Imprints of a Primordial Preferred Direction on the Microwave Background

By Lotty Ackerman, S. Carroll, M. Wise. 2007

295 citations recorded by the source corpus.

Rotational invariance is a well-established feature of low-energy physics. Violations of this symmetry must be extremely small today, but could have been larger in earlier epochs. In this paper we examine the consequences of a small breaking of rotational invariance during the inflationary era when the primordial density fluctuations were generated. Assuming that a fixed-norm vector picked out a preferred-direction during the inflationary era, we explore the imprint it would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes of the spherical-harmonic coefficients. We suggest that it is natural to expect that the imprint on the primordial power spectrum of a preferred spatial direction is approximately scale-invariant, and examine a simple model in which this is true.

View Paper: https://www.semanticscholar.org/paper/64d93d8355d3a7418fa89ce4d71dbc93aa2f83ad

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Citations in the corpus

Planck 2018 results. IX. Constraints on primordial non-Gaussianity (2019, background): “In these expressions g∗ is a parameter that measures the amplitude of a quadrupolar anisotropy in the power spectrum (see, e.g., Ackerman et al. 2007), while N is the number of e-folds (from the the end of inflation) at which the relevant scales cross outside the Hubble scale.”
Vector field models of inflation and dark energy (2008, unknown): “Contents”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: ARE THERE COSMIC MICROWAVE BACKGROUND ANOMALIES? (2010, methodology): “Motivated by an anisotropic model of the early universe proposed by Ackerman et al. (2007) that predicts such a signal, Groeneboom & Eriksen (2009) used a Gibbs sampler to claim “tentative evidence for a preferred direction” of (l, b) = (110◦, 10◦) in the five-year WMAP map.”
Cosmology and Fundamental Physics with the Euclid Satellite (2012, background): “The Ackerman–Carroll–Wise models, [10], employ a different Lagrangian of the form Lvector = − 1 4FμνF μν + λ(BBμ −m(2)), so that the norm of the vector field is fixed by the Lagrangian multiplier λ.”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2010, background): “…parameters (fNL from the bispectrum), parity-violation angle (∆α from the TB and EB correlations), modulated primordial power spectrum (g(k) from direction-dependent power spectra; Ackerman et al. 2007; Hanson & Lewis 2009; Groeneboom et al. 2010, see Bennett et al. 2010 for the 7-year limits).”
Gauge fields and inflation (2012, background): “It is usual to parameterize this anisotropy as [45], Pζ(k) = P iso ζ (k) [”
Planck2018 results (2018, background): “In PCI15 we found no evidence for such a modulation, but several inflationary models have been constructed which predict this effect (Ackerman et al. 2007; Soda 2012; Tsujikawa 2014).”
Accelerating Cosmologies with an Anisotropic Equation of State (2007, background): “In addition to these approaches, the anisotropic expansion rates have been exploited in inflationary considerations [11, 12, 15, 50, 51].”