Showing 1451 - 1500 of 5831 Items
CHY representations for gauge theory and gravity amplitudes with up to three massive particles
Date: 2015-05-28
Creator: Stephen G. Naculich
Access: Open access
- We show that a wide class of tree-level scattering amplitudes involving scalars, gauge bosons, and gravitons, up to three of which may be massive, can be expressed in terms of a Cachazo-He-Yuan representation as a sum over solutions of the scattering equations. These amplitudes, when expressed in terms of the appropriate kinematic invariants, are independent of the masses and therefore identical to the corresponding massless amplitudes.
Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide
Date: 2011-11-14
Creator: M. O. Battle, J. P. Severinghaus, E. D. Sofen, D. Plotkin, A. J., Orsi, M. Aydin, S. A. Montzka, T. Sowers, P. P. Tans
Access: Open access
- We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼10 m thick lock-in zone beginning at ∼67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr-1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of Δage (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process. © 2011 Author(s).
Probing quantum Hall state homogeneity with surface waves
Date: 2013-01-01
Creator: M. E. Msall, W. Dietsche, S. Schmult, K. Von Klitzing
Access: Open access
- We study single quantum wells and matched density bilayer samples. Simultaneous measurements of the Hall voltages using low frequency lock-in techniques and of the changes in the 232 MHz (12.6 μm) SAW propagation measured with a vector network-analyzer allow comparison of the complex bulk and edge conductivities. The vtotal 1 bilayer state is seen directly in the SAW measurement only when the conductivity is below ∼ 6 × 10 -7 Siemens and is destroyed at moderate SAW powers by localized heating. The simultaneous reduction of the conductivity minima extracted from Hall data and from SAW data conclusively demonstrates that the vtotal 1 state disappears simultaneously throughout the bulk and not by the formation of competing domains or conducting filaments. © Published under licence by IOP Publishing Ltd.
Approximate initial data for binary black holes
Date: 2006-09-21
Creator: Kenneth A. Dennison, Thomas W. Baumgarte, Harald P. Pfeiffer
Access: Open access
- We construct approximate analytical solutions to the constraint equations of general relativity for binary black holes of arbitrary mass ratio in quasicircular orbit. We adopt the puncture method to solve the constraint equations in the transverse-traceless decomposition and consider perturbations of Schwarzschild black holes caused by boosts and the presence of a binary companion. A superposition of these two perturbations then yields approximate, but fully analytic binary black hole initial data that are accurate to first order in the inverse of the binary separation and the square of the black holes' momenta. © 2006 The American Physical Society.
Effects of differential rotation on the maximum mass of neutron stars
Date: 2003-01-01
Creator: N.D. Lyford, T.W. Baumgarte, S.L. Shapiro
Access: Open access
Gravity darkening and brightening in binaries
Date: 2012-01-01
Creator: H.E. White, T.W. Baumgarte, S.L. Shapiro
Access: Open access
Unusual decay modes of D0 and D+ mesons
Date: 1991-01-01
Creator: R. Ammar, P. Baringer, D. Coppage, R. Davis, P., Haas, M. Kelly, N. Kwak, H. Lam, S. Ro, Y. Kubota, J. K. Nelson, D. Perticone, R. Poling, S. Schrenk, G. Crawford, R. Fulton, T. Jensen, D. Johnson, H. Kagan, R. Kass, R. Malchow, F. Marrow, J. Whitmore, P. Wilson, D. Bortoletto, D. N. Brown, J. Dominick, R. L. McIlwain, D. H. Miller, M. Modesitt, C. R. Ng
Access: Open access
- CLEO has measured decay modes of the D0 and D+ into final states consisting of K's, s, K0's and 0's, using data taken with the CLEO detector at the Cornell Electron Storage Ring. We report new results on the decays of D0's into 4, K-K+-+, 0K+K-, 0K+-, K0K-+, 3KS0 and 0 together with some of their resonant substructure. We also present the first observation of the decay D00K+ and give limits on the doubly-Cabibbo-suppressed decays of the D0 into K+- and K+-+-. © 1991 The American Physical Society.
Atmospheric potential oxygen: New observations and their implications for some atmospheric and oceanic models
Date: 2006-03-01
Creator: Mark Battle, Sara Mikaloff Fletcher, Michael L. Bender, Ralph F. Keeling, Andrew C., Manning, Nicolas Gruber, Pieter P. Tans, Melissa B. Hendricks, David T. Ho, Caroline Simonds, Robert Mika, Bill Paplawsky
Access: Open access
- Measurements of atmospheric O2/N2 ratios and CO2 concentrations can be combined into a tracer known as atmospheric potential oxygen (APO ≈ O2/N2 + CO2) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. (1998), we present a set of APO observations for the years 1996-2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. (2001), we compare these observations with predictions of APO generated from ocean O2 and CO2 flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere. Copyright 2006 by the American Geophysical Union.
A super MHV vertex expansion for n=4 SYM theory
Date: 2009-07-06
Creator: Michael Kiermaier, Stephen G. Naculich
Access: Open access
- We present a supersymmetric generalization of the MHV vertex expansion for all tree amplitudes in = 4 SYM theory. In addition to the choice of a reference spinor, this super MHV vertex expansion also depends on four reference Grassmann parameters. We demonstrate that a significant fraction of diagrams in the expansion vanishes for a judicious choice of these Grassmann parameters, which simplifies the computation of amplitudes. Even pure-gluon amplitudes require fewer diagrams than in the ordinary MHV vertex expansion. We show that the super MHV vertex expansion arises from the recursion relation associated with a holomorphic all-line supershift. This is a supersymmetric generalization of the holomorphic all-line shift recently introduced in arXiv:0811.3624. We study the large-z behavior of generating functions under these all-line supershifts, and find that they generically provide 1/z k falloff at (Next-to) kMHV level. In the case of anti-MHV generating functions, we find that a careful choice of shift parameters guarantees a stronger 1/z k+4 falloff. These particular all-line supershifts may therefore play an important role in extending the super MHV vertex expansion to = 8 supergravity. © SISSA 2009.
Carbon cycle studies based on the distribution of O2 in air
Date: 1999-01-01
Creator: Michael L. Bender, Mark O. Battle
Access: Open access
One-instanton predictions for non-hyperelliptic curves derived from M-theory
Date: 1998-12-21
Creator: Isabel P. Ennes, Stephen G. Naculich, Henric Rhedin, Howard J. Schnitzer
Access: Open access
- One-instanton predictions are obtained from certain non-hyperelliptic Seiberg-Witten curves derived from M-theory for N = 2 supersymmetric gauge theories. We consider SU(N1) × SU(N2) gauge theory with a hypermultiplet in the bifundamental representation together with hypermultiplets in the defining representations of SU(N1) and SU(N2). We also consider SU(N) gauge theory with a hypermultiplet in the symmetric or antisymmetric representation, together with hypermultiplets in the defining representation. The systematic perturbation expansion about a hyperelliptic curve together with the judicious use of an involution map for the curve of the product groups provide the principal tools of the calculations. © 1999 Elsevier Science B.V.
Linear relations between N ≥ 4 supergravity and subleading-color SYM amplitudes
Date: 2012-02-27
Creator: Stephen G. Naculich, Horatiu Nastase, Howard J. Schnitzer
Access: Open access
- The IR divergences of supergravity amplitudes are less severe than those of planar SYM amplitudes, and are comparable to those subleading-color SYM amplitudes that are most subleading in the 1/N expansion, namely O(1/ε L) for L-loop amplitudes. We derive linear relations between one- and two-loop four-point amplitudes and one-loop five-point amplitudes of N ≥ 4, 5, and 6 supergravity and the most-subleading-color contributions of the analogous amplitudes of N = 0, 1, and 2 SYM theory, extending earlier results for N = 8 supergravity amplitudes. Our work relies on linear relations between N = 4 supergravity and planar SYM amplitudes that were recently derived using the double-copy property of gravity, and color-kinematic duality of gauge theories. © SISSA 2012.
Level-rank duality of untwisted and twisted D-branes
Date: 2006-05-15
Creator: Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- Level-rank duality of untwisted and twisted D-branes of WZW models is explored. We derive the relation between D0-brane charges of level-rank dual untwisted D-branes of over(su, ̂) ( N )K and over(sp, ̂) ( n )k, and of level-rank dual twisted D-branes of over(su, ̂) ( 2 n + 1 )2 k + 1. The analysis of level-rank duality of twisted D-branes of over(su, ̂) ( 2 n + 1 )2 k + 1 is facilitated by their close relation to untwisted D-branes of over(sp, ̂) ( n )k. We also demonstrate level-rank duality of the spectrum of an open string stretched between untwisted or twisted D-branes in each of these cases. © 2006 Elsevier B.V. All rights reserved.
pp-wave limits and orientifolds
Date: 2003-02-03
Creator: Stephen G. Naculich, Howard J. Schnitzer, Niclas Wyllard
Access: Open access
- We study the pp-wave limits of various elliptic models with orientifold planes and D7-branes, as well as the pp-wave limit of an orientifold of AdS5 × T11. Many of the limits contain both open and closed strings. We also present pp-wave limits of theories which give rise to a compact null direction and contain open strings. Maps between the string theory states and gauge theory operators are proposed. © 2002 Elsevier Science B.V. All rights reserved.
Vacuum states of N =1* mass deformations of N =4 and N =2 conformal gauge theories and their brane interpretations
Date: 2001-08-27
Creator: Stephen G. Naculich, Howard J. Schnitzer, Niclas Wyllard
Access: Open access
- We find the classical supersymmetric vacuum states of a class of N =1* field theories obtained by mass deforming superconformal models with simple gauge groups and N =4 or N =2 supersymmetry. In particular, new classical vacuum states for mass-deformed N =4 models with Sp(2N) and SO(N) gauge symmetry are found. We also derive the classical vacua for various mass-deformed N =2 models with Sp(2N) and SU(N) gauge groups and antisymmetric (and symmetric) hypermultiplets. We suggest interpretations of the mass-deformed vacua in terms of three-branes expanded into five-brane configurations. © 2001 Elsevier Science B.V.
Fermions destabilize electroweak strings
Date: 1995-01-01
Creator: Stephen G. Naculich
Access: Open access
- Z strings in the Weinberg-Salam model including fermions are unstable for all values of the parameters. The cause of this instability is the fermion vacuum energy in the Z-string background. Z strings with nonzero fermion densities, however, may still be stable. © 1995 The American Physical Society.
Elliptic models and M-theory
Date: 2000-06-12
Creator: Isabel P. Ennes, Carlos Lozano, Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- We give a unified analysis of four-dimensional elliptic models with N = 2 supersymmetry and a simple gauge group, and their relation to M-theory. Explicit calculations of the Seiberg-Witten curves and the resulting one-instanton prepotential are presented. The remarkable regularities that emerge are emphasized. In addition, we calculate the prepotential in the Coulomb phase of the (asymptotically-free) Sp(2N) gauge theory with Nf fundamental hypermultiplets of arbitrary mass. © 2000 Elsevier Science B.V. All rights reserved.
Matrix model approach to the N = 2 U (N) gauge theory with matter in the fundamental representation
Date: 2003-01-01
Creator: Stephen G. Naculich, Howard J. Schnitzer, Niclas Wyllard
Access: Open access
- We use matrix model technology to study the N = 2 U (N) gauge theory with Nf massive hypennultiplets in the fundamental representation. We perform a completely perturbative calculation of the periods ai and the prepotential F(a) up to the first instanton level, finding agreement with previous results in the literature. We also derive the Seiberg-Witten curve and differential from the large-M solution of the matrix model. We show that the two cases Nf < N and N ≤ Nf < 2N can be treated simultaneously. © SISSA/ISAS 2003.
Production and decay of D1 (2420)0 and D2* (2460)0
Date: 1994-06-30
Creator: P. Avery, A. Freyberger, J. Rodriguez, R. Stephens, S., Yang, J. Yelton, D. Cinabro, S. Henderson, T. Liu, M. Saulnier, R. Wilson, H. Yamamoto, T. Bergfeld, B. I. Eisenstein, G. Gollin, B. Ong, M. Palmer, M. Selen, J. J. Thaler, K. W. Edwards, M. Ogg, B. Spaan, A. Bellerive, D. I. Britton, E. R.F. Hyatt, D. B. MacFarlane, P. M. Patel, A. J. Sadoff, R. Ammar, S. Ball, P. Baringer
Access: Open access
- We have investigated D+ π- and D*+ π- final states and observed the two established L = 1 charmed mesons, the D1 (2420)0 with mass 2421-2-2+1+2 MeV/c2 and width 20-5-3+6+3 MeV/c2 and the D2* (2460)0 with mass 2465 ± 3 ± 3 MeV/c2 and width 28-7-6+8+6 MeV/c2. Properties of these final states, including their decay angular distributions and spin-parity assignments, have been studied. We identify these two mesons as the jlight = 3 2 doublet predicted by HQET. We also obtain constraints on Γs/ (Γs + ΓD) as a function of the cosine of the relative phase of the two amplitudes in the D1 (2420)0 decay. © 1994.
Tau decays with one charged particle plus multiple π0's
Date: 1993-01-01
Creator: M. Procario, S. Yang, R. Balest, K. Cho, M., Daoudi, W. T. Ford, D. R. Johnson, K. Lingel, M. Lohner, P. Rankin, J. G. Smith, J. P. Alexander, C. Bebek, K. Berkelman, D. Besson, T. E. Browder, D. G. Cassel, H. A. Cho, D. M. Coffman, P. S. Drell, R. Ehrlich, R. S. Galik, M. Garcia-Sciveres, B. Geiser, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, K. Honscheid, C. D. Jones, S. L. Jones
Access: Open access
- With the CLEO-II detector at the Cornell Electron Storage Ring, we have measured branching fractions for tau lepton decay into one-prong final states with multiple π0's Bhnπ0, normalized to the branching fraction for tau decay into one charged particle and a single π0. We find Bh2π0/Bhπ0=0. 345±0.006±0.016, Bh3π0/Bhπ0=0.041 ±0.003±0. 005, and Bh4π0/Bhπ0=0.006±0.002±0.002. © 1993 The American Physical Society.
Measurement of gross photosynthesis, respiration in the light, and mesophyll conductance usingh2 18o labeling
Date: 2018-05-01
Creator: Paul P.G. Gauthier, Mark O. Battle, Kevin L. Griffin, Michael L. Bender
Access: Open access
- A fundamental challenge in plant physiology is independently determining the rates of gross O2 production by photosynthesis and O2 consumption by respiration, photorespiration, and other processes. Previous studies on isolated chloroplasts or leaves have separately constrained net and gross O2 production (NOP and GOP, respectively) by labeling ambient O2 with 18O while leaf water was unlabeled. Here, we describe a method to accurately measure GOP and NOP of whole detached leaves in a cuvette as a routine gas-exchange measurement. The petiole is immersed in water enriched to a d18O of ;9,000 , and leaf water is labeled through the transpiration stream. Photosynthesis transfers 18O from H2O to O2. GOP is calculated from the increase in d18O ofO2 as air passes through the cuvette. NOP is determined from the increase in O2/N2. Both terms are measured by isotope ratio mass spectrometry. CO2 assimilation and other standard gas-exchange parameters also were measured. Reproducible measurements are made on a single leaf for more than 15 h. We used this method to measure the light response curve of NOP and GOP in French bean (Phaseolus vulgaris) at 21% and 2% O2. We then used these data to examine the O2/CO2 ratio of net photosynthesis, the light response curve of mesophyll conductance, and the apparent inhibition of respiration in the light (Kok effect) at both oxygen levels. The results are discussed in the context of evaluating the technique as a tool to study and understand leaf physiological traits.
Bowdoin Orient, v. 12, no. 6
Date: 1882-07-12
Access: Open access
- includes frontmatter; "Commencement Number" issue