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Astrophysical tests of general relativity in the strong-field regime

Astrophysical tests of general relativity in the strong-field regime. Emanuele Berti , University of Mississippi/Caltech Texas Symposium, São Paulo, Dec 18 2012. What are “strong field ” tests? Alternatives to GR: massive scalars BH dynamics and superradiance

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Astrophysical tests of general relativity in the strong-field regime

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  1. Astrophysical tests of general relativity in the strong-field regime EmanueleBerti, University of Mississippi/Caltech Texas Symposium, São Paulo, Dec 18 2012

  2. What are “strong field” tests? Alternatives to GR: massive scalars BH dynamics and superradiance GWs: SNR and event rates(e)LISA and fundamental physics BH spins and photon mass bounds Coda: Advanced LIGO and astrophysics

  3. Strong field: gravitationalfield vs. curvature; probing vs. testing [Psaltis, Living Reviews in Relativity]

  4. Testing general relativity – againstwhat?

  5. Finding a contender • Action principle • Well-posed initial-value problem • At most second-order equations of motion • Testable predictions! [Clifton+, 1106.2476] Generic scalar-tensor theory Einstein-dilaton-Gauss-Bonnet Dynamical Chern-Simons

  6. A promisingopponent: massive scalar fields • 1) Phenomenology • Modern equivalent of planets [Bertschinger] • Well-posed, flexible (Damour & Esposito-Farése “spontaneous scalarization”) • f(R) and other theories equivalent to scalar-tensor theories • 2) High-energy physics • Standard Model extensions predict massive scalar fields (dilaton, axions, moduli…) • Not seen yet: dynamics must be frozen • small coupling x - or equivalently large wBD~1/x • large mass m>1/R (1AU~10-18eV!) • 3) Cosmology • “String axiverse”: light axions, 10-33eV < ms< 10-18eV [Arvanitaki++, 0905.4720]Striking astrophysical implications: bosenovas, floating orbits

  7. Are massive scalar fieldsviable? • Bounds from: • Shapiro time delay: wBD>40,000[Perivolaropoulos, 0911.3401] • Lunar Laser Ranging • Binary pulsars: wBD>25,000[Freire++, 1205.1450] [Alsing, EB, Will & Zaglauer, 1112.4903]

  8. Wavescattering in rotatingblackholes [Arvanitaki+Dubovsky, 1004.3558] • Quasinormal modes: • Ingoing waves at the horizon,outgoing waves at infinity • Discrete spectrum of damped exponentials (“ringdown”)[EB++, 0905.2975] • Massive scalar field: • Superradiance:black hole bombwhen0 < w< mWH • Hydrogen-like, unstable bound states [Detweiler, Zouros+Eardley…]

  9. Quasinormalmodes [Visualization: NASA Goddard] • In GR, each mode determined uniquely by mass and spin • One mode: (M,a)Any other mode frequency:No-hair theorem test • Relative mode amplitudes:pre-merger parameters[Kamaretsos++,Gossan++] • Feasibility depends on SNR:Need SNR>30 [EB++, 2005/07] • 1) Noise S(fQNM) 2) Signal h~E1/2, E=erdMerd~0.01(4h)2for comparable-mass mergers, h=m1m2/(m1+m2)2 f= 1.2 x 10-2 (106Msun)/M Hz t = 55 M/(106Msun) s

  10. (e)LISA vs. LIGO f= 1.2 x 10-2 (106Msun)/M Hz t = 55 M/(106Msun) s [Schutz; see Sesana’s talk] SNR=h/S: S comparable, h~hM1/2

  11. Ringdownas a probe of SMBH formation • LISA/eLISA studies:merger-tree models of SMBHformation • Light or heavy seeds?Coherent or chaotic accretion?[Arun++, 0811.1011] • eLISA can easily tell whetherseeds are light or heavy[Sesana++, 1011.5893] • Mergers: a~0.7Chaotic accretion: a~0Coherent accretion: a~1[EB+Volonteri, 0802.0025] • >10 binaries can be used for no-hair tests • Spin observations constrain SMBH formation [Sesana++, 2012]

  12. Massive bosonicfields and superradiantinstabilities • Superradiancewhenw< mWHAny light scalar can trigger a blackholebomb (“bosenova”)[Yoshino+Kodama, 1203.5070] • Strongestinstability: msM~1 • [Dolan, 0705.2880] • For ms=1eV, M=Msun: msM~1010Need light scalars (or primordialblackholes!) Negativescalar fluxat the horizoncloseto superradiantresonancesat [Detweiler 1980]

  13. Light scalars: floatingorbits (Press & Teukolsky 1972) [Cardoso++ 1109.6021; Yunes++, 1112.3351]

  14. Photon mass bound from rotatingblackholes • Procaperturbations in Kerrdo notdecouple • Use Kojima’s • slow-rotationapproximation • Strongerinstabilitythan for massive scalars • Maximum (again) for msM~1 • mg<10-20 (or 4x10-21) eVPDG: mg<10-18 eV [Data points: Brenneman++, 1104.1132] [Pani++, 1209.0465; 1209.0773]

  15. Spin-orbitresonances and spin alignment [Schnittman 04; Kesden++; Lousto’s talk]

  16. Can Advanced LIGO reconstructbinaryevolution? [Gerosa++, in preparation]

  17. Summary Tests within GR (e)LISA: Tens of events could allow us to test the no-hair theoremAdvanced LIGO/ET can also test no-hair theorem - if IMBHs exist! Spin measurements constrain SMBH merger/accretion history [EB++, 0905.2975; EB+Volonteri, 0802.0025] Massive bosons and superradiant instabilities 3) Weak-field: Solar System, binary pulsars Cassini:wBD>40,000 for ms<2.5x10-20 eVBinary pulsars will do better in a few years [Alsing++, 1112.4903; Horbatsch++, in preparation] 4) Massive scalars: floating orbits[Cardoso++, 1109.6021; Yunes++, 1112.3351] 5) Massive vectors and SMBH spins: best bounds on photon mass mg<10-20 (4x10-21eV) (Particle Data Group: mg<10-18eV)[Pani++, 1209.0465; 1209.0773] Advanced LIGO 6) Spin alignment may encode formation history of the binary Effect of tides? Reverse mass ratio?

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