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
• 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 ?
Primordial Gravitational Waves

            Inflation predicts a *small*
          stochastic background of GW,
                   but how small?

•   Energy spectrum
The search for tensor modes

            WMAP3 + SDSS :
              r < 0.2 (95%)
      at k = 0.002 Mpc-1 [Peiris, Easther]

  Planck, BICEP, CLOVER, QUIET etc.
Direct detections

    Nautilus (Rome)
  Joseph Weber 1969
What does inflation predict?

    Model       r         ωgw

              ∼0.1       ∼10-16

              ∼0.2       ∼10-16

   Hybrid      ∼0         ∼0

       But V(Φ) is unknown!
     Hamilton-Jacobi Formalism

                    Evolve “flow equations”
                       till inflation ends

Specify initial Taylor                     ≡   a potential V(Φ)
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 ωgw
                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 ωgw models

                                   (r= few x 10-3)
Directly detectable GW ⇔ “pathological” potential
 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
•   Formed by great overdensities during inflation
•   Slow-roll underestimate PBH abundance.
•   Precise calculations needed
•   “Absence” of PBH rules out very pathological

•   [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.

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