The research-level tag applies to questions that arise in graduate and post-secondary work. These questions often require domain-specific knowledge and could not be answered from a general source or may be beyond the level typically covered by Wikipedia and other popular sources. research-level ...
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155 views
Reduced density matrices for free fermions are thermal
Many recent papers study entanglement in eigenstates of fermionic free hamiltonians (normally on a lattice) using the basic assumption that the reduced density matrices are thermal (e.g. Peschel ...
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1answer
131 views
Some questions about the spectral function
If you think that this question is likely to get closed then please do not answer and only say that in the comments since this system doesn't let me delete the question once it has answers.
...
9
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1answer
41 views
Functional relations for Kochen-Specker proofs
Many proofs of the Kochen-Specker theorem use some form of the following argument (from Mermin's "Simple Unified Form for the major No-Hidden-Variables Theorems" )
[I]f some functional relation
...
9
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1answer
322 views
False vacuum in axiomatic QFT
There is an elegant way to define the concept of an unstable particle in axiomatic QFT (let's use the Haag-Kastler axioms for definiteness), namely as complex poles in scattering amplitudes. Stable ...
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1answer
192 views
What is the “BCS Cooper pair condensation” as a physical phenomenon in terms of experiments?
"Thought" experiments and "numerical" experiments are allowed.
This question is motivated by the question Has BCS Cooper pair condensate been observed in experiment? ,
and by our recent research on ...
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53 views
Fluctuations of an interface with hammock potential
This question is related to that one. I ask it here since comments are too short for the extended discussion that was going on there.
I am interested in a very simple interface model. To each ...
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3answers
48 views
Does the complex 3-sphere have a complex structure modulus?
This question has a flavor which is more mathematical than physical, however it is about a mathematical physics article and I suspect my misunderstanding occurs because the precise mathematical ...
8
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3answers
37 views
Depolarizing threshold for CSS codes
Many years ago, when CSS codes were first invented, the error threshold of p=0.11 was found when bit and phase flips are independent. Has a threshold yet been found for the case of depolarizing noise?
...
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2answers
136 views
Are there rigorous constructions of the path integral for lattice QFT on an infinite lattice?
Lattice QFT on a finite lattice* is a completely well defined mathematical object. This is because the path integral is an ordinary finite-dimensional integral. However, if the lattice is infinite, ...
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3answers
68 views
Constructing a Hamiltonian (as a polynomial of $q_i$ and $p_i$) from its spectrum
For a countable sequence of positive numbers $S=\{\lambda_i\}_{i\in N}$ is there a construction producing a Hamiltonian with spectrum $S$ (or at least having the same eigenvalues for $i\leq s$ for ...
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1answer
86 views
What evidence do we have for S-duality in N=4 Super-Yang-Mills?
Do we have anything resembling a proof*? Or is it just a collection of "coincidences"?
Also, do we have evidence from lattice gauge theory computations?
*Of course I'm not talking about a proof in ...
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1answer
255 views
Which qubit states are accessible with linear optics operations?
Given a quantum state of $n$ qubits, and being restricted to linear optics (that is, the output annihilation operators are linear combinations of the input annihilation operators):
Which states are ...
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1answer
258 views
AGT conjecture and WZW model
In 2009 Alday, Gaiotto and Tachikawa conjectured an expression for the Liouville theory conformal blocks and correlation functions on a Riemann surface of genus g and n punctures as the Nekrasov ...
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1answer
270 views
Quivers in String Theory
Why do a physicist, particularly a string theorist care about Quivers ?
Essentially what I'm interested to know is the origin of quivers in string theory and why studying quivers is a natural thing ...
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1answer
93 views
AdS/CFT at D = 3
AdS/CFT at D = 3 (on the AdS side) seems to have some special issues which I bundled into a single question
The CFT is 2D hence it has an infinite-dimensional group of symmetries (locally). The ...
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3answers
491 views
Why are some solitons formed from bosonic fields fermionic?
Some topological solitons formed from bosonic fields have fermionic statistics. Why?
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6answers
71 views
Papers and preprints worth reading, Jan-midFeb 2012 [closed]
Which recent (i.e. Jan-midFeb 2012) papers and preprint do you consider really worth reading?
References should be followed by a summary saying what is the result and (implicitly or explicitly) why ...
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1answer
80 views
Quantum gravity at D = 3
Quantization of gravity (general relativity) seems to be impossible for spacetime dimension D >= 4. Instead, quantum gravity is described by string theory which is something more than quantization ...
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2answers
131 views
Wilson Loops in Chern-Simons theory with non-compact gauge groups
VEVs of Wilson loops in Chern-Simons theory with compact gauge groups give us colored Jones, HOMFLY and Kauffman polynomials. I have not seen the computation for Wilson loops in Chern-Simons theory ...
8
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1answer
101 views
Do thermodynamic quantities in CFT correspond to something different in AdS/CFT?
From what I've (hopefully) understood from the AdS/CFT correspondence, physical quantities have a dual version. For example, the position in the bulk is the scale size (in renormalization), and waves ...
8
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1answer
53 views
Superconformal Multiplet Calculus in 6D
A convenient method for dealing with off-shell formulations of
supergravity theories is provided by the superconformal multiplet
calculus. This calculus was originally constructed for 4d ${\cal N}=2$
...
8
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1answer
23 views
Sub and super multiplicativity of norms for understanding non-locality
In relation to various problems in understanding entanglement and non-locality, I have come across the following mathematical problem. It is most concise by far to state in its most mathematical form ...
8
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1answer
174 views
Derivation of the basic equation for Witten diagrams
I could understand the derivation of the "bulk-to-boundary" propagators ($K$) for scalar fields in $AdS$ but the iterative definition of the "bulk-to-bulk" propagators is not clear to me.
On is ...
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1answer
263 views
How do you simulate chiral gauge theories on a computer?
David Tong and Lubos Motl have argued that our universe can't possibly be a digital computer simulation because chiral gauge theories can't be discretized, and the Standard Model is a chiral gauge ...
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1answer
305 views
Kramer's-Kronig relations for the electron Self-Energy Σ
I'm currently studying an article by Maslov, in particular the first section about higher corrections to Fermi-liquid behavior of interacting electron systems. Unfortunately, I've hit a snag when ...
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1answer
88 views
“finite” QFTs and short-distance singularities and vanishing beta functions
I am not sure that I can frame this question coherently enough - it springs from various things in QFT that I have recently been thinking and reading about. May be these thoughts are mis-directed but ...
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1answer
332 views
Schwinger representation of operators for n-particle 2-mode symmetric states
A bosonic (i.e. permutation-symmetric) state of $n$ particles in $2$ modes can be written as a homogenous polynomial in the creation operators, that is
$$\left(c_0 \hat{a}^{\dagger n} + c_1 ...
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0answers
48 views
Super Lie-infinity algebra of closed superstring field theory?
Bosonic closed string field theory is famously governed by a Lie n-algebra for $n = \infty$ whose $k$-ary bracket is given by the genus-0 (k+1)-point function in the BRST complex of the string.
One ...
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1answer
73 views
Many body quantum states analyzed as probabilistic sequences
Measurements of consecutive sites in a many body qudit system (e.q. a spin chain) can be interpreted as generating a probabilistic sequence of numbers $X_1 X_2 X_3 \ldots$, where $X_i\in ...
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36 views
Minimal strings and topological strings
In http://arxiv.org/abs/hep-th/0206255 Dijkgraaf and Vafa showed that the closed string partition function of the topological B-model on a Calabi-Yau of the form $uv-H(x,y)=0$ coincides with the free ...
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8answers
971 views
What is the name of the principle saying it is meaningless to talk/ask questions that can not be measured/tested?
Watching quantum mechanics lectures and it was mentioned that it is pointless/meaningless to try to talk/question things that can not be tested/measured.
Is this a principle? And if so what is it's ...
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3answers
602 views
Group Cohomology and Topological Field Theories
I have a two-part question:
First and foremost: I have been going through the paper by Dijkgraaf and Witten "Group Cohomology and Topological Field Theories". Here they give a general definition for ...
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4answers
209 views
Different kinds of S-matrices?
It seems to me that the notion of an "S-matrix" refers to several different objects
One construction you can find in the literature is allowing the coupling constant to adiabatically approach 0 in ...
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1answer
49 views
Why isn't there heterotic holographic QCD?
I think the question speaks for itself... Top-down holographic QCD, like Sakai-Sugimoto, always involves the Type II string. There are one or two papers on hQCD using the Type 0 string. But I can't ...
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3answers
92 views
Which are the simplest known contextual inequalities?
It is well-known that quantum mechanics does not admit a noncontextual ontological model, and there are countless different proofs of it. I'm interested in the simplest proofs that can be cast as an ...
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3answers
37 views
Operator norm directly from phase space representation of photonic quantum operator
I'm interested in calculating the operator norm of a Hermitian operator, say $B$, acting on the Hilbert space of square integrable functions. The context is I have an optical system in all its ...
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2answers
51 views
“tmf(n) is the space of supersymmetric conformal field theories of central charge -n”
I read this intriguing statement in John Baez' week 197 the other day, and I've been giving it some thought. The post in question is from 2003, so I was wondering if there has been any progress in ...
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2answers
2k views
Some Korean researchers saying that they solved Yang-mill existence and mass gap problem
Today, Korean media is reporting that a team of South Korean researchers solved Yang-Mill existence and mass gap problem. Did anyone outside Korea even notice this? I was not able to notice anything ...
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1answer
34 views
Are lens spaces classified via a Weinberg angle?
I am thinking about Kaluza Klein theory in the 3 dimensional lens spaces. These have an isometry group SU(2)xU(1), generically, and in some way interpolate between the extreme cases of manifolds $S^2 ...
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2answers
116 views
Simulation of QED
Can anyone point me to a paper dealing with simulation of QED or the Standard Model in general? I will particularly appreciate a review paper.
7
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1answer
127 views
Supersymmetric Nonrenormalization Theorems
I'm looking for approaches to nonrenormalization theorems in supersymmetric QFT which are as much as possible mathematical, elegant and involve few heavy straightforward computations
7
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1answer
66 views
How does one geometrically quantize the Bloch equations?
I've just now rated David Bar Moshe's post (below) as an "answer", for which appreciation and thanks are given.
Nonetheless there's more to be said, and in hopes of stimulating further posts, I've ...
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1answer
149 views
What is the significance of the branch cut in renormalization group logarithms?
What is the physical significance of the branch cut in renormalization group logarithms?
(Is this just an avatar of the optical theorem, or is there something to be understood about these logarithms ...
7
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1answer
85 views
Simple question on the foundations of spin foam formalism
To make it simple, take the spin foam formalism of ($SU(2)$) 3D gravity. My question is about the choice of the data that will replace the (smoothly defined) fields $e$ (the triad) and $\omega$ (the ...
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3answers
100 views
String-theoretic significance of extended CFT
Extended TQFT and CFT have been puzzling me for while. While I understand the mathematical motivation behind them, I don't quite understand the physical meaning. In particular, it's not clear to me to ...
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2answers
93 views
Group of symmetries of Lagrange's equations
Consider the following statements, for a classical system whose configuration space has dimension $d$:
Lagrange equations admit a smaller group of "symmetries" (coordinate change under which ...
7
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1answer
105 views
What makes background gauge field quantization work?
[Again I am unsure as to whether this is appropriate for this site since this is again from standard graduate text-books and not research level. Please do not answer the question if you think that ...
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2answers
452 views
Majorana zero mode in quantum field theory
Recently, Majorana zero mode becomes very hot in condensed matter physics.
I remember there was a lot of study of fermion zero mode
in quantum field theory, where advanced math, such as index ...
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2answers
164 views
Equivalence of definitions of ADM Mass
ADM Mass is a useful measure of a system. It is often defined (Wald 293)
$$M_{ADM}=\frac{1}{16\pi} \lim_{r \to \infty} \oint_{s_r} (h_{\mu\nu,\mu}-h_{\mu\mu,\nu})N^{\nu} dA$$
Where $s_r$ is two ...
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1answer
565 views
Is resonating valence bond (RVB) states long-range entangled?
Quantum liquid is at the core of condensed matter theory study, examples include superfluid in Bose Hubbard model, quantum spin liquid around the RK point of a quantum dimer model, string-net ...
