455 research outputs found
Axial anomaly and Ginsparg-Wilson fermions in the Lattice Dirac Sea picture
The axial anomaly equation in 1+1 dimensional QED is obtained on the lattice
for fermions obeying the Ginsparg-Wilson relation. We make use of the
properties of the Lattice Dirac sea to investigate the connection between the
anomaly and the Ginsparg-Wilson operator in the Hamiltonian picture. The
correct anomaly is reproduced for gauge fields whose characteristic time is
much larger than the lattice spacing, which is the regime where the adiabatic
approximation applies. A non-zero Wilson parameter is necessary to get the
correct anomaly. The anomaly is shown to be independent of for . The
generalization to 3+1 dimensions is also discussed.Comment: 19 pages latex,12 figures; manuscript revised, references adde
On the effective action of confining strings
We study the low-energy effective action on confining strings (in the
fundamental representation) in SU(N) gauge theories in D space-time dimensions.
We write this action in terms of the physical transverse fluctuations of the
string. We show that for any D, the four-derivative terms in the effective
action must exactly match the ones in the Nambu-Goto action, generalizing a
result of Luscher and Weisz for D=3. We then analyze the six-derivative terms,
and we show that some of these terms are constrained. For D=3 this uniquely
determines the effective action for closed strings to this order, while for D>3
one term is not uniquely determined by our considerations. This implies that
for D=3 the energy levels of a closed string of length L agree with the
Nambu-Goto result at least up to order 1/L^5. For any D we find that the
partition function of a long string on a torus is unaffected by the free
coefficient, so it is always equal to the Nambu-Goto partition function up to
six-derivative order. For a closed string of length L, this means that for D>3
its energy can, in principle, deviate from the Nambu-Goto result at order
1/L^5, but such deviations must always cancel in the computation of the
partition function. Next, we compute the effective action up to six-derivative
order for the special case of confining strings in weakly-curved holographic
backgrounds, at one-loop order (leading order in the curvature). Our
computation is general, and applies in particular to backgrounds like the
Witten background, the Maldacena-Nunez background, and the Klebanov-Strassler
background. We show that this effective action obeys all of the constraints we
derive, and in fact it precisely agrees with the Nambu-Goto action (the single
allowed deviation does not appear).Comment: 71 pages, 7 figures. v2: added reference, minor corrections. v3:
removed one term from the effective action since it is trivial. The
conclusions on the corrections to energy levels are unchanged, but the claim
that the holographic computation shows a deviation from Nambu-Goto was
modified. v4: added reference
Closed String Tachyon Condensation at c=1
The c=1 matrix model, with or without a type 0 hat, has an exact quantum
solution corresponding to closed string tachyon condensation along a null
surface. The condensation occurs, and spacetime dissolves, at a finite retarded
time on I^+. The outgoing quantum state of tachyon fluctuations in this
time-dependent background is computed using both the collective field and exact
fermion pictures. Perturbative particle production induced by the moving
tachyon wall is shown to be similar to that induced by a soft moving mirror.
Hence, despite the fact that I^+ for the tachyon is geodesicaly incomplete,
quantum correlations in the incoming state are unitarily transmitted to the
outgoing state in perturbation theory. It is also shown that,
non-perturbatively, information can leak across the tachyon wall, and tachyon
scattering is not unitary. Exact unitarity remains intact only in the free
fermion picture.Comment: Minor corrections; References added; 24 pages, 2 figures, harvma
Anomalous Superconducting Properties and Field Induced Magnetism in CeCoIn5
In the heavy fermion superconductor CeCoIn5 (Tc=2.3K) the critical field is
large, anisotropic and displays hysteresis. The magnitude of the critical-field
anisotropy in the a-c plane can be as large as 70 kOe and depends on
orientation. Critical field measurements in the (110) plane suggest 2D
superconductivity, whereas conventional effective mass anisotropy is observed
in the (100) plane. Two distinct field-induced magnetic phases are observed: Ha
appears deep in the superconducting phase, while Hb intersects Hc2 at T=1.4 K
and extends well above Tc. These observations suggest the possible realization
of a direct transition from ferromagnetism to Fulde-Ferrel-Larkin-Ovchinnikov
superconductivity in CeCoIn5.Comment: 4 pages, 3 figure
AdS Bubbles, Entropy and Closed String Tachyons
We study the conjectured connection between AdS bubbles (AdS solitons) and
closed string tachyon condensations. We confirm that the entanglement entropy,
which measures the degree of freedom, decreases under the tachyon condensation.
The entropies in supergravity and free Yang-Mills agree with each other
remarkably. Next we consider the tachyon condensation on the AdS twisted circle
and argue that its endpoint is given by the twisted AdS bubble, defined by the
double Wick rotation of rotating black 3-brane solutions. We calculated the
Casimir energy and entropy and checked the agreements between the gauge and
gravity results. Finally we show an infinite boost of a null linear dilaton
theory with a tachyon wall (or bubble), leads to a solvable time-dependent
background with a bulk tachyon condensation. This is the simplest example of
spacetimes with null boundaries in string theory.Comment: 45 pages, 6 figures, harvmac, eq.(2.16) corrected, references adde
Large-eddy simulation of low-frequency unsteadiness in a turbulent shock-induced separation bubble
The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. The large-eddy simulation has been run for much longer times than previous computational studies making a Fourier analysis of the low frequency possible. The broadband and energetic low-frequency component found in the interaction is in excellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run large-eddy simulation data were analyzed and a phase change in the wall pressure fluctuations was related to the global-mode structure, leading to a possible driving mechanism for the observed low-frequency motions
The Causal Structure of QED in Curved Spacetime: Analyticity and the Refractive Index
The effect of vacuum polarization on the propagation of photons in curved
spacetime is studied in scalar QED. A compact formula is given for the full
frequency dependence of the refractive index for any background in terms of the
Van Vleck-Morette matrix for its Penrose limit and it is shown how the
superluminal propagation found in the low-energy effective action is reconciled
with causality. The geometry of null geodesic congruences is found to imply a
novel analytic structure for the refractive index and Green functions of QED in
curved spacetime, which preserves their causal nature but violates familiar
axioms of S-matrix theory and dispersion relations. The general formalism is
illustrated in a number of examples, in some of which it is found that the
refractive index develops a negative imaginary part, implying an amplification
of photons as an electromagnetic wave propagates through curved spacetime.Comment: 54 pages, 19 figures, corrected some signs in formulae and graph
Measurement of the Neutron Spin Structure Function with a Polarized ^3He Target
Results are reported from the HERMES experiment at HERA on a measurement of
the neutron spin structure function in deep inelastic scattering
using 27.5 GeV longitudinally polarized positrons incident on a polarized
He internal gas target. The data cover the kinematic range
and . The integral evaluated at a fixed of is . Assuming Regge behavior at low , the first
moment is .Comment: 4 pages TEX, text available at
http://www.krl.caltech.edu/preprints/OAP.htm
Magnetogenesis and the dynamics of internal dimensions
The dynamical evolution of internal space-like dimensions breaks the
invariance of the Maxwell's equations under Weyl rescaling of the (conformally
flat) four-dimensional metric. Depending upon the number and upon the dynamics
of internal dimensions large scale magnetic fields can be created. The
requirements coming from magnetogenesis together with the other cosmological
constraints are examined under the assumption that the internal dimensions
either grow or shrink (in conformal time) prior to a radiation dominated epoch.
If the internal dimensions are growing the magnitude of the generated magnetic
fields can seed the galactic dynamo mechanism.Comment: 27 in RevTex style, four figure
Triangulation network of 1929-1944 of the first 1:500 urban map of València
[EN] Triangulation is a surveying method on which earlier maps made were based. Although the origins
of the method can be traced back to the 16th century, it is still used today, with minor changes, to
adjust networks observed with modern geodetic techniques. In this paper we present the geodetic
survey work that was carried out for the primary triangulation network of the first 1:500 urban map of
the city of València (Spain). It spanned from 1929 to 1944 and resulted in 421 maps covering about
174 square kilometres. We focus on four key elements to define the geometric framework of a map:
(1) the geodetic network, (2) the cartographic projection, (3) the baseline measurements, and (4)
the primary triangulation. The paper is based on the interpretation of original documents and
field books recovered from the archives of the València City Council. In order to check the
accuracy and consistency of the survey work, we recomputed all calculations directly from the
field data, following the mathematical procedures of the time. We obtained a set of
transformation parameters to convert the coordinates of 1929 to current coordinates based on
the European Terrestrial Reference System of 1989 (ETRS89). Results showed that the 1929
primary triangulation angles and coordinates are accurate to 8 s of arc and 35 cm respectively,
and that the coordinates transform well into the current reference system with average residuals
of 26 cm across nine control points, demonstrating the high quality of the 1929 work.Villar-Cano, M.; Marqués-Mateu, Á.; Jiménez-Martínez, MJ. (2020). Triangulation network of 1929-1944 of the first 1:500 urban map of València. Survey Review (Online). 52(373):317-329. https://doi.org/10.1080/00396265.2018.1564599S31732952373Bitelli, G., Cremonini, S., & Gatta, G. (2014). Cartographic heritage: Toward unconventional methods for quantitative analysis of pre-geodetic maps. Journal of Cultural Heritage, 15(2), 183-195. doi:10.1016/j.culher.2013.04.003Blachut, T. J., Chrzanowski, A., & Saastamoinen, J. H. (1979). Urban Surveying and Mapping. doi:10.1007/978-1-4612-6145-2Brinker, R. C., & Minnick, R. (Eds.). (1987). The Surveying Handbook. doi:10.1007/978-1-4757-1188-2Gatta, G. 2010. Valorizzazione di cartografia storica attraverso moderne tecniche geomatiche: recupero metrico, elaborazione e consultazione in ambiente digitale [Valuation of historic cartography using modern geomatics techniques: metric recovering, making and use in digital environment]. Doctoral thesis. Bologna: Universitá di Bologna. 295 pages. (In Italian).Gorse, C., Johnston, D., & Pritchard, M. (2012). A Dictionary of Construction, Surveying and Civil Engineering. doi:10.1093/acref/9780199534463.001.0001Hotine, M. (1939). THE RE-TRIANGULATION OF GREAT BRITAIN IV—BASE MEASUREMENT. Empire Survey Review, 5(34), 211-225. doi:10.1179/sre.1939.5.34.211Kahmen, H., & Faig, W. (1988). Surveying. doi:10.1515/9783110845716Leick, A., Rapoport, L., & Tatarnikov, D. (2015). GPS Satellite Surveying. doi:10.1002/9781119018612Murdin, P. (2009). Full Meridian of Glory. doi:10.1007/978-0-387-75534-2Schofield, W., & Breach, M. (2007). Engineering Surveying. doi:10.1201/b12847Seeber, G. (2003). Satellite Geodesy. doi:10.1515/9783110200089Snyder, J. P. (1987). Map projections: A working manual. Professional Paper. doi:10.3133/pp139
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