34 research outputs found
Leptogenesis as the origin of matter
We explore in some detail the hypothesis that the generation of a primordial
lepton-antilepton asymmetry (Leptogenesis) early on in the history of the
Universe is the root cause for the origin of matter. After explaining the
theoretical conditions for producing a matter-antimatter asymmetry in the
Universe we detail how, through sphaleron processes, it is possible to
transmute a lepton asymmetry -- or, more precisely, a (B-L)-asymmetry -- into a
baryon asymmetry. Because Leptogenesis depends in detail on properties of the
neutrino spectrum, we review briefly existing experimental information on
neutrinos as well as the seesaw mechanism, which offers a theoretical
understanding of why neutrinos are so light. The bulk of the review is devoted
to a discussion of thermal Leptogenesis and we show that for the neutrino
spectrum suggested by oscillation experiments one obtains the observed value
for the baryon to photon density ratio in the Universe, independently of any
initial boundary conditions. In the latter part of the review we consider how
well Leptogenesis fits with particle physics models of dark matter. Although
axionic dark matter and Leptogenesis can be very naturally linked, there is a
potential clash between Leptogenesis and models of supersymmetric dark matter
because the high temperature needed for Leptogenesis leads to an overproduction
of gravitinos, which alter the standard predictions of Big Bang
Nucleosynthesis. This problem can be resolved, but it constrains the
supersymmetric spectrum at low energies and the nature of the lightest
supersymmetric particle (LSP). Finally, as an illustration of possible other
options for the origin of matter, we discuss the possibility that Leptogenesis
may occur as a result of non-thermal processes.Comment: 53 pages, minor corrections, one figure and references added, matches
published versio
Supersymmetric Large Extra Dimensions and the Cosmological Constant Problem
This article briefly summarizes and reviews the motivations for - and the
present status of - the proposal that the small size of the observed Dark
Energy density can be understood in terms of the dynamical relaxation of two
large extra dimensions within a supersymmetric higher-dimensional theory.Comment: Talk presented to Theory Canada I, Vancouver, June 2005. References
added in V
Constraints on Supersymmetric Flavour Models from b->s gamma
We consider the effects of departures from minimal flavour violations (MFV)
in the context of CMSSM-like theories. Second and third generation off-diagonal
elements in the Yukawa, sfermion, and trilinear mass matrices are taken to be
non-zero at the GUT scale. These are run down together with MSSM parameters to
the electroweak scale. We apply constraints from fermion masses and CKM matrix
elements to limit the range of the new free parameters of the model. We
determine the effect of the departure from MFV on the branching ratio of b->s
gamma. We find that only when the expansion parameter in the down-squark sector
is relatively large there is a noticeable effect, which tends to relax the
lower limit from b->s gamma on the universal gaugino mass. We also find that
the expansion parameter associated with the slepton sector needs to be smaller
than the corresponding parameter in the down-squark sector in order to be
compliant with the bound imposed by the branching ratio of tau-> mu gamma.Comment: Comments: 43 pages, 14 figures. Version accepted for publication:
typos corrected, rewritten for better understanding and references adde
Experimental Precision Tests for the Electroweak Standard Model
This paper contains a review of recent precision measurements of electroweak
observables and resulting tests of the electroweak Standard Model.Comment: 78 page
Effective chiral Lagrangians for spin-1 mesons
The commonly used types of effective theory for vector mesons are reviewed
and their relationships clarified. They are shown to correspond to different
choices of field for spin-1 particles and the rules for transforming between
them are described. The importance of respecting chiral symmetry is stressed.
The choice of fields that transform homogeneously under the nonlinear
realisation of chiral symmetry imposes no preconceptions about the types of
coupling for the mesons. This representation thus provides a convenient
framework for relating different theories. It is also used to elucidate the
nature of the assumptions in specific hidden-gauge and massive Yang-Mills
models that have been widely used.Comment: 46 pages (RevTeX
Precision Electroweak Tests of the Standard Model
The present status of precision electroweak data is reviewed. These data
include measurements of e+e- -> f+fbar, taken at the Z resonance at LEP, which
are used to determine the mass and width of the Z boson. In addition,
measurements have also been made of the forward-backward asymmetries for
leptons and heavy quarks, and also the final state polarisation of the
tau-lepton. At SLAC, where the electron beam was polarised, measurements were
made of the left-right polarised asymmetry, A_LR, and the left-right
forward-backward asymmetries for b and c quarks.
The mass, MW, and width, GW, of the W boson have been measured at the
Tevatron and at LEP, and the mass of the top quark, Mt, has been measured at
the Tevatron. These data, plus other electroweak data, are used in global
electroweak fits in which various Standard Model parameters are determined. A
comparison is made between the results of the direct measurements of MW and Mt
with the indirect results coming from electroweak radiative corrections. Using
all precision electroweak data fits are also made to determine limits on the
mass of the Higgs boson. The influence on these limits of specific
measurements, particularly those which are somewhat inconsistent with the
Standard Model, is explored. The data are also analysed in terms of the quasi
model-independent epsilon variables.
Finally, the impact on the electroweak fits of the improvements in the
determination of the W-boson and top-quark masses, expected from the Tevatron
Run 2, is examined.Comment: 80 pages, 36 Figures, Late
The Standard Cosmological Model
The Standard Model of Particle Physics (SMPP) is an enormously successful
description of high energy physics, driving ever more precise measurements to
find "physics beyond the standard model", as well as providing motivation for
developing more fundamental ideas that might explain the values of its
parameters. Simultaneously, a description of the entire 3-dimensional structure
of the present-day Universe is being built up painstakingly. Most of the
structure is stochastic in nature, being merely the result of the particular
realisation of the "initial conditions" within our observable Universe patch.
However, governing this structure is the Standard Model of Cosmology (SMC),
which appears to require only about a dozen parameters. Cosmologists are now
determining the values of these quantities with increasing precision in order
to search for "physics beyond the standard model", as well as trying to develop
an understanding of the more fundamental ideas which might explain the values
of its parameters. Although it is natural to see analogies between the two
Standard Models, some intrinsic differences also exist, which are discussed
here. Nevertheless, a truly fundamental theory will have to explain both the
SMPP and SMC, and this must include an appreciation of which elements are
deterministic and which are accidental. Considering different levels of
stochasticity within cosmology may make it easier to accept that physical
parameters in general might have a non-deterministic aspect.Comment: 16 pages, 2 figures, invited talk at "Theory Canada 1", June 2005,
Vancouve
Review of Particle Physics
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances.
The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings
REVIEW OF PARTICLE PHYSICS
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,324 new measurements from 878 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on High Energy Soft QCD and Diffraction and one on the Determination of CKM Angles from B Hadrons. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 98 review articles. Volume 2 consists of the Particle Listings and contains also 22 reviews that address specific aspects of the data presented in the Listings. The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print and as a web version optimized for use on phones as well as an Android app.Peer reviewe
Neutrino Masses, Mixing, and Oscillations
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,873 new measurements from 758 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 118 reviews are many that are new or heavily revised, including a new review on Neutrinos in Cosmology. Starting with this edition, the Review is divided into two volumes. Volume 1 includes the Summary Tables and all review articles. Volume 2 consists of the Particle Listings. Review articles that were previously part of the Listings are now included in volume 1. The complete Review (both volumes) is published online on the website of the Particle Data Group (http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is also available. The 2018 edition of the Review of Particle Physics should be cited as: M. Tanabashi (Particle Data Group), Phys. Rev. D 98, 030001 (2018)