All Questions
59
questions
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
0
votes
1
answer
70
views
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 ...
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
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
1
vote
0
answers
88
views
Path integral of Quantum Gravity while keeping Einstein's relation satisfied
Suppose we have a field $\phi(x)$ and the metric field is $g_{\mu \nu}(x)$. The action is the functional $S[\phi (x) , g_{\mu \nu } (x)] $. We want to do the path integral:
$$\int d[\phi (x)] d[g_{\mu ...
- 6,355
5
votes
1
answer
294
views
On the range of validity of General Relativity and Quantum Field Theory in terms of energy and impact parameter (from Rovelli & Vidotto's book)
In Fig. 1.1 on page 5 in Rovelli & Vidotto's 2015 book Covariant Loop Quantum Gravity: An Elementary Introduction to Quantum Gravity and Spinfoam Theory (PDF), there is this graph giving a general ...
- 22.1k
7
votes
6
answers
1k
views
Limits of General Relativity and Quantum physics
I have often heard people say that you cannot use quantum mechanics and general relativity in particular regimes. Consider if we were to predict the orbit of the Earth around the Sun using quantum ...
- 433
1
vote
0
answers
59
views
Creation/Annihilation operators for general relativity?
I anticipate that GR would require these operators to be such that no QFT cannot accommodate their structure, and remain normalizable.
Nonetheless, I would also expect that a blind construction of ...
- 1,548
1
vote
2
answers
186
views
Is there a back-reaction in Hawking radiation?
Here, the following explanation for Hawking radiation in canonical quantum gravity is given:
The local energy density is well-defined as the 00 component of the stress-energy tensor. It is frame ...
-1
votes
1
answer
315
views
Research Proposal in Statement of purpose for integrated Phd Theoretical Physics [closed]
I wrote this following paragraph in my statement of purpose for my Integrated PhD Physics program in Theoretical physics at best research institute in India.
My research proposal in this field is to ...
- 195
2
votes
1
answer
1k
views
Graviton Scalar interaction - Feynman rules
Having the interaction lagrangian for scattering between two scalars and the graviton $h$
\begin{equation}
\mathcal{L}_{\phi \phi h}=\frac{\kappa}{2}\left(-\frac{1}{2} h_{\mu}^{\mu} \phi^{2} m^{2}+\...
- 900