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bio website motls.blogspot.com
location Czech Republic
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seen 11 hours ago

Hi, I am a string theorist and a publicist.


Jan
7
comment Advanced topics in string theory
And one more comment. I still feel that you underestimate the perturbative part of the theory. In the mid 1990s, there's been a huge activity that ultimately clarified many features of the non-perturbative behavior of string theory. But it's still true that most of the phenomena are accessible from one perturbative description or another - dualities are just statements of equivalences (sometimes nonperturbative equivalences) between different descriptions that were known perturbatively. But much of the "explicit" quantitative calculation has to use some expansions.
Jan
7
comment Advanced topics in string theory
Matrix string theory was reviewed in various papers e.g. Susskind-Bigatti and Taylor, see the resource letter by Marolf at the bottom of my 2006 page. Little string theory is extremely special. One should read the original papers and their most important followups. This is a domain intensely studied by a few people in the world so it's obviously not terribly efficient to write "textbooks" of it.
Jan
7
comment Advanced topics in string theory
Otherwise I skipped F-theory, Matrix theory, and little string theory. There are specialized reviews of those because they're really special. To understand F-theory including the applications that give it the "juice", one must understand lots of algebraic geometry, bundles, and so on. A great arena for people who love (advanced) geometry. The physical essence is really simple: it's type IIB where the axion-dilaton $\tau$ is interpreted as the complex structure of a $T^2$ fiber of two new dimensions attached to each point.
Jan
7
comment Advanced topics in string theory
Dear @Squark, thanks for your interest. SFT didn't really "fail". It is a totally consistent and from many viewpoints uniquely useful - "explicitly local, off-shell" - formulation of perturbative open string dynamics and the open-string-related solutions such as D-branes solutions (as tachyon condensation from other D-brane starting points). The most explicit and rigorous framework to discuss tachyon condensation etc. It's very manageable in the bosonic string case. People could have expected some other miraculous things from SFT but there have never been "rational justifications" for them.
Jan
7
comment Advanced topics in string theory
This URL was (for years) on the top of my page, too. ;-)
Jan
7
comment Derivation of the basic equation for Witten diagrams
I've re-edited backslash-box as backslash-Box (capitalized). Note that backslash-square is also possible. Also, there was a mistake in the big equation. The braces are not just braces - which are given a special role in TeX. They are written as backslash-braces (both left and right).
Jan
7
answered Uniqueness of the 5 string theories
Jan
7
comment String landscape in different dimensions
Dear @Squark, but even if the number of noncompact dimensions is well-defined, it's still sensible to subclassify the options according to the number of supercharges. For low number of noncompact dimensions, the number of supercharges may be very small and not too constraining. So only for high dimensions such as $D=9$, the classification is potentially manageable. In $D=9$, one gets various M-theories on Klein Bottle, Mobius strip, and similar funny extra choices aside from the circular compactifications. There are also papers on the $D=6$ landscape etc.
Jan
7
answered Advanced topics in string theory
Jan
6
awarded  mathematical-physics
Jan
5
answered Is it a total or an explicite time derivative in the Schrödinger equation?
Jan
5
comment Conservation of electric charge in Feynman diagram
Sorry, Philip, but concerning your last sentence, energy and momentum are also preserved at every place of the diagram, despite their uncertainty relations. In the same way, it is not true that the electric charge doesn't obey any uncertainty relation. The phase of a charged field becomes more uncertain when the charge becomes certain, and vice versa. You are attributing incorrect reasons to various properties.
Jan
5
comment Which symmetry is associated with conservation of flux?
There's none unless there are magnetic monopoles, of course, in which case the two situations are fully analogous and an S-duality may make it manifest.
Jan
4
revised Why is E6 favored over E8 for GUT building?
added 187 characters in body
Jan
4
reviewed Approve suggested edit on Does the measured mass of earth include that of the atmosphere?
Jan
4
answered Did Newton discover gravity waves without realizing it?
Jan
4
comment Does the measured mass of earth include that of the atmosphere?
Well, the mass of Earth can be and has been measured by Kepler's method as well – from the orbit of the Moon – and this method makes it completely clear that the atmosphere, like anything else linked to Earth, is included just like the bulk of the Earth.
Jan
4
revised Why is E6 favored over E8 for GUT building?
added 160 characters in body
Jan
4
revised Why is E6 favored over E8 for GUT building?
added 480 characters in body
Jan
4
answered Why is E6 favored over E8 for GUT building?