SciPost Phys. 7, 078 (2019) ·
published 9 December 2019
Conventional and unconventional superconductivity, respectively, arise from attractive (electron-phonon) and repulsive (many-body Coulomb) interactions with fixed-sign and sign-reversal pairing symmetries. Although heavy-fermions, cuprates, and pnictides are widely believed to be unconventional superconductors, recent evidence in one of the heavy fermion superconductor (CeCu$_2$Si$_2$) indicate the presence of a novel conventional type pairing symmetry beyond the electron-phonon coupling. We present a new mechanism of attractive potential between electrons, mediated by emergent boson fields (vacuum or holon) in the strongly correlated mixed valence compounds. In the strong coupling limit, localized electron sites are protected from double occupancy, which results in an emergent holon gauge fields. The holon states can, however, attract conduction electrons through valence fluctuation channel, and the resulting doubly occupied states with local and conduction electrons condense as Cooper pairs with onsite, fixed-sign, $s$ -wave pairing symmetry. We develop the corresponding self-consistent theory of superconductivity, and compare the results with experiments. Our theory provides a new mechanism of superconductivity whose applicability extends to the wider class of intermetallic/mixed-valence materials and other flat-band metals.
Daniele Coslovich, Andrea Ninarello, Ludovic Berthier
SciPost Phys. 7, 077 (2019) ·
published 6 December 2019
We study the equilibrium statistical properties of the potential energy
landscape of several glass models in a temperature regime so far inaccessible
to computer simulations. We show that unstable modes of the stationary points
undergo a localization transition in real space close to the mode-coupling
crossover temperature determined from the dynamics. The concentration of
localized unstable modes found at low temperature is a non-universal, finite
dimensional feature not captured by mean-field glass theory. Our analysis
reconciles, and considerably expands, previous conflicting numerical results
and provides a characteristic temperature for glassy dynamics that
unambiguously locates the mode-coupling crossover.
SciPost Phys. 7, 076 (2019) ·
published 5 December 2019
A common problem in a high energy physics experiment is extracting a signal from a much larger background.
Posed as a classification task, there is said to be an imbalance in the number of samples belonging to the signal class versus the number of samples from the background class.
In this work we provide a brief overview of class imbalance techniques in a high energy physics setting.
Two case studies are presented: (1) the measurement of the longitudinal polarization fraction in same-sign $WW$ scattering, and (2) the decay of the Higgs boson to charm-quark pairs.
SciPost Phys. 7, 075 (2019) ·
published 4 December 2019
Event generation for the LHC can be supplemented by generative adversarial
networks, which generate physical events and avoid highly inefficient event
unweighting. For top pair production we show how such a network describes
intermediate on-shell particles, phase space boundaries, and tails of
distributions. In particular, we introduce the maximum mean discrepancy to
resolve sharp local features. It can be extended in a straightforward manner to
include for instance off-shell contributions, higher orders, or approximate
SciPost Phys. 7, 074 (2019) ·
published 3 December 2019
We present quantum dimer models in two dimensions which realize metallic
ground states with Z2 topological order. Our models are generalizations of a
dimer model introduced in [PNAS 112,9552-9557 (2015)] to provide an effective
description of unconventional metallic states in hole-doped Mott insulators. We
construct exact ground state wave functions in a specific parameter regime and
show that the ground state realizes a fractionalized Fermi liquid. Due to the
presence of Z2 topological order the Luttinger count is modified and the volume
enclosed by the Fermi surface is proportional to the density of doped holes
away from half filling. We also comment on possible applications to magic-angle
twisted bilayer graphene.
SciPost Phys. 7, 073 (2019) ·
published 3 December 2019
Using Papadodimas and Raju construction of operators describing the interior of a black hole, we
present a general relation between partition functions of operators describing inside and outside
the black hole horizon. In particular for an eternal black hole the partition function
of the interior modes may be given in terms those partition functions associated
with the modes of left and right exteriors. By making use of this relation we observe
that setting a finite UV cutoff
will enforce us to
have a cutoff behind the horizon whose value is fixed by the UV cutoff. The resultant
cutoff is in agreement with what obtained in the context of holographic complexity.
SciPost Phys. 7, 072 (2019) ·
published 2 December 2019
We study the out-of-equilibrium probability distribution function of the
local order parameter in the transverse field Ising quantum chain. Starting
from a fully polarised state, the relaxation of the ferromagnetic order is
analysed: we obtain a full analytical description of the late-time stationary
distribution by means of a remarkable relation to the partition function of a
3-states classical model. Accordingly, depending on the phase whereto the
post-quench Hamiltonian belongs, the probability distribution may locally
retain memories of the initial long-range order. When quenching deep in the
broken-symmetry phase, we show that the stationary order-parameter statistics
is indeed related to that of the ground state. We highlight this connection by
inspecting the ground-state equilibrium properties, where we propose an
effective description based on the block-diagonal approximation of the
$n$-point spin correlation functions.