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TESTING MOND WITH LISA PATHFINDER

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

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  1. 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

  2. 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”

  3. 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.

  4. (Spiral) Galaxy rotation curves: • Flattening of rotation curves • Anomalous behaviour triggered by • Tully-Fisher relation

  5. 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)

  6. 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

  7. LISA Pathfinder mission

  8. 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…

  9. The intuition behind the basic prediction Bekenstein & Magueijo, astro-ph/0602266 NEWTONIAN MOND

  10. This intuition is corroborated by an exact calculation:

  11. Transverse tidal stress at impact 25, 100, 400 Km of the Earth-Sun saddle

  12. The coincidence of the century

  13. Simulating the signal and noise

  14. 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

  15. Optimal SNR for different b and noise, assuming v=1.5Km/sec

  16. THE ELEPHANT IN THE ROOM • Lagrange points • VS. • Saddle points.

  17. 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

  18. Transverse tidal stress at impact 25, 100, 400 Km of the Earth-Sun saddle

  19. 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

  20. 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!

  21. 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

  22. Let’s do the experiment! It would answer important questions: • Is dark matter a “Vulcan”? • Is modifying gravity unwarranted lunacy?

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