Questions tagged [qft-in-curved-spacetime]

Quantum field theory in curved spacetime (QFTCS) is a field of study that focuses on problems that arise when considering a quantum field on a fixed, curved spacetime. It allows the study of quantum effects in strong gravitational fields, and has led to many interesting conclusions, such as the Unruh effect and the Hawking effect.

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Hawking radiation question

A stationary observer near the black hole horizon will detect Hawking radiation proportional to their local acceleration. If we call $\alpha=\frac{GM}{r^{2}}\frac{1}{\sqrt{1-\frac{2GM}{r}}}$ the ...
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Emergent Gravity

One thing that I did not understood yet is how some physicists think of gravity, fundamentally, as a emergence phenomena? I see much of this "belief" through fluid dynamics approach to study ...
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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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Could the curvature of spacetime, as in general relativity, result from the interaction of quantum fields?

If both the general and special theories of relativity deal with space as spacetime, then the special theory of relativity deals with spacetime as flat, and the general theory of relativity deals with ...
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Some resources on quantising spin 2 fields in flat and curved space time

I want to understand how one can quantize spin 2 fields. Any resource which starts with a flat background before moving on to curved backgrounds would be great. So far, I have found this article but I ...
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Interacting QFT construction on curved spacetime

As far as I can tell, most of the concrete models considered in (rigorous) QFT on curved spacetime are either free or perturbative. In fact the only construction of an interacting QFT on curved ...
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Interpretation of temperature in General Relativity

I am reading the historical article by Hawking and Page. Their exposition of the Hawking-Page transition differentiates the notion of temperature in both AdS and SAdS spacetimes, as both of these ...
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How do we define the Heisenberg picture within functorial/path integral QFT?

In the functorial approach to QFT, each Cauchy surface $\Sigma$ has an associated Hilbert space $\mathcal{H}_\Sigma$, and each pair of Cauchy surfaces $\Sigma,\Sigma'$ has an associated unitary $U_{\...
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An example of the vacuum emitting photons?

Imagine we have two parallel wires with a potential difference of $V$ volts that form the opposite sides of a square of size $\lambda$. Any virtual electron-positron pairs that form between the wires ...
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Scattering cross-section in Curved space-time

Consider the following two definitions for differential cross-section $\sigma(\theta,\phi)$ that one often encounters in classical mechanics and in non-relativistic quantum mechanics: $\textbf{...
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What does general relativity's metric tensor have to do with quantum electrodynamics?

Sabine Hossenfelder recently posted a YouTube video titled, The Closest we have to a Theory of Everything. At 9:15, she shows the action $S$ for electrodynamics and, immediately after, the Einstein-...
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Review paper or book on Hawking radiation [duplicate]

Could someone suggest a book or a recent review on Hawking radiation? It should contain introductory material and possibly compare different theories and give some hint on possible observation.
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Do the null geodesics of photons emitted by Hawking radiation arise from the event horizon?

It is a well-known explanation of Hawking radiation that it originates from the quantum fluctuations near the horizon. Does it mean that one can look at the photons (part of the radiation) and follow ...
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How (if) is the metric of the quantum vacuum different from the metric of the classical vacuum?

The classical vacuum, with no matter or energy in it, has a flat metric. Meanwhile we know that the classical vacuum is a chimera. There are lots of things going on, even though it is called virtual. ...
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Symmetry restoration in accelerated frames

I am trying to understand the symmetry restoration in accelerated frames. I was reading 1 and 2. Can somebody help me to understand how they got Eq. 7.12 in 1 or Equation just after Eq.3.3 in 2? In ...
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In and out states of scattering in Asymptotically flat spacetimes

I am reading a paper called "New symmetries of massless QED", written by Temple He, Prahar Mitra, Achilleas P. Porfyriadis and Andrew Strominger (https://arxiv.org/abs/1407.3789). At some ...
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Riemann curvature tensor in an inertial frame

My understanding is that the mathematical definition of an inertial frame at $x_0$ is a choice of coordinates s.t: $g_{\mu\nu}(x_0) = \eta_{\mu\nu}(x_0)$ $\partial_\rho g_{\mu\nu}(x_0) = 0$ I've ...
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Carroll's derivation of Hawking radiation

In Carroll's Spacetime and Geometry: An Introduction to General Relativity, in his derivation of Hawking radiation Carroll makes the following statement: "as observed over length and timescales ...
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What does "conformally coupled scalar" mean?

"Conformally coupled scalar $\phi$" - I encounter it a lot, but I can't find what it means.
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Hawking radiation: how can gravity rip a pair of virtual particles apart without creating another pair of virtual particles in the process?

To the best of my (limited) knowledge of theoretical physics you cannot rip a pair of virtual particles apart without investing enough energy to create another pair of virtual particles... If Hawking ...
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Energy-momentum relation for Dirac spinor in curved spacetime

Consider the Dirac equation in curved spacetime \begin{equation} (i\gamma^\mu\nabla_\mu+m)\psi=0 \end{equation} where $\gamma^\mu=e^\mu_a\gamma^a$ is the curved spacetime Gamma matrices, and the ...
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On the history of field theories on curved spacetime [closed]

I would like to know what were the first actors studying the subject and the first articles written about it; also the first problems and results. If it's possible also the main steps in the evolution....
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Rindler decomposition using Euclidean path integral

In section 3.3 of Jerusalem Lectures on Black Holes and Quantum Information (arXiv:1409.1231), Daniel Harlow wants to calculate the following Euclidean path integral $$\langle\phi |\Omega\rangle\...
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In QFTCS, is the indeterminacy in the local energy density due to vacuum particle-antiparticle creation?

In QFT in curved spacetime, there is an indeterminacy in the local energy density (because of the indeterminacy in defining annihilation/creation operator) if the spacetime is not stationary. Is it ...
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In Hawking's original Hawking radiation paper, how can we understand where the radiation comes from in the collapsing star spacetime?

In the original Hawking's paper "Particle creation by black holes" he first studies the collapsing star spacetime, and then the quasi-stationary phase of the black hole. In the collapsing ...
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Stress tensor trace anomaly in two dimensions

I'm trying to calculate the expectation value of the stress tensor in 2D following the book "Quantum fields in curved space" (Birrell and Davies). In 2D the divergent contribution to the one-...
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How to derive the Unruh effect (or the thermofield double state) from the path integral?

I have been reading about the path integral approach to deriving the thermofield double state for the Minkowski vacuum in terms of the Rindler states: \begin{equation} \left|0_{M}(t=0)\right\rangle=\...
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$SU(N)$ gauge theory in black hole background

Assume you have standard $SU(N)$ gauge theory in a (non-asymptotically flat) black hole background (i.e., near the center of the black hole). Given the extreme pressure and temperature, I assume that ...
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Questions about the Unruh effect derivation in Wald's QFT in curved spacetime

So I'm currently reading chapter 5 of Wald's book on QFT in curved spacetime and I'm terribly confused with the notation in the last steps of his Unruh effect derivation. Context: In eq. 5.1.26, he ...
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The Equivalence Principle necessitates a mixed state description for the exterior of a black hole?

I am going through this review paper on the black hole information paradox. In section 2.2 page 10, the author argues the following: One of the basic tenet of general relativity is the Equivalence ...
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Why do we need a boundary condition in quantum field theories?

When we discuss quantum field theory defined on manifolds with a boundary, we always choose a boundary condition for the fields. And the argument usually says that we need the boundary condition to ...
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Is the experimental evidence confirming black hole entropy or Unruh radiation?

The question says it all: how does Bekenstein–Hawking entropy or radiation fare when compared with observation? Or maybe just the idea of Unruh radiation?
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Gravity's self-energy

Suppose we have a single massive point particle. In the absence of "potentials", the content of the stress-energy tensor would be dictated uniquely by the particle's mass and trajectory (...
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In the Unruh effect, where does the energy of the particles come from?

If you accelerate an object with constant acceleration, you will in effect create a black hole in the opposite direction in which you are traveling. This being due to light rays at a certain distance ...
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How can black holes evaporate into photons if they contain no anti-matter?

Hawking theorized the evaporation of black holes. Photons are pictured to slowly radiate their mass away. The higher the mass the longer it takes (due to smaller tidal forces). Which makes one ...
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4 votes
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Quantum pressure and chemical potential for a Schwarzschild black hole?

Just as Hawking showed that even Schwarzschild black holes have a temperature, shouldn't they also have a pressure and chemical potential? Are there any analytical formulae of those as well as $$ T_{...
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How does the quantum wave function behave within a black hole?

We have recently studied the wave function in physics and I was wondering how this behaves within a black hole, since within a black hole position cannot be determined so surely the wave function ...
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Quantum Field Theory on non-globally hyperbolic spacetimes?

In all the references I have found on QFT in curved spacetime, they treat only globally hyperbolic Lorentzian spacetimes, not Lorentzian spacetimes in general. Are there any references which discuss ...
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Commutation relations (QFT curved spacetime Wald)

So I'm currently reading Wald's QFT on curved spacetime. In section 2.3, he constructs the quantum theory of $n$ decoupled harmonic oscillators by choosing $\mathcal{H}$ as the set of positive ...
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Nuclear physics on gravitational background

Is there any treatment on nuclear physics in strong gravitational fields? (I tried to search over the Internet, but found references only on QFT on gravitational background)
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Why can't we use expected values for a "quantum general relativity"? [duplicate]

So, the equations for general relativity are as follows: $$G (mu, nu) = ĸ T (mu,nu)$$ I was told, that since energy, momentum and other observables are quantum then the stress-energy tensor $T$ is ...
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Why can't the information inside a black hole be reconstructed from what's left outside?

In trying to understand the significance of the black hole information paradox: regardless of what happens to information inside a black hole; how come it cannot, in principle, be reconstructed by ...
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Can the energy of a black hole's quantum field escape its event horizon?

From what I've read, Hawking radiation is produced far outside the event horizon. The radiation is produced by the quantum field of the black hole outside the event horizon. As more of these ...
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Question on the proof of Hawking radiation as done in "Quantum fields in curved space - Birrell,Davies"

In their proof of Hawking radiation, Birrell and Davies consider two dimensional model of a collapsing star with two set of coordinates, one outside the star: $$ds^2=C(r)du \space dv \tag{8.8}$$ $$u=t-...
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Physical significance of number operator in QFT

Does the expectation value of the number operator corresponds to any physical observable or has any significance in classical limit? This is probably a dumb question, but I'm struggling to identify ...
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Does wavefunction collapses near event horizon? [closed]

Picture an electron falling into an event horizon, so far from what I read gravity is either not a force or it is extremely weak therefore it doesn't cause wavefunction to collapse unless the strength ...
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Do we need Killing vectors to have wave vectors in a plane wave solution?

It is well known, and there are other questions in this website that answer this, that one needs a stationary Killing vector field to judge if a plane wave has positive or negative frequency. If our ...
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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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Is formation of a black hole thermodynamically favourable?

Isn't it like that the black hole is just swallowing suns and other parts of cosmos, and thus continuously absorbing matter. I know that it emits radiations also, which should be negligible in terms ...
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Why Unruh temperature is the temperature measured by observer with $\xi = 0$?

My coordinate transformation is: \begin{align} t=\frac{1}{a} e^{a \xi} \sinh (a \eta), \quad x=\frac{1}{a} e^{a \xi} \cosh (a \eta). \end{align} The free scalar field is quantized under this ...
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