Cosmic Microwave Background

Images of sky patches in the microwave band, from latest measures from BOOMERANG (left) and MAXIMA-I (right). See this page for more on CMB experiments and links.
 
 

The sky is dominated by the microwave fossil radiation predicted by George Gamow in 1948 as the most important relic in the hot Big Bang theory. It reproduces a black body radiation with temperature T~ 2.73 K with spectral fluctuations at the 1/100000 level.
Hot (white) and Cold (dark) spot are clearly visible. They are really small with respect to the background temperature, still at the 10^-5 level.
Since the image we are seeing was originated very far in space and time (almost 6000 Mpc or 18000000000 light years away from us, more then 10 billions of years ago, when the Universe was about 300,000 years old) they are interpreted as the seeds of the structure we observe today in planets, stars, galaxies, clusters of galaxies. It is the oldest electromagnetic picture we can get of the universe, the closest to the Big Bang.

This is the reason why it is being deeply investigated in all the world and at SISSA/ISAS in particular.

 Main Projects:

• Vacuum energy & CMB:Recent measurements from two different experiments on distant Type Ia supernovae (done respectively in Berkeley and at  the CFA) indicate that cosmic expansion is accelerating, causing an aggravation of the Cosmological Constant Problem in Physics. Phenomenological attempts to avoid it are under course by considering a slowly dynamical scalar field (also known as Quintessence) as driving cosmic acceleration. We are predicting the Quintessence imprint on the CMB: the low redshift dynamics of the universe  is strongly sensitive to the difference between Cosmological Constant and Quintessence, implying large effects on the CMB, Integrated Sachs Wolfe and acoustic peaks location (see paper 1,   paper 2). Independent inputs on this issues are expected from other investigation tools for the low redshift universe, such as Gravitational Lensing
• Theories of Gravity & CMB: Brans-Dicke theories have been extensively studied as natural extension of the General Relativity. They deserve particular attention in the light of latest developments in fundamental physics, where extra-dimensions phenomenology could imply a spacetime variation of Newtonian Gravitational constant. We built codes able to compute CMB anisotropy power spectrum in Brans-Dicke cosmology. We found that a time variation of the Gravitational constant which respects the existing constraints from Solar System Experiments cause CMB effects detectable by future whole sky, high resolution CMB measurements (see paper related).
• Comparison with existing data. Recent results from BOOMERANG and MAXIMA-I (see this page for more on CMB experiments and links) revealed the existence of acoustic features on degree and sub-degree angular scales. Maximum Likelihood studies are under way to constrain dynamical vacuum energy models (see paper related).
• Anisotropy from isolated, spatially limited seeds. We are studying how non-Gaussian spatially limited cosmological objects could appear on the Last Scattering Surface, the place of origin for the CMB radiation we observe today. Acoustic features are expected to play a fundamental role in revealing the presence of these objects, possible relics of topological defects or true vacuum bubbles. Formulas have been derived to describe CMB anisotropies from symmetric seeds (see paper related), and a first application has been performed by assuming spherical seeds (see paper related)
• Component Separation: Even if dominated by the CMB, microwave emission of the sky do contain contributions from Extragalactic as well as Galactic foregrounds. These components are expected to be statistically independent. Tools from Information Theory are being studied as possibly able to separate each component exploiting multifrequency observations (see paper related).
• (Polarized) Foreground Contamination. Estimating the level of foreground contamination to the CMB radiation is a crucial step toward the definitive capabilities of future experiments like Planck.  We are studying the existing database for diffuse Galactic synchrotron in the radio waveband to extrapolate it at the microwave frequencies. Results indicate that its contribution should be irrelevant on degree and   sub-degree angular scales where CMB polarized signal is most efficient (see paper related).



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Staff Members: Carlo Baccigalupi, Luigi Danese

Post-Docs: Samuel Leach

Ph.D. students: Federico Stivoli, Marcella Massardi

Main Collaborators:

IEI/CNR, Pisa: Luigi Bedini, Andrea Farusi, Emanuele Salerno, Anna Tonazzini
Mathematics Department, University of Pisa: Dario Bini
Padua Observatory: Gianfranco De Zotti
Physics Department, University of Oviedo (Spain): Luigi Toffolatti
Physics Department, University of Padua: Sabino Matarrese
Physics Department, University of Rome ``La Sapienza": Amedeo Balbi, Nicola Vittorio
TeSRE/CNR, Bologna: Carlo Burigana, Laura La Porta
Trieste Observatory: Davide Maino, Michele Maris