . . . . . . . . . . . . . . . 36
2.4.2 Scalar Portal Operators . . . . . . . . . . . . . . . 41
2.4.3 Fermion Portal Operators . . . . . . . . . . . . . . 45
2.4.4 Vector Portal Operators . . . . . . . . . . . . . . . 51
2.4.5 The Subset of |_F| = 1 Portal Operators . . . . . 54
3 PET Chiral Perturbation Theory 59
3.1 The External Current Picture . . . . . . . . . . . . . . . . 59
3.2 Aspects of QCD at Low Energies . . . . . . . . . . . . . . 62
3.2.1 The QCD Lagrangian . . . . . . . . . . . . . . . . 62
3.2.2 Conformal Anomaly . . . . . . . . . . . . . . . . . 63
3.2.3 Large Nc QCD . . . . . . . . . . . . . . . . . . . . 65
3.2.4 Chiral Symmetry . . . . . . . . . . . . . . . . . . . 68
3.2.5 Pseudo Nambu-Goldstone Bosons . . . . . . . . . . 71
3.3 QCD in the Presence of External Currents . . . . . . . . . 76
3.3.1 The Interaction Lagrangian . . . . . . . . . . . . . 76
3.3.2 Explicit Breaking of Scale Invariance . . . . . . . . 83
3.3.3 Generalized Chiral Symmetry . . . . . . . . . . . . 84
3.4 Construction of the PET _PT Lagrangian . . . . . . . . . 88
3.4.1 General Considerations . . . . . . . . . . . . . . . 88
3.4.2 The generalized _PT Action . . . . . . . . . . . . 91
3.4.3 Transition to the Physical Vacuum . . . . . . . . . 100
3.5 Low Energy Constants . . . . . . . . . . . . . . . . . . . . 104
3.5.1 Low energy Realizations of QCD Gauge Singlets . 104
3.5.2 LEC's for Scalar to Gluon Coupling . . . . . . . . 107
3.5.3 LEC's for the octet and 27-plet Terms . . . . . . . 108
4 Lepton Number Violation via Sterile Neutrino Decoherence 113
4.1 Lepton Number Violation at Colliders . . . . . . . . . . . 113
4.2 Introduction to Type-I Seesaw Models . . . . . . . . . . . 116
4.3 Criteria for Sterile Neutrino Decoherence . . . . . . . . . 120
4.3.1 General Considerations . . . . . . . . . . . . . . . 120
4.3.2 Benchmark Model with n = 2 . . . . . . . . . . . . 122
4.4 LNV in the n = 2 Benchmak Model . . . . . . . . . . . . 125
5 Relativistic and Spectator Effects in High-Scale Leptogenesis 127
5.1 Updating High-Scale Leptogenesis . . . . . . . . . . . . . 127
5.2 Simplified Model for High-Scale Leptogenesis . . . . . . . 132
5.3 The CTP Formalism . . . . . . . . . . . . . . . . . . . . . 137
5.3.1 CTP Correlation Functions . . . . . . . . . . . . . 137
5.3.2 Constraints from Finite Temperature QFT . . . . 140
5.3.3 Schwinger-Dyson Equations . . . . . . . . . . . . . 141
5.4 Relativistic Fluid Equations for Leptogenesis . . . . . . . 145
5.4.1 Derivation of the Fluid Equations . . . . . . . . . 145
5.4.2 Computation of the rates LNC and LNV . . . . . 156
5.4.3 Comparison with the Nonrelativistic Approximation165
5.5 Implications for the Final B − L Asymmetry . . . . . . . 168
5.5.1 Scenario without Spectators . . . . . . . . . . . . . 168
5.5.2 Scenario with Partially Equilibrated Spectators . . 179
6 Summary and Outlook 185
6.1 The Portal Effective Theory Framework . . . . . . . . . . 185
6.2 PET Chiral Perturbation Theory . . . . . . . . . . . . . . 186
6.3 Lepton Number Violation at Colliders . . . . . . . . . . . 188
6.4 Relativistic and Spectator Effects in High-Scale Leptogenesis189