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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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Are there exactly solvable problems in curved space, except for cases of constant curvature of space?

I have two questions. I know the expressions for geodesic distance in Minkowski, de Sitter and anti de Sitter space-time and their Euclidean analogues $R^n$, $S^n$ and $H^n$ [1]. For what other curved ...
grodta's user avatar
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What does the word "Observable" mean in Quantum Gravity?

I have seen the statement in several places that the only "observables" in general relativity or Quantum Gravity are measured at temporal or spatial infinity. This is often used as a ...
Josh Newey's user avatar
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Quantum field expansion and bogoliubov coefficients in the interior of a rotating black hole

I am trying to quantize a real scalar field in the interior of a rotating black hole (3+1 D, asymptotically flat). My question is regarding the modes of the radial part of the equation (obtained after ...
Ratul Thakur's user avatar
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120 views

On which bundle do QFT fields live?

In QFT, there is a vector field of electromagnetism, usually notated by $A$, which transforms as a 1-form under coordinate changes. Since quantum fields are operator-valued, I thought it is a section ...
Sung Kan's user avatar
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Gravitational waves created by quantum fluctuations as the source for dark energy and dark matter [closed]

Two generally accepted principles: Quantum fluctuations generate gravitational waves (Axion monodromy and inflation by Albion Lawrence, Brandeis/NYU) Gravitational waves can be absorbed (Numerically ...
VMT's user avatar
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Bogoliubov transformation of Bunch-Davies vacuum

Let $\left|0\right>$ be the Bunch-Davies vacuum state of a QFT, for example a free scalar field, in de Sitter space. The creation and annihilation operators w.r.t. this state is a vacuum, i.e. $a^...
Aralian's user avatar
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Canonical commutation relations of quantum fields in null coordinates

To quantize a scalar field, we impose the equal time commutation relations $$ [\Phi(t,\mathbf{x}),\partial_t\Phi(t,\mathbf{x}')] = i\hbar\delta^{(3)}(\mathbf{x-x'}). $$ This can also be generalized to ...
Ratul Thakur's user avatar
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Quantum experiments at different heights from Earth

If one were to perform the same Quantum mechanical experiment say the double slit experiment or any other quantum mechanical experiments with identical conditions, set ups and elements. while ...
Precious Adegbite's user avatar
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39 views

Is there an analogous Unruh effect for observers on a rigidly rotating ring?

I read up on the Unruh effect recently and what I got from it is that its basically a result of transforming to Rindler coordinates and using a Bogoliubov transformation to change the creation and ...
Aravind Karthigeyan's user avatar
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Can we define a quantum mechanical system on top of a classical GR spacetime? [duplicate]

I've heard my entire life that QM and GR are incompatible, but I don't exactly understand how. There are other questions about that general question, e.g. A list of inconveniences between quantum ...
user56834's user avatar
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Is there any notion of spin-statistics in curved spacetime?

It is a well established fact that all known particles obey either Fermi-Dirac statistics (for fermions) or Bose-Einstein statistics (for bosons), at least in the context of relativistic quantum ...
ouroboros's user avatar
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Does information always gravitate?

I'm trying to wrap my head around Bekenstein's loose argument that a bit of information added to the black hole corresponds to an added Planck surface area to its horizon. In it, he argues that one ...
Lourenco Entrudo's user avatar
4 votes
1 answer
187 views

Is gravitational particle production due to symmetry breaking?

A well-known fact about QFTs in curved spacetimes is that there is a phenomenon of particle production in expanding universes, these being described by the line element $$ds^2=-dt^2+b^2(t)d\vec x^2.$$ ...
TopoLynch's user avatar
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What if acceleration changes in the Unruh effect?

Based on the Unruh effect, when a observer accelerates then he will see a thermal bath. mathematically the vacuum state for a non-inertial observer is $$|0\rangle=\text{cos}^{-1}(r)\sum_{n=0}^{\infty}\...
reza's user avatar
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Non-Hermiticity of the Dirac Hamiltonian in curved spacetime

In flat spacetime, Dirac fermions are classically described by the action $$ S=\int d^Dx\;\bar\psi(x)\left(i\gamma^a\partial_a-m\right)\psi(x). $$ One can generalize this to a general curved spacetime ...
TopoLynch's user avatar
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Does the positive energy particle emitted from Hawking radiation directly equate to the amount of mass contained within the black hole?

With virtual particle-antiparticle pairs in Hawking radiation, one member of the pair falls into the black hole, typically with negative energy, while the other escapes, typically with positive energy....
Pinto's user avatar
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On the local form of the spin covariant derivative: is this an exterior derivative of a spinor?

I'm reading Hamilton's Mathematical Gauge Theory. I'm currently on section 6.10, about the spin covariant derivative. Letting $S$ be the (Dirac) spinor bundle, a section $\Psi \in \Gamma(S)$ can be ...
Níckolas Alves's user avatar
1 vote
2 answers
71 views

Hawking-like radiation will probably be difficult to detect (even if it can be detected). Why is that?

I was having a conversation in another physics forum about horizons (like the event horizon of a black hole, or a cosmological horizon) emitting Hawking radiation and I mentioned that if the universe ...
vengaq's user avatar
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4 votes
1 answer
159 views

Question regarding the backreaction of a scalar field in curved spacetime

Lets assume that I start with the following action: $$ {\mathcal L}_1 = \frac{1}{2} \sqrt{-g} \left( \partial_\mu \phi \partial^\mu \phi - m^2 \phi \right) $$ where $g_{\mu \nu}$ is a FRW metric and $\...
Rednuth's user avatar
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Scattering approach for massless scalar Hawking radiation and Bogoliubov coefficients in Schwarzschild metric

Reflection coefficient from the scattering approach in tortoise coordinates, looks exactly like relationship between modulus squared of Bogoliubov coefficients. However I'm not able to figure out a ...
Sachin Vaidya's user avatar
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1 answer
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Dervation of the first-order Klein-Gordon equation

How to derive the first-order perturbed Klein-Gordon equation: $$ \square \phi=\left[\frac{1}{\sqrt{-g}} \partial_{\mu}\left(\sqrt{-g}g^{\mu\nu} \partial_{\nu} \right) \right]\phi=0$$ For a first-...
Dr. phy's user avatar
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Hawking Radiation paradox

How does Hawking radiation help in information conservation? Doesn't it create a paradox, as the particle-antiparticle pair created at the event horizon has nothing to do with the matter that has ...
Bhavya Panda's user avatar
6 votes
1 answer
129 views

Does a localised particle created with a QFT on curved spacetime follow geodesics?

I was wondering if there is a result, analogous to the Ehrenfest theorem in quantum field theory (QFT), and in particular if the QFT is on a curved spacetime. In the last case, I would expect to ...
Sebastiano Tomasi's user avatar
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1 answer
121 views

Black hole information paradox

I read that it is generally believed that information is preserved in black hole evaporation, and people's views only diverge when it comes to how information is preserved. Is this true?
FACald's user avatar
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How do Geometric and Gauge symmetries interact in Curved space-times?

I am having trouble calculating the Noether charges of a charged particle in a curved background. To be more precise, I am considering a charged massive particle in a given coordinate system of the ...
MultipleSearchingUnity's user avatar
1 vote
1 answer
54 views

Unruh Radiation from hovering?

I know that masses on their own don't produce Unruh radiation outside of black holes which produce a similar effect known as Hawking radiation. However, what if some observer hovers above the Earth ...
Roghan Arun's user avatar
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How to derive the graviton propagator in curved spacetime?

Is it possible to derive the graviton propagator in curved spacetime from the graviton propagator in Minkowski spacetime?
physics_2015's user avatar
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1 answer
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Does matter in the outside universe affect Hawking radiation? [closed]

Is there a way to modify the event horizon to make it generate other particles by affecting quantum fields outside with a giant charge increasing quantum foam disruptions affecting the radiation? Is ...
Roghan Arun's user avatar
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Don't all objects that collapse have an apparent event horizon and so Hawking radiates?

So say there is an object that is in the form of gas and dust and a core that weighs 10 earths is in the center and there is a sphere of gas around it that weighs 50 Earths, so the final mass is only ...
Roghan Arun's user avatar
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Hawking radiation: what does a new external particle have to do with the mass of the black hole?

This question has been asked a few times here in a few different ways but the answers don't quite seem to land for me. Considering the virtual particle pair; one falls in, one escapes, both become ...
jazamm's user avatar
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3 votes
0 answers
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Relation between the Casimir energy and the central charge in CFT in general

In 2d CFT we know that the Casimir energy of the vacuum is proportional to the conformal central charge $c$. $$ F_L=f_0 L-\frac{\pi c}{6 L} \tag{1} $$ where $F$ is the free energy and L is the ...
Lu Zhang's user avatar
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41 views

Why are greybody factors necessary when dealing with Hawking radiation?

According to Wikipedia, greybody factors are corrections to the black hole Hawking radiation spectrum. They say that at the horizon the emission is that of a perfect black body, but the gravitational ...
Níckolas Alves's user avatar
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59 views

4-graviton vertex of which one is an emitting graviton

For a four graviton vertex function, suppose $h_{\alpha\beta}h_{\gamma\delta}h_{\varepsilon\zeta}h_{00}$, of which $h_{00}$ is the emitting graviton to infinity. Now if we associate four-momenta $p_1$,...
NovoGrav's user avatar
2 votes
0 answers
40 views

Sigma-Omega model on curved space-time

I'm trying to get the equations of motion for the scalar meson $\sigma$, vector meson field $\omega_{\mu}$ and finally for the nucleons $\Psi=(\Psi_n,\Psi_p)^{T}$ in the sigma omega model on a curved ...
martín canullán's user avatar
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0 answers
75 views

Point-splitting regularization for anomaly in curved spacetime

In flat spacetime, the point-splitting regularization for (chiral) anomaly is discussed in great details in Peskin and Schroeder's QFT. Does anyone know any good references for calculating anomaly ...
6 votes
1 answer
352 views

Why are von Neumann algebras not suitable for dealing with Locally Covariant Quantum Field Theory in Curved Spacetime?

I recently came across this post by Valter Moretti concerning the utility of von Neumann algebras in mathematical physics. In it, he mentions The closure of von Neumann algebras with respect to the ...
Níckolas Alves's user avatar
2 votes
2 answers
150 views

Does Hawking radiation depend of what's inside a black hole?

Or is it entirely based on the existence of an event horizon? Does the fact that black holes radiate depend on any properties of its interior?
Manuel's user avatar
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3 votes
1 answer
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Would pair production be affected by general relativity?

Given that during pair production a very small amount of energy from the photon becomes gravitational potential energy in the particles, I was curious how this would be affected by general relativity? ...
Daniel Warland's user avatar
4 votes
0 answers
111 views

Precise formulation of the ER = EPR conjecture

Maldacena and Susskind have "formulated" the now famous ER = EPR conjecture in their paper Cool horizons for entangled black holes, but as of today, I have not find a quantum theorist who ...
THC's user avatar
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3 votes
0 answers
111 views

Klein-Gordon mode functions in curved spacetime

I'm currently tackling QFT in curved spacetimes for the first time, mainly using "Quantum fields in curved space" by Birrell and Preskill's notes on QFT in curved spaces, to get a general ...
Ric's user avatar
  • 113
3 votes
1 answer
79 views

Cauchy problem for the Klein-Gordon equation

Let $(M, g_{\mu\nu})$ be a globally hyperbolic spacetime and let $\Sigma$ be a spacelike Cauchy surface. The covariant Klein-Gordon equation has a well-posed initial value formulation, in the ...
Ric's user avatar
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1 vote
1 answer
135 views

Choice of hypersurface in Klein-Gordon inner product

Let $M$ be a globally hyperbolic spacetime, with metric $g_{\mu\nu}$. Consider the covariant Klein-Gordon equation $$(g^{\mu\nu}\nabla_{\mu}\nabla_{\nu}+m^{2})\phi=0$$ Define the following indefinite ...
Ric's user avatar
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Orthonormality of the mode functions of the Klein-Gordon field in a globally hyperbolic space

In chapter 3 of "Quantum fields in curved space" of Birrell and Davies, the authors make the following statements. Consider a real Klein-Gordon field $\phi$ in a globally hyperbolic ...
Ric's user avatar
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Symplectic basis for the real solution space of the covariant Klein-Gordon equation

In lecture 12 of his course on "Quantum field theory for cosmology", that can be found for free on the web, professor Kempf makes the following statements. Consider a real Klein-Gordon field ...
Ric's user avatar
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3 votes
1 answer
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Counterexample to the observable algebra of a region and its causal completion being the same

I was reading a paper by Ed Witten called "Algebras, Regions and Observers". It can be found here: https://arxiv.org/abs/2303.02837 A major theme is theorems relating the algebra of ...
Andreas Christophilopoulos's user avatar
7 votes
1 answer
1k views

What is the Hilbert dimension of a Fock space?

Quantum field theory in curved spacetimes is often described in the algebraic approach, which consists of describing observables as elements of a certain $*$-algebra. To recover the notion of a ...
Níckolas Alves's user avatar
-2 votes
1 answer
141 views

Black holes as Quantum Computers

I have been hearing lately that Black holes could be Quantum Computers or that some processes in a black hole simulate the operation of Quantum Computers. This is not my field of study, but I am ...
8 votes
1 answer
565 views

Could information be transferred through a wormhole?

There was a paper published recently about the possibility of sending messages through a wormhole,see reference here. It has also been speculated that any entangled pair of particles—even particles ...
Cristian Dumitrescu's user avatar
2 votes
0 answers
94 views

Can the General Relativity Energy Relation of the Static Patch of deSitter Space be Quantized?

I am trying to play around with quantum field theory in de Sitter space. In reading a lecture about General Relativity, I found that, in the static patch of de Sitter space, the conserved quantity of ...
Gabriel Turner's user avatar
4 votes
1 answer
197 views

Boundary conditions and field quantization in AdS

While studying the AdS/CFT correspondence, one encounters very early the example of a scalar field in AdS. The general solution to the Klein-Gordon equation in the limit $z\rightarrow 0$ may be ...
SouthernLion's user avatar

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