Finding Cosmic Inflation Eiichiro Komatsu Max-Planck-Institut fr - PowerPoint PPT Presentation

Finding Cosmic Inflation Eiichiro Komatsu Max-Planck-Institut für Astrophysik “ Inflation and the CMB ”, NORDITA July 21, 2017

Well, haven’t we found it yet? • Single-field slow-roll inflation looks remarkably good: • Super-horizon fluctuation • Adiabaticity • Gaussianity • n s <1 • What more do we want? Gravitational waves . Why? • Because the “ extraordinary claim requires extraordinary evidence ”

Watanabe & EK (2006) Theoretical energy density Spectrum of GW today GW entered the horizon during the matter era GW entered the horizon during the radiation era

Watanabe & EK (2006) Theoretical energy density Spectrum of GW today CMB PTA Interferometers Wavelength of GW ~ Billions of light years!!!

You might not have noticed, but this conference has been very unique and remarkable

You might not have noticed, but this conference has been very unique and remarkable

You might not have noticed, but this conference has Gauge-fielders! been very unique Thanks for comments on the first part of my talk and remarkable

Are GWs from vacuum fluctuation in spacetime, or from sources? ⇤ h ij = − 16 π G π ij • Homogeneous solution : “GWs from vacuum fluctuation” • Inhomogeneous solution : “GWs from sources” • Contribution from scalars is too small • U(1) fields can produce detectable tensors, but not without di ffi culty • SU(2) fields can do it too!

A New Paradigm • We must not assume that detection of gravitational waves (GWs) from inflation immediately implies that GWs are from the vacuum fluctuation in tensor metric perturbation • The homogeneous solution is related to the energy scale (or the inflaton field excursion; “Lyth bound”) during inflation, but the inhomogeneous solution is not. • Detection of B-mode polarisation ≠ Quantum Gravity

From Matteo Fasiello

Important Message to Experimentalists ⇤ h ij = − 16 π G π ij • Do not write proposals saying that detection of the B- mode polarisation is a signature of “quantum gravity”! • Only the homogeneous solution corresponds to the vacuum tensor metric perturbation. There is no a priori reason to neglect an inhomogeneous solution! • Contrary, we have several examples in which detectable B-modes are generated by sources [U(1) and SU(2)]

Experimental Strategy Commonly Assumed So Far 1. Detect B-mode polarisation in multiple frequencies, to make sure that it is the B-mode of the CMB 2. Check for scale invariance: Consistent with a scale invariant spectrum? • Yes => Announce discovery of the vacuum fluctuation in spacetime • No => WTF?

New Experimental Strategy: New Standard! 1. Detect B-mode polarisation in multiple frequencies, to make sure that it is the B-mode of the CMB 2. Consistent with a scale invariant spectrum? 3. Parity violating correlations (TB and EB) consistent with zero? 4. Consistent with Gaussianity? • If, and ONLY IF Yes to all => Announce discovery of the vacuum fluctuation in spacetime

New Experimental Strategy: If not, you may have just New Standard! discovered new physics during inflation! 1. Detect B-mode polarisation in multiple frequencies, to make sure that it is the B-mode of the CMB 2. Consistent with a scale invariant spectrum? 3. Parity violating correlations (TB and EB) consistent with zero? 4. Consistent with Gaussianity? • If, and ONLY IF Yes to all => Announce discovery of the vacuum fluctuation in spacetime

New Experimental Strategy: If not, you may have just New Standard! discovered new physics during inflation! 1. Detect B-mode polarisation in multiple frequencies, to make sure that it is the B-mode of the CMB 2. Consistent with a scale invariant spectrum? You would not have to worry 3. Parity violating correlations (TB and EB) consistent with about super-Planckian field zero? excursion. Easier integration 4. Consistent with Gaussianity? with fundamental physics? • If, and ONLY IF Yes to all => Announce discovery of the vacuum fluctuation in spacetime

Further Remarks • “ Guys, you are complicating things too much! ” • No. These sources (eg., gauge fields) should be ubiquitous in a high-energy universe. They have every right to produce GWs if they are around • Sourced GWs with r>>0.001 can be phenomenologically more attractive than the vacuum GW from the large-field inflation [requiring super-Planckian field excursion]. Better radiative stability, etc • Rich[er] phenomenology: Better integration with the Standard Model; reheating; baryon synthesis via leptogenesis, etc. Testable using many more probes!

Dimastrogiovanni, Fasiello & Fujita (2017) Example Set Up • φ : inflaton field => To reproduce the scalar perturbation • χ : pseudo-scalar “axion” field. Spectator field (i.e., negligible energy density compared to the inflaton) • Field strength of an SU(2) field :

Scenario • The SU(2) field contains tensor, vector, and scalar components • The tensor components are amplified strongly by a coupling to the axion field in some parameter space • But, only one helicity is amplified => GW is chiral (well-known result) • GWs sourced by this mechanism are strongly non- Gaussian! Agrawal, Fujita & EK, arXiv:1707.03023

Dimastrogiovanni, Fasiello & Fujita (2017) Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 Example Tensor Spectra • Sourced tensor spectrum can be close to scale invariant, but can also be bumpy

Dimastrogiovanni, Fasiello & Fujita (2017) Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 Example Tensor Spectra r * σ • Sourced tensor spectrum can be close to scale invariant, but can also be bumpy

Dimastrogiovanni, Fasiello & Fujita (2017) Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 Example Tensor Spectra Tensor Power Spectrum, P(k) B-mode CMB spectrum, C lBB • Sourced tensor spectrum can be close to scale invariant, but can also be bumpy

Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 Parity-violating Spectra TB TB from angle mis-calibration EB • Angle mis-calibration can be distinguished easily!

Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 Signal-to-noise [LiteBIRD] [width of the tensor power spectrum] • S/N ~ a couple for the peak r * of 0.07. It’s something!

Thorne, Fujita, Hazumi, Katayama, EK & Shiraishi, arXiv:1707.03240 [also Caldwell’s and Sorbo’s talks] Not just CMB! LISA Planck BBO LiteBIRD

Agrawal, Fujita & EK, arXiv:1707.03023 Large bispectrum in GW from SU(2) fields B RRR ( k, k, k ) ≈ 25 h P 2 h ( k ) Ω A Tomo Fujita Aniket Agrawal (Stanford->Kyoto) (MPA) • Ω A << 1 is the energy density fraction of the gauge field • B h /P h2 is of order unity for the vacuum contribution [Maldacena (2003); Maldacena & Pimentel (2011)] • Gaussianity o ff ers a powerful test of whether the detected GW comes from the vacuum or sources

Agrawal, Fujita & EK, arXiv:1707.03023 NG generated at the tree level [GW] ~10 –2 [tensor SU(2)] [m Q ~ a few] [tensor SU(2)] [tensor SU(2)] • This diagram generates [GW] [GW] second-order equation of motion for GW

Agrawal, Fujita & EK, arXiv:1707.03023 NG generated at the tree level [GW] [tensor SU(2)] [m Q ~ a few] [tensor SU(2)] [tensor SU(2)] • This diagram generates [GW] [GW] second-order equation BISPECTRUM of motion for GW +perm.

Agrawal, Fujita & EK, arXiv:1707.03023 Result k 2 /k 1 k 3 /k 1 • This shape is similar to, but not exactly the same as, what was used by the Planck team to look for tensor bispectrum

Planck Collaboration (2015) Current Limit on Tensor NG • The Planck team reported a limit on the tensor bispectrum in the following form: NL ≡ B +++ ( k, k, k ) f tens h F equil . scalar ( k, k, k ) • The denominator is the scalar equilateral bispectrum template, giving F equil . scalar ( k, k, k ) = (18 / 5) P 2 scalar ( k ) • The current 68%CL constraint is f tens NL = 400 ± 1500

Agrawal, Fujita & EK, arXiv:1707.03023 SU(2), confronted • The SU(2) model of DFF predicts: • The current 68%CL constraint is f tens NL = 400 ± 1500 • This is already constraining!

Courtesy of Maresuke Shiraishi LiteBIRD would nail it! 10 2 RFG + LiteBIRD noise, 0% delens, f sky = 0.5 noiseless, 100% delens, f sky = 1 ( ∆ f tens NL = 100r 3/2 ) NL in 1502.01592 10 1 Err[f NLtens ] = a few! 50% sky, no delensing, LiteBIRD noise, ∆ f tens 10 0 and residual foreground CV limited 10 -1 10 -4 10 -3 10 -2 10 -1 tensor-to-scalar ratio r

What is LiteBIRD?

Finding Cosmic Inflation • No detection of polarisation from primordial GW yet • Many ground-based and balloon-borne experiments are taking data now The search continues!! 1989–1993 2001–2010 2009–2013 202X–

JAXA ESA + possibly NASA LiteBIRD 2025– [proposed] 2025– [proposed] Polarisation satellite dedicated to measure CMB polarisation from primordial GW, with a few thousand super-conducting detectors in space

JAXA ESA + possibly NASA LiteBIRD 2025– [proposed] 2025– [proposed] Target sensitivity: σ (r=0) = 0.001

JAXA ESA + possibly NASA LiteBIRD 2025– [proposed] 2025– [proposed] Down-selected by JAXA as one of the two missions competing for a launch in mid 2020’s