All Questions
Tagged with quantum-field-theory cosmology
151
questions
2
votes
0
answers
44
views
Feynman rule from dynamical Chern-Simons
Consider the following action that
\begin{equation}
S = \int d^4x\sqrt{-g}\left(-\frac{1}{2}(\partial\phi)^2 + V(\phi) + \frac{2R}{\kappa^2}
- \frac{\phi}{4f}{}^*RR\right)
\end{equation}
where
\...
- 714
4
votes
1
answer
210
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
47
views
Electrons keeping dynamical quantum fluctuations?
I was thinking about this paper (https://arxiv.org/abs/1405.0298) where the authors argue that there wouldn't be dynamical quantum fluctuations in a De Sitter space as fluctuations would be static ...
- 2,462
0
votes
1
answer
102
views
Trapping Hawking radiation in black holes?
I was reading this writing (https://davidwoolsey.com/AttO/AttO_blog/Entries/2020/7/13_Black_Holes_and_Transverse_Tidal_Effects%2C_a_revised_essay_on_some_thoughts.html) about considering tidal effects ...
- 2,462
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
2
votes
0
answers
24
views
Why is there an infinite supply of energy in slow-roll inflation?
The physical model of inflation includes a metastable false vacuum, or a slow-roll field on a flat potential. In either case, I just realized how this is completely insane. With the exponential growth ...
- 619
1
vote
3
answers
145
views
Why doesn't frozen-out dark matter annihilate later during structure formation?
The so-called freeze-out of dark matter is based on a homogeneous description. However, in the later stages of the universe, where structures form, it seems very likely that the reaction rate would ...
- 619
2
votes
2
answers
98
views
Why does the mechanism producing matter-antimatter asymmetry keep our universe electrically neutral? Any general argument?
I've noticed what seems to be a fine-tuning issue. To be more specific, electric neutrality implies that the amount of lepton asymmetry produced through some unknown processes precisely cancels out ...
- 619
0
votes
0
answers
52
views
False Vacuum State (QFT)
I am wondering if someone can refer me to a proof that the false vacuum state is a natural consequence of scalar field theories? I see that being said in a lot of texts on cosmology when discussing ...
- 1
0
votes
0
answers
99
views
Three-Point correlation function in cosmology
I have been studying this review article on Non-Gaussianity from inflation. It was mentioned that $n$-point correlation function can be obtained by the expression
\begin{equation}\label{eq:1}
\langle\...
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
1
vote
1
answer
89
views
Cosmological Constant Problem calculations involving energy densities
I am following Timo Weigand lecutre notes on QFT, on page 28, he breifly touches on the Cosmological Constant Problem.
But I am a little confused.
He begins with a Lagrangian and include a nonzero $V_{...
- 489
4
votes
1
answer
99
views
What do the authors of the paper mean here exactly by path integral?
First of all, please forgive me if i am asking a dumb question. I don't have a physics background. I was reading this paper by Hawking & Hertog on populating string theory landscape and came ...
- 67
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 ...
0
votes
2
answers
122
views
Quantum fluctuations and symmetries?
While reading this piece about symmetry breaking, in section 3 I came across the term "anomalous symmetry breaking", which happens when a symmetry is broken by quantum fluctuations:
Let us ...
- 2,462
2
votes
0
answers
48
views
Fourier expansion of positive and negative fields in In-In formalism
Recently, I am reading articles regarding In-In formalism, Schwinger-Keldysh formalism.
One advantage of this formalism is it is easy to construct the expectation values of operators in-state without ...
- 3,622
3
votes
1
answer
276
views
Can we just use the uncertainty principle to explain something from nothing? [closed]
I have been following the argument related to the early universe and the emergence of matter-energy from nothing.
They often refer to the notion of quantum fluctuations.
But I wonder if a simple ...
- 489
3
votes
1
answer
362
views
What is the energy density of the inflaton field?
I am trying to compare the theoretically calculated vacuum energy density according to quantum field theory with the energy density of the inflaton field, in joules per cubic meter (or Pascal). I ...
- 65
2
votes
1
answer
138
views
Second Law of Thermodynamics and Particle Creation/Annihilation
I have a question regarding the second law of thermodynamics:
In most proofs of the second law of thermodynamics (like Jaynes' proof) the phase space is considered to be of constant dimension.
However ...
- 1,488
2
votes
0
answers
75
views
Perturbative reheating
Are there any inflation models in which reheating would start perturbatively? I mean the non-perturbative process named as preheating (via parametric resonance) would be either inefficient or absent ...
- 3,691
4
votes
0
answers
109
views
What is the best way to describe a classical field in quantum field theory (coherent state)?
In quantum field theory, we have the following expansion on a scalar field (I follow the convention of Schwarz's book)
$$\phi(\vec{x},t)=\int d^3 p \frac{a_p exp(-ip_\mu x^\mu)+a_p^{\dagger}exp(ip_\mu ...
- 442
3
votes
1
answer
100
views
Which of these 2 ideas is correct about a "bubble" of false vacuum decay?
The whole volume of the bubble is true vacuum.
Only the surface layer of the bubble is true vacuum while the interior has turned back to false vacuum.
0
votes
1
answer
48
views
Commutation calculation and interpretation of Dirac equation solution acting on a vacuum
I have been solving this relatively simple problem of QFT:
$$<0|\psi_d(\vec{x})|\vec{p},s,c>$$
where
$$\psi_c(x)=\sum_s\int\frac{d^3p}{{(2\pi)}^3} \frac{1}{\sqrt{2E_p}} [b^s_{c,p}u^s(p)e^{ipx}+c^...
- 47
0
votes
1
answer
87
views
Is the early universe cosmology phase transition thermal or quantum? WHY?
In this question How does SSB happen?, one of the answers assumes the nature of the early universe phase transition to be thermal. I need to know why can't such phase transition be a quantum phase ...
- 1,268
7
votes
0
answers
132
views
Is GR the only theory in physics which cares about absolute energy?
In my QFT course, they justify dropping the vacuum energy as 'physics only cares about relative energies except for GR in the stress-energy tensor'.
Is this strictly true?
- 2,604
2
votes
1
answer
329
views
Fokker-Planck equation from Langevin equation in stochastic inflation
I'm reading this paper by Starobinsky and Yokoyama where they give the coarse-grained equation of motion,
$$
\dot{\bar{\phi}}({\bf x},t ) = -\frac{1}{3H}V'(\bar{\phi}) + f({\bf x},t)
$$
where $f({\bf ...
- 574
0
votes
0
answers
89
views
Quantum fluctuations in the early universe
A Quanta Magazine article on the relationship between inflation and the large-scale structure of the universe mentions the relationship between the spatial distribution of galaxies and quantum ...
- 576
0
votes
2
answers
83
views
Are there introductory reviews of trans-Planckian physics and inflation? Looking for something similar to Daniel Baumann's cosmology notes
Are there introductory reviews of trans-Planckian physics and inflation? Looking for something similar to Daniel Baumann's cosmology notes - things are explained assuming minimal background.
2
votes
1
answer
173
views
Decay of the time derivative of solutions of the Klein-Gordon equation in decelerating expanding space-times
Suppose that we have a model of a universe* given by a flat FLRW metric.* In short, the model universe has $n\in\mathbb N$ dimensions, is homogeneous, isotropic and its expansion is governed solely by ...
2
votes
2
answers
125
views
How should we deal with interactions not from a “fundamental force”? [closed]
Question
Should the cosmological constant and/or vacuum energy be listed as one of the fundamental interactions?
If not, how can we have actual energy and forces that are not assignable to one of the ...
- 3,365