Speaker
Description
Neutron-star measurements constrain the
pressure–energy-density relation but leave the micro-
scopic composition of dense matter unresolved. A poly-
tropic index Γε < 1.75 and sound speed C2
s = 1/3 have
both been used as signatures of quark degrees of free-
dom. We test these interpretations by calibrating a nu-
cleonic reference domain in the (Γε, P/Pfree) plane. A
Taylor metamodel conditioned on current mass, radius
and tidal data defines this domain, whose boundary sta-
bilizes when fourth-order density terms are retained. Its
extension below Γε = 1.75 shows that the threshold can
also be reached by purely nucleonic matter. We next gen-
erate a broad set of observationally admissible, smooth
single-branch EOSs using neural networks and symbolic
regression. Of these trajectories, 59.8% remain entirely
within the nucleonic domain and 88.6% remain inside
it over at least 90% of the sampled density interval.
Constrained minimization over the admissible EOS class
gives minEadm maxn c2 s = 0.38, requiring the sound speed
to exceed the conformal value 1/3 somewhere within this
class. Such an exceedance, like a sound-speed maximum
or a low polytropic index, constrains the evolution of
stiffness but does not establish deconfinement. The ref-
erence domain thus tests compatibility with a nucleonic
null hypothesis while leaving the identity of any alterna-
tive phase open.
