axions presentation

8/14/2019 Axions Presentation

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WHAT IS AN AXION?

1.Axion and The Strong CP problem2.Limits for the mass of axions

3.Axion and Dark Matter4.Identity Card of Axions

5.How does one look for Axions?

6.The CAST experiment7.The PVLAS experiment

8.Results

9. Conclusion


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Reminder of P,C and CP Oprations

Parity Operator (P)

Charge Conjugaison Operator (C)

(CP) Operation


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The Strong CP problem

The rules followed by theStrong interaction obeydiscrete symmetries P

and CP.

These symmetries havebeen known for a longtime. The discovery that

weak interaction violates

P and CP = big surprise

Indeed, physicists usedto see strong and EMinteractions obeying Pand CP.

Kaons Violate CP

symmetry by weak

interaction


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Strong Cp problem and Axions

how can the strong interaction, which is part of the Standard Model,

conserve P and CP?

Here is the guy:

there are some natural terms whichappear in the QCD Lagrangian expressionto be potentially able to describe abreaking of the CP theory.

Problem is:


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Strong CP problem and Axions

the most sensitive test of P

and CP violation by the

strong int. : requires the teta

of QCD be less than 10^(-9).

Peccei-Quinn

solution:modifiy the Model by

adding a new sym.(PQ) andmaking the teta angle of

QCD a dynamical variable

rather than a simple arbitrary

constant

in quantum field: each field

produces a particle

the hypothetical particle

corresponding to this field

was called axion.

The potential which this fieldnaturally obtains causes it to

have a value which makes

the effective parameter

vanish.no problem anymore


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Mass Limits on Axions THEORICAL ARGUMENT

As for the Pecceni-Quinn theory: ~1.8MeV

REACTION OBSERVATION ARGUMENT

an axion heavier than 1keV would lead to new particles physics

reactions (decay into K+ and +), but these never occured

< 1keV

ASTROPHYSICAL OBSERVATION ARGUMENT

axion mass must be no more than 103 electronvolts < 103 eV

COSMOLOGICAL ARGUMENT

If axion is lihgter than 1microeV, its relique density in primitive

universe would be higher than the actual observed density of total

energy in the Universe > 106 eV


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Mass Limits and Dark Matters To sum up the most likely mass limits on axion are:

106

< m(axion) < 103

eV Now: what is dark matter?

mass of matter in the universe that cannot be observed by direct observations of its

emitted or absorbed electromagnetic radiation.

number of astrophysical observations that suggest that the actual mass of universe is

greater than estimated by observation using optical telescopes, radiotelescopes..etc.

It is thought to be a considerable amount of dark matter (hidden matter) causing thisdiscrepancy


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Mass limits and Dark Matter

Various explanations have been put

forward for this missing mass, including

black holes, brown dwarfes, cosmic

strings, neutrinos, monopoles, WIMPS

and...

As we can see, the axion seem

to be a good candidate to be a

part of the dark matter!


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Properties of Axions

Hypothetical pseudo-Goldstone boson particles, stable

particles, almost do not interact with matter

Axion mass is given by :

Axions coupling with photon is given by:

with :

Primakoff effect: conversion of photons into axions


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How does one look for axions?It depends where do they come from

Galactical Axions- Haloscopes (ADMX, CARRACK)

microwave cavity + magnetic field

Laboratory Axions- Regeneration Light Shinning through wall

- Polarisation (PVLAS)

laser + magnetic field

Axions produced in the sun- Helioscopes (CAST, TOKYO)

- Cristal detectors (SOLAX, COSME,

DAMA)

sun + magnetic/electrical field


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How does one look like for Axions?

Axions in laboratory

Light shinning through a

wall

Axions in the Sun

Helioscopes

Polarisation:

polarised laser through a

vacuum with a tranverse

magn.field.

Cristalline detectors:

Primakoff + Braggs

condition


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CAST:Cern Axion Solar Telescope

Moving LHC dipole: L= 9.3m B= 9 Tesla

Sun tracking 3hours/day

3 X-Rays detectors

Measured signal: excess of X-rays when

pointing to the sun


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CAST: Production and detection Production in the Sun

Inside the

sun:interaction photon-

nucleons by primakoff

Detection Principle

Conversion probability:

Expected # photons:

~ 7events/day

A


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CAST:X-Ray detector


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PVLAS:Polarizzazione del Vuoto con Laser Polarized laser through B=5T

Goal: measure modification of polarization of light QED forecast interaction btw photons-B:ellipticity Ellipticity due to birefringence of vacuum (changes in refractive

indices for different polarization vectors) depending on B

Linear polarization(45)

Elliptical polarization


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PVLAS: experimental Setup

Photo elsastic Modulator

6.5T

Fabry-Perrot resonator


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PVLAS:measured effects

Production and destruction

of virtual particle:change of

ellipticity

Real production of

particle:rotation of the plane

of polarization(dichroisme)


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Results


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Conclusion

Axions remain to be a promising

solution to the CP problem

They additionally provide a well-motivated candidate for dark matter

Experiments are being pursued and

improved for dicover certainly in acouple of years axions.

axions presentation

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