761 research outputs found
Overlap singularity and time evolution in integrable quantum field theory
We study homogeneous quenches in integrable quantum field theory where the
initial state contains zero-momentum particles. We demonstrate that the
two-particle pair amplitude necessarily has a singularity at the two-particle
threshold. Albeit the explicit discussion is carried out for special
(integrable) initial states, we argue that the singularity is inevitably
present and is a generic feature of homogeneous quenches involving the creation
of zero momentum particles. We also identify the singularity in quenches in the
Ising model across the quantum critical point, and compute it perturbatively in
phase quenches in the quantum sine-Gordon model which are potentially relevant
to experiments. We then construct the explicit time dependence of one-point
functions using a linked cluster expansion regulated by a finite volume
parameter. We find that the secular contribution normally linear in time is
modified by a term. We additionally encounter a novel type of secular
contribution which is shown to be related to parametric resonance. It is an
interesting open question to resum the new contributions and to establish their
consequences directly observable in experiments or numerical simulations.Comment: 30+45 pages, 7 figure
Fast ALS-based tensor factorization for context-aware recommendation from implicit feedback
Albeit, the implicit feedback based recommendation problem - when only the
user history is available but there are no ratings - is the most typical
setting in real-world applications, it is much less researched than the
explicit feedback case. State-of-the-art algorithms that are efficient on the
explicit case cannot be straightforwardly transformed to the implicit case if
scalability should be maintained. There are few if any implicit feedback
benchmark datasets, therefore new ideas are usually experimented on explicit
benchmarks. In this paper, we propose a generic context-aware implicit feedback
recommender algorithm, coined iTALS. iTALS apply a fast, ALS-based tensor
factorization learning method that scales linearly with the number of non-zero
elements in the tensor. The method also allows us to incorporate diverse
context information into the model while maintaining its computational
efficiency. In particular, we present two such context-aware implementation
variants of iTALS. The first incorporates seasonality and enables to
distinguish user behavior in different time intervals. The other views the user
history as sequential information and has the ability to recognize usage
pattern typical to certain group of items, e.g. to automatically tell apart
product types or categories that are typically purchased repetitively
(collectibles, grocery goods) or once (household appliances). Experiments
performed on three implicit datasets (two proprietary ones and an implicit
variant of the Netflix dataset) show that by integrating context-aware
information with our factorization framework into the state-of-the-art implicit
recommender algorithm the recommendation quality improves significantly.Comment: Accepted for ECML/PKDD 2012, presented on 25th September 2012,
Bristol, U
Collaborative Filtering via Group-Structured Dictionary Learning
Structured sparse coding and the related structured dictionary learning
problems are novel research areas in machine learning. In this paper we present
a new application of structured dictionary learning for collaborative filtering
based recommender systems. Our extensive numerical experiments demonstrate that
the presented technique outperforms its state-of-the-art competitors and has
several advantages over approaches that do not put structured constraints on
the dictionary elements.Comment: A compressed version of the paper has been accepted for publication
at the 10th International Conference on Latent Variable Analysis and Source
Separation (LVA/ICA 2012
Quantum Integrability vs Experiments: Correlation Functions and Dynamical Structure Factors
Integrable Quantum Field Theories can be solved exactly using bootstrap
techniques based on their elastic and factorisable S-matrix. While knowledge of
the scattering amplitudes reveals the exact spectrum of particles and their
on-shell dynamics, the expression of the matrix elements of the various
operators allows the reconstruction of off-shell quantities such as two-point
correlation functions with a high level of precision. In this review, we
summarise results relevant to the contact point between theory and experiment
providing a number of quantities that can be computed theoretically with great
accuracy. We concentrate on universal amplitude ratios which can be determined
from the measurement of generalised susceptibilities, and dynamical structure
factors, which can be accessed experimentally e.g. via inelastic neutron
scattering or nuclear magnetic resonance. Besides an overview of the subject
and a summary of recent advances, we also present new results regarding
generalised susceptibilities in the tricritical Ising universality class.Comment: 53 pages, 12 figures. arXiv admin note: text overlap with
arXiv:2109.0976
Variations on vacuum decay: the scaling Ising and tricritical Ising field theories
We study the decay of the false vacuum in the scaling Ising and tricritical
Ising field theories using the Truncated Conformal Space Approach and compare
the numerical results to theoretical predictions in the thin wall limit. In the
Ising case, the results are consistent with previous studies on the quantum
spin chain and the quantum field theory; in particular we confirm
that while the theoretical predictions get the dependence of the bubble
nucleation rate on the latent heat right, they are off by a model dependent
overall coefficient. The tricritical Ising model allows us on the other hand to
examine more exotic vacuum degeneracy structures, such as three vacua or two
asymmetric vacua, which leads us to study several novel scenarios of false
vacuum decay by lifting the vacuum degeneracy using different perturbations.Comment: 17 pages, 16 figures, 3 table
Does Incentive Provision Increase the Quality of Peer Review? An Experimental Study
Although peer review is crucial for innovation and experimental discoveries in science, it is poorly understood in scientific terms. Discovering its true dynamics and exploring adjustments which
improve the commitment of everyone involved could benefit scientific development for all disciplines and consequently increase innovation in the economy and the society. We have reported the results of an innovative experiment developed to model peer review. We demonstrate that offering material rewards to referees tends to decrease the quality and efficiency of the reviewing process. Our findings help to discuss the viability of different options of incentive provision, supporting the idea that journal editors and responsible of research funding agencies should be extremely careful in offering material incentives on reviewing, since these might undermine moral motives which guide referees' behavior
Scaling Functions in the Odd Charge Sector of Sine-Gordon/Massive Thirring Theory
A non-linear integral equation (NLIE) governing the finite size effects of
excited states of even topological charge in the sine-Gordon (sG) / massive
Thirring (mTh) field theory, deducible from a light-cone lattice formulation of
the model, has been known for some time. In this letter we conjecture an
extension of this NLIE to states with odd topological charge, thus completing
the spectrum of the theory. The scaling functions obtained as solutions to our
conjectured NLIE are compared successfully with Truncated Conformal Space data
and the construction is shown to be compatible with all other facts known about
the local Hilbert spaces of sG and mTh models. With the present results we have
achieved a full control over the finite size behaviour of energy levels of
sG/mTh theory.Comment: LaTeX2e, 12 pp., 3 eps figs. Remarks on locality adde
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