721 research outputs found
Use of delta N formalism - Difficulties in generating large local-type non-Gaussianity during inflation -
We discuss generation of non-Gaussianity in density perturbation through the
super-horizon evolution during inflation by using the so-called
formalism. We first provide a general formula for the non-linearity parameter
generated during inflation. We find that it is proportional to the slow-roll
parameters, multiplied by the model dependent factors that may enhance the
non-gaussianity to the observable ranges. Then we discuss three typical
examples to illustrate how difficult to generate sizable non-Gaussianity
through the super-horizon evolution. First example is the double inflation
model, which shows that temporal violation of slow roll conditions is not
enough for the generation of non-Gaussianity. Second example is the ordinary
hybrid inflation model, which illustrates the importance of taking into account
perturbations on small scales. Finally, we discuss Kadota-Stewart model. This
model gives an example in which we have to choose rather unnatural initial
conditions even if large non-Gaussianity can be generated.Comment: 16 pages, 3 figures, revised version to include the referees'
comments, references added
An Accurate Graph Generative Model with Tunable Features
A graph is a very common and powerful data structure used for modeling
communication and social networks. Models that generate graphs with arbitrary
features are important basic technologies in repeated simulations of networks
and prediction of topology changes. Although existing generative models for
graphs are useful for providing graphs similar to real-world graphs, graph
generation models with tunable features have been less explored in the field.
Previously, we have proposed GraphTune, a generative model for graphs that
continuously tune specific graph features of generated graphs while maintaining
most of the features of a given graph dataset. However, the tuning accuracy of
graph features in GraphTune has not been sufficient for practical applications.
In this paper, we propose a method to improve the accuracy of GraphTune by
adding a new mechanism to feed back errors of graph features of generated
graphs and by training them alternately and independently. Experiments on a
real-world graph dataset showed that the features in the generated graphs are
accurately tuned compared with conventional models.Comment: This paper was presented at the 32nd International Conference on
Computer Communications and Networks (ICCCN 2023) Poster Trac
Reheating processes after Starobinsky inflation in old-minimal supergravity
We study reheating processes and its cosmological consequences in the
Starobinsky model embedded in the old-minimal supergravity. First, we consider
minimal coupling between the gravity and matter sectors in the higher curvature
theory, and transform it to the equivalent standard supergravity coupled to
additional matter superfields. We then discuss characteristic decay modes of
the inflaton and the reheating temperature . Considering a simple
model of supersymmetry breaking sector, we estimate gravitino abundance from
inflaton decay, and obtain limits on the masses of gravitino and supersymmetry
breaking field. We find GeV and the allowed
range of gravitino mass as GeV GeV,
assuming anomaly-induced decay into the gauge sector as the dominant decay
channel.Comment: 24 pages, 1 figure, appendix added for clarification, typos fixed,
results unchanged, version accepted in JHE
Quantum-number projection in the path-integral renormalization group method
We present a quantum-number projection technique which enables us to exactly
treat spin, momentum and other symmetries embedded in the Hubbard model. By
combining this projection technique, we extend the path-integral
renormalization group method to improve the efficiency of numerical
computations. By taking numerical calculations for the standard Hubbard model
and the Hubbard model with next nearest neighbor transfer, we show that the
present extended method can extremely enhance numerical accuracy and that it
can handle excited states, in addition to the ground state.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
Characterization of entangling properties of quantum measurement via two-mode quantum detector tomography using coherent state probes
Entangled measurement is a crucial tool in quantum technology. We propose a
new entanglement measure of multi-mode detection, which estimates the amount of
entanglement that can be created in a measurement. To illustrate the proposed
measure, we perform quantum tomography of a two-mode detector that is comprised
of two superconducting nanowire single photon detectors. Our method utilizes
coherent states as probe states, which can be easily prepared with accuracy.
Our work shows that a separable state such as a coherent state is enough to
characterize a potentially entangled detector. We investigate the entangling
capability of the detector in various settings. Our proposed measure verifies
that the detector makes an entangled measurement under certain conditions, and
reveals the nature of the entangling properties of the detector. Since the
precise characterization of a detector is essential for applications in quantum
information technology, the experimental reconstruction of detector properties
along with the proposed measure will be key features in future quantum
information processing.Comment: 18 pages, 6 figure
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