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Scientific Report 2007-2009
Astronomy & Astrophysics
A16. Testing fundamental physics with cosmology
Our research interests are focused on theoretical cosmology,
with a particular emphasis on the study of the
Cosmic Microwave Background (herafter CMB). The
CMB provides indeed an unexcelled probe of the early
universe. Its close approximation to a blackbody spectrum
constrains the thermal history of the universe. Its
isotropy provides a fundamental probe of our standard
theories for the origin of large-scale structure back to the
effective ‘photosphere’ of the universe, when the universe
was only one-thousandth of its present size. The future
of cosmology as a mature and testable science lies in the
realm of observations of CMB anisotropy and its polarization.
Near future experiments as the Planck satellite
(in which we are fully involved) will soon provide
new data that will help in solving some key cosmological
questions taht we list below.
Constraints on Dark Energy - A major goal of
modern cosmology is to investigate the nature of the dark
energy component, responsable for the current accelerated
expansion of the Universe. Despite the fact that
it accounts for about 70% of the total energy density of
the universe, dark energy is largely unclustered and is
typically measured just by its effect on the evolution of
the expansion history (i.e. the Hubble parameter). Since
the cosmic expansion depends on other key parameters
as curvature or matter density, the nature of dark energy
can therefore be revealed only by combination of different
observables and/or observations over a wide redshift
range.
A key parameter for determining the nature of dark
energy is the equation of state. Recently, in collaboration
with Asantha Cooray at the University of California
Irvine and Daniel Holtz of Los Alamos Labs we
performed a complete analysis of current cosmological
datasets. The results, presented in [1], shows that current
data are compatible with an equation of state as
expected from a cosmological constant, showing no deviations
from this simple, yet puzzling, model. In a recent
paper in collaboration with Prof. George Smoot at the
University of Berkeley (Nobel Prize 2006 in Physics) we
studied the possibility of constraining dark energy with
the CMB anisotropies weak lensing [2].
Cosmological Constraints on Neutrino Physics
- Neutrinos play a relevant role in large scale structure
formation and leave key signatures in several cosmological
datasets. More specifically, neutrinos suppress the
growth of fluctuations on scales below the horizon when
they become non relativistic. if neutrinos have masses in
the (sub)eV range would then produce a significant suppression
in the galaxy clustering. It is therefore possible
to derive strong, albeit indirect, constraints on the mass
of the neutrino particle by analyzing cosmological data.
The nice aspect of this investigation is that neutrino
masses in the (sub)eV range of energies can be probed
directly in laboratory. A comparison of the cosmological
constraints with those that will soon obtained from,
for example, single or double beta decay experiments,
could either provide a strong confirmation of the theory
or reveal the presence of new physics.
In [3] we showed that future cosmological data could
reach a sensitivity close to ∼ 0.01eV , probing the neutrino
mass hierarchy.
Cosmological Constraints on Inflation - Inflation
has become the dominant paradigm for understanding
the initial conditions for structure formation and
for CMB anisotropies. In the inflationary picture, primordial
density and gravitational-wave fluctuations are
created from quantum fluctuations, “redshifted” beyond
the horizon during an early period of superluminal expansion
of the universe, then “frozen”. Perturbations at
the surface of last scattering are observable as temperature
anisotropies in the CMB.
In the past years we made use of the most recent CMB
data to discriminate among the various inflationary models.
More recently, we have investigated the ability of future
experiments in constraining single field scenarios in [4].
References
1. P. Serra, et al, Phys.Rev. D, 80, 121302, (2009).
2. E. Calabrese et al, Phys.Rev. D, 80, 103516 (2009).
3. F. De Bernardis, et al., Phys.Rev. D, 80, 123509 (2009).
4. L. Pagano, et al, JCAP, 0804:009, (2008).
Authors
A. Melchiorri, E. Calabrese, F. De Bernardis, M. Martinelli,
L. Pagano
Sapienza Università di Roma 163 Dipartimento di Fisica