A class of theories that attempt to explain all existing particles (including force carriers) as vibrational modes of one-dimensional objects.
61
votes
14answers
9k views
What experiment would disprove string theory?
I know that there's big controversy between two groups of physicists:
those who support string theory (most of them, I think)
and those who oppose it.
One of the arguments of the second group is ...
22
votes
10answers
5k views
Discreteness and Determinism in Superstrings?
So Gerard 't Hooft has a brand new paper (thanks to Mitchell Porter for making me aware of it) so this is somewhat of a expansion to the question I posed on this site a month or so ago regarding 't ...
20
votes
4answers
3k views
What if the LHC doesn't see SUSY?
A question in four parts.
What are the main problems which supersymmetry purports to solve?
What would constitute lack of evidence for SUSY at the proposed LHC energy scales (e.g. certain predicted ...
16
votes
4answers
1k views
What is your simplest explanation of the string theory?
How would you explain string theory to non physicists such as myself? I'm specially interested on how plausible is it and what is needed to successfully prove it?
15
votes
2answers
1k views
How does string theory reduce to the standard model?
It is said that string theory is a unification of particle physics and gravitation.
Is there a reasonably simple explanation for how the standard model arises as a limit of string theory?
How does ...
15
votes
2answers
3k views
What is tension in string theory?
One often hears the words "string tension" in string theory. But what does it really mean? In ordinary physics "tension" in an ordinary classical string arises from the fact that there are elasticity ...
15
votes
3answers
918 views
Is decoherence even possible in anti de Sitter space?
Is decoherence even possible in anti de Sitter space? The spatial conformal boundary acts as a repulsive wall, thus turning anti de Sitter space into an eternally closed quantum system. Superpositions ...
14
votes
2answers
274 views
BPS states : Mathematical definition
First of all, let me congratulate the theoretical physics community for this site. I am a mathematics student with very little background in phyiscs. The question I want to ask is:
What is the proper ...
14
votes
1answer
168 views
Is string theory local?
By locality I mean something like the Atiyah-Segal axioms for Riemannian cobordisms (see e.g. http://ncatlab.org/nlab/show/FQFT). I.e. to any (spacelike) hypersurface in the target we associate a ...
14
votes
1answer
640 views
How does classical GR concept of space-time emerge from string theory?
First, I'll state some background that lead me to the question.
I was thinking about quantization of space-time on and off for a long time but I never really looked into it any deeper (mainly because ...
14
votes
2answers
461 views
Does the exact string theory $S$-matrix describe all physics there is?
Suppose someone manages to evaluate the string theory $S$-matrix to all orders for any and all vertex operator insertions including non-perturbative contributions from world-sheet instantons and ...
13
votes
2answers
128 views
Which CFTs have AdS/CFT duals?
The AdS/CFT correspondence states that string theory in an asymptotically anti-De Sitter spacetime can be exactly described as a CFT on the boundary of this spacetime.
Is the converse true? Does any ...
13
votes
1answer
95 views
realization of: CFT generating fuction = AdS partition function
An important aspect of the AdS/CFT correspondence is the recipe to compute correlation functions of a boundary operator $\mathcal{O} $ in terms of the supergravity fields in the interior of the ...
13
votes
7answers
2k views
Applications of Algebraic Topology to physics
I have always wondered about applications of Algebraic Topology to Physics, seeing as am I studying algebraic topology and physics is cool and pretty. My initial thoughts would be that since most ...
13
votes
2answers
64 views
Uniqueness of supersymmetric heterotic string theory
Usually we say there are two types of heterotic strings, namely $E_8\times E_8$ and $Spin(32)/\mathbb{Z}_2$. (Let's forget about non-supersymmetric heterotic strings for now.)
The standard argument ...
13
votes
2answers
2k views
Is there a T-dual of Witten's twistor topological string theory?
In late 2003, Edward Witten released a paper that revived the interest in Roger Penrose's twistors among particle physicists. The scattering amplitudes of gluons in $N=4$ gauge theory in four ...
13
votes
1answer
429 views
How come random matrices can predict energy spectra of heavy atoms?
Some of the applications of random matrices is to find the spectra of heavy atoms in nuclear physics which are usually difficult to find otherwise.
How can starting from randomness of some kind, ...
13
votes
1answer
31 views
SuperHiggs Mechanism on different Backgrounds & Compactifications
I've been studying Bagger & Giannakis paper on the SuperHiggs Mechanism found here.
The paper shows how SUSY is broken by a $B_{\mu\nu}$ gauge field background restricted to $T^3$ in $M^7\times ...
13
votes
1answer
402 views
Multi-loop beta function of gauge theory (*without* Feynman diagrams)
I would like to point to the beautiful section 4.3 (page 42) of these lecture notes. I think this is the most educative exposition I have ever seen anywhere about Yang-Mill's beta function. What I ...
12
votes
5answers
915 views
What's so special about AdS?
This question is coming from someone who has very little experience with M-Theory but is intrigued by the AdS/CFT correspondence and is beginning to study it.
Why is the gauge/gravity duality ...
12
votes
2answers
181 views
Renormalization in string theory
I'm taking a course in string theory and have encountered renormalization for the first time (and I suspect it isn't the last).
Specifically, while quantizing the bosonic and spinning strings, an ...
12
votes
2answers
164 views
Generalized Complex Geometry and Theoretical Physics
I have been wondering about some of the different uses of Generalized Complex Geometry (GCG) in Physics. Without going into mathematical detail (see Gualtieri's thesis for reference), a Generalized ...
12
votes
7answers
955 views
What are the strings in string theory made of?
This is a follow-up to an intriguing question last year about tension in string theory.
What are the strings in string theory composed of?
I am serious. Strings made of matter are complex objects ...
12
votes
3answers
781 views
Has the black hole information loss paradox been settled?
This question was triggered by a comment of Peter Shor's (he is a skeptic, it seems.) I thought that the holographic principle and AdS/CFT dealt with that, and was enough for Hawking to give John ...
12
votes
1answer
954 views
Good introductory text for matrix string theory
Where can I find a good introductory text for matrix string theory? Most textbooks don't cover it, or only cover it very superficially.
What is the basic idea behind matrix string theory? How can ...
12
votes
1answer
50 views
Local Fermionic Symmetry
That is perhaps a bit of an advertisement, but a couple of collaborators and myself just sent out a paper, and one of the results there is a little bit surprising. We found (in section 6E) a fermionic ...
12
votes
0answers
203 views
Anomalous target space diffeomorphisms for one-loop world-line integrals
The Schwinger effect can be calculated in the world-line formalism by coupling the particle to the target space potential $A$.
My question relates to how this calculation might extend to computing ...
10
votes
4answers
1k views
What are the details around the origin of the string theory?
It is well-known even among the lay public (thanks to popular books) that string theory first arose in the field of strong interactions where certain scattering amplitudes had properties that could be ...
10
votes
1answer
1k views
What evidence exists for string theory viability?
I know that string theory is still under heavy development, and as such it still can't make predictions (or not that many predictions anyways).
On the other hand, it is clear from the number of years ...
10
votes
3answers
1k views
Mathematics of AdS/CFT
To date, what is the most mathematically precise formulation of the AdS/CFT correspondence, and what are the most robust tests of the conjecture?
10
votes
1answer
387 views
Why one-dimensional strings, but not higher-dimensional shells/membranes?
One way that I've seen to sort-of motivate string theory is to 'generalize' the relativistic point particle action, resulting in the Nambu-Goto action. However, once you see how to make this ...
10
votes
1answer
46 views
Physical interpretation of superstrings
The scalar fields $X^\mu$ in bosonic string theory have a clear physical interpretation - they describe the embedding of the string in spacetime.
Adding fermionic fields on the worldsheet is a ...
10
votes
8answers
1k views
What reasons are there to suspect string theory may be an incorrect theory?
It's a truism that in science it is at least as important to state the reasons why a theory or idea might be wrong, as to state the reasons why it is might be correct. For example, early ...
10
votes
3answers
439 views
Space-time in String Theory
I would like to understand how Physicists think of space-time in the context of String Theory. I understand that there are $3$ large space dimensions, a time dimension, and $6$ or $7$ (or $22$) extra ...
10
votes
2answers
1k views
Beginners questions concerning Conformal Field Theory
I started reading about Conformal Field Theory a few weeks ago.
I'm from a more mathematical background. I do know Quantum Mechanics/Classical Mechanics,
but I'm not really an expert when it comes ...
10
votes
3answers
967 views
What is a brief formulation of string theory?
I know that similar questions have been asked before, but none of them is exactly what I would like to know.
I want to have a general idea of what string theory is, without having to read several ...
10
votes
4answers
658 views
Introduction to AdS/CFT
AdS/CFT seems like a really hot topic and I'd like to start reading about. I am looking for the best introduction at my level, i.e. I have a background in QFT, CFT and general relativity at the level ...
10
votes
2answers
44 views
Examples of heterotic CFTs
I'm trying to get a global idea of the world of conformal field theories.
Many authors restrict attention to CFTs where the algebras of left and right movers agree. I'd like to increase my intuition ...
10
votes
0answers
278 views
A dictionary of string - standard physics correspondences
Motivated by the (for me very useful) remark
''Standard model generations in string theory are the Euler number of
the Calabi Yau, and it is actually reasonably doable to get 4,6,8, or 3
...
9
votes
2answers
540 views
Does string theory have a notion of vacuum?
Does string theory have a notion of vacuum? If yes, what is known about it?
9
votes
2answers
168 views
Virasoro constraints in quantization of the Polyakov action
The generators of the Virasoro algebra (actually two copies thereof) appear as constraints in the classical theory of the Polyakov action (after gauge fixing). However, when quantizing only "half" of ...
9
votes
1answer
89 views
Is there a background independent closed string field theory?
Analogous to the background independent open string field theory by Witten. If there isn't, what are the main stumbling blocks preventing its construction?
9
votes
1answer
64 views
Global symmetry in string theory
It is often stated that in quantum gravity only charges coupled to gauge fields can be conserved. This is because of the no hair theorem. If a charge is coupled to a gauge field then when it falls ...
9
votes
3answers
588 views
Does gravity require strings?
OK, before I ask my question, let me frame it with a few (uncontroversial?) statements:
The low-field-limit plane-wave solution to Einstein's equations is helicity-2.
In the early days of string ...
9
votes
2answers
634 views
Steps for going from Polyakov action to low-energy effective action (SUGRA?) in String Theory
A lot of string-theory questions have been asked here. This one is, hopefully, different in that this inquiry is specific and the expected answer would be more mathematical than philosophical in ...
9
votes
3answers
439 views
Is there any quantum-gravity theory that has flat space-time and gravitons?
Many quantum-gravity theories are strongly interacting. It is not clear
if they produce the gravity as we know it at low energies. So I wonder, is there
any quantum-gravity theory that
a) is a well ...
9
votes
1answer
360 views
What are some predictions from string theory that say some crystalline materials “will end up in one of many lowest-energy ground states?”
I am referring to this recent "news feature" by Zeeya Merali from Nature magazine www.nature.com/uidfinder/10.1038/478302a. Here is the specific quote:
"To make matters worse, some of the testable ...
9
votes
1answer
265 views
How do I find constraints on the Nambu-Goto Action?
Let $X^\mu (t,\sigma ^1,\ldots ,\sigma ^p)$ be a $p$-brane in space-time and let $g$ be the metric on $X^\mu$ induced from the ambient space-time metric. Then, the Nambu-Goto action on $X^\mu$ is ...
9
votes
1answer
262 views
Symmetries in Wilsonian RG
I wanted to know if there is a theorem that in writing a Lagrangian if one missed out a term which preserves the (Lie?) symmetry of the other terms and is also marginal then that will necessarily be ...
9
votes
1answer
307 views
Can the connectivity of space change in string theory?
A flop transition changes the second homotopy group of a Calabi-Yau compactifation, but not the fundamental group or the number of connected components. Can the number of connected spatial components ...
