50 research outputs found

### "So what will you do if string theory is wrong?"

I briefly discuss the accomplishments of string theory that would survive a
complete falsification of the theory as a model of nature and argue the
possibility that such a survival may necessarily mean that string theory would
become its own discipline, independently of both physics and mathematics

### String and M-theory: answering the critics

Using as a springboard a three-way debate between theoretical physicist Lee
Smolin, philosopher of science Nancy Cartwright and myself, I address in
layman's terms the issues of why we need a unified theory of the fundamental
interactions and why, in my opinion, string and M-theory currently offer the
best hope. The focus will be on responding more generally to the various
criticisms. I also describe the diverse application of string/M-theory
techniques to other branches of physics and mathematics which render the whole
enterprise worthwhile whether or not "a theory of everything" is forthcoming.Comment: Update on EPSRC. (Contribution to the Special Issue of Foundations of
Physics: "Forty Years Of String Theory: Reflecting On the Foundations",
edited by Gerard 't Hooft, Erik Verlinde, Dennis Dieks and Sebastian de Haro.
22 pages latex

### Chern-Simons Number Diffusion and Hard Thermal Loops on the Lattice

We develop a discrete lattice implementation of the hard thermal loop
effective action by the method of added auxiliary fields. We use the resulting
model to measure the sphaleron rate (topological susceptibility) of Yang-Mills
theory at weak coupling. Our results give parametric behavior in accord with
the arguments of Arnold, Son, and Yaffe, and are in quantitative agreement with
the results of Moore, Hu, and Muller.Comment: 43 pages, 6 figure

### Classical Sphaleron Rate on Fine Lattices

We measure the sphaleron rate for hot, classical Yang-Mills theory on the
lattice, in order to study its dependence on lattice spacing. By using a
topological definition of Chern-Simons number and going to extremely fine
lattices (up to beta=32, or lattice spacing a = 1 / (8 g^2 T)) we demonstrate
nontrivial scaling. The topological susceptibility, converted to physical
units, falls with lattice spacing on fine lattices in a way which is consistent
with linear dependence on $a$ (the Arnold-Son-Yaffe scaling relation) and
strongly disfavors a nonzero continuum limit. We also explain some unusual
behavior of the rate in small volumes, reported by Ambjorn and Krasnitz.Comment: 14 pages, includes 5 figure

### Lattice Chern-Simons Number Without Ultraviolet Problems

We develop a topological method of measuring Chern-Simons number change in
the real time evolution of classical lattice SU(2) and SU(2) Higgs theory. We
find that the Chern-Simons number diffusion rate per physical 4-volume is very
heavily suppressed in the broken phase, and that it decreases with lattice
spacing in pure Yang-Mills theory, although not as quickly as predicted by
Arnold, Son, and Yaffe.Comment: 26 pages including 6 figures, uses psfig. Corrected for an algebra
error in the original draft of hep-lat/9610013; minor rewriting and more
analysi

### The Sphaleron Rate in SU(N) Gauge Theory

The sphaleron rate is defined as the diffusion constant for topological
number NCS = int g^2 F Fdual/32 pi^2. It establishes the rate of equilibration
of axial light quark number in QCD and is of interest both in electroweak
baryogenesis and possibly in heavy ion collisions. We calculate the
weak-coupling behavior of the SU(3) sphaleron rate, as well as making the most
sensible extrapolation towards intermediate coupling which we can. We also
study the behavior of the sphaleron rate at weak coupling at large Nc.Comment: 18 pages with 3 figure

### A critical comparison of different definitions of topological charge on the lattice

A detailed comparison is made between the field-theoretic and geometric
definitions of topological charge density on the lattice. Their
renormalizations with respect to continuum are analysed. The definition of the
topological susceptibility, as used in chiral Ward identities, is reviewed.
After performing the subtractions required by it, the different lattice methods
yield results in agreement with each other. The methods based on cooling and on
counting fermionic zero modes are also discussed.Comment: 12 pages (LaTeX file) + 7 (postscript) figures. Revised version.
Submitted to Phys. Rev.

### String theory and the crisis of particle physics II or the ascent of metaphoric arguments

This is a completely reformulated presentation of a previous paper with the
same title; this time with a much stronger emphasis on conceptual aspects of
string theory and a detailed review of its already more than four decades
lasting history within a broader context, including some little-known details.
Although there have been several books and essays on the sociological impact
and its philosophical implications, there is yet no serious attempt to
scrutinize its claims about particle physics using the powerful conceptual
arsenal of contemporary local quantum physics. I decided to leave the previous
first version on the arXiv because it may be interesting to the reader to
notice the change of viewpoint and the reason behind it. Other reasons for
preventing my first version to go into print and to rewrite it in such a way
that its content complies with my different actual viewpoint can be found at
the end of the article. The central message, contained in sections 5 and 6, is
that string theory is not what string theorists think and claim it is. The
widespread acceptance of a theory whose interpretation has been obtained by
metaphoric reasoning had a corroding influence on the rest of particle physics
theory as will be illustrated in several concrete cases. The work is dedicated
to the memory of Juergen Ehlers with whom I shared many critical ideas, but
their formulation in this essay is fully within my responsibility.Comment: A dedication and an epilog to the memory of Juergen Ehlers. Extension
of the the last two sections, removal of typos and changes in formulation, 68
pages late