All Questions
Tagged with cosmology quantum-field-theory
151
questions
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
361
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
137
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)
$$\phi(\vec{x},t)=\int d^3 p \frac{a_p exp(-ip_\mu x^\mu)+a_p^{\dagger}exp(ip_\mu ...
- 442
3
votes
1
answer
99
views
Which of these 2 ideas is correct about a "bubble" of false vacuum decay?
The whole volume of the bubble is true vacuum.
Only the surface layer of the bubble is true vacuum while the interior has turned back to false vacuum.
0
votes
1
answer
48
views
Commutation calculation and interpretation of Dirac equation solution acting on a vacuum
I have been solving this relatively simple problem of QFT:
$$<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
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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
327
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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