65 research outputs found
Large-N supersymmetric beta-functions
We present calculations of the leading and O(1/N) terms in a large-N
expansion of the \beta-functions for various supersymmetric theories: a
Wess-Zumino model, supersymmetric QED and a non-abelian supersymmetric gauge
theory. In all cases N is the number of a class of the chiral superfields in
the theory.Comment: 9 pages, tex, five figures. Uses harvmac and epsf. Revised to include
a discussion of higher loop DRED ambiguities. Some references added, and
notation clarifie
The massless supersymmetric ladder with L rungs
We show that in the massless N=1 supersymmetric Wess-Zumino theory it is
possible to devise a computational strategy by which the x-space calculation of
the ladder 4-point correlators can be carried out without introducing any
regularization. As an application we derive a representation valid at all loop
orders in terms of conformal invariant integrals. We obtain an explicit
expression of the 3-loop ladder diagram for collinear external points.Comment: LaTeX, 17 pages, 8 figure
Pole masses of quarks in dimensional reduction
Pole masses of quarks in the quantum chromodynamics are calculated to the
two-loop order in the framework of the regularization by dimensional reduction.
For the diagram with a light quark loop, the non-Euclidean asymptotic expansion
is constructed with the external momentum on the mass shell of a heavy quark.Comment: the version accepted for publication in Nucl.Phys.B. The new
references are added, new Appendix are presented, little misprints fixed in
eqs. (2), (14), (17). LaTex, 23 pages, including 1 eps-figur
Scheme dependence and the NSVZ -function
We investigate the connection between the NSVZ and the DRED forms of the
gauge -function in an supersymmetric gauge theory. We construct a
coupling constant redefinition that relates the two forms up to four loops. By
abelian calculations, we are able to infer the complete non-abelian form of
, and also except for one undetermined
parameter.Comment: 29 pages, including 4 figures (in 7 files). Plain TeX. Uses Harvmac
and eps
Cluster-Cluster Lensing and the Case of Abell 383
Extensive surveys of galaxy clusters motivate us to assess the likelihood of
cluster-cluster lensing (CCL), namely, gravitational-lensing of a background
cluster by a foreground cluster. We briefly describe the characteristics of
CCLs in optical, X-ray and SZ measurements, and calculate their predicted
numbers for CDM parameters and a viable range of cluster mass
functions and their uncertainties. The predicted number of CCLs in the
strong-lensing regime varies from several () to as high as a few dozen,
depending mainly on whether lensing triaxiality bias is accounted for, through
the c-M relation. A much larger number is predicted when taking into account
also CCL in the weak-lensing regime. In addition to few previously suggested
CCLs, we report a detection of a possible CCL in A383, where background
candidate high- structures are magnified, as seen in deep Subaru
observations.Comment: 9 pages, 5 figures, submitted to MNRA
TSIL: a program for the calculation of two-loop self-energy integrals
TSIL is a library of utilities for the numerical calculation of dimensionally
regularized two-loop self-energy integrals. A convenient basis for these
functions is given by the integrals obtained at the end of O.V. Tarasov's
recurrence relation algorithm. The program computes the values of all of these
basis functions, for arbitrary input masses and external momentum. When
analytical expressions in terms of polylogarithms are available, they are used.
Otherwise, the evaluation proceeds by a Runge-Kutta integration of the coupled
first-order differential equations for the basis integrals, using the external
momentum invariant as the independent variable. The starting point of the
integration is provided by known analytic expressions at (or near) zero
external momentum. The code is written in C, and may be linked from C, C++, or
Fortran. A Fortran interface is provided. We describe the structure and usage
of the program, and provide a simple example application. We also compute two
new cases analytically, and compare all of our notations and conventions for
the two-loop self-energy integrals to those used by several other groups.Comment: 31 pages. Updated to reflect new functionality through v1.4 May 2016
and new information about use with C++. Source code and documentation are
available at http://www.niu.edu/spmartin/TSIL or
http://faculty.otterbein.edu/DRobertson/tsil
Pade Approximants, Optimal Renormalization Scales, and Momentum Flow in Feynman Diagrams
We show that the Pade Approximant (PA) approach for resummation of
perturbative series in QCD provides a systematic method for approximating the
flow of momentum in Feynman diagrams. In the large- limit, diagonal
PA's generalize the Brodsky-Lepage-Mackenzie (BLM) scale-setting method to
higher orders in a renormalization scale- and scheme-invariant manner, using
multiple scales that represent Neubert's concept of the distribution of
momentum flow through a virtual gluon. If the distribution is non-negative, the
PA's have only real roots, and approximate the distribution function by a sum
of delta-functions, whose locations and weights are identical to the optimal
choice provided by the Gaussian quadrature method for numerical integration. We
show how the first few coefficients in a perturbative series can set rigorous
bounds on the all-order momentum distribution function, if it is positive. We
illustrate the method with the vacuum polarization function and the Bjorken sum
rule computed in the large- limit.Comment: 28 pages, LaTeX, including 6 figures requires epsfig.st
Effective action of beta-deformed N = 4 SYM theory: Farewell to two-loop BPS diagrams
Within the background field approach, all two-loop sunset vacuum diagrams,
which occur in the Coulomb branch of N = 2 superconformal theories(including N
= 4 SYM), obey the BPS condition m_3 = m_1 + m_2, where the masses are
generated by the scalars belonging to a background N = 2 vector multiplet.
These diagrams can be evaluated exactly, and prove to be homogeneous quadratic
functions of the one-loop tadpoles J(m_1^2), J(m_2^2) and J(m_3^2), with the
coefficients being rational functions of the squared masses. We demonstrate
that, if one switches on the beta-deformation of the N = 4 SYM theory, the BPS
condition no longer holds, and then generic two-loop sunset vacuum diagrams
with three non-vanishing masses prove to be characterized by the following
property: 2(m_1^2 m_2^2 +m_1^2 m_3^2 +m_2^2 m_3^2) > m_1^4 +m_2^4 +m_3^4. In
the literature, there exist several techniques to compute such diagrams. For
the beta-deformed N = 4 SYM theory, we carry out explicit two-loop calculations
of the Kahler potential and F^4 term. Our considerations are restricted to the
case of beta real.Comment: 42 pages, latex, 1 eps figure; V2: references adde
CLASH-X: A Comparison of Lensing and X-ray Techniques for Measuring the Mass Profiles of Galaxy Clusters
We present profiles of temperature (Tx), gas mass, and hydrostatic mass
estimated from new and archival X-ray observations of CLASH clusters. We
compare measurements derived from XMM and Chandra observations with one another
and compare both to gravitational lensing mass profiles derived with CLASH HST
and ground-based lensing data. Radial profiles of Chandra and XMM electron
density and enclosed gas mass are nearly identical, indicating that differences
in hydrostatic masses inferred from X-ray observations arise from differences
in Tx measurements. Encouragingly, cluster Txs are consistent with one another
at ~100-200 kpc radii but XMM Tx systematically decline relative to Chandra Tx
at larger radii. The angular dependence of the discrepancy suggests additional
investigation on systematics such as the XMM point spread function correction,
vignetting and off-axis responses. We present the CLASH-X mass-profile
comparisons in the form of cosmology-independent and redshift-independent
circular-velocity profiles. Ratios of Chandra HSE mass profiles to CLASH
lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range.
However, the mean mass biases inferred from the WL and SaWLens data are
different. e.g., the weighted-mean value at 0.5 Mpc is = 0.12 for the WL
comparison and = -0.11 for the SaWLens comparison. The ratios of XMM HSE
mass profiles to CLASH lensing profiles show a pronounced radial dependence in
the 0.3-1.0 Mpc range, with a weighted mean mass bias of value rising to
~0.3 at ~1 Mpc for the WL comparison and of 0.25 for SaWLens comparison.
The enclosed gas mass profiles from both Chandra and XMM rise to a value 1/8
times the total-mass profiles inferred from lensing at 0.5 Mpc and remain
constant outside of that radius, suggesting that [8xMgas] profiles may be an
excellent proxy for total-mass profiles at >0.5 Mpc in massive galaxy clusters.Comment: Accepted to ApJ; 24 pages; scheduled to appear in the Oct 10, 2014
issue. This version corrects the typographical error in the superscripts for
Equation (2) to include the square of (r/r_core). The correct version of this
equation was used in the analysi
- …