Extra Dimensions, Dark Energy and the Gravitational InverseSquare Law

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Extra Dimensions, Dark Energy and the
GravitationalInverse-Square Law
Liam J. Furniss, Humboldt State University
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Motivation

• Some string theories predict stronger gravity at
  short distances.
• Accelerating expansion of the Universe could be
  explained by weaker gravity at short distances.
• Testing gravitation in this regime offers us a
  chance to test both theories at once.

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Modeling

• To model any new behavior we use the Yukawa
  potential

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Our Method

• Stepped pendulum with large, modulated attractor
  plate
• Newtonian torque is weak and analytic
• Principal challenge is achieving 0.1mm separation

Modulate separation
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Our Method

• Observed Yukawa component of torque

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Sensitivity

• Torque sensitivity fundamentally limited by
• Thermal noise in the torsion fiber
• Optical readout uncertainty due to torsion
  pendulum resonance
• Thermal noise caused by random atomic motion
  varies with signal frequency

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Sensitivity

• Equation of motion for torsion pendulum
• Optical readout uncertainty also varies with
  signal frequency

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Sensitivity
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Limiting Systematic Error

• Other sources of systematic noise include
• Viscous damping of pendulum motion
• Electrostatic charge buildup
• Seismic vibrations
• Numerous experimental steps to eliminate these
  factors
• High vacuum (µTorr)
• Electrostatic shield
• High resolution tilt sensor
• Magnetic damper

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Thermal Isolation

• Tests of our isolation chamber and temperature
  controller show greatly increased thermal
  stability.

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Apparatus

• Construction of thermal enclosure, vacuum
  chamber, magnetic damper, optical system and
  readout electronics complete
• Preliminary pendulum tests this summer
• Week-long run of experiment by year end

Thermal Isolation Enclosure
Vacuum Chamber
Torsion Fiber
Pendulum
Optical Readout
Laser Beam
Attractor
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Expectations

• Provided we can restrict noise to near its
  fundamental limit, we expect to exceed previous
  experiments by a factor of 100

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Our Research

• Tests theories of the very large and the very
  small simultaneously
• Stepped pendulum is both simple and sensitive
• 100x more sensitivity than previous experiments
• Official experimental runs by year end
• Financial support provided by Research
  Corporation grant CC6839 and the HSU College of
  Natural Resources and Sciences

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Couplings of a light dilaton and violations of.
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(2000). 3. S. Perlmutter et al., "Measurements of
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