- Email: [email protected]
Super Acceleration from Dark-Dark Interaction
Individual seminars
547
SUPER ACCELERATION FROM DARK-DARK INTERACTION Subinoy Das Center for Cosmology and Particle Physics, New York University, USA
An exciting possibility for dark energy is that its effective equation of state might well be w < −1 as various independent analyses of the “Gold” SNIa dataset already suggest. In [S. Das, P.S. Corasaniti and J. Khoury, Phys. Rev. D73 (2006) 083509, arXiv:astro-ph/0510628], we show that an interaction between dark matter and dark energy generically results in an effective dark energy equation of state of w < −1. This can be obtained with a quintessence field φ which couples ¯ where is f to the dark matter via, e.g., a Yukawa-like interaction f (φ/MPl )ψψ is an arbitrary function of φ and ψ is a dark matter Dirac spinor. In the presence of this dark-sector interaction, the dark matter energy density no longer redshifts as a −3 but instead scales as ρDM ∼ f (φ/MPl )/a 3 . For a run-away potential, the dynamics of φ is such that dark matter density redshifts slower than that of CDM during recent past. For a fixed matter density today it implies less matter in the past compared to CDM. An observer unaware of this interaction and fitting the data assuming a CDM universe will ascribe this energy deficit in DM to the dark energy density. As a result, the effective dark energy density has two components and its density can be found to increase in the recent past, resulting in an effective equation of state w < −1. We also note that this interaction can lead to other important cosmological signatures. With such a fifth force structure formation gets modified. The fact that baryons do not experience the fifth force, however, may provide us with an explanation for the recent bullet cluster observation.
547
SUPER ACCELERATION FROM DARK-DARK INTERACTION Subinoy Das Center for Cosmology and Particle Physics, New York University, USA
An exciting possibility for dark energy is that its effective equation of state might well be w < −1 as various independent analyses of the “Gold” SNIa dataset already suggest. In [S. Das, P.S. Corasaniti and J. Khoury, Phys. Rev. D73 (2006) 083509, arXiv:astro-ph/0510628], we show that an interaction between dark matter and dark energy generically results in an effective dark energy equation of state of w < −1. This can be obtained with a quintessence field φ which couples ¯ where is f to the dark matter via, e.g., a Yukawa-like interaction f (φ/MPl )ψψ is an arbitrary function of φ and ψ is a dark matter Dirac spinor. In the presence of this dark-sector interaction, the dark matter energy density no longer redshifts as a −3 but instead scales as ρDM ∼ f (φ/MPl )/a 3 . For a run-away potential, the dynamics of φ is such that dark matter density redshifts slower than that of CDM during recent past. For a fixed matter density today it implies less matter in the past compared to CDM. An observer unaware of this interaction and fitting the data assuming a CDM universe will ascribe this energy deficit in DM to the dark energy density. As a result, the effective dark energy density has two components and its density can be found to increase in the recent past, resulting in an effective equation of state w < −1. We also note that this interaction can lead to other important cosmological signatures. With such a fifth force structure formation gets modified. The fact that baryons do not experience the fifth force, however, may provide us with an explanation for the recent bullet cluster observation.