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Paper IPM / P / 8034  


Abstract:  
We study the variation of the effective finestructure constant alpha for DiracBornInfeld (DBI) type dark energy models. The DBI action based on string theory naturally gives rise to a coupling between gauge fields and a scalar field responsible for accelerated expansion of the universe. This leads to the change of alpha due to a dynamical evolution of the scalar field, which can be compatible with the recently observed cosmological data around the redshift z less than or similar to 3. We place constraints on several different DBI models including exponential, inverse powerlaw and rolling massive scalar potentials. We find that these models can satisfy the varying alpha constraint provided that mass scales of the potentials are finetuned. When we adopt the mass scales which are motivated by string theory, both exponential and inverse powerlaw potentials give unacceptably large change of alpha, thus ruled out from observations. On the other hand the rolling massive scalar potential is compatible with the observationally allowed variation of alpha. Therefore the information of varying alpha provides a powerful way to distinguish between a number of stringinspired DBI dark energy models.
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