Showing 4801 - 4850 of 5840 Items
Bowdoin Orient, v. 12, no. 4
Date: 1882-06-14
Access: Open access
- includes frontmatter; "Ivy Number" issue
Inelastic channels in WW scattering
Date: 1993-01-01
Creator: S. G. Naculich, C. P. Yuan
Access: Open access
- If the electroweak symmetry-breaking sector becomes strongly interacting at high energies, it can be probed through longitudinal W scattering. We present a model with many inelastic channels in the WLWL scattering process, corresponding to the production of heavy fermion pairs. These heavy fermions affect the elastic scattering of WL's by propagating in loops, greatly reducing the amplitudes in some charge channels. We conclude that the symmetry-breaking sector cannot be fully explored by using, for example, the WL±WL± mode alone, even when no resonance is present; all WLWL→WLWL scattering modes must be measured. © 1993 The American Physical Society.
Higgs-regularized three-loop four-gluon amplitude in N = 4 SYM: Exponentiation and Regge limits
Date: 2010-01-01
Creator: Johannes M. Henn, Stephen G. Naculich, Howard J. Schnitzer, Marcus Spradlin
Access: Open access
- We compute the three-loop contribution to the N = 4 supersymmetric Yang- Mills planar four-gluon amplitude using the recently-proposed Higgs IR regulator of Alday, Henn, Plefka, and Schuster. In particular, we test the proposed exponential ansatz for the four-gluon amplitude that is the analog of the BDS ansatz in dimensional regularization. By evaluating our results at a number of kinematic points, and also in several kinematic limits, we establish the validity of this ansatz at the three-loop level. We also examine the Regge limit of the planar four-gluon amplitude using several different IR regulators: dimensional regularization, Higgs regularization, and a cutoff regularization. In the latter two schemes, it is shown that the leading logarithmic (LL) behavior of the amplitudes, and therefore the lowest-order approximation to the gluon Regge trajectory, can be correctly obtained from the ladder approximation of the sum of diagrams. In dimensional regularization, on the other hand, there is no single dominant set of diagrams in the LL approximation. We also compute the NLL and NNLL behavior of the L-loop ladder diagram using Higgs regularization. © SISSA 2010.
Isospin mass splittings from precision measurements of D*-D mass differences
Date: 1992-01-01
Creator: D. Bortoletto, D. N. Brown, J. Dominick, R. L. Mcilwain, T., Miao, D. H. Miller, M. Modesitt, S. F. Schaffner, E. I. Shibata, I. P.J. Shipsey, M. Battle, J. Ernst, H. Kroha, S. Roberts, K. Sparks, E. H. Thorndike, C. H. Wang, S. Sanghera, T. Skwarnicki, R. Stroynowski, M. Artuso, M. Goldberg, N. Horwitz, R. Kennett, G. C. Moneti, F. Muheim, S. Playfer, Y. Rozen, P. Rubin, S. Stone, M. Thulasidas
Access: Open access
- Using the decay modes, D*+→D+π0 and D*0→D0π0, we have measured the D*+-D+ and D*0-D0 mass differences to be 140±0.08±0.06 and 142.12±0.05±0.05 MeV, respectively. Combining these measurements with the Particle Data Group average for the D*+-D0 mass difference, we obtain isospin mass splittings for D*+-Dusp*0 and D+-D0 of 3.32±0.08±0.05 and 4.80±0.10 ±0.06 MeV. We discuss the implications of these measurements for models of isospin mass differences and model-dependent estimates of fD. © 1992 The American Physical Society.
Inelastic channels in the electroweak symmetry-breaking sector
Date: 1992-10-29
Creator: S. G. Naculich, C. P. Yuan
Access: Open access
- It has been argued that if light Higgs bosons do not exist then the self-interactions of W's become strong in the TeV region and can be observed in longitudinal WW scattering. We present a model with many inelastic channels in the WW scattering process, corresponding to the creation of heavy fermion pairs. The presence of these heavy fermions affects the elastic scattering of W's by propagating in loops, greatly reducing the amplitudes in some charge channels. Consequently, the symmetry-breaking sector cannot be fully explored by using, for example, the W+W+ mode alone; all WW→WW scattering modes must be measured. © 1992.
Symmetric-group decomposition of SU(N) group-theory constraints on four-, five-, and six-point color-ordered amplitudes at all loop orders
Date: 2012-01-01
Creator: Alexander C. Edison, Stephen G. Naculich
Access: Open access
- Color-ordered amplitudes for the scattering of n particles in the adjoint representation of SU(N) gauge theory satisfy constraints that arise from group theory alone. These constraints break into subsets associated with irreducible representations of the symmetric group Sn, which allows them to be presented in a compact and natural way. Using an iterative approach, we derive the constraints for six-point amplitudes at all loop orders, extending earlier results for n = 4 and n = 5. We then decompose the four-, five-, and six-point group-theory constraints into their irreducible Sn subspaces. We comment briefly on higher-point two-loop amplitudes. © SISSA 2012.
Atmospheric measurements of the terrestrial O2 : CO2 exchange ratio of a midlatitude forest
Date: 2019-07-10
Creator: Mark O. Battle, J. William Munger, Margaret Conley, Eric Sofen, Rebecca, Perry, Ryan Hart, Zane Davis, Jacob Scheckman, Jayme Woogerd, Karina Graeter, Samuel Seekins, Sasha David, John Carpenter
Access: Open access
- Measurements of atmospheric O2 have been used to quantify large-scale fluxes of carbon between the oceans, atmosphere and land since 1992 (Keeling and Shertz, 1992). With time, datasets have grown and estimates of fluxes have become more precise, but a key uncertainty in these calculations is the exchange ratio of O2 and CO2 associated with the net land carbon sink (B). We present measurements of atmospheric O2 and CO2 collected over a 6-year period from a mixed deciduous forest in central Massachusetts, USA (42.537 N, 72.171 W). Using a differential fuel-cellbased instrument for O2 and a nondispersive infrared analyzer for CO2, we analyzed airstreams collected within and 5m above the forest canopy. Averaged over the entire period of record, we find these two species covary with a slope of -1:081±0:007 mol of O2 per mole of CO2 (the mean and standard error of 6 h periods). If we limit the data to values collected on summer days within the canopy, the slope is -1:03±0:01. These are the conditions in which biotic influences are most likely to dominate. This result is significantly different from the value of -1.1 widely used in O2-based calculations of the global carbon budget, suggesting the need for a deeper understanding of the exchange ratios of the various fluxes and pools comprising the net sink.
Large N universality of the two-dimensional Yang-Mills string
Date: 1995-07-17
Creator: Michael Crescimanno, Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- We exhibit the gauge-group independence ("universality") of all normalized non-intersecting Wilson loop expectation values in the large N limit of two-dimensional Yang-Mills theory. This universality is most easily understood via the string theory reformulation of these gauge theories. By constructing an isomorphism between the string maps contributing to normalized Wilson loop expectation values in the different theories, we prove the large N universality of these observables on any surface. The string calculation of the Wilson loop expectation value on the sphere also leads to an indication of the large N phase transition separating strong- and weak-coupling phases. © 1995.
Amplitudes for massive vector and scalar bosons in spontaneously-broken gauge theory from the CHY representation
Date: 2015-09-26
Creator: Stephen G. Naculich
Access: Open access
- Abstract: In the formulation of Cachazo, He, and Yuan, tree-level amplitudes for massless particles in gauge theory and gravity can be expressed as rational functions of the Lorentz invariants ka · kb, ϵa · kb, and ϵa · ϵb, valid in any number of spacetime dimensions. We use dimensional reduction of higher-dimensional amplitudes of particles with internal momentum κ to obtain amplitudes for massive particles in lower dimensions. In the case of gauge theory, we argue that these massive amplitudes belong to a theory in which the gauge symmetry is spontaneously broken by an adjoint Higgs field. Consequently, we show that tree-level n-point amplitudes containing massive vector and scalar bosons in this theory can be obtained by simply replacing ka · kb with ka · kb − κaκb in the corresponding massless amplitudes, where the masses of the particles are given by |κa|.
One-loop SYM-supergravity relation for five-point amplitudes
Date: 2011-11-21
Creator: Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- We derive a linear relation between the one-loop five-point amplitude of N = 8 supergravity and the one-loop five-point subleading-color amplitudes of N = 4 supersymmetric Yang-Mills theory. © 2011 SISSA.
Regge behavior of gluon scattering amplitudes in N = 4 SYM theory
Date: 2008-05-01
Creator: Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- It is shown that the four-gluon scattering amplitude for N = 4 supersymmetric Yang-Mills theory in the planar limit can be written, in both the weak- and strong-coupling limits, as a reggeized amplitude, with a parent trajectory and an infinite number of daughter trajectories. This result is not evident a priori, and relies crucially on the fact that the leading IR-divergence and the finite log2 (s / t)-dependent piece of the amplitude are characterized by the same function for all values of the coupling, as conjectured by Bern, Dixon, and Smirnov, and proved by Alday and Maldacena in the strong-coupling limit. We use the Alday-Maldacena result to determine the exact strong-coupling Regge trajectory. © 2007 Elsevier B.V. All rights reserved.
One-instanton test of a Seiberg-Witten curve from M-theory: The antisymmetric representation of SU(N)
Date: 1998-11-16
Creator: Stephen G. Naculich, Henric Rhedin, Howard J. Schnitzer
Access: Open access
- One-instanton predictions are obtained from the Seiberg-Witten curve derived from M-theory by Landsteiner and Lopez for the Coulomb branch of N = 2 supersymmetric SU(N) gauge theory with a matter hypermultiplet in the antisymmetric representation. Since this cubic curve describes a Riemann surface that is non-hyperelliptic, a systematic perturbation expansion about a hyperelliptic curve is developed, with a comparable expansion for the Seiberg-Witten differential. Calculation of the period integrals of the SW differential by the method of residues of D'Hoker, Krichever, and Phong enables us to compute the prepotential explicitly to one-instanton order. It is shown that the one-instanton predictions for SU(2), SU(3), and SU(4) agree with previously available results. For SU(N), N ≥ 5, our analysis provides explicit predictions of a curve derived from M-theory at the one-instanton level in field theory. © 1998 Elsevier Science B.V.
Measurement of cabibbo-suppressed decays of the τ lepton
Date: 1994-01-01
Creator: M. Battle, J. Ernst, Y. Kwon, S. Roberts, E. H., Thorndike, C. H. Wang, J. Dominick, M. Lambrecht, S. Sanghera, V. Shelkov, T. Skwarnicki, R. Stroynowski, I. Volobouev, G. Wei, P. Zadorozhny, M. Artuso, M. Goldberg, D. He, N. Horwitz, R. Kennett, R. Mountain, G. C. Moneti, F. Muheim, Y. Muheim, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt
Access: Open access
- Branching ratios for the dominant Cabibbo-suppressed decays of the τ lepton have been measured by CLEO II in e+e- annihilation at the Cornell Electron Storage Ring (s∼10.6 GeV) using kaons with momenta below 0.7 GeV/c. The inclusive branching ratio into one charged kaon is (1.60 ± 0.12 ± 0.19)%. For the exclusive decays, B(τ-→K-ντ)=(0.66±0.07±0.09)%, B(τ-→K-π0ντ)=(0.51±0.10±0.07)%, and, based on three events, B(τ-→K-2π0ντ)<0.3% at the 90% confidence level. These represent significant improvements over previous results. B(τ-→K-π0ντ) is measured for the first time with exclusive π0 reconstruction. © 1994 The American Physical Society.