fundamental physics. may 3rd 2006 1 clive speake g.hammond, a. matthews, f.pena, s. aston, e.rocco....

Fundamental Physics. May 3rd 2006

1

Clive SpeakeG.Hammond, A. Matthews, F.Pena, S. Aston, E.Rocco.

Gravitation Group, University of Birmingham.

• Motivation

• Brief overview of laboratory tests of gravitation

• Work at University of Birmingham

• Summary

Precision tests of gravity: Particle physics at Precision tests of gravity: Particle physics at the low energy Frontier.the low energy Frontier.


2

Motivation• Standard Model of Particle Physics successfully

describes Electro-weak and Strong interactions up to ~102 GeV.

• Standard Model of Cosmology (founded on classical General Relativity) successfully ‘explains’ observations of the Universe from a second or so after ‘Big-Bang’.

BUT...

rqq

Vem21

041 r

mmGV Ng

21

rnn

cM

mV

p

f

g21

2

2

rnn

cc

eVem

21

0

2

4


3

But...• Gravitation cannot be renormalised like the other quantum interactions as there

is no mf in nature.

• The natural scale for a quantum theory of gravity is the Planck scale: Mpc2~1019GeV. What happens between the Electro-Weak scale and the Planck scale (16 orders of energy)? Hierarchy problem.

• We need new symmetries eg Supersymmetry, Peccei-Quinn symmetry, but we have no direct evidence for these.

• Cosmology needs Dark Matter but we have not observed it yet.

• We require the majority of the mass/energy density of the Universe to consist of a zero-point fluctuation vacuum energy: Dark Energy.


4

Motivation

• Recent attempts at solving these problems suggest the possibility of new macroscopic forces.

• New gauge symmetries and conserved quantities lead to new forces eg axion, new forces coupling to conserved charges B, B-L.

• String theories predict a number of phenomena: macroscopic compactified dimensions, dilaton, moduli and others...


5

T

Generic form of new interactions

• Assume a Yukawa-type potential:

• with

• mm for mbc2~0.2 meV

/rni e

rqq

gcV 212

cm/ b


6Adapted From Smith and Lewin 1990.

weak Force Physics


7

Tests of gravitation

• Equivalence Principle.

• Searches for G-dot.

• Macroscopic forces coupling to intrinsic spin: search for axion-like particles, search for cosmic spin fields, breakdown of Lorentz invariance.

• Inverse square law/ Casimir force.

For a review see Gundlach New J. Phys. 7 205 (2005)


8

Superconducting Torsion Balance

Cavendish Balance (1798-Present) Birmingham Instrumentin Casimir mode (1998-Present)

Based on Meissner effect zero stiffness suspension utilising Niobium Temperature of 4.2K Lift capacity 600g Superconducting magnetic torque feedback. We will eventually utilise a novel homodyne interferometric readout MkI Noise 10-13Nm/Hz Rev. Sci. Instrum. 75, 955 (2004)


9

The Spherical Superconducting Torsion Balance:

Levitation Bearing

Float

Cryogenic analogue of a spherical air-bearing

Copper shell 0.2mm, coated with Pb, (Nb).

Hard drawn Nb wire.


10Piezo

Sphere-Plane

Float

Interferometer

Spark eroded Nb foil feedback coils


11

Interferometer development for SSTB


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Birmingham interferometer for LISA:Schematic of first prototype.

C&QG 2005

A1,2 Polarising BeamsplitterB /4 PlateC Non-Polarising BeamsplitterD PlatePD1,2,3 PhotodiodeP PolariserL1,2,3 Lens

Laser Diode

A1

B

C

B

A2

PD

PD1

PD2PD3

Proof Mass

Reference Mirror

L3L2L1Main beamsplitter

Cat’s eye

A2


13

Birmingham Interferometer:

First prototype (40x70x25mm).


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Birmingham interferometer: Performance.

Using a 664nm VCSEL with 60 nW of optical power on diodes. Shot noise limited above 20 Hz.

Nominally equal optical path lengths.


15

Casimir’s Calculation

• Zero-point energy of modes between plates of dimension L:

z

x

d

zyxzyxk,k,k yxk,k,k

z,y,x

dn

kkc)d(E2

2222

22


16

Shortcomings of Casimir’s analysis

• Thermal Correction

When , corresponding to d=7m at room temperature,

. thermal photons contribute to Casimir force.

• How to model conductivity of real metals?

• Roughness correction

• Electrostatic forces due to patch-potentials.

kTc

d


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• Conductivity, roughness, thin film and patch-potential corrections are minimised by using larger spacings between conductors. But force is smaller!

• The controversial thermal correction is minimised at larger separations at 4K.

• Plasmons have larger effect at shorter spacing?

Reynaud and Lambrecht et al 2001


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Birmingham work

• Assuming sensitivity of Mk1 device (Hammond et al 2004), we can resolve 0.5% of Casimir force at 4m in 1 hour (R=10cm).

• Aim at ‘precision’ determination of Casimir force 0.1%.

• Crucial to damp parasitic modes of oscillation:

– horizontal and vertical translational modes damped using copper-cored inductor in series with levitation bearing.

– Simple pendulum mode damped using copper disk attached to the inside of float at its pole with superconducting electromagnet.


19

Experimental Tests of Newton’s law• University of Washington

• Currently testing Newtonian gravity at 150m.

• Aiming at 50m.

• Employ conducting membrane as electrostatic shield between source and test mass.

Eot-wash website

Source mass

Test mass

Optical leverTorsion fibre


20

Birmingham work in progress

• Push to shorter ranges by dispensing with the electrostatic shield.

• Use transverse geometry to eliminate forces due to long and short range electrostatic interactions and Casimir force

• Exploit novel features of Spherical Superconducting torsion balance being developed at University of Birmingham.

np

nPP zC

z

cE

2

1720 3

2


21

Long range stick-slip piezo

Modulated masses

Test of the inverse square law:

Basic concept

Centre of simple pendulum motion coincides with centre of buoyancy.


22

Source/Test mass manufacture at RAL

Al mandrill

150m deep

400m pitch, 50% fill.


23


Electroplate with Au. Cover Al relief.


24


Skim off the top layer to uncover Al.


25


Sputter coat Au to thickness of 3m


26


Dissolve Al mandrill.


27

Al mandrill

Au plating prior to skimming

Courtesy of Peter Huggard, RAL.


28

Current Status

• We have completed development of Mk2 SSTB with capacitative angular readout.

• Current sensitivity is limited by capacitive sensor noise. This can be improved.

• Completion of cryogenic interferometer is due in 2-3 months.


29

Parametrisation of violation of inverse square law

/r

ni ermGm

V 121


30

moduli

Dilaton

Radion Vacuum energy scenario

2 compact extra dimensions

Possible signals


31

Potential upper limits


32

Summary

• Ideas beyond the Standard Model of Particle physics and, perhaps, also that of Cosmology are needed to make sense of gravity.

• Searches for new weak interactions are complementary to direct searches for new bosons in particle accelerators.

• Fundamental physics experiments in the lab or, perhaps, space can contribute.


33

Acknowledgements

• PPARC

• EPSRC

• BAE

• Leverhulme

fundamental physics. may 3rd 2006 1 clive speake g.hammond, a. matthews, f.pena, s. aston, e.rocco....

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