A class of theories that attempt to explain all existing particles (including force carriers) as vibrational modes of one-dimensional objects.
4
votes
2answers
321 views
What is currently incomplete in M-theory?
As it is, what is currently and seemingly incomplete in M-theory?
One example I can give is explaining dark matter proportions
and.. how do we perceive the world as 4-dimensional.
Thanks everyone.
3
votes
1answer
39 views
Spectrum of Free Strings
As far as I understand, both in bosonic and superstring theory one considers initially a free string propagating through D-dimensional Minkowskispace. Regardless of what quantization one uses, at the ...
3
votes
1answer
231 views
Why is Compactification restricted to Toroids, Calabi-Yau & Co.?
I think I've missed this point somehow. I've just started with Compactification and so far, I don't really see why it is restricted to the above mentioned types of manifolds?
I have to admit, when ...
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?
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 ...
8
votes
5answers
575 views
How does the string worldsheet affect the space-time in which they live?
I don't understand much about string theory and never really got much further past the Nambu-Goto action and very basic supersymmetry (SUSY) lectures in my undergraduate courses, but the only thing ...
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 ...
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
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 ...
3
votes
1answer
217 views
Causality in String Theory
For a point particle we have light cone:
String Theory- with it's extended body concepts- however will not admit a light cone such as this. In particular the most problematic causal issue would be ...
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
2answers
163 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 ...
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
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 ...
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 ...
7
votes
4answers
1k views
Number of dimensions in string theory and possible link with number theory
This question has led me to ask somewhat a more specific question. I have read somewhere about a coincidence. Numbers of the form $8k + 2$ appears to be relevant for string theory. For k = 0 one gets ...
7
votes
2answers
632 views
Do traversable wormholes exist as solutions to string theory?
There has been some heated debate as to whether the laws of physics allow for traversable wormholes. Some physicists claim we require exotic matter to construct wormholes, but then others counter the ...
6
votes
1answer
413 views
Do we need a quantum deformation of the diffeomorphism group in string theory?
Let me justify my question before I go on. In string theory, gravitons are strings extended over space. Longitudinal gravitons are pure gauge modes of the diffeomorphism group. However, in string ...
6
votes
0answers
425 views
Why is there a deep mysterious relation between string theory and number theory, elliptic curves, $E_8$ and the Monster group? [closed]
Why is there a deep mysterious relation between string theory and number theory (Langlands program), elliptic curves, modular functions, the exceptional group $E_8$, and the Monster group as in ...
5
votes
1answer
254 views
In what limit does string theory reproduce general relativity?
In quantum mechanical systems which have classical counterparts, we can typically recover classical mechanics by letting $\hbar \rightarrow 0$. Is recovering Einstein's field equations (conceptually) ...
5
votes
1answer
635 views
Some questions on Conformal Field Theory, Current algebras and the Sugawara construction
Since I don't know how to add another question to an already existing topic,
I'm opening a new thread. However I'm referring to:
Beginners questions concerning Conformal Field Theory
As noted, a ...
4
votes
1answer
249 views
What is the essence of BCFW recursion techniques?
I have recently briefly read about new methods as the Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion method.
Can anybody please tell me about the essence of it?
What does it mean for the ...
4
votes
3answers
728 views
Give a description of M-theory your grandmother can understand
Inspired by this question, let me ask a similar question. Is it possible to do the same (give a description of M-theory your grandmother could understand)for M theory? While I know even experts don't ...
4
votes
2answers
408 views
Global symmetries in quantum gravity
In several papers (including a recent one by Banks and Seiberg) people mention a "folk-theorem" about the impossibility to have global symmetries in a consistent theory of quantum gravity. I remember ...
4
votes
2answers
321 views
T-duality approaches
The textbook approach to explaining T-dualities is to show that a type of T-duality transformation "inverts the radius of the circle, that is, it maps $R\rightarrow\tilde{R} = \alpha'/R$ and it ...
2
votes
1answer
407 views
Is anti-gravity possible in theoretical physics?
Is anti-gravity http://en.wikipedia.org/wiki/Anti-gravity possible in string theory?
I have read some articles about scientists making assumptions about the existence of anti-gravity, but is it ...
8
votes
1answer
845 views
What is a D-brane?
I know that in string theory, D-branes are objects on which open strings are attached with Dirichlet boundary conditions. But what exactly is a brane? Are they equally fundamental objects like string? ...
5
votes
2answers
614 views
How much can AdS/CMT tell us?
I will begin my research on AdS/CMT, however I find AdS/CMT is only a phenomelogical method, so I want to know can AdS/CMT give some results the condensed matter physicists can not give, or even ...
4
votes
1answer
163 views
Defining a CFT using beta-functions
Won't it be correct to define a CFT as a QFT such that the beta-function of all the couplings vanish?
But couldn't it be possible that the beta-function of a dimensionful coupling vanishes but it ...
4
votes
1answer
81 views
Negative open string norms after BRST cohomology?
The question Disappearance of moduli for condensate of open strings made me think.
Suppose we have a Dp-brane completely wrapped over a $T^d$ compactification with $p\leqslant d$. Look at an open ...
4
votes
4answers
856 views
Is spacetime discrete or continuous?
Is the spacetime continuous or discrete?
Or better, is the 4-dimensional spacetime of general-relativity discrete or continuous? What if we consider additional dimensions like string theory ...
4
votes
2answers
314 views
Why do we have so many dualities in string theory?
Why do we have so many dualities in string theory? Is there a reason for that?
3
votes
2answers
489 views
How does String Theory predict Gravity?
Firstly, General Relativity states that Spacetime is dynamic and is consonant with the distribution of matter/energy. How does String Theory predict gravity, when it is background dependent, that is ...
3
votes
0answers
146 views
Some more questions on conformal spinors of $SO(n,2)$
This is somewhat of a continuation of my previous question.
I had stated there that a conformal spinor ($V$) of $SO(n,2)$ can be created by taking a direct sum of two $SO(n-1,1)$ spinors $Q$ and $S$ ...
3
votes
2answers
364 views
Conversion of the Nambo-Goto action into the Polyakov action?
I`ve read that the Nambo-Goto action containing the induced metric $\gamma_{\alpha\beta}$
$$\tag{1} S_{NG} ~=~ -T\int_{\tau_i}^{\tau_f} d\tau \int_0^{\ell} d\sigma \sqrt{-\gamma}$$
can be converted ...
3
votes
1answer
336 views
Pedagogical explanations of critical dimensions of string theories
Once you understand the formalism, I think it's clearest to say the critical dimension of the space-time arises because we need to cancel the central charge of the (super)conformal ghosts on the ...
1
vote
2answers
326 views
Non-renormalizable corrections to GUT unification
While writing these answers: Hypercharge for U(1) in SU(2)xU(1) model and Is there a concise-but-thorough statement of the Standard Model? , it occured to me that the unification prediction for ...
8
votes
1answer
446 views
The measure problem in the anthropic principle
The anthropic principle is based upon Bayesian reasoning applied to the ensemble of universes, or parts thereof, conditioned upon the existence of conscious observers. That still leaves us with the ...
7
votes
7answers
1k views
Why are extra dimensions necessary?
Some theories have more than 4 dimensions of spacetime. But we only observe 4 spacetime dimensions in the real world, cf. e.g. this Phys.SE post.
Why are the theories (e.g. string theory) that ...
6
votes
1answer
200 views
Reference for the ${\cal N}=3$ Chern-Simons Lagrangian at general $N_c$, $N_f$
I was wondering if someone could give me a reference where someone has explicitly written the Lagrangian for ${\cal N}=3$ $SU(N_c)$ Chern-Simons theory coupled to $N_f$ fundamental hypermultiplets.
...
6
votes
1answer
408 views
What's with Mandelstam's argument that only linear regge trajectories are stable?
While thinking about how to answer a "describe string theory" question, I remembered an old argument of Stanley Mandelstam's that linear Regge trajectories implies stability. I never fully understood ...
5
votes
1answer
229 views
Bosonic Tachyon Condensation?
The tachyonic string mode in perturbative bosonic string theory indicates that the "vacuum", flat Minkowski $\mathbb{R}^{25,1}$, is not really a vacuum. What is conjectured about tachyon condensation ...
5
votes
2answers
306 views
Is string length in string theory quantized?
Is there a minimal string length (maybe the Plank length?), and is it quantized?
Do strings have a 0-dimensional (ie point) cross-section?
5
votes
2answers
333 views
More questions on string theory and the standard model
This is a followup question to
How does string theory reduce to the standard model?
Ron Maimon's answer there clarified to some extent what can be expected from string theory, but left details open ...
4
votes
2answers
242 views
Fundamental equation(s) of string theory?
I often hear about string theory and its complicated mathematical structure as a physical theory, but I can't say that I've ever actually seen any of the related math. In general, I'm curious as to ...
4
votes
0answers
164 views
The ${\cal N} = 3$ Chern-Simons matter lagrangian
This question is sort of a continuation of this previous question of mine.
I would like to know of some further details about the Lagrangian discussed in this paper in equation 2.8 (page 7) and in ...
4
votes
1answer
497 views
On black holes, Hawking radiation and gravitational atoms
Over the past hour or so I've been following one of my standard physics-based, wanders-through-the-internet. Specifically, I began by reviewing some details of dark energy theory but soon found myself ...
4
votes
1answer
156 views
What is the stress-energy distribution of a string in target space?
If $| \psi \rangle$ is a string mode, how do you compute $\langle \psi | \hat{T}^{\mu\nu}(\vec{x}) | \psi \rangle$ where $\vec{x}$ is a point in target space? This information will tell us the energy ...
4
votes
1answer
236 views
What are the current (popular(ish)) approaches to modelling the quantum nature of spacetime at the Planck scale?
My guess at a list of them would be: spin foams, casual sets, non-commutative geometry, Machian theories, twistor theory or strings and membranes existing in some higher-dimensional geometry...
...
3
votes
1answer
164 views
Lorentz spinors of $SO(n,1)$ and conformal spinors of $SO(n,2)$
It would be great if someone can give me a reference (short enough!) which explains the (spinor) representation theory of the groups $SO(n,1)$ and $SO(n,2)$.
I have searched through a few standard ...
