A class of theories that attempt to explain all existing particles (including force carriers) as vibrational modes of extended objects, such as the 1-dimensional fundamental string.

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7
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3answers
562 views

How can string theory work without supersymmetry?

This question is inspired from reading Mitchell Porter's nice answer here to a question asking why supersymmetry should be expected naturally. Among other things, he explains that since weak scale ...
0
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1answer
72 views

Modular invariance of CFT

I am looking at the Cardy formula for entropy in CFT, and in the article 'Kerr/CFT correspondence and its Extensions' there is a sentence: In any unitary and modular invariant CFT, the asymptotic ...
3
votes
0answers
52 views

Are there any stable (not metastable) string theory compactifications with a positive cosmological constant?

Previously, on Save us from swallowing baby universes, please!, I asked how we can be saved from false vacuum decay assuming we are living in a false vacuum. What if we are living in a stable vacuum ...
16
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3answers
12k views

What is the current status of string theory (2013)?

I've seen a bunch of articles talking about how new findings from the LHC seem to disprove (super)string theory and/or supersymmetry, or at least force physicists to reformulate them and change ...
5
votes
2answers
465 views

Is there an intuitive way of thinking about the extra dimensions in M-Theory?

Why are 11 dimensions needed in M-Theory? The four I know (three spatial ones plus time) have an intuitive meaning in everyday life. How can I think of the other seven? What is their nature (spatial, ...
1
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0answers
89 views

Gauge fixing the Einstein's gravity action

This is in reference to this paper, arXiv:1204.4061. I was wondering if someone can give me a reference which explains this gravitational gauge fixing that they have done in $2.10$ and how that ...
7
votes
1answer
107 views

Counting D0-D4 Bound States

I have a slightly technical combinatorics question. Consider the degeneracy $D_n$ of bound states of $n$ D0 branes and one D4 brane. This is given in Polchinski by (13.6.24), \begin{align} ...
1
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0answers
143 views

Introductory exercise set with solutions for string theory

I am trying to self-study string theory, beginning with Ibanez and Uranga (String Theory and Particle Physics). Unfortunately, the book contains no problems, so I'm not sure whether I am fully ...
2
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1answer
471 views

What are the implications of the Holographic principle?

What are the implications for the Holographic principle? I understand the basics of the principle, the relationship with black holes and string theory but what this is going to tell us? Does it help ...
3
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2answers
125 views

Symmetry transformation in AdS space

In AdS/CFT papers the action of the SO(D,2) symmetry is usually given at the boundary where the transformations are just the conformal transformations (Poincare, scaling and special) for D+1 ...
1
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1answer
36 views

Pre-gauge-fixed superspace action of the RNS superstring

When writing down the the action of the RNS superstring in superspace, all of the sources I have checked (BBS, GSW, Polchinski) seem to just write down the action in conformal gauge, that is $$ ...
7
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3answers
363 views

SUSY's Critical role in String Theory

In many popsci articles it is claimed that String Theory (ST) birthed SUSY. Yet ST was originally invented as a bosons-only theory, that later on brought fermions into the fold. This was only ...
-1
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1answer
114 views

Explanation for the minus sign in $\Omega_3$ in the Kappa symmetry of the Green - Schwarz formalism for F1 strings

Just so that there can be more higher - level physics questions here, let me post this question + answer. Also because I'm a bit sad that there are almost no questions on the Green-Schwarz ...
4
votes
1answer
282 views

Is there an open oriented superstring?

Type I superstring theory is unoriented, and it seems that it needs to be so in order to exist. Now, we always have open-closed duality, that connects at least the ultraviolet sector of a theory ...
0
votes
0answers
27 views

Lower bound bound on the mass of scalar bosons

Is there any lower bound bound on the mass of scalar bosons in nature. I know that a massless scalar boson would lead to a fifth force which would violate the equivalence principle. But is there any ...
2
votes
0answers
37 views

Lorentzian interpretation of open-closed string duality

In open-closed string duality, we can reinterpret the one-loop open string diagram (an annulus or cylinder) as a propagating closed string, depending on the direction in which we take time to be. This ...
15
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2answers
680 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 ...
7
votes
1answer
386 views

How algebraic geometry and motives appears in physics?

First, I'm not a physicist so I have just a little background in physics. I have been reading some noncommutative geometry books and papers (Connes, Rosenberg, Kontsevich etc) and a lot of high ...
5
votes
0answers
91 views

“Light” states in critical $O(N)$ model in $2+1$ (and holography)

Let me split the question in a few parts, Can someone give me a reference which explains the CFT properties of the critical $O(N)$ model in $2+1$? Like how are the CFT correlators (in a $1/N$ ...
2
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1answer
438 views

Why doesn't string theory have a mass gap?

Gravitons are string modes which can have arbitrarily small energies. Just make the wavelength arbitrarily large. String theory has no mass gap, but why? A classical string can only have positive ...
2
votes
1answer
156 views

Diagonalize mass matrix term for fermions and “doubling trick” in m(atrix) theory

Can someone help me understand the "Doubling trick" at page 36 in http://inspirehep.net/record/887513/files/sis-2002-060.pdf (named "Scattering in Supersymmetric M(atrix) Models" by Robert Helling) or ...
8
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2answers
208 views

What are orbifolds and why are they useful and interesting for physics?

Just what the title says. What's the basic definition of an orbifold? How do they arise in physics and why are they interesting?
1
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1answer
58 views

Ghosts on Torus worldsheet

Why after the expansion, only 0-mode of bc-ghost contributes to the 4-points ghost function on a torus worldsheet? $$<c(z_1)b(z_2)\tilde{c}(\bar{z}_3)\tilde{b}(\bar{z}_4)>_{T^2} ...
7
votes
2answers
3k 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 ...
1
vote
1answer
470 views

Is this pseudo science or real: code found in superstring

Article in question: http://humansarefree.com/2013/01/science-strange-computer-code.html Problem: no credible looking or sounding site has anything on it. Only bunch of youtube videos. And some ...
-3
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2answers
479 views

Since when were Loop Quantum Gravity (LQG) and Einstein-Cartan (EC) theories experimentally proven?

Can this template at Wikipedia be true? It seems to suggest that Einstein-Cartan theory, Gauge theory gravity, Teleparalleism and Euclidean Quantum Gravity are fully compatible with observation! It ...
2
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0answers
134 views

Picture changing operators

What is a picture-changing operator in string theory? How do they work?
2
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1answer
103 views

Particles from String theory

I understand that the strings in string theory are posited to be many, many orders of size smaller than say, a quark, electron or any other particle. But if this is so, how does the string "expand" to ...
6
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2answers
318 views

How does the full string theory potential look?

Is the full stringy potenetial (for which it is claimed to be 10^500 vacua) written down explicitly somewhere? Any references? Thanks, Dave
3
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1answer
96 views

Hyperkahler manifolds and their use in theoretical physics

Just as the title says: What is the easiest definition of a Hyperkahler Manifold? Could you give some examples of Hyperkahler manifolds, and manifolds which fail to be hyperkahler? Why are such ...
5
votes
0answers
118 views

Some questions about calculation central charge in a CFT in $d$ spacetime dimensions

This is based on this paper, http://arxiv.org/abs/hep-th/0212138 For a CFT on a $S^d$ spacetime (of radius R) it seems to be claimed that the central charge is given by, $ c = \langle \int_{S^d_R} ...
6
votes
1answer
133 views

Renormalizability of the Polyakov Action

I was told today that the Polyakov action for a $p$-brane is (superficially) re-normalizable iff $p\leq 1$. Of course, when I went to check for myself, I screwed up my power-counting, and I'm having ...
3
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1answer
54 views

String total cross sections at asymptotically high energy

I only have a vague understanding of string theory, but a solid understanding of particle physics. At asymptotically high energy (Regge limit), the string cross section is dominated by the exchange ...
6
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1answer
189 views

The double-trace deformation effect in AdS/CFT

Let me use this paper as the reference for this. I want to understand better the argument at the bottom of page 6. If the bulk $AdS$ metric is written as $\frac{1}{r^2}(dr^2 + ...
-3
votes
2answers
152 views

How Come string theory is based on the fact that a “string”, a theoretical dimension, exists?

I See no explanations beyond concise explanations that a "string" is nothing more than a hypothetical, one-dimensional subatomic particle. If so, why imagine that they are "strings" instead of just ...
2
votes
0answers
56 views

Question on Tachyon Correlator (GSW)

I'm reading through chapter 7 of Green-Schwarz-Witten and I have a problem with the derivation of the M-tachyon correlation function. Basically I'm trying to get 7.A.17 from 7.A.12 and eq 7.A.22 in ...
2
votes
1answer
110 views

Deriving entanglement entropy from Renyi entropy

My questions are based on this paper - http://arxiv.org/abs/0905.4013 Firstly I want to know as to whether some assumptions are needed about the relationship between the systems $A$ and $B$ for the ...
10
votes
3answers
2k 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 ...
0
votes
3answers
7k views

Total number of subatomic particles in the universe. Are they finite ? assuming any of GR or QM or even ST

Total number of subatomic particles in the universe. Are they finite ? assuming any of GR or QM or even ST.
18
votes
10answers
3k 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 ...
20
votes
1answer
993 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 ...
12
votes
3answers
681 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 ...
12
votes
1answer
1k views

Is String Theory formulated in flat or curved spacetime?

String Theory is formulated in 10 or 11 (or 26?) dimensions where it is assumed that all of the space dimensions except for 3 (large) space dimensions and 1 time dimension are a compact manifold with ...
13
votes
4answers
619 views

Isn't gravity non-local and non-causal?

The way I think of this is that, I can ask physical questions about a space-time which are impossible to answer unless one knows the full space-time, and hence I am inclined to believe that gravity is ...
4
votes
1answer
125 views

Curved spacetime as a coherent state in string theory

I have a question about Polchinski's string theory book, volume I, p 108. When we write the Polyakov action in curved spacetime, it is said $$ S_{\sigma} = \frac{1}{4\pi\alpha'} \int_M d^2 \sigma ...
0
votes
1answer
179 views

Why isn't there a Heterotic string theory which tensors the fermionic state with the Type II state?

The Heterotic (HO and HE) string is found by tensoring the left movers of the bosonic string theory state and the right movers of the Type II string theory state: ...
16
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2answers
738 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 ...
1
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0answers
103 views

Questions about Type HE Matrix String Theory

I was reading the heterotic string section of this thesis desertation by Luboš Motl, since I think I now understand the Type IIA Matrix String Theory. The only thing I knew about Type HE Matrix ...
3
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0answers
84 views

Schwarzschild radius in matrix models

The Schwarzschild radius for 11D BHs is given by $l_{11}(l_{11}m)^{1/8}$, which is the special case ($D=11$) of the general dimensional case of $(G_Dm)^{\frac{1}{D-3}}$. Here $m$ is the BH mass and ...
2
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3answers
429 views

Do extra-dimensional theories like ADD or Randall-Sundrum require string theory to be true?

What I mean is could it turn out that the world is not described by string theory / M-Theory, but that nevertheless some version of one of these extra-dimensional theories is true? I have no real ...