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Primordial Gravitational Waves. and Black Holes:. Is it worth the search?. Sirichai Chongchitnan (with George Efstathiou) Institute of Astronomy University of Cambridge 25th September 2006. Questions. What will we learn about inflation? e.g. Energy scale

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Primordial gravitational waves
Primordial Gravitational Waves

and Black Holes:

Is it worth the search?

  • Sirichai Chongchitnan

  • (with George Efstathiou)

  • Institute of Astronomy

  • University of Cambridge

  • 25th September 2006


  • What will we learn about inflation?

  • e.g. Energy scale

  • Shape of potential

  • Small-scale physics …

  • Does inflation predict directly detectable gravitational waves?

  • Is it worth all that ?

Primordial gravitational waves1
Primordial Gravitational Waves

Inflation predicts a *small*

stochastic background of GW,

but how small?

  • Energy spectrum

The search for tensor modes
The search for tensor modes


r < 0.2 (95%)

at k = 0.002 Mpc-1[Peiris, Easther]


Direct detections
Direct detections

Joseph Weber 1969

Nautilus (Rome)

What does inflation predict
What does inflation predict?

But V(Φ) is unknown!

Hamilton jacobi formalism
Hamilton-Jacobi Formalism

Evolve “flow equations” till inflation ends

≡a potential V(Φ)

Specify initial Taylor coefficients of H(Φ)

[Hoffman&Turner’01] [Kinney’02]

✱H(Φ) determines ωgw directly

✱Dynamics well-understood [Chongchitnan and Efstathiou PRD’05]

Generic constraint on gw
Generic constraint onωgw

At f ≃ 0.1 - 1 Hz,

for all models of single field inflation

[Chongchitnan and Efstathiou PRD’06]

0.92 ≲ns≲1.06

-1.04≲≲ 0.03

[Viel et al’04] ,[Seljak’05]

High gw models
High ωgwmodels

(r= few x 10-3)

Directly detectable GW ⇔ “pathological” potential

Energy scale of inflation
Energy scale of inflation

Future GW experiments will probe

a tiny range of energy scales

[Efstathiou and Chongchitnan Prog.Theor.Phys.’06]

e.g. , r ≃ 10-10 , V1/4 ≃ 1014 GeV

Primordial black holes
Primordial Black Holes

  • Formed by great overdensities during inflation

  • Slow-roll underestimate PBH abundance.

  • Precise calculations needed

  • “Absence” of PBH rules out very pathological models.

  • [Chongchitnan and Efstathiou, astroph/0610…]


  • Large scales, Planck/CLOVER can rule out large-field (chaotic) inflation models

  • Small scales, BBO/DECIGO will improve limit of energy scale of inflation by only a few. Will test only pathological models.

  • Worth looking at other signatures of inflation : Non-gaussianity from multi-field inflation or distinctive signatures of cosmic strings from brane inflation.