All Questions
Tagged with quantum-field-theory general-relativity
292
questions
2
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0
answers
128
views
Prerequisites to learn/work on double copy theory and amplitude methods for gravity
I am a PhD student in classical gravity; specifically in BH perturbation and GW.
I am interested in learning about the double copy and the use of scattering amplitudes in understanding GW physics. I ...
32
votes
8
answers
5k
views
Explain to a non-physicist what goes wrong when trying to quantize gravity
I am not a physicist, but I'm trying to get a little bit of an understanding of why it is hard to extend the standard model with quantum gravity (i.e. why it's hard to combine QM and GR), cf. e.g. A ...
- 1,772
4
votes
1
answer
209
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 $$ds^2=-dt^2+b^2(t)d\vec x^2.$$
...
- 503
0
votes
1
answer
70
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Is the background independence of dynamics a necessary condition for physical theories?
I read in the answer of Lubos Motl to this question that
the dynamics of string theory is demonstrably background-independent
while
the (manifest) background independence is an aesthetic ...
1
vote
1
answer
92
views
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 ...
- 503
0
votes
0
answers
38
views
Bitensors at three or more space-time points
Bitensors, i.e. tensors at two points that have indices belonging to either of them, have been used in the literature quite a bit and there are many calculations involving them. They are the go-to ...
0
votes
0
answers
97
views
If dark energy has constant density, would it still be subject to quantum variations; would increase/decrease be symmetrical, or would one take over?
There are different suggestions, but it stills seems like the basic scenario is for dark energy to have constant density, as a property of space (and as represented by the cosmological constant in ...
- 15
0
votes
2
answers
69
views
Variation in the context of symmetries
I’m rephrasing a suggestion as a question because there was an aspect to it where I wanted to know more as well.
I have studied both general relativity and particle physics, though in both cases my ...
1
vote
0
answers
33
views
Accelerating frame of reference, fermions and probability conservation
I'm looking at solutions to the massless Dirac equation in an accelerating frame of reference in $(1+1)$-dimensions but the wave functions I get appear to violate probability conservation.
My ...
- 841
1
vote
0
answers
75
views
Use of mathematical structure on physics [closed]
I want resources for studying in detail the connection between the mathematical structures of physical theories and said physical theories.
For example, i know what a Hilbert space or a principal ...
0
votes
0
answers
49
views
How does the asymptotic metric fluctuation in $n \to m$ scattering relates to the soft factor in Weinberg's soft graviton theorem?
I'm reading arXiv: 1411.5745 [hep-th]. In Sec. 5, the authors show how the memory effect and Weinberg's soft graviton theorem are two faces of the same coin. I'm interested in understanding a specific ...
- 22.1k
4
votes
0
answers
84
views
Is the only consistent massless spin-2 QFT really exactly General Relativity in the classical limit or only linearized limit?
I'm trying to understand to what extent it is a "miracle" that a massless spin-2 field "postdicts" general relativity. I think there is some early theorem of Weinberg that shows ...
- 7,398
0
votes
2
answers
645
views
Can we regard metric as the Higgs field of gravity?
The longer version of the question is: should we regard special relativity just as a spontaneous symmetry breaking phase of general relativity, driven by the non-zero vacuum expectation value (VEV) of ...
- 4,452
1
vote
0
answers
45
views
Calculating the Energy density of a static spherically symmetric Boson Star in the Newtonian Approximation using the Energy momentum tensor
I'm referring this paper here and I was trying to work out the calculation of the energy density which is the 00th element of the energy momentum tensor $T_{\mu\nu}$ which is given as:
$$
T_{\mu \nu}=\...
- 63
1
vote
0
answers
74
views
Exact solution to the Mukhanov-Sasaki equation for a massless scalar field
I am reading some cosmology review papers and I am at the section in which the equation of motion for a massless scalar field in a de Sitter spacetime is derived. The equation of motion for the ...
- 11
2
votes
1
answer
158
views
Is there a general argument for why non-dynamical degrees of freedom show up in the propagation of massless gauge bosons?
In both spin-1 and spin-2 gauge theories, the gauge bosons (e.g. the photon & gluon and the graviton respectively) have two physical degrees of freedom, which can be observed quantum mechanically ...
- 858
1
vote
2
answers
152
views
Whether vacuum energy gravitate?
What is the relationship between vacuum energy and gravity, particularly in terms of gravitational effects and its contribution to the overall cosmological constant? Does vacuum energy possess ...
1
vote
0
answers
68
views
Calculation of the source term for the Einstein-Dirac equation in the weak field limit
I have seen the same being done for Einstein- Klein Gordon equations quite successfully. However, I'm struggling with it in the case of the E-D equations. I know that the einstein equations in the ...
- 63
4
votes
1
answer
152
views
Is quantization chart-dependent?
I have a bit of confusion because when doing QFT and QFT in curved spaces this particular issue seems to be avoided.
I have this feeling that when we quantize a theory, we somehow choose a chart and ...
3
votes
0
answers
123
views
One-loop gravity $\beta$ function
Gravity is renormalizable at one loop, see e.g. Why is GR renormalizable to one loop?
What is the one loop gravity $\beta$ function?
- 5,707
2
votes
0
answers
34
views
Generating Functional for Massless Spin 2 Particle
I'm trying to derive the generating functional for a massless, spin 2 field. However, I am getting a left over term that needs to go away. I'm working in de Donder gauge so that $\partial_\mu h^{\mu\...
- 41
3
votes
0
answers
193
views
How do electrons interact with a graviton?
The spin of graviton is 2 and spin of electron is $\frac{1}{2}$. Of course, since electrons have mass, they pull each other in respect to gravitational force.
Whenever i tried to draw Feynman diagram ...
- 108
1
vote
0
answers
62
views
Studying the Renormalizability of classically equivalent theories
I am currently studying the effect that a massive, uncharged, non-minimally coupled spin $\frac{1}{2}$ field has on the background geometry upon quantization, and compare this with results in General ...
- 353
7
votes
2
answers
1k
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How can the graviton be both massless and self-interacting?
Gravity is non-linear, so if it is mediated by gravitons, gravitons must interact with each other. On the other hand, the effects of gravity moves with the speed of light, so if it is mediated by ...
- 525
0
votes
0
answers
65
views
Axiomatic Theories [duplicate]
In Number Theory and other areas of Pure Mathematics, whatever theorems we have are there forever because they are derived logically from a set of axioms. I would like to know which theories in ...
6
votes
2
answers
496
views
Hawking Radiation without a horizon?
I’m reading this article for a straightforward derivation of the Hawking effect https://www.researchgate.net/publication/...
user310742
2
votes
0
answers
63
views
QFTCS: Spacelike Surfaces in Different Coordinates for Comparing Vacuum
For a globally hyperbolic manifold $(M, g)$ we can always pose a well defined Cauchy problem through a foliation in terms of pairs $(t, \Sigma_t)$ where $t$ acts as a time-coordinate and $\Sigma_t$ is ...
- 136
6
votes
1
answer
558
views
QFT on curved spacetime, uniqueness of spacelike hypersurface
Consider the Lagrangian of a real, scalar field coupled to gravity via the metric $g_{\mu\nu}$ and covariant derivative $\nabla_\mu$
$$\mathcal{L} = \sqrt{-g} (-\frac{1}{2} g^{\mu\nu} \nabla_\mu \phi \...
- 136
0
votes
1
answer
51
views
Equivalent theories of general relativity and graviton spin
Are there equivalent theories of general relativity that assume a graviton has a spin-1?
- 31
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1
answer
78
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Gravitational energy and its conservation in quantum field theory
How does conservation of energy in quantum field theories reconcile with gravitational energy that is not modeled with quantum field theories? Does this mean that conservation of energy is only ...
