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String/Brane Cosmology

String/Brane Cosmology. COSMO 07 – University of Sussex C.P. Burgess. String/Brane Cosmology. …for those who have not yet drunk the Kool-Aid. with J.Blanco-Pillado, J.Cline, K. das Gupta, C. de Rham,

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String/Brane Cosmology

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  1. String/Brane Cosmology COSMO 07 – University of Sussex C.P. Burgess

  2. String/Brane Cosmology …for those who have not yet drunk the Kool-Aid with J.Blanco-Pillado, J.Cline, K. das Gupta, C. de Rham, C.Escoda, M.Gomez-Reino, D. Hoover, R.Kallosh, A.Linde,F.Quevedo, G. Tasinato and A. Tolley

  3. On the shoulders of giants A. Salam, E. Sezgin, H. Nishino,G. Gibbons, S. Kachru E. Silverstein, R. Guven, C. Pope, K. Maeda, M. Sasaki, V. Rubakov, R. Gregory, I. Navarro, J. Santiago, S. Carroll, C. Guica, C. Wetterich, S. Randjbar-Daemi, F. Quevedo, Y. Aghababaie, S. Parameswaran, J. Cline, J. Matias, G. Azuelos, P-H. Beauchemin, A. Albrecht, C. Skordis, F. Ravndal, I. Zavala, G. Tasinato, J. Garriga, M. Porrati, H.P. Nilles, A. Papazoglou, H. Lee, N. Arkani-Hamad, S. Dimopoulos, N. Kaloper, R. Sundrum, D. Hoover, A. Tolley, C. de Rham, S. Forste, Z. Lalak, S. Lavingnac, C. Grojean, C. Csaki, J. Erlich, T. Hollowood, H. Firouzjahi, J. Chen, M. Luty, E. Ponton, P. Callin, D. Ghilencea, E. Copeland, O. Seto, V. Nair, S. Mukhoyama, Y. Sendouda, H. Yoshigushi, S. Kinoshita, A. Salvio, J. Duscheneau, J. Vinet, M. Giovannini, M. Graesser, J. Kile, P. Wang, P. Bostok, G. Kofinas, C. Ludeling, A. Nielsen, B. Carter, D. Wiltshire. C. K. Akama, S. Appleby, F. Arroja, D. Bailin, M. Bouhmadi-Lopez, M. Brook, R. Brown, C. Byrnes, G. Candlish, A. Cardoso, A. Chatterjee, D. Coule, S. Creek, B. Cuadros-Melgar, S. Davis, B. de Carlos, A. de Felice, G. de Risi, C. Deffayet, P. Brax, D. Easson, A. Fabbri, A. Flachi, S. Fujii, L. Gergely, C. Germani, D. Gorbunov, I. Gurwich, T. Hiramatsu, B. Hoyle, K. Izumi, P. Kanti, S. King, T. Kobayashi, K. Koyama, D. Langlois, J. Lidsey, F. Lobo, R. Maartens, N. Mavromatos, A. Mennim, M. Minamitsuji, B. Mistry, S. Mizuno, A. Padilla, S. Pal, G. Palma, L. Papantonopoulos, G. Procopio, M. Roberts, M. Sami, S. Seahra, Y. Sendouda, M. Shaeri, T. Shiromizu, P. Smyth, J. Soda, K. Stelle, Y. Takamizu, T. Tanaka, T. Torii, C. van de Bruck, D. Wands, V. Zamarias, H. Ziaeepour Cosmo 07

  4. Outline • Motivation • String Cosmology: Why Does it Make Sense? • Branes and ‘late-Universe’ cosmology • Some Dark (Energy) Thoughts • String inflation • A Sledgehammer for a Nutcracker? • Outlook Cosmo 07

  5. Outline • Motivation • String Cosmology: Why Does it Make Sense? • Branes and ‘late-Universe’ cosmology • Some Dark (Energy) Thoughts • String inflation • A Sledgehammer for a Nutcracker? • Outlook Cosmo 07

  6. Outline • Motivation • String Cosmology: Why Does it Make Sense? • Branes and ‘late-Universe’ cosmology • Some Dark (Energy) Thoughts • String inflation • A Sledgehammer for a Nutcracker? • Outlook Cosmo 07

  7. Outline • Motivation • String Cosmology: Why Does it Make Sense? • Branes and ‘late-Universe’ cosmology • Some Dark (Energy) Thoughts • String inflation • A Sledgehammer for a Nutcracker? • Outlook Cosmo 07

  8. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? Cosmo 07

  9. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? Science progresses because short- distance physics decouples from long distances. Cosmo 07

  10. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? * Inflationary fluctuations could well arise at very high energies: MI» 10-3 Mp Science progresses because short distance physics decouples from long distances. Cosmo 07

  11. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? * Inflationary fluctuations could well arise at very high energies: MI» 10-3 Mp * Cosmology (inflation, quintessence, modified gravity, etc) relies on properties which can be extremely sensitive to short distances. Science progresses because short distance physics decouples from long distances. Cosmo 07

  12. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? * Inflationary fluctuations could well arise at very high energies: MI» 10-3 Mp * Cosmology (inflation, quintessence, modified gravity, etc) relies on properties which can be extremely sensitive to short distances. * String theory suggests important changes in the low-energy degrees of freedom: branes. Science progresses because short distance physics decouples from long distances. Cosmo 07

  13. Strings, Branes and Cosmology Polchinski • Why doesn’t string theory decouple from cosmology? • Why are branes important for cosmology and particle physics? D branes in string theory are surfaces on which some strings must end, ensuring their low-energy modes are trapped on the brane. Cosmo 07

  14. Strings, Branes and Cosmology Ibanez et al • Why doesn’t string theory decouple from cosmology? • Why are branes important for cosmology and particle physics? In some cases this is where the Standard Model particles live. Cosmo 07

  15. Strings, Branes and Cosmology Rubakov & Shaposhnikov • Why doesn’t string theory decouple from cosmology? • Why are branes important for cosmology and particle physics? Leads to the brane-world scenario, wherein we are all brane-bound. Cosmo 07

  16. Strings, Branes and Cosmology • Why doesn’t string theory decouple from cosmology? • Why are branes important for cosmology and particle physics? Identifies hidden assumptions about low energy theory whose relaxation might help with low energy naturalness problems. Cosmo 07

  17. Naturalness • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Cosmo 07

  18. Naturalness BUT: effective theory can be defined at many scales • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Cosmo 07

  19. Naturalness BUT: effective theory can be defined at many scales • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Cosmo 07

  20. Naturalness BUT: effective theory can be defined at many scales • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Hierarchy Problem:These must cancel to 20 digits!! Cosmo 07

  21. Naturalness • Three approaches to solve the Hierarchy problem: • Compositeness: H is not fundamental at energies E À Mw • Supersymmetry: there are new particles at E À Mw and a symmetry which ensures cancellations so m2 ~ MB2 – MF2 • Extra Dimensions: the fundamental scale is much smaller than Mp , much as GF-1/2 > Mw • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Hierarchy problem: Since the largest mass dominates, why isn’t m ~ MGUT or Mp ?? Cosmo 07

  22. Naturalness in Crisis • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. • The Standard Model’s dirty secret: there are really two unnaturally small terms. + dimensionless Cosmo 07

  23. Naturalness in Crisis • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. Can apply same argument to scales between TeV and sub-eV scales. + dimensionless Cosmological Constant Problem: Must cancel to 32 decimal places!! Cosmo 07

  24. Naturalness in Crisis • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. • The Standard Model’s dirty secret: there are really two unnaturally small terms. Harder than the Hierarchy problem: Integrating out the electron already gives too large a contribution!! + dimensionless Cosmo 07

  25. Naturalness in Crisis • Dark energy vs vacuum energy • Why must the vacuum energy be large? Seek to change properties of low-energy particles (like the electron) so that their zero-point energy does not gravitate, even though quantum effects do gravitate in atoms! Why is this seen………………but not this? Cosmo 07

  26. Naturalness in Crisis • Approaches to solve the Hierarchy problem at m ~ 10-2 eV? • Compositeness: graviton is not fundamental at energies E Àm • Supersymmetry: there are new particles at E Àm and a symmetry which ensures cancellations so m2 ~ MB2 – MF2 • Extra Dimensions: the fundamental scale is much smaller than Mp • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless Cosmological constant problem: Why is m ~ 10-3 eV rather than me , Mw , MGUT or Mp? Cosmo 07

  27. Naturalness in Crisis • Approaches to solve the Hierarchy problem at m ~ 10-2 eV? • Compositeness: graviton is not fundamental at energies E Àm • Supersymmetry: there are new particles at E Àm and a symmetry which ensures cancellations so m2 ~ MB2 – MF2 • Extra Dimensions: the fundamental scale is much smaller than Mp • Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’. • Motivated by belief that SM is an effective field theory. + dimensionless ?? Cosmological constant problem: Why is m ~ 10-3 eV rather than me , Mw , MGUT or Mp? Cosmo 07

  28. How Extra Dimensions Help • 4D CC vs 4D vacuum energy • Branes and scales Cosmo 07

  29. How Extra Dimensions Help • 4D CC vs 4D vacuum energy • Branes and scales A cosmological constant Cosmo 07

  30. How Extra Dimensions Help • 4D CC vs 4D vacuum energy • Branes and scales A cosmological constant is not distinguishable from a Lorentz invariant vacuum energy vs Cosmo 07

  31. How Extra Dimensions Help • 4D CC vs 4D vacuum energy • Branes and scales A cosmological constant is not distinguishable* from a Lorentz invariant vacuum energy vs * in 4 dimensions… Cosmo 07

  32. How Extra Dimensions Help In higher dimensions a 4D vacuum energy, if localized in the extra dimensions, can curve the extra dimensions instead of the observed four. • 4D CC vs 4D vacuum energy • Branes and scales Chen, Luty & Ponton Arkani-Hamad et al Kachru et al, Carroll & Guica Aghababaie, et al Cosmo 07

  33. How Extra Dimensions Help • 4D CC vs 4D vacuum energy • Branes and scales These scales are natural using standard 4D arguments. Cosmo 07

  34. How Extra Dimensions Help Arkani Hamed, Dvali, Dimopoulos Extra dimensions could start here, if there are only two of them. • 4D CC vs 4D vacuum energy • Branes and scales These scales are natural using standard 4D arguments. Cosmo 07

  35. How Extra Dimensions Help Must rethink how the vacuum gravitates in 6D for these scales. SM interactions do not change at all! • 4D CC vs 4D vacuum energy • Branes and scales Only gravity gets modified over the most dangerous distance scales! Cosmo 07

  36. Suppose physics is extra-dimensional above the 10-2 eV scale. Suppose the physics of the bulk is supersymmetric. The SLED Proposal Aghababaie, CB, Parameswaran & Quevedo Cosmo 07

  37. Suppose physics is extra-dimensional above the 10-2 eV scale. Suppose the physics of the bulk is supersymmetric. 6D gravity scale: Mg ~ 10 TeV KK scale: 1/r ~ 10-2 eV Planck scale: Mp ~ Mg2 r The SLED Proposal Arkani-Hamad, Dimopoulos & Dvali Cosmo 07

  38. Suppose physics is extra-dimensional above the 10-2 eV scale. Suppose the physics of the bulk is supersymmetric. 6D gravity scale: Mg ~ 10 TeV KK scale: 1/r ~ 10-2 eV Planck scale: Mp ~ Mg2 r Choose bulk to be supersymmetric (no 6D CC allowed) The SLED Proposal Nishino & Sezgin Cosmo 07

  39. Suppose physics is extra-dimensional above the 10-2 eV scale. Suppose the physics of the bulk is supersymmetric. 6D gravity scale: Mg ~ 10 TeV KK scale: 1/r ~ 10-2 eV Planck scale: Mp ~ Mg2 r SUSYBreaking on brane: TeV in bulk: Mg2/Mp ~1/r The SLED Proposal Cosmo 07

  40. The SLED Proposal Particle Spectrum: SM on brane – no partners Many KK modes in bulk 4D scalar: ef r2 ~ const 4D graviton Cosmo 07

  41. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding Cosmo 07

  42. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? Search for solutions to 6D supergravity: What bulk geometry arises from a given brane configuration? What is special about the ones which are 4D flat? What Needs Understanding Cosmo 07

  43. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? Search for solutions to 6D supergravity: What bulk geometry arises from a given brane configuration? What is special about the ones which are 4D flat? What Needs Understanding • Bulk solutions known for most properties for 2 brane sources; • Most have runaway behaviour, with extra dimensions growing or collapsing • Sufficient condition for flatness is absence of brane-dilaton coupling. Cosmo 07

  44. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding Cosmo 07

  45. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding • When both branes have conical singularities all static solutions have 4D minkowski geometry. • Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant) Cosmo 07

  46. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding • When both branes have conical singularities all static solutions have 4D minkowski geometry. • Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant) • Brane loops on their own cannot generate dilaton couplings from scratch. Cosmo 07

  47. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding • When both branes have conical singularities all static solutions have 4D minkowski geometry. • Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant) • Brane loops on their own cannot generate dilaton couplings from scratch. • Bulk loops can generate brane-dilaton coupling but TeV scale modes are suppressed at one loop by 6D supersymmetry Cosmo 07

  48. Classical part of the argument: What choices must be made to ensure 4D flatness? Quantum part of the argument: Are these choices stable against renormalization? What Needs Understanding • When both branes have conical singularities all static solutions have 4D minkowski geometry. • Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant) • Brane loops on their own cannot generate dilaton couplings from scratch. • Bulk loops can generate brane-dilaton coupling but TeV scale modes are suppressed at one loop by 6D supersymmetry • Each bulk loop costs power of ef ~ 1/r2 and so only a few loops must be checked….. Cosmo 07

  49. Quintessence cosmology Modifications to gravity Collider physics Neutrino physics? And more! Observational Consequences SUSY broken at the TeV scale, but not the MSSM! Cosmo 07

  50. Summary • It is too early to abandon naturalness as a fundamental criterion! Cosmo 07

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