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Exploring the Fundamental Particlesin the Universe

Exploring the Fundamental Particles in the Universe – p.1/29

Outline

Standard Model of Particle Physics

Beyond the Standard Model

Astroparticle Physics

Standard Model of Particle Physics

LEPTONS : e− e+ µ− µ+ τ− τ+

νe νe νµ νµ ντ ντ

QUARKS : u u d d s s

c c b b t t

GAUGEBOSONS : γ W± Z g(8) G

HIGGSBOSON : φ

Antiparticle - same mass, opposite charge Exploring the Fundamental Particles in the Universe – p.3/29

PARTICLE DISCOVERIES

Cathode Ray Tube Electron (1897)

Compton scattering expt Photon (1923)

Cosmic Rays Positron (1932), Muon (1936)

Beta decay Electron neutrino (1956)(nuclear reactors)

ACCELERATORS

FERMILAB pp

KEK e+e−

CERN(LHC) pp

BROOKHAVEN HeavyIonCollisions

CERN - [27km, 100m, 11K rev/s, 1011 p per bunch]

The LHC tunnel

Decaying Higgs after a p-p collision600mill/s

The decay of a Higgs particle following a collision oftwo protons (simulation). [600 million collisionseverysecond]

Accelerators Muon and Tau neutrino, Tau lepton

Up and Down quarks

s,c,b,t quarks

Gluons, W±, Z (1962-2000)

Higgs particle is not yet discovered. (LHC?)

Accelerators Muon and Tau neutrino, Tau lepton

Up and Down quarks

s,c,b,t quarks

Gluons, W±, Z (1962-2000)

Higgs particle is not yet discovered. (LHC?)Exploring the Fundamental Particles in the Universe – p.10/29

Theoretical Calculations

Quantum Mechanics Non-relativistic particlesQuantum Field Theory Relativistic particles

Represent each particle by a field

As in QM, work with a Hamiltonian (or Lagrangian)

Use perturbation theory (like in QM) to calculate howparticles decay, interact with each other, etc.

Compare theoretical and experimental results

The Lagrangian of the Standard Model

L = −1

µνW iµν − 1

4BµνBµν − 1

µνGjµν +θ2g2

16π2Tr

GjµνGjµν

+fDγµ(1− γ5)

i∂µ − g1

2τ iW i

µ − g′Y

2Bµ − gs

2λjGj

+fγµ(1 + γ5)

i∂µ − g′Y

2Bµ − gs

2λjGj

i∂µ − g1

2τ iW i

µ − g′Y

2Bµ − gs

2λjGj

− V (φ)

−mfφf1f1 −mfφcf2f2 [i = 1, 2, 3; j = 1, 2, .., 8]

where f are fermions ( leptons and quarks), Gjµ, W j

µ andBi

µ are the strong and electroweak gauge bosonsrespectively, and φ is the Higgs boson. The Lagrangianhas SU(3)c × SU(2)L × U(1)Y mathematical symmetry,which spontaneously breaks into SU(3)c × U(1)EM.

Unease with the Standard Model

The Standard Model of Particle Physics has 19parameters.The large number of arbitrary parameters in theStandard Model is a cause of concern.

Also neutrinos are massless in the Standard Model.(1998 - ν mass)

Some theoretical calculations of the Higgs massmake it too large (unless one carefully adjustsparameters).

GO BEYOND THE STANDARD MODEL

GO BEYOND THE STANDARD MODELExploring the Fundamental Particles in the Universe – p.13/29

High Energy Theory −→ Standard Model(like Special Relativity −→ Newtonian Physics)

GRAND UNIFIED THEORIES (GUTs)(larger mathematical symmetry, neutrino mass)

SUPERSYMMETRY (controls the Higgs mass)

FERMION ←→ BOSON

BOSON ←→ FERMION

γ (PHOTON) ←→ γ (PHOTINO)

e (ELECTRON) ←→ e (SELECTRON)

Discoveries at the LHC?

Discoveries at the LHC? Exploring the Fundamental Particles in the Universe – p.14/29

The Standard Model and Beyond

THE STANDARD MODEL OF PARTICLE PHYSICS

Theory: Lagrangian (Quantum Field Theory)Experiment: Cosmic Rays, Accelerators

BEYOND THE STANDARD MODEL

Grand Unified Theories (GUTs)Supersymmetry

LARGE HADRON COLLIDERExploring the Fundamental Particles in the Universe – p.15/29

What about Gravity?

CLASSICAL GRAVITY −− GENERAL THEORY OF RELATIVITY

QUANTUM GRAVITY −− ?

SUPERSTRING THEORY

Elementary particles like the photon and the electron are not point-likeobjects but are extended objects.To see the string like behaviour need very high energy probes.

Supersymmetric GUTs are included in superstring theory and theGRAVITON appears naturally in the particle spectrum. So it is aUNIFIED QUANTUM THEORY of PARTICLE PHYSICS and GRAVITY.

What about Gravity?

SUPERSTRING THEORY

What about Gravity?

SUPERSTRING THEORY

What about Gravity?

SUPERSTRING THEORY

d > 4 Exploring the Fundamental Particles in the Universe – p.16/29

Cosmology and Particle Physics

Particle Physics theories find applications inastrophysical scenarios and in the context of the EarlyUniverse. Particularly in the latter case, they allow us totest interactions of particles at very high energies.

Solar Neutrino DeficitDark MatterMatter-Antimatter Asymmetry

Solar Neutrino Deficit

Nuclear reactions in the Sunp + p → 2H + e+ + νe

p +2 H → 3He + γ3He +3 He → 4He + 2p3He +4 He → 7Be + γ

7Be + e− → 7Li + νe

7Be + p → 8B + γ8B → 8Be∗ + e+ + νe

8Be → 4He +4 He

We detect only 1/3 of the neutrinos νe that we expect.Exploring the Fundamental Particles in the Universe – p.18/29

Neutrino Oscillations

No solution from Solar Physics.

Is something happening to neutrinos as they travel fromthe sun to the earth?

No solution from Solar Physics.

Is something happening to neutrinos as they travel fromthe sun to the earth?

Electron neutrinos emitted by the sun transform intomuon and tau neutrinos. Therefore we detect only 1/3 ofthe neutrinos emitted by the sun.

This hypothesis of neutrino oscillations has beenconfirmed by experiments. (νe ↔ νµ ↔ ντ)

Neutrino oscillations requires neutrino massessPhysics of stars tells us about fundamental particles ν

Electron neutrinos emitted by the sun transform intomuon and tau neutrinos. Therefore we detect only 1/3 ofthe neutrinos emitted by the sun.

This hypothesis of neutrino oscillations has beenconfirmed by experiments. (νe ↔ νµ ↔ ντ)

Neutrino oscillations requires neutrino massessPhysics of stars tells us about fundamental particles ν

Dark Matter

Velocity Rotation Curves of Galaxies

Expect v ∼ 1√r, since mv2

r= GMm

r2 and M is constant.BUT ....

Take v ∼ constant. How can this be explained?

If M(r) = Ar, then v ∼ constant.

But M(r) = Ar ⇒ matter beyond the central luminousregion which we can not see.

This non-luminous matter (does not emit or scatter light)is called DARK MATTER.

DARK MATTER does not emit or scatter light so it isdifficult to detect.What is it?

Consists primarily of non-Standard Model matter –supersymmetric particles, axions, massive neutrinos, ...

High energy physics theories provide possible candidatesfor dark matter

Matter-Antimatter Asymmetry

Observed Universe is made up of only matter.M + M → photons

Antimatter seen in laboratories since 1930s.

We believe that at early times (t < 1s) there wereequal amounts of matter and antimatter in the Universe.

WHERE DID THE ANTIMATTER GO?

Matter-Antimatter Asymmetry

WHERE DID THE ANTIMATTER GO?

Disequilibrium in the early Universe

100 M + 100 M −→ 103 M + 101 M −→ 2 M

Possible mechanism of creating matter excess is via thedecay of GUT bosons X at t ∼ 10−34 s (T ∼ 1026K).

X −→ M

−→ M

r > r ⇒ N(M) > N(M).Particle physics theories to explain the M-A asymmetry

Conclusion

We have a good understanding of the history andevolution of our Universe, but there are sillimportant outstanding questions – Big Bang, DarkMatter, Dark Energy

The Standard Model of Particle Physics is good butnot good enoughNeed to consider theories Beyond the StandardModel valid at higher energies

Conclusion

Problems in Particle Physics are often linked toCosmology and vice versa

High energy particle physics theories such as StringTheory may explain the Big Bang, Supersymmetricmodels may provide the Dark Matter, GUTs mayexplain the Matter-Antimatter Asymmetry, SolarPhysics provides clues to the nature of Neutrinos

Accelerators such as the LHC will (hopefully)discover the dark matter particle

Cosmology and Particle Physics

The First Three Minutes by S. Weinberg

The Big and the Small, vol. I and II by G.Venkataraman

raghavan@prl.res.inExploring the Fundamental Particles in the Universe – p.29/29

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