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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.

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Expression for energy dissipation in electron hydrodynamics

I was looking at the paper Hydrodynamic Description of Transport in Strongly Correlated Electron Systems by Andreev, Spivak and Kivelson. The paper covers how resistivity in an electron fluid depends ...
xyz1234's user avatar
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2 votes
3 answers
57 views

What is the dual asymptotic spacetime of a CFT on a particular flat manifold?

According to AdS/CFT correspondence, the dual theory of a boundary CFT on flat spacetime is defined on an asymptotically AdS spacetime. The nature of the bulk spacetime depends on the topology of the ...
Sanjana's user avatar
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1 vote
0 answers
22 views

How to derive Feffermann-Graham expansion for AdS Vaidya geometries?

Introduction The Feffermann-Graham expansion for an asymptotically AdS spacetime [0] looks like Poincare AdS but with the flat space replaced by a more general metric i.e. $$ds^2=\frac{1}{z^2}(g_{\mu \...
Sanjana's user avatar
  • 785
4 votes
1 answer
281 views

Why Dirac's spin-$\frac12$ theory proves wrong Kaluza-Klein theory?

I recently saw Sabine's short video that mentions that Dirac's spin-$\frac12$ theory proves wrong Kaluza-Klein theory unless supersymmetry is amended to the Kaluza-Klein. Is there a more detailed ...
Markoul11's user avatar
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0 votes
1 answer
63 views

Is there any deeper explanation behind this simple acoustic experiment?

my question is a bit inconvenient but let me explain: I recently saw an experiment for primary school where two strings are attended to a coat hanger (see here: https://www.youtube.com/watch?v=...
Blue2001's user avatar
  • 308
2 votes
1 answer
195 views

Determining free Fermi/Bose gas chemical potentials, given temperature, number density, and baryon density

I'm attempting to recreate some plots of individual particle chemical potentials from S. Reddy et. al.'s paper on neutrino interactions in hot and dense matter (of the same title). The specifics aren'...
10GeV's user avatar
  • 799
1 vote
0 answers
48 views

JT gravity metric - solution to the dilaton equations of motion

I am reading Closed universes in two dimensional gravity by Usatyuk1, Wang and Zhao. The question is not too technical, it is about the solutions to the equations of motion that result from the ...
schris38's user avatar
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2 votes
1 answer
143 views

Spontaneous Symmetry Breaking, Vacuum Degeneracy, and Goldstone Bosons applied to large gauge transformations

I am reading Strominger's lecture notes on the infrared structure of gravity and gauge theory. I am trying to understand subchapter 2.11, where the author focuses on the notions of "Spontaneous ...
schris38's user avatar
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0 votes
0 answers
17 views

Force on Neodymium Magnet due to Magnetic Field from Electromagnet

I am a mechanical engineer currently in a university research program, and my project involves mixing bonded neodymium powder (Magnequench for those who are interested) into a polymer in order to ...
Thomas's user avatar
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1 vote
0 answers
66 views

Rigorous justification for firewalls?

Jerusalem lectures by Harlow does a good job in giving a heuristic derivation of firewalls. But the details are not done and no reference is given except for a "related" calculation by ...
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0 answers
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Why do we expect isometries of bulk side to be equivalent to symmetries of the CFT?

One can clearly see that the AdS bulk isometries form the $SO(d,2)$ symmetry of the $d$ dimensional CFT explicitly. Why does this occur: why don't the isometries of the spacetimes match up or the ...
Sanjana's user avatar
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3 votes
0 answers
95 views

Why is empty AdS identified with CFT vacuum and what do excited states correspond to?

I have a few questions regarding the AdS/CFT dictionary regarding the state-state map. I have seen people identifying the empty AdS spacetime with a CFT vacuum. What do they mean by "empty" ...
Sanjana's user avatar
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7 votes
0 answers
83 views

How to derive the probability distribution of reduced density matrix eigenvalues for randomly chosen pure states in Page's theorem?

Motivation I am trying to reproduce the proof in Page's theorem as conjectured in the seminal paper Average Entropy of a Subsystem by Don N. Page. It is crucial in various resolutions of black hole ...
Sanjana's user avatar
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1 vote
0 answers
71 views

$(\mathcal{S}\mathcal{T})^3=\mathcal{S}^2=+1$ mistake in CFT big yellow book?

In Conformal Field Theory Philippe by Di Francesco, Pierre Mathieu David Sénéchal Sec 10.l. Conformal Field Theory on the Torus eq.10.9 says the modular transformation $\mathcal{T}$ and $\mathcal{S}$ ...
zeta's user avatar
  • 149
1 vote
0 answers
53 views

2-loop correction to the Beta function in Fradkin's OPE-based RG

In chapter 4.5 of Fradkin's book "Field Theories for Condensed Matter Physics" (page 81 in my version) he claims that "it is straightforward to see that this [the perturbative ...
Noctis's user avatar
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0 answers
123 views

Looking for research papers in General relativity to read as a non-expert

I work in tech but I at some point I almost took a career path into theoretical physics. I changed my studies very late to data science and machine learning (my last masters year) and before that I ...
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0 answers
55 views

Questions on Lorentz generators in Spinor-Helicity formalism

I have read the following PSE posts on Lorentz generators in Spinor-Helicity formalism: Total Angular Momentum Operator in Spinor-Helicity formalism Derivation of conformal generators in spinor ...
schris38's user avatar
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2 votes
1 answer
94 views

Questions on Britto-Cachazo-Feng-Witten (BCFW) recursion method

I am reading about amplitude techniques, such as the spinor-helicity formalism: more specifically, the BCFW recursion relations. The lecture notes I am reading are titled as Scattering Amplitudes, and ...
schris38's user avatar
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1 vote
0 answers
78 views

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 ...
just a phase's user avatar
3 votes
0 answers
290 views

Understanding the factorization of subleading soft contributions-massless QED

I am reading The SAGEX Review on Scattering Amplitudes Chapter 11: Soft Theorems and Celestial Amplitudes. In subsection 2.2, the subleading soft photon theorem is derived. The result is $$A^{\mu}=\...
schris38's user avatar
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1 vote
0 answers
101 views

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 ...
schris38's user avatar
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0 votes
1 answer
78 views

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 ...
Lukephil Brecht's user avatar
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1 answer
32 views

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 ...
jlim1234's user avatar
2 votes
0 answers
73 views

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 ...
Níckolas Alves's user avatar
6 votes
2 answers
255 views

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 ...
YaGoi Root's user avatar
0 votes
1 answer
63 views

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 ...
Sanjana's user avatar
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1 vote
0 answers
46 views

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, ...
just a phase's user avatar
3 votes
3 answers
150 views

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 ...
Vashu's user avatar
  • 629
0 votes
1 answer
70 views

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 ...
schris38's user avatar
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0 votes
2 answers
58 views

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 ...
Carinha logo ali's user avatar
0 votes
0 answers
68 views

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 ...
schris38's user avatar
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0 votes
0 answers
129 views

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\...
schris38's user avatar
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1 vote
0 answers
85 views

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 ...
schris38's user avatar
  • 3,982
1 vote
0 answers
33 views

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 ...
1 vote
0 answers
65 views

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) ...
schris38's user avatar
  • 3,982
3 votes
0 answers
179 views

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 ...
AccidentalFourierTransform's user avatar
1 vote
1 answer
194 views

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 ...
baba26's user avatar
  • 513
1 vote
0 answers
210 views

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-...
schris38's user avatar
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2 votes
0 answers
159 views

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_{\...
schris38's user avatar
  • 3,982
2 votes
0 answers
415 views

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 ...
Sonali Gera's user avatar
1 vote
1 answer
135 views

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 ...
schris38's user avatar
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2 votes
0 answers
113 views

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 ...
schris38's user avatar
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3 votes
0 answers
123 views

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 ...
schris38's user avatar
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-1 votes
1 answer
227 views

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 ...
AHMED RAZA's user avatar
0 votes
1 answer
141 views

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 ...
modellatore's user avatar
3 votes
0 answers
256 views

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 ...
Rosa Luxemberg's user avatar
1 vote
0 answers
84 views

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 ...
LionCereals's user avatar
3 votes
1 answer
144 views

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 ...
schris38's user avatar
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3 votes
0 answers
264 views

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 ...
schris38's user avatar
  • 3,982
4 votes
1 answer
235 views

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 ...
schris38's user avatar
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