CS du LAL 28/06/2011 1

FLOWER

Fluctuations of the Light velOcity WhatEver the Reason

François Couchot, Xavier Sarazin, Marcel UrbanLAL Orsay

Jérome Degert, Eric Freysz, Jean Oberlé, Marc TondussonLOMA, Bordeaux

Presented by Xavier SarazinConseil Scientifique du LAL

28 juin 2011

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Time-variation of c c(t)

Is the speed of light a fundamental constant ?

Three types of possible effects

Fluctuation of c c

c is constant in average but possible stochastic fluctuations around c

Chromatic dispersion of c c(E) c depends on the energy of the photon

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Variation of c in space

- Initially formulated by Einstein The constancy of the velocity of light can be maintained only insofar as one restricts oneself to spatio-temporal regions of constant gravitational potential (Ann. Physik 38 (1912) 1059)

- Proposed as an analogy to General Relativity GR Refractive index of vacuum modified by gravitational field Curvature and Delay due to varying index in space

Eddington 1920Felice 1971Evans, Nandi and Islam 1996

Variation of c in time ?

- A possible way to explain the apparent Dark Energy J. Barrow and J. Magueijo, APJ, 532 (2000)

Time-variation of c

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Singularities in space-time at Planck scale ~ 10 m (MPlanck~1019 GeV)

At this energy scale, the dispersion relation is not linear any more

The vacuum refractive index depends upon the energy of the photon

c depends on the energy of the photon c(E)

Chromatic dispersion of c

Figure of merit to constrain this model is (L/t)×E

Best experimental limits with Gamma-ray bursts

G. Amelino, J. Ellis, et al., Nature 393, 763 (1998)

J. Ellis, N. E. Mavromatos and D. V. Nanopoulos, Gen. Rel. and Grav., 32, (2000), 127-144

J. Ellis, N. E. Mavromatos and D. V. Nanopoulos, Phys. Lett. B 665, 412 (2008)

Abdo et al, Nature, 2009

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Light-cone fluctuations (quantum metric fluctuation from quantum gravity) H.Yu et L.H. Ford, Phys. Rev. D 60 084023 (1999)

L t

Correlated to any discontinuity or discrete properties of the photon

propagation in vacuum.

Leads to fluctuations of the transit time of photons

Corpuscular model of photon propagation

M. Urban, F. Couchot et X. Sarazin arXiv:1106.3996

Fluctuations of c

~ fs.kpc1/2

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A coherent corpuscular model of quantum vacuum to explain the three electromagnetic constants 0, 0 and c ?

Preprint arXiv:1106.3996

Average energy of the pair:

Life-time of the pair:

Minimum Distance between fermions in the same spin-state:

Density (Two f-f spin combinations)

New hypothesis in this model (compare to standard QED):

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Vacuum Permittivity 0

Polarisation P of the molecules by the field E

opposite charges on the dielectric plates

Voltage decreases C is increased

EP .+

E

+

+

+d

SC

With vacuum: 0 = 0 !!!

In our model: virtual pairs f f bear a mean electric dipole

The virtual pairs are polarized, BUT only during their life-time depends on the coupling energy of the pair to the field E

En moyennant sur En sommant sur l’ensemble des fermions(3 familles)

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Vacuum Permeability 0

I

B

B = 0nI + 0MM = magnetization of the matterIf matter is removed: B = 0nI 0

In our model of vacuum: 0 originates from the magnetization of the virtual pairs

The vacuum is paramagnetic

• Virtual fermion pair has a magnetic moment: • It is aligned during its life-time • depends on the coupling energy of the pair to the field E

En moyennant sur En sommant sur l’ensemble des fermions(3 familles)

i

ii m

eQ

2

22

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NNtLv

col

11

/

Light velocity

Transit time of a photon to cross L: t = Ncol ×

Fluctuations of Ncol Fluctuations of the transit time LN colt 0

Number of interactions to cross L: Ncol = N × × L

Cross-section for photon capture

Photon propagation = successive interactions and transient captures by virtual particles

If we sum over all the types of fermions

Our model predicts

cK

v

1

(Thomson)

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We were really excited to find that similar ideas (but different mechanism) have

been proposed recently by G. Leuchs, A.S. Villar and L.L. Sanchez-Soto where they

also derive 0 and 0

G. Leuchs et al. Appl. Phys. B 100 (2010) 9-13

We never found any other calculation/derivation of 0, 0 or c

Within this framework: 0 0 and c are only observables of quantum vacuum

They can vary if the vacuum is modified by an external stress new predictions ?

• High fields E,B: one expects variation of c stronger than QED predictions

See current tests LNCM Toulouse (Rikken) and LCAR Toulouse (Rizzo)

• mumesic atoms : one expects short distance deviations to standard electrostatics @ r~200fm

See LKB (Indelicato) and anomaly of energy level in muonic Hydrogen

Comments The experimental values of 0, 0 and c constrains our model and its “fudge” factors

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At least two approaches predict fluctuations of c

At Planck scale from quantum gravity

~ 0.1 – 1 fs.m1/2 from corpuscular photon propagation

The experimental way to test fluctuations is to measure a possible time broadening

t of a light pulse travelling a distance L of vacuum

Fluctuations vary as L

The figure of merit is tL /

Measurements of possible fluctuations of c

There is today no existing experimental limit !!!

So we did the job ourself…

In any case, we think that it is a fundamental test of physics

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Astrophysics Constraints Gamma Ray Burst

Fermi observations: Only one “short” GRB with afterglow and redshift measurement

GRB 090510 measured by Fermi -ray Space Telescope

Z = 0.9 dL = 1.8 1026 m

t 10 ms

0 ~ 0.7 fs.m-1/2

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Astrophysics Constraints Millisecond pulsars

Strong Dispersion ~ 1 ms / 6 MHz @ GHz

Very short pulses observed from the crab pulsar with

Arecibo Radio Telescope (0.1 – few GHz)

Requires Dedispersion Technique (computing)

Crossley et al., Astrophys. J. , 722 (2010) 1908

1.428 GHz

1.368 GHz

~10 ms

0 ~ 0.2 fs.m-1/2

t 1 s @ 5 GHz

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Vacuum LengthL (pc)

Tim

e W

idth

rm

s (s

)

Pulsar ~kpct ~ s

GRB ~ 1-10 Gpct ~ 1-10 ms

fs )(2.0t mL

We can improve the sensitivity using femto laser

10 fpc = 300 mt ~ 4 fs

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The FLOWER Setup

Primary pulse

Ti:SapphirePulsed Laser10 nJ / pulse

t0 (rms) ~ 20 fs(rms) ~ 15 nm

Motorstage

Diode

Non linearcrystal

Intensity Autocorrelation

RC = 1.8 mConcave Mirror M2Planar Mirror M1

M

The length of the cavitycan be modified

The number of round tripscan be modified

Input/output Hole

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The number of round trips can be modified

Allow measurements of different vacuum path lengths Lvacuum

For a given number of round trips, the length of the cavity can be modified

The systematic due to possible mirror dispersions can be separately measured

We will first validate and calibrate the setup by filling the Herriot cell with a gas

chromatic dispersion (Argon@1 atm, L=50m,=80015nm) ~ 60 fs

General solution = k./ N N = number of round trips

RC = 1.8 mLength (m) of the Herriot cell

(r

ad)

Example with 5 round trips

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Preliminary Tests in LOMA

Gold metallic concave mirror already available“Ultra high” quality

= 15 cm

Preliminar planar mirror Dedicated high quality mirror with a

hole will be purchased next month

Here an example with 11 round trips

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Preliminary simulation for 21 round trips and RC = 1.8 m

Stable solution for = 16/21 and L = 1.56 m

By construction: the outgoing beam is similar to the incoming beam

With the available gold concave mirror, we can already reach a vacuum path length

Lvacuum = 2×21×1.56 = 65.5 meters

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In 2010-2011 we have performed a series of dispersion measurements in SiO2

using the autocorrelation technique

The proposed experiment is based on expertise gained

from a collaboration with the LOMA

Suprasil-311 from Hereaus,

High uniformity and purity

n/n ~ 10-6

COLA Platform: tuned pulsed laser (OPG/OPA) to generate frequencies

around the minimum SiO2 dispersion =1272 nm

Primary pulse

Ti:Sapphire LaserOPA generatort0 (rms) ~ 25 fs

(rms) ~ 20 nm

Motorstage

Diode

Non linearcrystal

Intensity Autocorrelation

SiO2 Rod L=20cm

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• With SIO2, we are dominated by chromatic dispersion which limits the systematic

uncertainty to 0 ~ 20 fs.m1/2

• It demonstrates the high sensitivity and high precision of that technique

• Accuracy of the pulse width (rms) measurement ~ 2 fs

(It might be sligthly improved with a pure pulse directly from the oscillator)

• Optics Publication in preparation

• It must be much simpler with vacuum because the chromatic dispersion is null

First direct measurement of group index (pulse velocity) with very high accuracy ~ 10

Results in agreement with expected values at the level of 10

(102 – 103 better than previous measurements)

Dispersion measurement by intensity correlation

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Flower Phase 12011-2012

Herriot cell Lcell < 1.8 m

Can reach at least Lvacuum = 65 m with 21 round trips

Width (rms) of COLA laser pulses ~ 20 fs

Accuracy autocorrelation measurement ~ 2 fs (width rms)

Expected sensitivity of vacuum fluctuations: 0 ~ 1 fs.m1/2

With new femto laser: rms ~ 5 fs

~ 40 round trips

Improved accuracy of autocorrelation meas. ~ 0.5 fs (150 nm step)

0 ~ 0.2 fs.m1/2Better than GRBSimilar to microburst from Crab pulsar

Equipment already funded

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Extra gains in senstivitySuper-Flower ?

Herriot cell Lcell ~ 50 m (as CALVA)

~ 50 round trips

Can reach Lvacuum = 5 km

Expected sensitivity of vacuum fluctuations: 0 ~ 0.02 fs.m1/2

Width (rms) of initial laser pulses ~ 1 fsAutocorrelation accuracy ~ 0.1 fs (30 nm)

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Funding for 2011• GRAM Funding for 2011: 1500 euros• LAL funding for 2011: 3000 euros• LOMA similar contribution

Request for 2012• Travel: 7 keuros• We plan to submit a proposal to ANR 2012 and GRAM 2012• We plan to propose a thesis

Participation physicists 2011-2012LOMA: Jérôme Degert 25%

Eric Freysz (25%)Jean Oberlé (25%)Marc Tondusson (25%)

LAL: François Couchot (70%)Xavier Sarazin (50%)Marcel Urban (100%)

Equipment• Laser and room on optical table available for 2011-2012 full time in LOMA (COLA)• Optical elements and autocorrelators available in LOMA

• Flat mirror and extra elements will be purchased next months by LAL and LOMA

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The measurement of possible fluctuation of c (fluctuation of the transit time of photons)

is a fundamental test in physics

With FLOWER Phase-1 (2011-2012) we can achieve stringent limits (0~ 0.2 fs.m1/2)

with a relative simple setup

the equipments are available or already funded

perfect setup to study all the systematics and artefacts

Our model of vacuum predicts other effects

Variation of c with strong E,B fields (see QED)

Variation of the Coulomb law in short distance (see mumesic atoms)

We have started discussions with LKB (Paris) and LCAR (Toulouse)

Travel budget required for 2012

CONCLUSIONS

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Il a été décidé que votre demande concerne les thématiques du GRAM et qu'un financement est a terme envisageable

Il apparait dans votre demande qu'une telle analyse est en cours (analyse théorique détaillée de l'exactitude attendue pour l'expérience et de sa comparaison à d'autre expériences, notamment astrophysiques recherchant les mêmes effets) et le CS du GRAM vous encourage vivement à la mener à terme et de la publier. A cette fin une somme de 1500 € vous est accordée pour couvrir les missions associées à cette activité théorique.

Le CS du GRAM vous encourage à re-soumettre une demande expérimentale lors des prochains appels d'offres, dès lors que l'analyse théorique déboucherait sur une comparaison favorable avec les autres expériences dans le même domaine. Une éventuelle future demande devant être examinée dans les contraintes budgétaires et programmatiques de l'appel d'offre en question, le présent texte ne présume pas d'un engagement du GRAM concernant ces futures demandes.

Pour le CS du GRAM : Peter Wolf et Gilles Métris

GRAM (Gravitation, References, Astronomie, Metrologie)Action Spécifique crée par l’INSU début 2010

Appel d’offre 2011: financement du projet FLOWER de 1500 euros

Avis du Conseil Scientifique