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TESTING MOND WITH LISA PATHFINDER . Jo ã o Magueijo Theoretical Physics Group Imperial College. Based on Bekenstein & Magueijo, astro-ph/0602266; Bevis, Magueijo, Trenkel, Kemble, arXiv: 0912.0710; Trenkle, Kemble, Bevis, Magueijo, arXiv: 1001.1303.

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testing mond with lisa pathfinder

TESTING MOND WITH LISA PATHFINDER

João Magueijo

Theoretical Physics Group

Imperial College

Based on

Bekenstein & Magueijo, astro-ph/0602266;

Bevis, Magueijo, Trenkel, Kemble, arXiv:0912.0710;

Trenkle, Kemble, Bevis, Magueijo, arXiv:1001.1303

slide2

The schism “dark matter vs modified gravity” is an old story

  • LeVerrier prediction of Neptune from Uranus orbital anomalies
  • VERSUS
  • his attempts to explain the anomalous precession of the perihelion of Mercury with “Vulcanus”
slide3

The issue is very topical:

  • History shows that anomalies can be either dark matter or modified gravity (or a combination).
  • Experiment will settle the matter.
  • A direct (solar system or laboratory test) would be cleaner.
slide4

(Spiral) Galaxy rotation curves:

  • Flattening of rotation curves
  • Anomalous behaviour triggered by
  • Tully-Fisher relation
slide5

Take these facts as “Kepler’s laws” for a new theory of gravity

  • Milgrom’s insight:
  • Explains observations:

(often quoted as a rule of thumb)

slide6

This rule of thumb can be incorporated into a consistent theory

  • There are several Lagrangian relativistic theories that do this
  • In the non-relativistic limit they typically reduce to a non-linear Poisson equation
lisa pathfinder as gravitational laboratory

We want to exploit this!

LISA Pathfinder as Gravitational Laboratory
  • LISA Pathfinder and its Payload will offer the following (see ESA-SCI(2007)1):
    • Differential Force Measurement Sensitivity:

≈ 1.3x10-14N / √Hz around 1mHz

    • Drag-Free Platform Stability:Platform Free-Fall Quality of ≈ 10-13ms-2/ √Hz around 1mHz ≈ 10-9ms-2 at DC
    • Gravity Gradiometer Sensitivity: ≈ 1.5x10-14s-2/ √Hz around 1mHz
    • … and more…
slide9

The intuition behind the basic prediction Bekenstein & Magueijo, astro-ph/0602266

NEWTONIAN

MOND

slide14

Data analysis:

  • Borrow noise-matched filters from gravity wave detection (but with a significant simplification: we know where the starting time of the signal).
  • The optimal SNR is:

Fourier transform of the signal

Noise power

spectrum

slide16

THE ELEPHANT IN

THE ROOM

  • Lagrange points
  • VS.
  • Saddle points.
potential trajectories for lisa pathfinder
Potential Trajectories for LISA Pathfinder
  • Illustration of the chaotic nature of the problem:

Single dV manoeuvres between 0.5m/s and 1m/s applied at 0.25 day intervals

1.5mio km

Earth

Sun

slide21

How generic a test of MOND is this?

  • There is a free function in the theory
  • It should be constrained:
  • - To produce the required astrophysical effects
  • - Not to renormalize the gravitational constant by more then a few percent
slide22

A negative result would be pretty damning

  • A triple power law in would bypass a negative result
  • The intermediate power would have to be very large
  • RIDICULOUS!
conclusions
Conclusions:
  • A LPF redirection to the Earth-Sun (Moon) saddle(s) would be a direct test of MOND; it would add a science case to LPF.
  • Systematics are under control (Self-gravity isn’t an issue; the Moon isn’t an issue….)
  • SNR ratios hit double/triple figures easily.
  • A negative result would kill MOND in (almost) all of its relativistic incarnations
slide24

Let’s do the experiment!

It would answer important questions:

  • Is dark matter a “Vulcan”?
  • Is modifying gravity unwarranted lunacy?