Questions tagged [quantum-gravity]
Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
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Making background curvature variable in QFT on curved spacetime
In QFT on curved spacetime one may start with a Klein-Gordon like equation
$$(\square_g - m^2 j) \phi = j,$$
where $\square_g := g^{\mu \nu} \nabla_\mu \nabla_\mu$ is the D'Alembertian operator, and $...
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Gravity cause wavefunction collapse? (Roger penrose) [closed]
Roger Penrose suggested that gravity might play a role in the collapse of the wave function (which describes a system as a superposition of multiple values of Position, momentum etc.). According to ...
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Is it possible that if the universe collapses, it reaches the same state as in its beginning? [closed]
Suppose the universe were to eventually collapse in a Big Crunch. How closely could the universe's final moments resemble those at the beginning of the universe? Could the universe return to its ...
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Introductory Reference for Asymptotically Safe Gravity
I have a fairly solid understanding of "classical" quantum field theory (Weinberg 1 & 2) and also of General Relativity with its various formulations. Being one that works in the field ...
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Is there a "unification" explanation of why the mixed gauge-gravitational anomaly cancels in the standard model?
Quoting the Review of Particle Physics (93.2.3):
all representations of SO(10) are anomaly free in four dimensions... the absence of anomalies in ... a SM generation can be viewed as deriving from ...
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Are non-trivial topologies in the gravitational path integral related to large gauge transformations in Yang-Mills?
While the gravitational path integral is not a well-understood concept mathematically, a number of works (particularly in recent research connected to AdS/CFT) emphasize the importance of integrating ...
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Number of 3-loop diagrams for 3-vertex correction
How would I determine the number of three-loop diagrams that are irreducible for the 3-vertex interaction of, lets say, a graviton where the internal exchange is only a scalar particle. I am sure ...
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Particles, strings, and field theories
I work in quantum field theory in curved spacetime. Within QFTCS, we have a bunch of phenomena showing that the notion of "particle" is quite subtle. For example, the Unruh effect let's us ...
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Would this experiment potentially work for detecting whether gravitons exist?
Take a primordial black hole and measure the Hawking radiation over a large amount of time by gamma-ray detectors, as well as a Large neutrino detector.
Using theoretical calculations about the ...
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Could the observed GZK limit exceeding cosmic rays be due to hawking radiation?
In this question here, it was asked whether a black hole could emit protons with energies exceeding the GZK limit via Hawking radiation, the answer given was yes. So I ask, what proportion if observed ...
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Do evaporating black holes emit gravitons? [duplicate]
Do evaporating black holes emit gravitons? I know that hawking radiation consists of photons, and that for very small black holes it can also consists of sun atomic particles, but what about gravitons?...
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Recommendation: Intermediate level books on quantum gravity
i have already read carlo rovelli's 'reality is not what it seems' and lee smolin's three roads to quantum gravity, how should i proceed from here and what books do i read that balance theoretical ...
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Why has it been so hard to come up with testable predictions for string theory? [closed]
String theory has yet to come up with any easily testable predictions despite decades of work.
Why is this? Why is it so difficult to come up with testable predictions for string theory?
Why is it ...
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Expansion about a background classical solution to the Kaluza-Klein five-dimensional field equations
This is a paper I am reading Five-dimensional quantum gravity and the residual length by Roberto Balbinot and Antonio Barletta.
I am not able to figure out how he got the expressions in equations 2.11-...
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How Atlas differentiated that the di-photon produced was not by a graviton but instead by a Higgs Boson decay?
The Wikipedia article here, https://en.wikipedia.org/wiki/Higgs_boson#Confirmation_of_existence_and_current_status , confirms (see "zero spin requirement" table row test) that the graviton (...
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Can gravity be the high-energy regularizer for QFTs?
In order for QFTs to be mathematically well-defined some sort of regularization scheme needs to be introduced, which typically looks like a discrete cutoff of all modes outside of some shell with ...
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Can a massless virtual graviton decay into a Higgs Boson and two γ-photons in the LHC at CERN? [closed]
Τheoretically, is it possible?
G--> H--> γγ
And if not, why?
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The relationship between dimensionality and space [duplicate]
The number dimensions defined by new theories keep going up. Is there a limit as to how many dimensions the universe can have?
Weird question. The curse of dimensionality in computer science ...
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Is quantum gravity compatible with unitary evolution?
I am thinking that they aren't strictly compatible. I have the following logical argument for this:
The unitary evolution postulate says that the state of a system is given by a time-depending state ...
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Estimating graviton background temperature
I want to estimate the the graviton temperature at $T=1$MeV assuming that the gravitons decoupled at $T \sim m_\text{pl}$, the Planck mass.
My reasoning was the following. We know that due to ...
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Why is Black Hole Information paradox so important to physicists?
It's a very general question. Black hole paradox is an interesting problem but why is it something that physicists are so worried about? As neither can it be directly experimentally tested nor do I ...
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Holographic derivation of correlations functions in $\text{AdS}_3$/$\text{CFT}_2$
Intro
I am interested in finding the correlations functions $\langle A^{a_1}_z(z_1) \cdots A^{a_k}_z(z_k) \rangle$ in the frame of $\text{AdS}_3$/$\text{CFT}_2$ correspondance for 3D gravity and two ...
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Why is the Polyakov action background dependent if gravitons are a property of string theories?
In a theory that predicts gravitons, shouldn't the background be flat and gravitational interaction then be modeled as a scattering event?
Answer included below.
Credit to /u/broguetrain on Reddit ...
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Superposition of Page times - is the Hawking radiation maximally mixed?
Suppose we have a black hole of mass $M$ at time $t_0$. The black hole has already been radiating Hawking radiation for some time. If no further mass is added to the black hole, suppose over half of ...
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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?
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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\...
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How do we determine when a modular Hamiltonian is local?
I'm trying to deepen my understanding of Von Neumann entropy (out of interest in the quantum Bekenstein bound) by learning more about the reduced density matrix (aka local density matrix), which is ...
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Writing Einstein-Hilbert and Gravity-matter Hamiltonian in terms of creation/annihilation operators
I am trying to understand how to write the gravity-matter and gravity-gravity hamiltonians in terms of daggered/undaggered operators. Is there any pedagogic review paper on writing such hamiltonians ...
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The relation between $F^2=f_{\mu\nu}f^{\mu\nu}$ and $H^2=H_{\mu\nu\lambda}H^{\mu\nu\lambda}$ [closed]
there are two papers https://arxiv.org/abs/hep-th/0411105 and https://arxiv.org/abs/hep-th/9406216. What is relation between the $H^2=H_{\mu\nu\lambda}H^{\mu\nu\lambda}$ in the second paper and $F^2=...
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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 ...
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Is there any empirical evidence for the existence of the graviton?
In the standard model of particle physics, there are four fundamental forces/interactions, each governed or conveyed by its respective fundamental particle:
Strong force: quark/gluons
Weak force: ...
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What are the constraints on a quantum gravity theory? [duplicate]
My question is: what are the main constraints or challenges that prevent us from finding a consistent and complete theory of quantum gravity? Are they conceptual, mathematical, physical, or ...
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Does Noether's theorem apply to bouncing black holes? [closed]
Noether's theorem states that every differentiable symmetry of the action of a physical system with conservative forces has a corresponding conservation law. Energy, however, is not conserved in an ...
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Is the quest for a theory unifying gravity and quantum mechanics just wishful thinking? [closed]
What is the basis of the believe that there should be a unified theory which simultaneously gives quantum physics (the regime small things moving very fast) and gravity (the regime of big things ...
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Loop Quantum Gravity vs Polymer Quantization
What is the linkage between Loop Quantum Gravity and the approach of the Polymer Quantization?
I know you get a lattice using the correct polymer representation, so that's a good toy model for the ...
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Why does square of Planck length come as coupling constant when quantizing gravity in 3+1D?
In Birrell and Davies, the author says in the Introduction that
If the gravitational field is treated as a small perturbation, and attempts are made to quantize it along the lines of quantum ...
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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 ...
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Do blackbodies emit gravitational waves?
It was previously my understanding that the reason blackbodies only emit light was because light was the only massless particle, so there exist excitations of the electromagnetic field of arbitrarily ...
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Why gravitational waves have 2 possible polarizations? [duplicate]
I was under the impression that light waves have 2 polarizations because even if the photon is spin 1, the photon is massless which imposes additional constraints. In the case of gravity, it is ...
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Gravitons in a vacuum
I'm new so please be nice if I don't know too much about anything.
I was kind of curious about the idea of gravitons in a vacuum. (using string theory, or even superstring theory.) if space is a near-...
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Why is it ok to set the dilaton to its classical value in Jackiw-Teitelboim (JT) gravity?
I am reading arXiv:1606.01857 (Maldacena-Stanford-Yang), one of the main papers on Jackiw-Teitelboim (JT) gravity. To derive the Schwarzian action, they use the classical solution for the dilaton, eq....
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Do black holes emit equal amounts of gravitons in addition to photons via Hawking radiation?
According to Hawking’s theory, black holes have temperatures inversely proportional to their masses and emit photons like an ideal black body. However, besides EM radiation there is also gravitational ...
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References to difficulties with quantization of gravity?
We always hear from the community that gravity is difficult to quantize, and quantum gravity field theories have some difficulties in terms of renormalization and are associated with quantum anomalies,...
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Perturbative non-renormalizability and viability?
Does perturbative non-renormalizability indicate the unviability of the theory if we were to define it non-perturbatively (for example through a lattice discretization of the continuum QFT or other ...
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How is a black hole compatible with quantum theory? [duplicate]
A black hole has a radius of $R = \frac {2Gm}{c^2}$, in this context, if we take a single proton and neutron as a black hole, its Schwarzschild radius will be near about $4.8 \times 10^{-52} \mathrm{m}...
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Breakdown of quantum mechanical observables in cosmology
In several different contexts, I've heard the claim that quantum gravity in an accelerating universe messes with our ability to define precise quantum observables.* One version of the argument goes ...
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Research progress in the symmetries of flat space holography
I was studying the papers
[$1$] Arjun Bagchi. The BMS/GCA correspondence
[$2$] Duval, C., Gibbons, G. W., & Horvathy, P. A. (2014). Conformal carroll groups. Journal of Physics A: Mathematical ...
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Why doesn't the double slit experiment disprove general relativity? (or vice-versa for G.R. tests with Q.M.) [closed]
I learned that General Relativity and Quantum Mechanics are fundamentally incompatible models of the world, yet we have observations with evidence for both. Thus, I am confused about why we cannot ...
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How to derive gravitational path integral from the Hamiltonian operator formalism?
How does one derive the gravitational path integral $\int [dg]\exp(iS_{\text{EH}}/\hbar)$ from the Hamiltonian operator formalism?
The connection between the Hamiltonian operator formalism and the ...
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Jackiw-Teitelboim (JT) gravity as a matrix integral
I am reading https://arxiv.org/abs/1903.11115 by Saad, Shenker and Stanford. They relate an (averaged) $n$-point function in a random double-scaled matrix model to a path integral genus expansion in ...
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