Transcript Document
String Inflation @ Very Early Universe + 25 C.P. Burgess with N. Barnaby, J.Blanco-Pillado, J.Cline, K. das Gupta, C.Escoda, H. Firouzjahi, M.Gomez-Reino, R.Kallosh, A.Linde,and F.Quevedo Outline • String inflation • Why build models only a mother could love? • Emerging features • Mechanisms and naturalness issues • Multiple scalars and robustness • Mind-broadening: cosmic strings; reheating; … • Open issues • Scales; control of approximations; … VEU + 25 Outline • String inflation • Why build models only a mother could love? • Emerging features • Mechanisms and naturalness issues • Multiple scalars and robustness • Mind-broadening: cosmic strings; reheating; … • Open issues • Scales; control of approximations; … VEU + 25 Outline • String inflation • Why build models only a mother could love? • Emerging features • Mechanisms and naturalness issues • Multiple scalars and robustness • Mind-broadening: cosmic strings; reheating; … • Open issues • Scales; control of approximations; … VEU + 25 String Inflation • What might one hope to learn? • about strings • about inflation • Why is it hard? VEU + 25 String Inflation • What might one hope to learn? • about strings • about inflation • Why is it hard? VEU + 25 String Inflation • What might one hope to learn? • about strings • about inflation • Why is it hard? Difficult to identify where we live within the string landscape. Seek ‘modules’ encoding low-energy features: standard model; dark energy; inflation; … VEU + 25 String Inflation • What might one hope to learn? • about strings • about inflation • Why is it hard? VEU + 25 String Inflation • What might one hope to learn? • about strings • about inflation • Why is it hard? Inflation is under ever closer scrutiny due to the recent wealth of cosmological data. What are these measurements telling us? VEU + 25 String Inflation Batfit courtesy of Stephane Coutu • What might one hope to learn? • about strings • about inflation • Why is it hard? Inflation is under ever closer scrutiny due to the recent wealth of cosmological data. What are these measurements telling us? VEU + 25 String Inflation • What we’d like string theory to tell us about inflation: What might one How generic is it in the landscape? hope to learn? Initial conditions, flat potentials, … • about strings • about inflation • Why is it hard? VEU + 25 String Inflation • What we’d like string theory to tell us about inflation: What might one How generic is it in the landscape? hope to learn? Initial conditions, flat potentials, … • about strings How does reheating work? Does SM couple strongly enough to inflaton? • about inflation Do other channels couple even more strongly? • Why is it hard? VEU + 25 String Inflation • • What we’d like string theory to tell us about inflation: What might one How generic is it in the landscape? hope to learn? Initial conditions, flat potentials, … • about strings How does reheating work? Does SM couple strongly enough to inflaton? • about inflation Do other channels couple even more strongly? How robust are inflationary inferences drawn Why is it using hard? simple single-field slow-roll models? VEU + 25 String Inflation • • What we’d like string theory to tell us about inflation: What might one How generic is it in the landscape? hope to learn? Initial conditions, flat potentials, … • about strings How does reheating work? Does SM couple strongly enough to inflaton? • about inflation Do other channels couple even more strongly? How robust are inflationary inferences drawn Why is it using hard? simple single-field slow-roll models? Are qualitatively new kinds of signatures or mechanisms possible? VEU + 25 Emerging Picture • Mechanisms • Robustness • Mind broadening VEU + 25 Emerging Picture • Mechanisms • Robustness • Mind broadening VEU + 25 Emerging Picture • Mechanisms • Robustness Why is it so hard to find inflation in string theory? • Mind broadening It has many scalars, which SUSY gives flat potentials, but SUSY breaking is hard to compute reliably. VEU + 25 Emerging Picture • Mechanisms • Robustness What is so hard about finding inflation in string theory? • Mind broadening It has many scalars, which SUSY gives flat potentials, but SUSY breaking was hard to compute reliably. A convincing case for inflation requires knowing the potential for all of the relevant low-energy fields. VEU + 25 Emerging Picture Giddings, Kachru & Polchinski Kachru, Kallosh, Linde & Trivedi • For Type IIB strings it is now known how to compute Mechanisms the potentials for many of these scalars, when close to an N=1 4D vacuum. • Robustness Key ingredients: • D3 and D7 branes & orientifolds Mind Fluxes broadening sourced by these branes, wrapping extra dimensions Gmnp H mnp Fmnp VEU + 25 Emerging Picture Klebanov & Strassler • Mechanisms ds 2 h 1/ 2mndx mdx n h1/ 2 dr 2 r 2d2 h 1/ r4 dr 2 ds r mndx dx 2 d2 r 2 • Robustness 2 m n Strongly warped throats arise in response to specific flux configurations. • Mind broadening Warped throats strongly redshift energies à la Randall & Sundrum VEU + 25 Emerging Picture Denef & Douglas • Mechanisms • Robustness • K 2 ln V 2 ln 13 / 2 23 / 2 W W0 A1ea1T1 A2ea2T2 f i ab Ti ab Low-energy dynamics of last few moduli are by a low-energy Mind described broadening 4D supergravity. Inflationary solutions make sense if H ¿ MKK VEU + 25 Emerging Picture BMNQRZ Dvali et al KKLMMT Silverstein & Tong Baumann et al Two classes of moduli to be considered as inflatons • Mechanisms Brane-antibrane separation • Robustness • Mind broadening VEU + 25 Emerging Picture CB, Quevedo, Rajesh & Zhang Blanco-Pillado et al Conlon & Quevedo Bond, Kofman & Prokushkin Two classes of moduli to be considered as inflatons • Mechanisms • Rolling moduli (volume and shape of extra Robustness dimensions, or their superpartner axions) • Mind eg: broadening Better Racetrack: K 2 ln V 2 ln 13 / 2 23 / 2 W W0 A1ea1T1 A2ea2T2 f i ab Ti ab VEU + 25 Emerging Picture • Mechanisms • Robustness • Mind broadening VEU + 25 Emerging Picture • In all cases the inflationary dynamics involves multiple Mechanisms fields moving in a complicated potential. Slow rolls appear not to be generic. • Robustness • Warning: It is insufficient in all known cases to fix fields by hand, while Mind some broadening evolving others (despite there being many papers which do so). VEU + 25 Emerging Picture Blanco-Pillado et al • Single-field slow-roll analyses nonetheless capture much Mechanisms of the generic predictions for the CMB • Robustness But must check: The • presence of multiple scalars allows in new features Mind principle broadening like isocurvature perturbations, etc. VEU + 25 Emerging Picture • Because inflation is found in 4D effective theory, Mechanisms predictions tend to be contained within those of the corresponding 4D mechanism • Robustness Small-field models • Large-field models models Mind Hybrid broadening VEU + 25 Emerging Picture Kallosh & Linde Baumann & McAllister • Because inflation is found in 4D effective theory, Mechanisms predictions tend to be contained within those of the corresponding 4D mechanism • Robustness Small-field models • Large-field models models Mind Hybrid broadening Only stringy implication so far is small tensor amplitude VEU + 25 Emerging Picture Kaloper, Kleban, Lawrence & Shenker CB, Cline, Holman & Lemieux • Heavy physics (M À H) decouples in string theory, and Mechanisms so tends not to interfere with inflationary predictions. • Robustness Two kinds of effects can • be larger than the naïve H2/M2 suppression: Mind Non-adiabatic broadeningeffects near horizon exit; or m2/M2 where H = m2/Mp H-1(t) Length 10-30 e-foldings Inflation (t) Post-Inflation oscillations 60 e-foldings p Time VEU + 25 Emerging Picture Conlon & Quevedo • Inflation may be more natural in Kahler modulus Mechanisms inflation, with 3 moduli in large-volume framework. • Robustness K 2 ln 13 / 2 23 / 2 33 / 2 W W0 A1ea1T1 A2ea2T2 A3ea3T3 f i ab Ti ab • Mind Slow broadening roll relies on large field values rather than tuned parameters in the potential Veff A B( / M )n exp b( / M )n i ( / M )n À 1 VEU + 25 Emerging Picture • Mechanisms • Robustness • Mind broadening VEU + 25 Emerging Picture BMNQRZ Dvali et al Several novel features and mechanisms have emerged • Mechanisms Brane-antibrane annihilation, and the absence of the inflaton in the post-inflationary low-energy theory; • Robustness • Mind broadening VEU + 25 Emerging Picture Barnaby et al Kofman & Yi Chialva, Shiu & Underwood Langfelder Several novel features and mechanisms have emerged • Mechanisms Brane-antibrane annihilation, and the absence of the inflaton in the post-inflationary low-energy theory; • Robustness Warped reheating, and the relatively efficient cascade of inflationary energy into the lowest throat. • Mind broadening VEU + 25 Emerging Picture Sarangi & Tye BMNQRZ Jones, Stoica & Tye Copeland, Myers & Polchinski Several novel features and mechanisms have emerged • Mechanisms Brane-antibrane annihilation, and the absence of the inflaton in the post-inflationary low-energy theory; • Robustness Warped reheating, and the relatively efficient cascade of inflationary energy into the lowest throat. • Mind broadening Cosmic strings, and the leaving of inflationary relics. VEU + 25 Emerging Picture Silverstein & Tong Several novel features and mechanisms have emerged • Mechanisms Brane-antibrane annihilation, and the absence of the inflaton in the post-inflationary low-energy theory; • Robustness Warped reheating, and the relatively efficient cascade of inflationary energy into the lowest throat. • Mind broadening Cosmic strings, and the leaving of inflationary relics. Inflation from relativistic motion (DBI inflation) VEU + 25 Emerging Picture Khoury, Ovrut, Steinhardt & Turok Other ways our minds may yet broaden: • Mechanisms Are there stringy alternatives to inflation? • Robustness • Mind broadening VEU + 25 Open Issues • Problem of scales • Control over approximations VEU + 25 Open Issues • Problem of scales • Control over approximations VEU + 25 Open Issues Kallosh & Linde CB, Quevedo, Rajesh & Zhang • • To address reheating issues must know where ‘we’ live Problem and of howscales we couple to the inflating sector. Problem: in the available models the string scale, Ms, required to obtain the right amplitude for primordial scalar perturbations gives a supersymmetry breaking Control over scale which is too high to solve the hierarchy problem. approximations eg: for warped models: cannot make 2nd throat too deep if inflation occurs in 1st throat or: for large-volume models: Ms ~ Mp/V1/2; m3/2 ~ Mp/V ~ Ms/V1/2 VEU + 25 Open Issues Possible ways out: • Problem of scales Low-scale inflation (German, Ross & Sarkar) • Generate inflationary perturbations through other Control over means (eg: a curvaton mechanism – nongaussianity?) approximations Allow Ms to roll to larger values after inflation (Conlon, Kallosh, Linde & Quevedo) VEU + 25 Open Issues • Problem of scales • Control over approximations VEU + 25 Open Issues • • String inflation models are baroque in order to keep Problem of scales control over all approximations being used. Some remaining weaknesses: Size of corrections to the equations used Control* over if dynamics is not given as a 4D supergravity approximations * if SUSY breaking comes from anti-branes VEU + 25 Open Issues • • String inflation models are baroque in order to keep Problem of scales control over all approximations being used. Some remaining weaknesses: Size of corrections to the equations used Control* over if dynamics is not given as a 4D supergravity approximations * if SUSY breaking comes from anti-branes Inflation seekers scan through parameters of 4D action as if these are free and not calculable. VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • Not easy to obtain and keep control over approximations VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • Not easy to obtain and keep control over approximations • Possible progress on fine-tunings, but not generically VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • Not easy to obtain and keep control over approximations • Possible progress on fine-tunings, but not generically • New insights on reheating (warping, cosmic strings); VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • • • • Not easy to obtain and keep control over approximations Possible progress on fine-tunings, but not generically New insights on reheating (warping, cosmic strings); Inflationary signals largely robust, except near horizon exit VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • • • • • Not easy to obtain and keep control over approximations Possible progress on fine-tunings, but not generically New insights on reheating (warping, cosmic strings); Inflationary signals largely robust, except near horizon exit Small tensor perturbations? VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • • • • • Not easy to obtain and keep control over approximations Possible progress on fine-tunings, but not generically New insights on reheating (warping, cosmic strings); Inflationary signals largely robust, except near horizon exit Small tensor perturbations? • Possibly even more novel physics can arise! VEU + 25 Outlook • There are plausible formulations of inflation in string theory, but still at the stage of mapping out what is possible • • • • • Not easy to obtain and keep control over approximations Possible progress on fine-tunings, but not generically New insights on reheating (warping, cosmic strings); Inflationary signals largely robust, except near horizon exit Small tensor perturbations? • Possibly even more novel physics can arise! VEU + 25 fin VEU + 25