![]() The development of irregularities in a single bubble inflationary universe. Quantum fluctuations and a nonsingular universe. Cosmology’s Century: An Inside History of Our Modern Understanding of the Universe (Princeton Univ. Measurements of Ω and Λ from 42 high redshift supernovae. Observational evidence from supernovae for an accelerating universe and a cosmological constant. Everything you always wanted to know about the cosmological constant problem (but were afraid to ask). The goal of measuring cosmic birefringence and testing the statistical properties of primordial GWs will require new observational and calibration strategies for future CMB experiments. Matter fields, such as non-Abelian gauge fields, might have produced non-scale-invariant, non-Gaussian and parity-violating GWs that could be measured in the CMB polarization, with profound implications for the fundamental physics behind ‘cosmic inflation’, the period of accelerated expansion in the very early Universe. ![]() Quantum-mechanical vacuum fluctuations in spacetime in the early Universe might have produced a stochastic background of primordial gravitational waves (GWs) that are scale-invariant, Gaussian and parity-symmetric. The polarization of the cosmic microwave background (CMB), the afterglow of the primordial fireball Universe, is sensitive to new physics that violates parity symmetry and may shed new light on these three elements.ĭark matter and dark energy might be a new pseudoscalar field (like a pion in the SM or an axion in the extension of the SM) that couples to photons in a parity-violating manner and that has rotated the plane of linear polarization of CMB photons as they have been travelling for more than 13 billion years, an effect dubbed ‘cosmic birefringence’.Ī tantalizing hint of cosmic birefringence has been found in the CMB polarization data of the Planck mission with a statistical significance of 3 σ. The current cosmological model includes at least three elements (the nature of dark matter and of dark energy, and the origin of all structures in the Universe) whose explanation requires new physics beyond the standard model (SM) of elementary particles and fields. The goal of observing these two phenomena will influence how data from future CMB experiments are collected, calibrated and analysed. These might have been generated by vacuum fluctuations in spacetime or by matter fields and could be measurable in the CMB polarization. Second, the period of accelerated expansion in the very early Universe, called ‘cosmic inflation’, might have produced a stochastic background of primordial gravitational waves (as yet unobserved). A tantalizing hint of such a signal has been found with a statistical significance of 3 σ. This effect is known as ‘cosmic birefringence’. First, if the physics behind dark matter and dark energy violates parity symmetry, their coupling to photons should have rotated the plane of linear polarization as the CMB photons have been travelling for more than 13 billion years. Here, I discuss two phenomena that could be uncovered in CMB observations. Polarized light of the cosmic microwave background (CMB) may hold the answer to these fundamental questions. Their nature is unknown and so is that of the initial fluctuations in the early Universe that led to the creation of the cosmic structure we see today. The current cosmological model requires new physics beyond the standard model of elementary particles and fields, such as dark matter and dark energy.
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