Questions tagged [research-level]
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 questions should not require new or groundbreaking research and results to answer.
662
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Representing quantum channels, and especially measurements, via C*-algebras
I have not been able to find in my searches a concise explanation of how to think of measurement channels in particular in the $C^*$-algebraic formulation of quantum mechanics. It is also difficult to ...
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Spin Operator in Massless QED
I am reading Subleading soft dressings of asymptotic states in QED and perturbative quantum gravity by Choi and Akhoury. I wish to understand how to derive the subleading soft theorem in massless QED, ...
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Covariant Spin Operator for Massless Fermions
I have been reading the paper The Covariant Definition Of Spin in Relativistic QFT by Hilgevoord and De Kerf, in which the authors derive the spin operator in relativistic quantum theories of free ...
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Can, in theory, information escape an event horizon via a specialized setup?
Can, in theory, information escape an event horizon via a specialized setup?
Specifically, send a beam of photons to be barely—just barely—inside the event horizon, then wait for hawking radiation to ...
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Problem measuring local reflectance through objective lens
Measuring the reflectance of copper substrates using only reflection probes gives an expected reflectance (orange plot). But when an objective lens is used to focus the incident light, I can see the ...
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Definition of Asymptotically Flat at Null, Spacelike, and Timelike Infinities
Most books I've looked into discuss asymptotic flatness in general relativity for the null and spacelike case (e.g. Wald), or for the null and timelike case (e.g. arXiv: 1706.09666 [math-ph]), but I ...
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Specific experiments that affirm particle-in-a-box QM theory
The infinite square well (and variations) are some of the best-studied systems in quantum mechanics and are often used as the starting point for any quantum mechanical education, as the Schrodinger ...
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Are there non-trivial two-party stabilizers in bipartite entanglement for product states?
In this recent paper where the authors discuss finite classification of entanglement types, on pg. 29 in appendix A, it is claimed that in bipartite entanglement for product state $|00\rangle$ there ...
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Is there any limit to the utility of quantum measurements in the sense of a Lieb-Robinson bound?
So the Lieb-Robinson bound of 1972 derives an emergent maximum speed $v \ll c$ of the propagation of quantum information under time evolution generated by some local Hamiltonian $H(t)$. Basically, ...
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Negative energy particle effect on observable object
A recent paper "Gravitational Pair Production and Black Hole Evaporation" (discussed in short here) says that any spacetime curvature would produce Hawking radiation, no need for event ...
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Fulling–Davies–Unruh effect with non-uniform acceleration
Can there be some version of the Fulling–Davies–Unruh effect, in which the accelerating observer is moving with a non-uniform acceleration? Can someone refer some papers to read?
If there can not be ...
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Can Neutron Activation Analysis differ isotopes?
I know to carry out an NAA analysis, the specimen is placed into a suitable irradiation facility and bombarded with neutrons. This creates artificial radioisotopes of the elements present. Following ...
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Coherent States and Temperature for Scalar QFT with Source
This is a follow-up question on a question I previously asked, namely Coherent states and thermal properties. The authors of the article I am referring to in the previous question (Thermodynamics of ...
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Coherent states and thermal properties
I am reading a paper called Thermodynamics of Coherent States and Black Hole Entropy, written by Bashkirov and Sukhanov. If I understand correctly, they define a coherent state by the equation
$$a|d\...
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Taylor expanding amplitudes in QED
I would like to explore a particular amplitude in the low electron mass limit. I write the amplitude
$$i\mathcal{M}=ie^3\bar{u}(q)
\frac{(q\cdot\epsilon_{\lambda}^*+i\epsilon_{\lambda\rho}^*k_{\sigma}...
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Lagrange multipliers not obeying classical EoMs
I will ask my question about Lagrange multipliers by using an example in string theory, as this question was inspired by my string theory course, but it applies to every theory with Lagrange ...
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Holomorphic sections that lead to the original parameterization of the gauged STU model
The original action, given in 9903214, comes from the $\mathcal{N} = 2$ abelian truncation of the maximal $\mathcal{N} = 8$, $SO(8)$ gauged supergravity that can be obtained from $S^
7$
reduction of ...
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Off-shell Photons and Collinear Divergences
I am reading Weinberg's book "The Quantum Theory of Fields", vol. 1. Weinberg suggests that the effect of radiative corrections involving $N$ soft photons is to multiply the (non-radiative) ...
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Witten anomaly and bound states of fermions
In his famous paper "An SU(2) anomaly", Witten begins by noting that an SU(2) gauge theory with a single fermion in the doublet representation is weird, since there is "no obvious ...
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1
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How is this term an angle?
This question is regarding the $\Theta_{\mu\nu}$ term given in equation (3.8) of the paper (https://arxiv.org/abs/2206.07725). The term ( I have typed it below )is defined right below in (3.9) and ...
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Question on the Background Field Method for Non-Abelian Gauge theory
I am reading Peskin's and Schroeder's book "An Introduction to Quantum Field Theory". In Chapter 16.6 the authors use the Background Field Method to determine the $\beta$ function for a non-...
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Disgreement with Birrell's and Davies' book on QFT in curved space
In B&D (Birrel and Davies) and more specifically, at the end of Chapter two, the authors define the non-zero temperature Green functions, as
$$G_{\beta}^+(x,x')=\langle{\phi(x)}\phi(x')\rangle_{\...
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Cavity Input-Output Formalism: Physical significance and intuitive understanding
I have spent a lot of time trying to understand the input-output formalism for cavities. I sort of understand the idea
Fields inside an optical cavity(our system) will have losses because the mirrors ...
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1
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Follow up Question on the Hadamard's Function - Birrell and Davies
My question is a follow up question of the following one: Schwinger and Hadamard functions derivation in Birrell's and Davies' book
So, in Birrell's and Davies' book the authors derive an ...
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Understanding the Yennie-Frautschi-Suura (YFS) Infrared Exponentiation
I am trying to understand an alternative derivation of the Yennie-Frautschi-Suura (YFS) virtual photon exponentiation, given by Grammer and Yennie, in their paper "Improved treatment of the ...
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Decomposition of the Photon Propagator into $K$ and $G$ propagators
I am reading a paper by B. Sahoo and A. Sen, called "Classical and Quantum Results on Logarithmic Terms in the Soft Theorem in Four Dimensions". To determine the logarithmically divergent ...
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Time's Arrow, or Why does time seem to be flowing in one direction? [duplicate]
I have been working on this topic for the past 6 months, and I Understand what is time, but why does it have a direction? Why was the Entropy low in the Early Universe? I have got success in some ...
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1
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Field of research treating tetrads (vierbeins) as fundamental objects?
After a lot of research on tetrads I think I found the subject I'd like to specialize in for postgrad/phd, as they seem to express many interesting and (perhaps) fundamental physical properties. So i ...
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An equation satisfied by harmonic coordinates in a Schwarzschild spacetime
(Full disclosure, this is very much a "fish out of water" type situation: I'm working on something in an area very far away from the stuff I usually work with, so this is hopefully something ...
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Photon number autocorrelation in Cavity QED
I am studying this paper dealing with optomechanical strong coupling, and I don't understand one very relevant part of it.
In particular, the authors define (equation (8)) a photon number ...
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118
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Question about field configurations on the boundary of $\mathcal{I}^+$
I am reading Strominger's lecture notes "The infrared structure of gravity and gauge theory" (https://arxiv.org/abs/1703.05448). In chapter two, while trying to derive an expression about ...
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209
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Faddeev - Kulish paper questions
I have several questions regarding the paper Asymptotic conditions and infrared divergences in QED, written by Faddeev and Kulish in 1970. This is not a post about one question, but since all the ...
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Subleading soft theorem and gauge invariance
I am reading a paper by Burnett-Norman and Kroll, called extension of the Low soft photon theorem (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.20.86). The authors claim that in order to ...
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2
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String theory hilbert space - Gas of free gravitons
I am trying to understand the arguments given in MAGOO in chapter 3.4.1(Hilbert Space of String Theory). The authors give descriptions of the Hilbert space of String Theory when we consider our theory ...
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Conserved charge at null infinity associated with Large gauge transformation
I am reading Strominger's lecture notes "Lectures on the infrared structure of gravity and gauge theory" (https://arxiv.org/abs/1703.05448). At some point, following (I guess) the authors of ...
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1
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Momentum integral yielding $\delta$ function
I am reading the paper Asymptotic conditions and infrared divergences in quantum electrodynamics by P. P. Kulish & L. D. Faddeev (the paper is not important for the question I think, but I will ...
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1
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Faddeev-Kulish Asymptotic Dynamics Question
I am reading a paper by Faddeev and Kulish ("Asymptotic conditions and infrared divergences in QED" written in 1970) and I have a question regarding the nonrelativistic problem of Coulomb ...
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An Exotic Transport Phenomena with Zero-Current at Different Voltage Values
I am a researcher working with active matters, and in one of my experiment I've seen a very exotic transport phenomena which we obtain zero-current for many different values of voltage (those values ...
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How to apply the boundary condition in the derivation of the 2-point function in MAGOO?
In the famous AdS/CFT review, in section 3.3.1 the authors give the two-point function of the operator $\mathcal{O}$ for which $\phi_0$ is a source, we write
$$
\langle\mathcal{O}(p)\mathcal{O}(q)\...
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Momentum Conserving Delta Function and Soft Gravitons
I am reading a paper called "Testing subleading multiple soft graviton theorem for
CHY prescription" written by Subhroneel Chakrabarti, Sitender Pratap Kashyap, Biswajit Sahoo, Ashoke Sena ...
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In Quantum Field Theory in Curved Spacetime, are particle states energy eigenstates?
I've been reading the paper Particle and energy cost of entanglement of Hawking radiation with the final vacuum state, by R. M. Wald (arXiv: 1908.06363 [gr-qc], DOI: 10.1103/PhysRevD.100.065019). It ...
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QED Soft Theorems and Momentum Conserving $\delta$ function
The sub-leading soft theorem (or Low theorem) states that the radiative Feynman amplitude is associated to the non-radiative Feynman amplitude in the following way
$$\mathcal{M}_{\text{rad}}(\omega_k,\...
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There is any kind of research on the use of a "Light-Gas Gun" on the production of Metallic Hydrogen?
Well, if it was that simple, there would already be some research on it, but I couldn't find any.
Light-Gas Gun:
If you don't know, a Light-Gas Gun is basically an apparatus that is able to shot ...
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Restoration of symmetry explicitly broken by anomaly
What is the meaning of the restoration at finite temperature of a symmetry that is "broken" by the presence of an anomaly. If the symmetry is not there why is it restored at finite ...
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Symmetry group of QCD
In "Remarks on the chiral phase transition in chromodynamics" (1984) by Pisarski and Wilczek it is stated that the (classical) global flavor symmetry is $SU(2)\times SU(2) \times U_A(1)$ ...
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1
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140
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Transformations generated by asymptotic Killing vectors
I want to know how tensors transform under the transformations generated by Killing vectors. In particular I am interested in asymptotic symmetries and asymptotic Killing vectors. In order to ...
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Question regarding the asymptotic values of out-of-time order correlators (OTOCs)
Quoting A bound on chaos by Maldacena, Shenker and Stanford:
Strong chaos, the butterfly effect, is a ubiquitous phenomenon in physical systems, explaining thermal behavior, among other things. In ...
user242231
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Resources to start research on the SYK model, with AdS/CFT in mind
What are the main resources to learn the SYK model, focusing more on the AdS/CFT side rather than pure condensed matter theory, assuming a comfortable background in QFT, GR, and a bit of bosonic ...
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Scaling of Precision in Measurements as inverse of square root of Mass of Objects involved
I am currently reading this article: Direct observation of deterministic
macroscopic entanglement https://science.sciencemag.org/content/372/6542/622
The line that I am referring to is in the second ...
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How does the Kalmeyer-Laughlin argument work?
I want to ask about the argument in the Kalmeyer-Laughlin paper that connects the Heisenberg Hamiltonian to a quantum Hall one. I know there is a related question about the same paper. My question is ...
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