The Origin of Matter

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The Origin of Matter

Tsutomu T. Yanagida (IPMU , Tokyo)

台湾大学 3月8日、2016年


Energy Content of the Universe


From Wikipedia FF


Galaxy and Cluster of galaxies


No antimatter is present

Observations have ruled out the presence of

antimatter in the Universe up to the scale of

clusters of galaxies ( ). Most significant

upper limits are given by annihilation gamma



Upper bounds of antimatter fraction

G. Steigman (2008)

The universe is composed of only matter and

not antimatter


However, antimatter could have been

equally present in our universe, since there is no difference between particles and

antiparticles except for their charges.

In fact, Paul A.M. Dirac proposed a matter-

antimatter symmetric universe in his Nobel

Lecture in 1933.


If we accept the view of complete symmetry between positive and negative electric charge so far as concerns the fundamental laws of Nature, we must regard it rather as an accident that the Earth (and presumably whole solar

system), contains a preponderance of negative electrons and positive protons.

It is quite possible that for some of the stars it is the other way about, these stars being built up mainly of positrons and negative protons. In fact, there may be half the stars of each kind. The two kinds of stars would both show exactly the same spectra, and there would be no way of distinguishing them by present astronomical methods.

The symmetric Universe

was proposed by Paul Dirac

In 1933.


I. Why is the present universe NOT symmetric?

How much asymmetric ?

Matter = Atoms  Matter Abundance = Numbers of Protons and Neutrons

The baryon asymmetry


The baryon asymmetry

Spergel et al (WMAP) Tegmark et al

Kirkman et al

Very small !!!

Our universe may have begun symmetric


If our universe began baryon symmetric,

those tiny imbalances in numbers of baryons and antibaryons must be generated by some physical processes in the early universe.

What are the processes ?

The present particle physics may answer to this fundamental question

(If the universe had been symmetric, baryons and antibaryons started to annihilate each others when the temperature became well below the nucleon mass. The number of post-annihilation nucleons would be a billion times less abundant than observed today.)


Generation of the baryon asymmetry

A.D.Sakharov (1966)

The theory of the expanding universe, which presupposes a superdense initial state of matter, apparently excludes the possibility of macroscopic separation of matter from antimatter; it must therefore be assumed that there are no antimatter bodies in nature, i.e., the universe is asymmetrical with respect to the number of particles and antiparticles (C asymmetry)…..

We wish to point out a possible explanation of C asymmetry in the hot model of the expanding universe by making use of effects of CP invariance violation (see [2])……...

The discovery of CMB in 1964

The discovery of CP Violation in 1964

in the decays of neutral kaons

A. A. Penzias and R. W. Wilson

J. Cronin, V. Fitch


Three conditions must be satisfied to produce an imbalance of baryons and antibaryons

I. Violation of baryon number conservation II. Violation of C and CP invariance

III. Out-of-thermal equilibrium process


II. Baryogenesis in the standard theory

C violation was discovered in 1957

CP violation was discovered in 1964 J. Cronin, V. Fitch C.-S. Wu

The second condition is satisfied

Is the first condition of baryon number

violation also satisfied ?


Baryon number violation in the standard theory

G. ‘t Hooft (1976)

The baryon number is not conserved at quantum level

The weak instanton induces baryon number violation, but the amplitude is suppressed by

The proton decay is suppressed as


Saddle-point solution in the standard theory (Weinberg-Salam Model)

N.S. Manton (1983)

F.R. Klinkhamer , N.S. Manton (1984)


0 1

-1 ===========> Q (A,H)






Unsuppressed baryon number violation in the early universe

V.A. Kuzmin, V.A. Rubakov, M.E. Shaposhnikov (1985)

The rate baryon number violation :

It exceeds the expansion rate of the universe above

The first condition is satisfied

P. Arnold, L. McLerran


The third condition may be satisfied if the electro- weak phase transition is the first order

This requires the Higgs boson mass,

But, it is excluded by LEP experiments

The condition III is not satisfied !!!


The standard theory is unable to explain the baryon number asymmetry

I. No out-of-thermal equilibrium process II. Too small CP violation

Jarlskog determinant

cf. cold electroweak baryogenesis


The Nobel Prize in Physics 2015 was awarded for the discovery of neutrino oscillations, which show that neutrinos have small masses

The presence of small neutrino masses may

give us a natural mechanism for creating the

observed baryon asymmetry in the Universe!!!


III. Discovery of neutrino oscillation

The solar neutrino problem

Raymond Davis

Davis found only one-third of the neutrinos predicted by the standard solar theories

John Bahcall

Yoji Totsuka

Superkamiokande confirmed the result of Davis in 1998 Superkamiokand dicovered the oscillation of

the atmospheric neutrinos in 1998

(1964-1996 at Homestake)


Masses and mixing angles for neutrinos

The recent global analysis gives

T. Schwetz, M. Tortola, J.W.F. Valle (2011)


Why are neutrino masses so small ?


Introduction of right-handed neutrinos

neutrino mass term :

The standard theory

cf. top-quark mass term :

So small !!!


Seesaw mechanism

T. Yanagida (1979)

Gell-Mann, Ramond, Slansky (1979) P. Minkowski (1977)

is singlet and has no charge. Thus it may have a large Majorana mass

neutrino mass matrix :

Pauli-Gursey transformation: Weyl fermion  Majorana fermion


Two mass eighen values :

The observed small neutrino masses strongly suggest the presence of super heavy Majorana neutrinos N

Out-of-thermal equilibrium processes may be easily realized around the threshold of the super heavy neutrinos N

The Yukawa coupling constants can be a new source of CP violation


GUT Baryogenesis

M. Yoshimura (1978)

Ignatiev, Krosnikov, Kuzmin, Tvkhelidze (1978)

Delayed decay of heavy colored Higgs boson

S. Weinberg (1979)

Baryon asymmetry can be produced in the decay processes But, we have two serious problems:

I. It predicts proton decay, but the decay was NOT observed II. The produced B asymmetry is washed out by the sphaleron




If , the B asymmetry is washed out by the sphaleron processes. The generation of B-L asymmetry is necessary

B-L is conserved !!!

However, the GUT preserves the B-L and hence the B-L asymmetry is not generated


IV. Leptogenesis

M. Fukugita, T. Yanagida (DESY 1986)

Decay of the super heavy Majorana neutrino N :

If CP is broken, the lepton asymmetry is generated in the delayed decay of N in the early universe

Two decay channels

The lepton asymmetry is converted to baryon asymmetry by the sphaleron processes

J.A. Harvey, M.S. Turner (1990)


The first detailed calculation for the baryon asymmetry

M. Plumacher (1997)

Asymmetry parameter:

Assume decay is most important

for the maximal CP violation



(neglecting the flavor effects)


In the early universe , the heavy Majorana were

produced by the scattering processes in the thermal bath. As the temperature went down , the started to decay and produced the lepton asymmetry. This lepton

asymmetry was converted to the baryon asymmetry.

The out-of equilibrium decay condition (delayed decay)



The washing out effects ;

We have the upper bound

Very consistent with the observed neutrino masses !!!

W. Buchmuller, P. Di Bari, M. Plumacher (2004)

The baryon asymmetry in the present universe

can be explained for and

G.F. Giudice et al (2004)


The produced B-L asymmetry is calculated by solving the Boltzmann equations;

accounts for decays and inversed decays represents the scattering

is the total washout term of B-L asymmetry


Produced lepton asymmetry for ,

Buchmuller, Bari, Plumacher (2002)


V. Summary

In particular,

Very consistent with observation :

(pre-existing B-L may be washed out)


Test of the Leptogenesis

The standard theory + right-handed neutrinos

It explains two fundamental parameters simultaneously:

I. Small neutrino masses

II. Universe’s baryon asymmetry

Very Consistent !!

Can we test the leptogenesis ?


A robust prediction is

It may be impossible to test this prediction The leptogenesis has two testable predictions

I. CP violation in neutrino oscillations

II. Neutrinoless double beta decays

T2K experiments (2011)

We will see it in future

N N’

e e

W.H. Furry (1939)


CP violation in neutrino oscillations


T2K experiments


What is the Next ?

The neutrino masses observed in neutrino oscillation experiments strongly support the leptogenesis

See my talk at NCU

“The Seesaw Mechanism --- 37 Years Later ---”




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