3,017 research outputs found
Large reduction with the Twisted Eguchi-Kawai model
We examine the breaking of symmetry recently reported for the Twisted
Eguchi-Kawai model (TEK). We analyse the origin of this behaviour and propose
simple modifications of twist and lattice action that could avoid the problem.
Our results show no sign of symmetry breaking and allow us to obtain values of
the large infinite volume string tension in agreement with extrapolations
from results based upon straightforward methods.Comment: latex file 14 pages, 4 figure
Conservation laws and tachyon potentials in the sliver frame
Conservation laws have provided an elegant and efficient tool to evaluate the
open string field theory interaction vertex, they have been originally
implemented in the case where the string field is expanded in the Virasoro
basis. In this work we derive conservation laws in the case where the string
field is expanded in the so-called sliver -basis. As an
application of these conservation laws derived in the sliver frame, we compute
the open string field action relevant to the tachyon condensation and in order
to present not only an illustration but also an additional information, we
evaluate the action without imposing a gauge choice.Comment: 26 pages, some typos fixed, comments added, references adde
Solutions from boundary condition changing operators in open string field theory
We construct analytic solutions of open string field theory using boundary
condition changing (bcc) operators. We focus on bcc operators with vanishing
conformal weight such as those for regular marginal deformations of the
background. For any Fock space state phi, the component string field
of the solution Psi exhibits a remarkable factorization property: it is given
by the matter three-point function of phi with a pair of bcc operators,
multiplied by a universal function that only depends on the conformal weight of
phi. This universal function is given by a simple integral expression that can
be computed once and for all. The three-point functions with bcc operators are
thus the only needed physical input of the particular open string background
described by the solution. We illustrate our solution with the example of the
rolling tachyon profile, for which we prove convergence analytically. The form
of our solution, which involves bcc operators instead of explicit insertions of
the marginal operator, can be a natural starting point for the construction of
analytic solutions for arbitrary backgrounds.Comment: 21 pages, 1 figure, LaTeX2e; v2: minor changes, version published in
JHE
The Tachyon Potential in the Sliver Frame
We evaluate the tachyon potential in the Schnabl gauge through off-shell
computations in the sliver frame. As an application of the results of our
computations, we provide a strong evidence that Schnabl's analytic solution for
tachyon condensation in open string field theory represents a saddle point
configuration of the full tachyon potential. Additionally we verify that
Schnabl's analytic solution lies on the minimum of the effective tachyon
potential.Comment: v1: 19 pages, 1 figure, 1 table; v2: 20 pages, 1 figure, 2 tables, 1
reference added, comments added; v3: 21 pages, 1 figure, 2 tables, 4
references added, comments adde
Thermal Phase Transition in Mixed Action SU(3) Lattice Gauge Theory and Wilson Fermion Thermodynamics
We study the thermal phase diagram of pure SU(3) lattice gauge theory with
fundamental and adjoint couplings. We improve previous estimates of the
position of the bulk transition line and determine the thermal deconfinement
transition lines for and 8. The endpoint of the bulk transition
line improves upon earlier estimates
obtained using smaller lattice sizes. For the deconfinement
transition line splits cleanly away from the bulk transition line. With
increasing the thermal deconfinement transition lines shift to
increasingly weaker coupling, joining onto the bulk transition line at
increasingly larger in a pattern consistent with the usual
universality picture of lattice gauge theories. We also discuss the possible
consequences of an induced adjoint term from the fermionic determinant and
determine this induced term numerically with a microcanonical demon method for
two flavors of dynamical Wilson fermions.Comment: 21 pages. LaTeX file. 11 postscript figures added. Complete
postscript file available via anonymous ftp at
ftp://ftp.scri.fsu.edu/pub/heller/scri94-123.p
Reduced Models and Noncommutative Gauge Theories
This is a short review of the relation between the Reduced Models and
Noncommutative Yang-Mills Theories (NCYM) based on the work done in
collaboration with J. Ambjorn, J. Nishimura and R. Szabo. Contents: 1.Twisted
Eguchi-Kawai model (TEK), 2.Mapping onto NCYM, 3.Morita equivalence,
4.Fundamental matter, 5.Wilson loops in NCYM, 6.D-brane interpretation. Talk
given at the 11th International Seminar "Quarks'2000", Pushkin, Russia, May
13-21, 2000 and the E.S.Fradkin Memorial Conference, Moscow, June 5-10, 2000.Comment: Talk at the Seminar "Quarks'2000" and the E.S. Fradkin Memorial
Conference; 12pp., Late
Relevant Deformations in Open String Field Theory: a Simple Solution for Lumps
We propose a remarkably simple solution of cubic open string field theory
which describes inhomogeneous tachyon condensation. The solution is in
one-to-one correspondence with the IR fixed point of the RG-flow generated in
the two--dimensional world-sheet theory by integrating a relevant operator with
mild enough OPE on the boundary. It is shown how the closed string overlap
correctly captures the shift in the closed string one point function between
the UV and the IR limits of the flow. Examples of lumps in non-compact and
compact transverse directions are given.Comment: 45 pages. v2: typos and minor improvements. v3: submitted to jhe
The energy of the analytic lump solution in SFT
In a previous paper a method was proposed to find exact analytic solutions of
open string field theory describing lower dimensional lumps, by incorporating
in string field theory an exact renormalization group flow generated by a
relevant operator in a worldsheet CFT. In this paper we compute the energy of
one such solution, which is expected to represent a D24 brane. We show, both
numerically and analytically, that its value corresponds to the theoretically
expected one.Comment: 45 pages, former section 2 suppressed, Appendix D added, comments and
references added, typos corrected. Erratum adde
THE ISPRS-EUROSDR GEOBIM BENCHMARK 2019
Standardised data formats and data models are essential for data integration and interoperability, which in turn adds value to data by allowing its reuse in multiple contexts. For this reason, in recent years extensive efforts have been focused on standards development. When representing the built environment, 3D city models and Building Information Models are particularly relevant, and their integration is now required to underpin use cases that cover the full life-cycle of a built asset, including design and planning as well as operations and management, and to support legal applications such as cadastral systems. For those kinds of data, CityGML by the Open Geospatial Consortium and Industry Foundation Classes by buildingSMART are the most popular reference standards. However, many users report, often through informal channels, the difficulties of working with these formats. This paper summarizes the outcomes of the GeoBIM Benchmark 2019, a scientific initiative funded by ISPRS and EuroSDR to collect insights into the most relevant issues encountered in the management of CityGML and IFC within existing software. Alongside data management (import, visualisation, analysis, export) problems, issues of particular consequence in terms of integration relate to georeferencing IFC files and the conversions among the two kinds of formats and models. Thus, the benchmark was designed to explore these tasks in available software. Following analysis of the benchmark results, a key outcome is the impossibility to find clear patterns in the behaviour of tools, which consequently means there is no consistency in the implementation of standards. Although the results could seem disappointing, the criticality in managing these standards as they are was described and this awareness can be the starting point for further research or further standards development. Finally, this project was useful to gather a wide community around this topic, and the discussion about the GeoBIM-related issues was definitely pushed
Electronic structure and optical properties of lightweight metal hydrides
We study the electronic structures and dielectric functions of the simple
hydrides LiH, NaH, MgH2 and AlH3, and the complex hydrides Li3AlH6, Na3AlH6,
LiAlH4, NaAlH4 and Mg(AlH4)2, using first principles density functional theory
and GW calculations. All these compounds are large gap insulators with GW
single particle band gaps varying from 3.5 eV in AlH3 to 6.5 eV in the MAlH4
compounds. The valence bands are dominated by the hydrogen atoms, whereas the
conduction bands have mixed contributions from the hydrogens and the metal
cations. The electronic structure of the aluminium compounds is determined
mainly by aluminium hydride complexes and their mutual interactions. Despite
considerable differences between the band structures and the band gaps of the
various compounds, their optical responses are qualitatively similar. In most
of the spectra the optical absorption rises sharply above 6 eV and has a strong
peak around 8 eV. The quantitative differences in the optical spectra are
interpreted in terms of the structure and the electronic structure of the
compounds.Comment: 13 pages, 10 figure
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