All Questions
Tagged with cosmology quantum-field-theory
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
\...
- 704
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
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
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
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
328
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
6
votes
1
answer
348
views
What's the mathematical explanation of the emergence of magnetic monopoles during the early universe?
I would "simply" like to know the full mathematical explanation of:
Why do these topological defects occur in the first place?
And more importantly,
Why must these defects/particles carry ...
4
votes
2
answers
298
views
Scalar field displacement from the minimum of the potential gives rise to particles/dark matter, why?
In This paper (Kobayashi et al -- Lyman-alpha Constraints on Ultralight Scalar Dark Matter: Implications for the Early and Late Universe) it says, at the beginning of Section 3.1:
A light scalar ...
- 2,347
1
vote
1
answer
1k
views
What is time till false vacuum decay? (Which source is in error?)
https://arxiv.org/abs/1308.4686 says that the time till false vacuum collapse is just about the age of the universe:
ΛCDM ... can be achieved if the top quark pole mass is approximately 178 GeV
That ...
- 375
1
vote
1
answer
171
views
What is the third quantization and the creation and annihilation operators of universes?
We have only recently begun to undergo secondary quantization, and I know that for the introduction of the creation and annihilation operators, the existence of interacting quantum fields is necessary,...
- 956
7
votes
1
answer
511
views
Does zero point energy really contribute to the cosmological constant?
The zero point energy is usually supposed to contribute to the cosmological constant. And the mismatch between the small cosmological constant compared with the huge zero point energy is deemed as one ...
- 4,452
4
votes
0
answers
406
views
What is the current status or resolution of Greisen–Zatsepin–Kuzmin (GZK) cosmic-ray paradox?
The Greisen–Zatsepin–Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy.
A number of ...
- 4,336
1
vote
1
answer
69
views
Is the inflation theory based on the inflaton field or electronuclear force carriers decay? [duplicate]
Some sources introduce the inflaton field as the cause of the inflation period in the big bang theory, and some others relate it to the decay of electronuclear bosons. Which one of these is ...
- 11
8
votes
0
answers
258
views
The emergence of space-time from entangled states
I recently read an article by Yasunori Nomura (https://arxiv.org/abs/1711.05263), in which he says that space-time is an emerging phenomenon. At the same time, space-time disappears when the ...
- 956
4
votes
1
answer
79
views
Is the value of the scalar components of the Higgs field known?
As I understand the relevant popular sources (example), since the end of the Electroweak epoch, the Higgs field became fixed in the whole known Universe. Thus, we are somewhere on the deep blue part (...
- 8,247
6
votes
1
answer
147
views
Does Goldstone theorem have anything to do with Cosmic string
Cosmic strings are formed due to topological defects during symmetry breaking phase transition in early universe.
While Goldstone theorem states whenever we have continuous symmetry and it is ...
- 3,043
1
vote
1
answer
826
views
How are Dark Energy and the Inflaton Field related?
My understanding of Inflation Theory:
Before $10^{-35}$ seconds the universe began to cool and the Inflaton Field approached a false vacuum. When it reached this false vacuum, there was a constant ...
- 105
3
votes
1
answer
518
views
Cut-off energy necessary to avoid vacuum catastrophe
My understanding is that to obtain a finite vacuum energy density prediction from QFT, one must choose a cut-off point for the maximum allowed energy of a photon. Two seemingly natural choices are the ...
- 153
4
votes
2
answers
445
views
Can Higgs potential provide a cosmological constant?
Usually, in particle physics, people do not care about a constant term in scalar field potential. Rather, attentions are paid to the local profile at the minimum. But in the context of cosmology, the ...
- 3,691
1
vote
0
answers
85
views
To which particles does the inflaton field preferably couple?
I am studying the (p)reheating dynamics and I would like to know if it is a reasonable assumption to consider a generic inflaton field (not the Higgs-inflaton) to be coupled with the same intensity to ...
6
votes
1
answer
1k
views
In-in (Schwinger-Keldysh) formalism in cosmology
I'm working on some application of the Schwinger-Keldysh formalism in cosmology (studying correlation function during inflation).
I saw both the operator and the path integral approach, maybe ...
- 900
3
votes
0
answers
139
views
Is it possible to treat fermion reheating from inflaton decay only perturbatively?
In case of an inflaton Lagrangian
$
\mathcal{L} = \frac{1}{2} (\partial_\mu \phi)^2 - \frac{1}{2}m_\phi^2 \phi^2 -h \overline{\psi} \phi \psi
$
where the inflaton field is coupled only to fermions ...
1
vote
3
answers
104
views
Vacuum energy density with respect to what reference frame?
Wikipedia quotes the observed vacuum energy density to be around $10^{-9}\frac{J}{m^3}$. Whatever the real energy density is, my question is, with respect to what reference frame is this being quoted?
- 13
5
votes
1
answer
186
views
Amplitude for neutron-proton conversion from first principles
I'm reading Dodelson's Modern Cosmology, and in one of the exercises on Big Bang nucleosynthesis it is quoted without reference that the amplitude for neutron-to-proton conversion is given by
$$|\...
- 349
2
votes
1
answer
704
views
Main idea behind this paper on Closed-time-path functional formalism
I tried to understand following paper: Closed-time-path functional formalism in curved spacetime: Application to cosmological back-reaction problems but I can't understand what is going on because I ...
- 3,043
5
votes
2
answers
301
views
Is the cosmological constant problem real? [duplicate]
The cosmological constant problem assumes that the cosmological constant (determined experimentally) can be identified with the vacuum energy density. Theroretical arguments from quantum gravity ...
- 191