fundamental physics. may 3rd 2006 1 clive speake g.hammond, a. matthews, f.pena, s. aston, e.rocco....
TRANSCRIPT
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Fundamental Physics. May 3rd 2006
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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.
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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...
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041 r
mmGV Ng
21
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g21
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eVem
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4
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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.
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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...
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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
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Fundamental Physics. May 3rd 2006
6Adapted From Smith and Lewin 1990.
weak Force Physics
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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)
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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)
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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.
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Fundamental Physics. May 3rd 2006
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Sphere-Plane
Float
Interferometer
Spark eroded Nb foil feedback coils
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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
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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.
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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
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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.
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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
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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
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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.
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Source/Test mass manufacture at RAL
Al mandrill
150m deep
400m pitch, 50% fill.
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Source/Test mass manufacture at RAL
Electroplate with Au. Cover Al relief.
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Source/Test mass manufacture at RAL
Skim off the top layer to uncover Al.
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Source/Test mass manufacture at RAL
Sputter coat Au to thickness of 3m
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Source/Test mass manufacture at RAL
Dissolve Al mandrill.
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Al mandrill
Au plating prior to skimming
Courtesy of Peter Huggard, RAL.
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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.
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Parametrisation of violation of inverse square law
/r
ni ermGm
V 121
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moduli
Dilaton
Radion Vacuum energy scenario
2 compact extra dimensions
Possible signals
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Potential upper limits
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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.
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Acknowledgements
• PPARC
• EPSRC
• BAE
• Leverhulme