[Paper Review] Trapped Brane Features in DBI Inflation

Philippe Brax, Emeline Cluzel|arXiv (Cornell University)|Oct 21, 2010

Cosmology and Gravitation Theories37 references3 citations

TL;DR

This paper investigates how trapped branes in DBI inflation induce a discontinuous jump in the power spectrum of inflaton perturbations when branes cross, with the feature appearing at the sound horizon scale corresponding to the crossing time. The effect arises from a modification of the effective inflaton potential due to brane trapping, leading to observable imprints in primordial fluctuations.

ABSTRACT

We consider DBI inflation with a quadratic potential and the effect of trapped branes on the inflationary fluctuations. When going through a trapped brane the effective potential of the inflaton receives a contribution whose effect is to induce a jump in the power spectrum of the inflaton perturbations. This feature appears in the power spectrum at a scale corresponding to the size of the sound horizon when the two branes cross each other.

Motivation & Objective

• To study the influence of trapped branes on inflationary fluctuations in the DBI inflation framework.
• To analyze how brane trapping modifies the effective inflaton potential during brane collisions.
• To identify the imprint of brane crossing on the primordial power spectrum of perturbations.
• To determine the scale and nature of the resulting feature in the power spectrum.

Proposed method

• Modeling DBI inflation with a quadratic potential and incorporating trapped brane effects via modified effective potential dynamics.
• Tracking the evolution of the inflaton field through the trapped brane configuration using the DBI action formalism.
• Calculating the power spectrum of inflaton perturbations and identifying discontinuities induced by brane crossing.
• Relating the timing of the feature in the power spectrum to the sound horizon scale at brane crossing.
• Using the effective field theory approach to describe the interaction between the inflaton and the trapped brane degrees of freedom.

Experimental results

Research questions

• RQ1 How does the presence of a trapped brane alter the effective potential of the inflaton in DBI inflation?
• RQ2 At what scale in the power spectrum does the feature induced by brane crossing appear?
• RQ3 What is the physical origin of the jump in the power spectrum due to brane trapping?
• RQ4 How does the sound horizon scale relate to the timing of the brane crossing event?

Key findings

• A jump in the power spectrum of inflaton perturbations is induced when the branes cross, due to a sudden change in the effective potential.
• The feature appears at a scale corresponding to the sound horizon size at the time of brane crossing.
• The modification to the potential from trapped brane effects leads to a non-smooth evolution of the power spectrum.
• The jump is a direct consequence of the discontinuous change in the effective dynamics during brane interaction.