Astrophysical tests of general relativity in the strong-field regime
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Transcript of 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/CaltechTexas Symposium, São Paulo, Dec 18 2012
1) What are “strong field” tests?2) Alternatives to GR: massive
scalars3) BH dynamics and
superradiance4) GWs: SNR and event rates
(e)LISA and fundamental physics
5) BH spins and photon mass bounds
Coda: Advanced LIGO and astrophysics
Strong field: gravitational field vs. curvature; probing vs. testing
[Psaltis, Living Reviews in Relativity]
Testing general relativity – against what?
Finding a contender Action principle Well-posed initial-value problem At most second-order equations of motion Testable predictions!
Dynamical Chern-SimonsEinstein-dilaton-Gauss-Bonnet
Generic scalar-tensor theory
[Clifton+, 1106.2476]
A promising opponent: 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
Are massive scalar fields viable?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]
Wave scattering in rotating black holes
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 bomb when 0 < w < mWH
Hydrogen-like, unstable bound states [Detweiler, Zouros+Eardley…]
[Arvanitaki+Dubovsky, 1004.3558]
f = 1.2 x 10-2 (106Msun)/M Hzt = 55 M/(106Msun) s
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=erdM
erd~0.01(4h)2 for comparable-mass mergers, h=m1m2/(m1+m2)2
Quasinormal modes[Visualization: NASA Goddard]
(e)LISA vs. LIGO
[Schutz; see Sesana’s talk]
SNR=h/S: S comparable, h~hM1/2
f = 1.2 x 10-2 (106Msun)/M Hzt = 55 M/(106Msun) s
LISA/eLISA studies:merger-tree models of SMBH formation
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
Ringdown as a probe of SMBH formation
[Sesana++, 2012]
Massive bosonic fields and superradiant instabilities
Superradiance when w < mWH
Any light scalar can trigger a black hole bomb (“bosenova”)[Yoshino+Kodama, 1203.5070]
Strongest instability: msM~1[Dolan, 0705.2880]
For ms=1eV, M=Msun : msM~1010
Need light scalars (or primordial black holes!)
Negative scalar flux at the horizon close to superradiant resonances at
[Detweiler 1980]
Light scalars: floating orbits (Press & Teukolsky 1972)
[Cardoso++ 1109.6021; Yunes++, 1112.3351]
Photon mass bound from rotating black holes
Proca perturbations in Kerrdo not decouple
Use Kojima’sslow-rotation approximation
Stronger instabilitythan for massive scalars
Maximum (again) for msM~1
mg<10-20 (or 4x10-21) eVPDG: mg<10-18 eV
[Pani++, 1209.0465; 1209.0773]
[Data points: Brenneman++, 1104.1132]
[Schnittman 04; Kesden++; Lousto’s talk]
Spin-orbit resonances and spin alignment
Can Advanced LIGO reconstruct binary evolution?[Gerosa++, in preparation]
Tests within GR1) (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!
2) Spin measurements constrain SMBH merger/accretion history
[EB++, 0905.2975; EB+Volonteri, 0802.0025]
Massive bosons and superradiant instabilities3) Weak-field: Solar System, binary pulsars
Cassini: wBD>40,000 for ms<2.5x10-20 eV Binary 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 LIGO6) Spin alignment may encode formation history of the binary
Effect of tides? Reverse mass ratio?
Summary