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Baryon Acoustic Oscillation (BAO) surveys will be a leading method foraddressing the dark energy challenge in the next decade. We explore in detailthe effect of allowing for small amplitude admixtures of general isocurvatureperturbations in addition to the dominant adiabatic mode. We find thatnon-adiabatic initial conditions leave the sound speed unchanged but insteadexcite different harmonics. These harmonics couple differently to Silk damping,altering the form and evolution of acoustic waves in the baryon-photon fluidprior to decoupling. This modifies not only the scale on which the sound wavesimprint onto the baryon distribution, which is used as the standard ruler inBAO surveys, but also the shape, width and height of the BAO peak. We discussthese effects in detail and show how more general initial conditions impact ourinterpretation of cosmological data in dark energy studies. We find that theinclusion of these additional isocurvature modes leads to an increase in theDark Energy Task Force Figure of merit by 140% and 60% for the BOSS and ADEPTexperiments respectively when considered in conjunction with Planck data. Wealso show that the incorrect assumption of adiabaticity has the potential tobias our estimates of the dark energy parameters by $3\sigma$ ($1\sigma$) for asingle correlated isocurvature mode, and up to $8\sigma$ ($3\sigma$) for threecorrelated isocurvature modes in the case of the BOSS (ADEPT) experiment. Wefind that the use of the large scale structure data in conjunction with CMBdata improves our ability to measure the contributions of different modes tothe initial conditions by as much as 100% for certain modes in the fullycorrelated case.

The sensitivity of BAO Dark Energy Constraints to General Isocurvature Perturbations