2,708 research outputs found
Nucleation of quark matter in protoneutron star matter
The phase transition from hadronic to quark matter may take place already
during the early post-bounce stage of core collapse supernovae when matter is
still hot and lepton rich. If the phase transition is of first order and
exhibits a barrier, the formation of the new phase occurs via the nucleation of
droplets. We investigate the thermal nucleation of a quark phase in supernova
matter and calculate its rate for a wide range of physical parameters. We show
that the formation of the first droplet of a quark phase might be very fast and
therefore the phase transition to quark matter could play an important role in
the mechanism and dynamics of supernova explosions.Comment: v3: fits version published in Physical Review
The universal character of Zwanziger's horizon function in Euclidean Yang-Mills theories
In light of the recently established BRST invariant formulation of the
Gribov-Zwanziger theory, we show that Zwanziger's horizon function displays a
universal character. More precisely, the correlation functions of local BRST
invariant operators evaluated with the Yang-Mills action supplemented with a
BRST invariant version of the Zwanziger's horizon function and quantized in an
arbitrary class of covariant, color invariant and renormalizable gauges which
reduce to the Landau gauge when all gauge parameters are set to zero, have a
unique, gauge parameters independent result, corresponding to that of the
Landau gauge when the restriction to the Gribov region in the latter
gauge is imposed. As such, thanks to the BRST invariance, the cut-off at the
Gribov region acquires a gauge independent meaning in the class of the
physical correlators.Comment: 14 pages. v2: version accepted by Phys.Lett.
Some remarks on the spectral functions of the Abelian Higgs Model
We consider the unitary Abelian Higgs model and investigate its spectral
functions at one-loop order. This analysis allows to disentangle what is
physical and what is not at the level of the elementary particle propagators,
in conjunction with the Nielsen identities. We highlight the role of the
tadpole graphs and the gauge choices to get sensible results. We also introduce
an Abelian Curci-Ferrari action coupled to a scalar field to model a massive
photon which, like the non-Abelian Curci-Ferarri model, is left invariant by a
modified non-nilpotent BRST symmetry. We clearly illustrate its non-unitary
nature directly from the spectral function viewpoint. This provides a
functional analogue of the Ojima observation in the canonical formalism: there
are ghost states with nonzero norm in the BRST-invariant states of the
Curci-Ferrari model.Comment: 32 pages, 12 figure
More on the non-perturbative Gribov-Zwanziger quantization of linear covariant gauges
In this paper, we discuss the gluon propagator in the linear covariant gauges
in Euclidean dimensions. Non-perturbative effects are taken into
account via the so-called Refined Gribov-Zwanziger framework. We point out
that, as in the Landau and maximal Abelian gauges, for , the gluon
propagator displays a massive (decoupling) behaviour, while for , a
scaling one emerges. All results are discussed in a setup that respects the
Becchi-Rouet-Stora-Tyutin (BRST) symmetry, through a recently introduced
non-perturbative BRST transformation. We also propose a minimizing functional
that could be used to construct a lattice version of our non-perturbative
definition of the linear covariant gauge.Comment: 15 pages, 1 figure; V2 typos fixed and inclusion of section on the
ghost propagator. To appear in PhysRev
An exact nilpotent non-perturbative BRST symmetry for the Gribov-Zwanziger action in the linear covariant gauge
We point out the existence of a non-perturbative exact nilpotent BRST
symmetry for the Gribov-Zwanziger action in the Landau gauge. We then put
forward a manifestly BRST invariant resolution of the Gribov gauge fixing
ambiguity in the linear covariant gauge.Comment: 8 pages. v2: version accepted for publication in PhysRev
A Virtual Conversational Agent for Teens with Autism: Experimental Results and Design Lessons
We present the design of an online social skills development interface for
teenagers with autism spectrum disorder (ASD). The interface is intended to
enable private conversation practice anywhere, anytime using a web-browser.
Users converse informally with a virtual agent, receiving feedback on nonverbal
cues in real-time, and summary feedback. The prototype was developed in
consultation with an expert UX designer, two psychologists, and a pediatrician.
Using the data from 47 individuals, feedback and dialogue generation were
automated using a hidden Markov model and a schema-driven dialogue manager
capable of handling multi-topic conversations. We conducted a study with nine
high-functioning ASD teenagers. Through a thematic analysis of post-experiment
interviews, identified several key design considerations, notably: 1) Users
should be fully briefed at the outset about the purpose and limitations of the
system, to avoid unrealistic expectations. 2) An interface should incorporate
positive acknowledgment of behavior change. 3) Realistic appearance of a
virtual agent and responsiveness are important in engaging users. 4)
Conversation personalization, for instance in prompting laconic users for more
input and reciprocal questions, would help the teenagers engage for longer
terms and increase the system's utility
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