71 research outputs found
What Can be Learned Studying the Distribution of the Biggest Fragment ?
In the canonical formalism of statistical physics, a signature of a first
order phase transition for finite systems is the bimodal distribution of an
order parameter. Previous thermodynamical studies of nuclear sources produced
in heavy-ion collisions provide information which support the existence of a
phase transition in those finite nuclear systems. Some results suggest that the
observable Z1 (charge of the biggest fragment) can be considered as a reliable
order parameter of the transition. This talk will show how from peripheral
collisions studied with the INDRA detector at GSI we can obtain this bimodal
behaviour of Z1. Getting rid of the entrance channel effects and under the
constraint of an equiprobable distribution of excitation energy (E*), we use
the canonical description of a phase transition to link this bimodal behaviour
with the residual convexity of the entropy. Theoretical (with and without phase
transition) and experimental Z1-E* correlations are compared. This comparison
allows us to rule out the case without transition. Moreover that quantitative
comparison provides us with information about the coexistence region in the
Z1-E* plane which is in good agreement with that obtained with the signal of
abnormal uctuations of configurational energy (microcanonical negative heat
capacity).Comment: 8 page
Confronting the nucleonic hypothesis with current neutron star observations from GW170817 and PSR J0740+6620
The nuclear matter equation of state is relatively well constrained at
sub-saturation densities thanks to the knowledge from nuclear physics. However,
studying its behavior at supra-saturation densities is a challenging task.
Fortunately, the extraordinary progress recently made in observations of
neutron stars and neutron star mergers has provided us with unique
opportunities to unfold the properties of dense matter. Under the assumption
that nucleons are the only constituents of neutron star cores, we perform a
Bayesian inference using the so-called meta-modeling technique with a
nuclear-physics-informed prior. The latest information from the GW170817 event
by the LIGO-Virgo Collaboration (LVC) and from the radius measurement of the
heaviest known neutron star PSR J0740+6620 by the Neutron Star Interior
Composition Explorer (NICER) telescope and X-ray Multi-Mirror (XMM-Newton) are
taken into account as likelihoods in the analysis. The impacts of different
constraints on the equation of state as well as on the predictions of neutron
star properties are discussed. The obtained posterior reveals that all the
current observations are fully compatible with the nucleonic hypothesis. Strong
disagreements between our results with future data can be identified as a
signal for the existence of exotic degrees of freedom.Comment: Contribution to the "Journees de Rencontre des Jeunes Chercheurs
(JRJC) 2021" proceeding
Boundary conditions for star matter and other periodic fermionic systems
Bulk fermionic matter, as it can be notably found in supernova matter and
neutrons stars, is subject to correlations of infinite range due to the
antisymmetrisation of the N-body wave function, which cannot be explicitly
accounted for in a practical simulation. This problem is usually addressed in
condensed matter physics by means of the so-called Twist Averaged Boundary
Condition method. A different ansatz based on the localized Wannier
representation has been proposed in the context of antisymmetrized molecular
dynamics. In this paper we work out the formal relation between the two
approaches. We show that, while the two coincide when working with exact
eigenstates of the N-body Hamiltonian, differences appear in the case of
variational approaches, which are currently used for the description of stellar
matter. Some model applications with Fermionic Molecular Dynamics are shown
Generalised description of Neutron Star matter with nucleonic Relativistic Density Functional
In this work, we propose a meta-modelling technique to nuclear matter on the
basis of a relativistic density functional with density-dependent couplings.
Identical density dependence for the couplings both in the isoscalar and
isovector sectors is employed. We vary the coupling parameters of the model to
capture the uncertainties of the empirical nuclear matter parameters at
saturation. Then, we construct a large ensemble of unified equations of state
in a consistent manner both for clusterized and uniform matter in
-equilibrium at zero temperature. Finally, we calculate neutron star
properties to check the consistency with astrophysical observations within a
Bayesian framework. Out of the different sets of astrophysical data employed,
constraint on tidal deformability from the GW170817 event was found to be the
most stringent in the posteriors of different neutron star properties explored
in the present study. We demonstrate in detail the impact of the isovector
incompressibility () on high-density matter that leads to a
considerable variation in the composition of neutron star matter. A couple of
selected models with extreme values of , which satisfy various modern
nuclear physics and neutron star astrophysics constraints, are uploaded in the
\textsc{CompOSE} \cite{Typel:2013rza} database for use by the community
Phase Transitions in Finite Systems using Information Theory
(abridged) In this paper, we present the issues we consider as essential as
far as the statistical mechanics of finite systems is concerned. In particular,
we emphasis our present understanding of phase transitions in the framework of
information theory. Information theory provides a thermodynamically-consistent
treatment of finite, open, transient and expanding systems which are difficult
problems in approaches using standard statistical ensembles. As an example, we
analyze is the problem of boundary conditions, which in the framework of
information theory must also be treated statistically. We recall that out of
the thermodynamical limit the different ensembles are not equivalent and in
particular they may lead to dramatically different equation of states, in the
region of a first order phase transition. We recall the recent progresses
achieved in the understanding of first-order phase transition in finite
systems: the equivalence between the Yang-Lee theorem and the occurrence of
bimodalities in the intensive ensemble and the presence of inverted curvatures
of the thermodynamic potential of the associated extensive ensemble.Comment: To be published in AIP Conference Proceeding
Science with the Einstein Telescope: a comparison of different designs
The Einstein Telescope (ET), the European project for a third-generation
gravitational-wave detector, has a reference configuration based on a
triangular shape consisting of three nested detectors with 10 km arms, where in
each arm there is a `xylophone' configuration made of an interferometer tuned
toward high frequencies, and an interferometer tuned toward low frequencies and
working at cryogenic temperature. Here, we examine the scientific perspectives
under possible variations of this reference design. We perform a detailed
evaluation of the science case for a single triangular geometry observatory,
and we compare it with the results obtained for a network of two L-shaped
detectors (either parallel or misaligned) located in Europe, considering
different choices of arm-length for both the triangle and the 2L geometries. We
also study how the science output changes in the absence of the low-frequency
instrument, both for the triangle and the 2L configurations. We examine a broad
class of simple `metrics' that quantify the science output, related to compact
binary coalescences, multi-messenger astronomy and stochastic backgrounds, and
we then examine the impact of different detector designs on a more specific set
of scientific objectives.Comment: 197 pages, 72 figure
Nuclear physics inputs for dense-matter modelling in neutron stars. The nuclear equation of state
International audienceIn this contribution, we briefly present the equation-of-state modelling for application to neutron stars and discuss current constraints coming from nuclear physics theory and experiments. To assess the impact of model uncertainties, we employ a nucleonic meta-modelling approach and perform a Bayesian analysis to generate posterior distributions for the equation of state with filters accounting for both our present low-density nuclear physics knowledge and high-density neutron-star physics constraints. The global structure of neutron stars thus predicted is discussed in connection with recent astrophysical observations
Nucleonic metamodelling in light of multimessenger, PREX-II and CREX data
The need of reconciling our understanding of the behavior of hadronic matter across a wide range of densities, especially at the time when data from multimessenger observations and novel experimental facilities are flooding in, has provided new challenges to the nuclear models. Particularly, the density dependence of the isovector channel of the nuclear energy functionals seems hard to pin down if experiments like PREX-II (or PREX) and CREX are required to be taken on the same footing. We put to test this anomaly in a semi-agnostic modelling technique, by performing a full Bayesian analysis of static properties of neutron stars, together with global properties of nuclei as binding energy, charge radii and neutron skin calculated at the semi-classical level. Our results show that the interplay between bulk and surface properties, and the importance of high order empirical parameters that effectively decouple the subsaturation and the supersaturation density regime, might partially explain the tension between the different measurements and observations. If the surface behaviors, however, are decoupled from the bulk properties, we found a rather harmonious situation among experimental and observational data
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