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SUMMARY:Current constraints and forecasts on the tilt and running of the p
rimordial tensor spectrum
DTSTART;VALUE=DATE-TIME:20151214T155500Z
DTEND;VALUE=DATE-TIME:20151214T161500Z
DTSTAMP;VALUE=DATE-TIME:20200407T112723Z
UID:indico-contribution-786957@indico.cern.ch
DESCRIPTION:Speakers: Giovanni Cabass (Physics Department and INFN\, “La
Sapienza” University of Rome)\nGravitational waves can be produced by a
wide range of astrophysical phenomena\, such as inspiral and merging of n
eutron stars and black holes\, supernova of massive stars\, accreting neut
ron stars\, etc. This talk is focused\, instead\, on a stochastic backgrou
nd of gravitational waves (GWs) of cosmological origin\, like the one pred
icted by inflation.\n\nI start by considering a power law parametrization
of the frequency spectrum of primordial tensor modes\, with tilt $n_T$ and
tensor-to-scalar ratio $r$. I discuss the constraints that can be placed
on these parameters by Cosmic Microwave Background (CMB) temperature and p
olarization anisotropies alone\, and then show how such constraints become
stronger if one takes into account the contribution of gravitational wave
s to the radiation energy density. GWs add to the effective number of rela
tivistic degrees of freedom $N_\\text{eff} = 3.046 + N_\\text{eff}^\\text{
GW}$\, and then have an effect on the CMB angular spectra and the primordi
al abundances. More precisely\, we find that the $95\\%$ CL limits on the
tilt $n_T$ at a pivot scale of $0.01\\\,\\text{Mpc}^{-1}$ go from $n_T = 1
.7^{+2.1}_{-2.0}$ (Planck + BKP dataset\, no $N_\\text{eff}^\\text{GW}$) t
o $n_T = 0.06^{+0.78}_{-0.56}$ (with $N_\\text{eff}^\\text{GW}$).\n\nIn th
e second part of the talk I discuss the forecasts on a spectrum described
by a spectral index $n_T$ and its running $n_{T\,\\text{run}}$: our analys
is considers a future COrE-like satellite mission combined with direct-det
ection experiments like AdvLIGO. When the contribution of primordial tenso
r modes to CMB spectral distortions of the $\\mu$-type is taken into accou
nt\, we add the future measurements of the CMB spectrum by a PIXIE-like ex
periment.\n\nFor these forecasts two fiducial cosmologies are considered:
at first a cosmology with no primordial gravitational waves\, in order to
see how well future experiments will be able to measure the tensor paramet
ers. The second forecast takes as fiducial model one where the tensor-to-s
calar ratio is of order $10^{-2}$ (a value that can be reached by futurist
ic ground-based experiments such as AdvACT)\, and the tilt and running are
fixed by the consistency relations of single-field slow-roll inflation.\n
\nIn the final part of the talk\, I discuss the implications of our result
s for models of single-field slow-roll inflation.\n\nhttps://indico.cern.c
h/event/336103/contributions/786957/
LOCATION:International Conference Centre Geneva Level 0\, Room 4
URL:https://indico.cern.ch/event/336103/contributions/786957/
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