1. Bose, 2005/12/14, GWDAW10, Brownsville Sukanta Bose Washington State University, Pullman Acknowledgements: Roy Maartens, U. Portsmouth, Aaron Rogan, Yuri Gusev, Wash. State NSF-PHY-0239735 Probing extra dimensions with gravitational wave observations

2. Bose, 2005/12/14, GWDAW10, Brownsville Literature R. Maartens, “Brane-world gravity,” Living Rev.Rel.7, 7 (2004) [gr-qc/0312059]. D. Langlois et al., “Gravitational waves from inflation on the brane,” Phys. Lett B489, 259 (2000). V. Sahni et al., “Relic gravity waves from brane-world inflation,” Phys. Rev. D65, 023518 (2001). S. Seahra et al. “Detecting extra dimensions with gravity- wave spectroscopy,” Phys. Rev. Lett. 94, 121302 (2005).

3. Bose, 2005/12/14, GWDAW10, Brownsville The brane-world scenario Basic idea: The universe has extra dimensions, but only gravity can propagate in the bulk space-time We live on a 3+1 brane and do not “feel” the other sub-millimeter dimension Such space-times arise as solutions in super-string theories, but need not be limited to them Might be experimentally constrained / falsified.

4. Bose, 2005/12/14, GWDAW10, Brownsville Brane-world: Old paradoxes & new physics Hierarchy problem: Running coupling constants: Gravity is weak owing to a faster than fall off at short length scales. Unification may occur at closer than 10TeV. Black hole hairs: The gravitational degrees of freedom in the bulk leave an imprint on the brane as a non-local tensor field. This field can encode information about the astrophysical source that forms a black hole

5. Bose, 2005/12/14, GWDAW10, Brownsville Brane-world: Experiments Particle accelerators: »Proton-proton smash-ups are being studied at Fermilab (574 GeV); 10TeV accessible to the LHC, which is under construction »Black hole evaporation: A non- negligible probability for the production of black hole pairs in such smash-ups exists and can be detected from excess photon emissions. The Large Hadron Collider

6. Bose, 2005/12/14, GWDAW10, Brownsville Brane-world: Experiments (contd.) 1. Table-tops: Testing the law of gravity at sub-millimeter scales. Places the bound: 2. Indirect: Hawking luminosity is considerably enhanced: Existence of BH X-ray binaries then => [Hoyle et al., Phys.Rev.Lett. (2001)]

7. Bose, 2005/12/14, GWDAW10, Brownsville Solutions for GW detections: The black-string Chamblin et al., Phys.Rev.D61 (2000)] Our brane Shadow brane Large Black hole Small Black hole

8. Bose, 2005/12/14, GWDAW10, Brownsville Allowed Black String Configurations d appears as a massless field and effective theory is Brans-Dicke-like: Unstable solutions Permissible configurations Scalar-tensor limit

9. Bose, 2005/12/14, GWDAW10, Brownsville GW Modes in Braneworld The Kaluza-Kline tower of massive modes in flat space: 0 The BH QNM signal (m=0) in GR

10. Bose, 2005/12/14, GWDAW10, Brownsville Black string: Quasi-Normal Modes Massive modes in Anti-deSitter: [Seahra et al., Phys.Rev.Lett. (2005)]

11. Bose, 2005/12/14, GWDAW10, Brownsville Total QNM waveform-I A time-series of a superposition of the first 9 modes for d / l = 6. Fractional energy in n=0 is over 99%. For a black hole – black string collision:

12. Bose, 2005/12/14, GWDAW10, Brownsville Total QNM waveform-II A time-series of a superposition of the first 9 modes for d / l = 20. Fractional energy in n=0 is over 2e-13%. For a black string – black string collision:

13. Bose, 2005/12/14, GWDAW10, Brownsville Black string QNMs in ground-based detectors Massive modes, with n=1,…,13 (with increasing frequencies) for a single brane separation, d=2.2, and l=0.1mm

14. Bose, 2005/12/14, GWDAW10, Brownsville Black string: QNM frequencies (n=1) vs d/l [Hoyle et al., Phys.Rev.Lett. (2001)] The frequency of a mode (here n=1) decreases with increasing brane separation d.

15. Bose, 2005/12/14, GWDAW10, Brownsville Detecting black string QNMs 1.Matched filtering well suited as detection strategy. The massive waveform frequencies are dependent on d and l, but independent of black string/black hole mass 2.The mode frequencies and amplitudes (sans the “fine structure”) well understood and robust 3.Clearly, if there were a GR QNM trigger (m=0), a follow up search for the massive waveforms must be implemented 4.However, since it is also possible that the massive modes dominate the massless one, they must be searched for independently anyway. 5.A slow fall-off suggests that when looking up to sufficiently far distances, these waveforms may form a stochastic background [Clarkson & Maartens (2005)]. Once this background is modeled, it should be possible to fold it into the LSC search pipeline

16. Bose, 2005/12/14, GWDAW10, Brownsville GW Predictions: Stochastic GW background Current prediction for the SGWB spectra: [Sahni et al., Phys.Rev.D65 (2001)] The best COBE-normalized transitions are for the “exponential” potential, at:

17. Bose, 2005/12/14, GWDAW10, Brownsville Future work 1.Construct template banks based on values of parameters d and l 2.Account for differences between arrival times of different modes based on different initial conditions and dispersion 3.Properties of the 3 other polarizations remain to be studied 4.The stochastic GW background remains to be calculated more carefully to account for coupling of the massless modes with the massive modes

18. Bose, 2005/12/14, GWDAW10, Brownsville Brane-world: Experiments 1. Table-tops: Testing the law of gravity at sub-millimeter scales. 2. Particle accelerators: »Proton-proton smashups are being studied at Fermilab (574 GeV); 10TeV accessible to the LHC under construct. »Black hole evaporation: A non-negligible probability for the production of black hole pairs in such smashups exists and can be detected from excess photon emissions. 3. Gravitational-wave experiments: Tell- tale deviations in the spectra of: »Black hole ringdowns GR Black hole ringdown spectra [Seahra et al. Phys.Rev.Lett (2005)]

19. Bose, 2005/12/14, GWDAW10, Brownsville Brane-world: Experiments Table-tops: Testing the law of gravity at sub-millimeter scales. Particle accelerators: »Proton-proton smashups are being studied at Fermilab (574 GeV); 10TeV accessible to the LHC under construct. »Black hole evaporation: A non-negligible probability for the production of black hole pairs in such smashups exists and can be detected from excess photon emissions. Gravitational-wave experiments: Tell- tale deviations in the spectra of both: »Black hole ringdowns »Cosmic graviton background Grav. wave energy density [Ichika, Nakamura (2004), Bose, Phys.Rev.D (2005); Rogan, Bose, Class.Quant.Grav.(2004)]

20. Bose, 2005/12/14, GWDAW10, Brownsville Interferometric Observatories Present & Future

21. Bose, 2005/12/14, GWDAW10, Brownsville The Sensitivities: LISA vs LIGO

22. Bose, 2005/12/14, GWDAW10, Brownsville Why Quantize Gravity? Since we have a theoretical framework that unifies the other 3 fundamental forces. »Gravity is the weakest of those forces: 1/(10 trillion trillion trillion) weaker than E! »Allowing for extra dimensions makes it probable that all forces unify at as for electroweak. Since matter is quantized: