Primordial Gravitational Waves

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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

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Questions

• Does inflation predict directly detectable
  gravitational waves?

• What will we learn about inflation?
• e.g. Energy scale
• Shape of potential
• Small-scale physics

• Is it worth all that ?

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Primordial Gravitational Waves
Inflation predicts a small stochastic
background of GW, but how small?

• Energy spectrum

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The search for tensor modes
WMAP3 SDSS r lt 0.2 (95) at k 0.002 Mpc-1
Peiris, Easther
Planck, BICEP, CLOVER, QUIET etc.
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Direct detections
Joseph Weber 1969
Nautilus (Rome)
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What does inflation predict?
Model r ?gw
0.1 10-16
0.2 10-16
Hybrid 0 0
But V(F) is unknown!
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Hamilton-Jacobi Formalism
Evolve flow equations till inflation ends
a potential V(F)
Specify initial Taylor coefficients of H(F)
HoffmanTurner01 Kinney02
? H(F) determines ?gw directly
? Dynamics well-understood Chongchitnan and
Efstathiou PRD05
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Generic constraint on ?gw
At f ? 0.1 - 1 Hz,
for all models of single field inflation
Chongchitnan and Efstathiou PRD06
0.92 ? ns ? 1.06 -1.04 ? ? 0.03
Viel et al04 ,Seljak05
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High ?gw models
(r few x 10-3)
Directly detectable GW ? pathological potential
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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
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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

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Conclusions

• 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.

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