Presentazione di PowerPoint

V. Ferrari
Cascina March 4th, 2014
Note (preliminari) sull’incontro
“INFN:What next?” Roma, 7-8 aprile 2104, Sent by A. Masiero
Innanzitutto, cosa NON vuol essere questo incontro:
un workshop sul futuro della fisica di area INFN in Italia e nel mondo in
cui si invitano esperti per darci lo status e le prospettive; due giornate del
piano decennale INFN, o qualcosa del genere in cui si guarda allo sviluppo
delle linee di ricerca scientifico-tecnologica e delle infrastrutture INFN nel
prossimo decennio.
Questo incontro vuole rispondere in profondita’ a una sfida precisa:
2) Sessione GW
– ma alla fine c’e’ o non c’e’ il “no-lose theorem”: o nel ’16 abbiamo visto le GW (e quindi
abbiamo vinto, (o almeno chi le ha viste per primo ha vinto), o nel ’16 non le abbiamo
viste e allora la GR e’ messa in crisi (e quindi abbiamo vinto)?
– Ammesso che nel ’16 le abbiamo viste, e poi che si fa? Si va
(o meglio l’INFN e’ interessato ad andare) verso la “GW"astronomy
– osservatorio di onde gravitazionali, es. verso l’ Einstein telescope visto che di Lisa se ne
parlera’ nel’30...?
– Come estrarre nuova fisica dalla GW astronomy? Relic density di GW?
MASIERO: about the “no-lose theorem”: either by ’16 (or later) we have a GW detection
and therefore we “win”, or, there is no detection and consequently General Relativity
has a serious flaw (and we “win” again)
main target: NS-NS coalescence
NS-NS evolve according to General Relativity, emitting GWs: there is a clear,
observational evidence
PSR 1913+16, PSR J0737-3039
This is a weak field evidence
(v/c ≈ 10-3 , M/r << 1).
The signal is described by a sinusoid with amplitude and frequency increasing according to
a well known law up to a few orbit before merging, where strong field effects take over.
Corrections computed using alternative theories of gravity are very small and do not affect
the main features of the inspiral part of the signalsignal.
If the coalescing source is within the detector horizon
it must be seen, no question about that.
MASIERO: about the “no-lose theorem”: either by ’16 (or later) we have a GW detection
and therefore we “win”, or, there is no detection and consequently General Relativity
has a serious flaw (and we “win” again)
The question posed by Masiero sould be refrased as following : what if, running the detectors
for a few years, we do not see any signal from coalescing binaries.
The only uncertainty concerns the coalescence rate
of compact binaries in a given volume of space.
these uncertainties arise
- from the small sample of observed galactic binary pulsars
- from poorly contrained population-synthesis models
- from the lack of knowledge in a number of astrophysical parameters, such as
the pulsar luminosity distribution, or evolution processes, as the common envelope
phase in binary evolution.
These uncertainties lead to estimates of coalescence rates which may differ by
1-2 orders of magnitude
The question posed by Masiero sould be refrased as following : what if, running the detectors
for a few years, we do not see any signal from coalescing binaries.
Estimates of coalescence rates differ by orders of magnitude
SNR=8
dH=33 Mpc
dH=161 Mpc
dH=445 Mpc
dH=2187 Mpc
LIGO/Virgo collab. Classical and Quantum Gravity, 2010
No detection over a few years of data taking would mean that there is
something deeply wrong in the way we model the process of stellar evolution
and interaction in galaxy populations
MASIERO: If by ’16 GWs have been detected, what do we do next? Shall we go for
(or better, is INFN interested in going for) a GW astronomy?
Gw detection will certainly open a new observational window on the universe, and
one of the main outcomes will be what we call gravitational wave astronomy.
But this is not the only goal of the GW-enterprise:
we want to test and explore gravitational interations in a strong field regime,
where they have never been tested .
We want to probe the behaviour of matter at densities of the order of 1015 gr/cm3,
typical of the inner core of neutron stars, unreachable by experiments in a laboratory
these goals are in the main stream of INFN’s interests and purposes:
Masiero: La missione dell’ente e’ lo studio della fisica dei costituenti fondamentali e
delle loro interazioni, facciamo WHATNEXT perche’ vogliamo andare avanti su questa
strada.
MASIERO: GW observatory? shall we go for the Einstein telescope (given that
for LISA we will have to wait until 2030?) ?
- How to extract new physics from GW astronomy? GW relic density ?
MASIERO:
there are two complementary needs:
1) consolidate already explored physics which, however is not
completely understood, and
2) open new routes
These issues and questions are related.
I will discuss them giving a teoretician’s point of view
Some open issues in astrophysics/nuclear physics on which GWs would shed light
Within 5 years of operation, advanced detector network should confirm
whether NS-NS or NS-BH mergers are progenitor of Short Gamma Ray Bursts
Detection of signals from NS-NS or NS-BH close to merging would set constraints the
equation of state of matter in the interior of a neutron star, i.e. at densities well above
the nuclear saturation density
Advanced detectors could also observe weak galactic sources such as neutron stars
with an ellipticity of ε ∼ 10−9- 10−7 (with spin frequencies in the range 0.1-1 kHz)
Which is the mechanism through which supernova explode?
AdV Virgo/LIGO could observe, for the first time, NS-BH and BH-BH binaries. Although
radio, x-ray and gamma-ray observations could soon discover a NS-BH system, observation
of a stellar-mass BH-BH system is most likely to come from GW observations. BH-BH
systems could be observed up to z ∼ 0.45, with rate of many tens per
Some open issues in astrophysics/nuclear physics on which GWs would shed light
Within 5 years of operation, advanced detector network should confirm
whether NS-NS or NS-BH mergers are progenitor of Short Gamma Ray Bursts
Detection of signals from NS-NS or NS-BH close to merging would set constraints the
equation of state of matter in the interior of a neutron star, i.e. at densities well above
the nuclear saturation density
synergy
of
Advanced detectors could also observe weak galactic sources such as
neutron stars
with an ellipticity of ε ∼ 10−9- 10−7 (with spin frequencies in the
range 0.1-1 kHz)
multi-messenger
astronomy
Which is the mechanism through which supernova explode?
AdV Virgo/LIGO could observe, for the first time, NS-BH and BH-BH binaries. Although
radio, x-ray and gamma-ray observations could soon discover a NS-BH system, observation
of a stellar-mass BH-BH system is most likely to come from GW observations. BH-BH
systems could be observed up to z ∼ 0.45, with rate of many tens per year (up to
Some open issues related to cosmology (but not only) on which GWs would shed
light
Compact binaries are standard sirens that could be used to precisely measure the luminosity
distance to a source without the aid of any cosmic distance ladder. Additionally, if one can also
identify their host galaxies and measure their red-shifts, then one could infer the cosmological
parameters, i.e. the Hubble parameter, dark matter and dark energy densities, as well as the dark
energy equation-of-state parameter. ET and eLISA will be crucial for this issue
How did supermassive BHs sitting at the centre of many galaxies form?
How did they grow?
Advanced LIGO/Virgo, ET, eLISA, will allow to measure the mass distribution of coalescing compact
binaries (from NS-NS to BH-BH at any mass scale). With this information we will validate the models of
formation and evolution of binaries as a function of redshift for a given cosmological model, and all the
physics involved
gravitational wave background generated by galactic and extra-galactic populations of GW sources.
Estimates of the extra-galactic background are based on assumptions on the source initial mass funtion,
on the star formation rate history, on the signal modeling, all to be tested
The cosmological stochastic background of GW is an unique window on the very early Universe, as GWs
propagate uncorrupted to us from cosmic events occurred at the highest temperatures and densities,
potentially up to the GUT scale 1016 GeV.
The detection of any such background would have huge consequences for fundamental physics, possibly
giving us direct indications of inflation, phase transitions or formation of topological defects.
Virgo/LIGO already ruled out some proposed models LIGO-Virgo coll. Letters to Nature 460, 2009
Open issues in fundamental physics on which GWs would shed light
Do gravitational waves travel at the speed of light ?
Does the graviton have mass?
if mG ≠ 0, the wave propagation speed is
vG ≈ 1- λ/ λG
for λ<< λG ,
λG =Compton wavelenght
Irrespective of the alternative theory which predicts
a massive graviton, the phasing of a coalescence
signal would be distorted because of the shifted time
of arrival
Δt ≈ D (- λ/ λG )2
Open issues in fundamental physics on which GWs would shed light
Do gravitational waves travel at the speed of light ?
Does the graviton have mass?
Are there more than two transverse modes of propagation?
Does gravity couple to other dynamical fields, such as, massless or massive scalars?
Is Lorentz invariance exact?
What is the behavior of gravity in dynamically evolving space-times?
What is the structure of space-time just outside astrophysical black holes? Do their space-times
have horizons? Are they described by the Kerr metric (i.e. by general relativity)?
Do black holes have no-hair?
coalescing binaries + Black Hole quasi-normal modes would provide the answer
… AND MUCH MORE WILL COME FROM UNKNOWN SOURCES!