Gravitational Waves from Inflation

Abstract. Kaluza-Klein compactifications with four-dimensional inflationary geometry combine the attractive idea of higher dimensional models with an attempt to incorporate four-dimensional early-time or late-time cosmology. We analyze the mass spectrum of cosmological perturbations around such compactifications, including the scalar, vector and tensor sector. Whereas scalar perturbations were discussed before, the spectrum of vector and tensor perturbations is a new result of this paper. Moreover, the complete analysis shows that possible instabilities of such compactifications are restricted to the scalar sector. The mass squares of the vector and tensor perturbations are all non-negative. We discuss form fields with a non-trivial background flux in the extra space as matter degrees of freedom. They provide a source of scalar and vector perturbations in the effective four-dimensional theory. We analyze the perturbations in Freund-Rubin compactifications. Although it can only be considered as a toy model, we expect the results to qualitatively generalize to similar configurations. We find that there are two possible channels of instabilities in the scalar sector of perturbations, whose stabilization has to be addressed in any cosmological model that incorporates extra dimensions and form fields. One of the instabilities is associated with the perturbations of the form field.

“…It carries no information about the extra dimensional nature of the full spacetime. Similar conclusions were derived for braneworld models in [22].…”

Section: The Generation Of Perturbations During Inflationsupporting

confidence: 85%

Cosmological perturbations in flux compactifications

Martin¹

2005

“…These Kaluza-Klein modes can be considered to arise from gravity in the bulk. These modes are typically massive, with masses m > 3H/2 where H is the brane Hubble parameter [18,21,29]. The presence of these modes introduces processes, absent in four dimensions, where quintessence can interact with gravity off the brane, or with the Kaluza-Klein hierarchy.…”

Section: Radiative Constraints On Brane Quintessencementioning

confidence: 99%

Radiative constraints on brane quintessence

Seery¹,

Bassett²

2004

Abstract. We investigate the constraints on quintessence arising from both renormalisable and non-renormalisable couplings where the 5d Planck mass is around the TeV scale. The quintessence field vacuum expectation value is typically of order the 4d Planck mass, while non-renormalisable operators are expected to be suppressed by the 5d Planck mass. Non-renormalisable operators are therefore important in computing the 4d effective quintessence potential. We then study the quantum corrections to the quintessence potential due to fermion and graviton loops. The tower of Kaluza-Klein modes competes with the TeV-scale cut-off, altering the graviton contribution to the vacuum polarization of quintessence. Nevertheless we show that, as in four dimensions, the classical potential is stable to such radiative corrections.

“…where A ν 3/2 is a linear combination of associated Legendre functions. Equation (A7) indicates the existence of a mass gap [5,7,15] between the zero mode and the start of the massive KK tower at m = 3 2 H 0 .…”

Section: Jcap 10(2003)014mentioning

confidence: 99%

Evolution of gravitational waves in Randall–Sundrum cosmology

Easther

Langlois

Maartens

et al. 2003

We investigate the evolution of gravitational wave perturbations about a brane cosmology embedded in a five-dimensional anti-de Sitter bulk. During slow-roll inflation in a Randall-Sundrum brane-world, the zero mode of the 5-dimensional graviton is generated, while the massive modes remain in their vacuum state. When the zero mode re-enters the Hubble radius during radiation domination, massive modes are generated. We show that modes decouple in the low-energy/nearbrane limit and develop perturbative techniques to calculate the mode-mixing at finite energy.