Questions tagged [cosmological-inflation]

Cosmological inflation refers to an era of expansion that lasted for approximately $10^{-34}$ seconds, during which the universe expanded by a factor of approximately $10^{26}$ in every direction. This is different from ordinary space expansion and from the acceleration in expansion we experience now and questions tagged by inflation should pertain to this era and not be about the expansion of the universe in general.

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How smooth does reheating (after inflation) need to be?

Let's estimate the size of perturbations in the very early (GUT scale or earlier) universe required for consistency with CMB. The CMB fractional temperature (and hence density) perturbations are of ...
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Why can't primordial fluctuations be super-“horizon” without inflation?

I am trying to understand why, in cosmology, it is said that the presence of fluctuations at scales above the Hubble distance would not be expected in the absence of inflation or something like it. We ...
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Runaway potential in cosmology inflation

I'm looking for a review articles that explaining the issues with runaway potential in cosmology inflation, when a potential has a hilltop and then it goes to zero at infinity. I read somewhere that ...
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Primordial perturbations, scale invariance and fundamental length

In cosmology, the initial perturbations to the metric can be described as $$\mathrm ds^2=-\mathrm dt^2+a(t)^2e^{2\zeta(\mathbf x)}\mathrm d^2x,\qquad(1)$$ where $\zeta(\mathbf x)$ is a gaussian random ...
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Any good Cosmology book recommendations (undergrad->postgrad level) [duplicate]

I am looking to study cosmology at graduate level. Does any one recommend any introductory and comprehensive books for cosmology principles? I am interested in the maths too but I really want a book ...
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Order of three-point function in cosmology using in-in formalism

In early universe cosmology, the three-point correlation function of the curvature perturbation can be solved using \begin{equation}\langle \zeta_{k_1}(t)\zeta_{k_2}(t)\zeta_{k_3}(t)\rangle = -i \int_{...
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How do you express conformal time $eta$ as a function of the scale factor $a$ [duplicate]

I am trying to find a way to express $\eta_0$ - $\eta(a)$ where a is the scale factor of the expansion of the universe in order to calculate the expected number of vacuum bubbles in the early universe ...
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Cut-off Regularization - Renomalization - Definition of counter-terms - in Curved Spacetimes

I'm trying to study renormalization in QFT in curved spacetime. So let's say we have a fixed de Sitter background and we have an interacting theory (e.g. massive $\lambda \phi^4$) and I'm going to ...
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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 ...
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How are the constants in the inflationary hypothesis derived?

The inflationary hypothesis as I understand it is a correction to GR to account for the observed flatness of the universe in a model in which the universe is expanding. How are the constants behind ...
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In the big bang model did the universe reach its current size in less than one day? [closed]

I read that the Inflationary Epoch is posited to have lasted $10^{-32}s$. That seems quite quick. In the big bang model did the universe therefore essentially reach the size it is now in less than ...
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Why is the CMB fluctuations (two-point correlation) approximately Gaussian?

I was learning about the Inflaton model and by quantizing it ,I can derive a $1/k^3$ power spectra , which is the Fourier transform of the fluctuation correlation function. But that doesn't give a ...
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Will entropy continue to increase in an accelerating-expanding universe?

Before/at/during the Big Bang, quantum fluctuations progressed until there was a constant energy density somewhere which caused inflation. The slight variations in energy due to those quantum ...
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How was matter in other parts of the universe affected by the Big Bang and inflation in an infinitely sized universe?

I'm trying to understand how the idea of an infinite universe with presumably infinite matter works with the Big Bang and inflation. I understand that if the universe is infinite, then it's always ...
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Operatorial CTP / in-in formalism for sourced GW production?

Introduction / context - The inflationary paradigm of modern cosmology is a very powerful and predictive framework in which we can trace the primordial cosmological perturbations as originated by zero-...
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Is Big Bang Theory the only one to explain the creation of the Universe?

Is Big Bang Theory the only one to explain the creation of the Universe? I have read about Big-Bang Theory explaining the creation of Universe. Is there no other theory to explain the creation of ...
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Inflation theory and the flatness problem

Recently I have watched videos on how the inflation theory solves some problems that arise from the Big Bang Theory. In particular, I have a few questions regarding the flatness problem and how the ...
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Inflationary Klein Gordon Field, derivation of a result [closed]

Good afternoon, I have a problem whilst studying an Inflationary Klein Gordon field theory. The main problem arises when I try to derive the following result: what I have is: $$\ddot\phi + 3H\dot\...
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Vacuum state in “in-in” formalism

While dealing with correlation functions of fields in cosmology, we often use the formula, $⟨Q(\eta)⟩=⟨0|\overline{T}\left[\exp\left(i\int^{\eta}_{\infty}H^I(\eta')d\eta'\right)\right]Q^I(\eta)T\left[...
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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 ...
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30 views

Energy density of a universe with inflation

What is the function discribing the energy density of the universe including inflation and a dark energy dominated phase?
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Why is the flatness problem a problem?

Friedmann equation states $$ H^2 \equiv \left( \frac{\dot{a}}{a} \right) = \frac{8\pi G \rho}{3} - \frac{k}{a^2} $$ which describes the evolution of the expansion of the universe. Writing $\Omega(t)...
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How to calculation 'lifetime' of inflation model [closed]

How to calculate the 'lifetime' of an inflation model? How are calculations performed with the help of a Hubble parameter for an inflation model?
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Casimir operators of de Sitter space

De-Sitter space can be thought of as a 4 dimensional hyperboloid embedded in 5D Minkowski space. Hence, the symmetry group of dS is $SO(1,4)$ whose generators are, $J_{AB}=i\left(X_A\frac{\partial}{\...
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How to calculate how far two points expand from each other depending on their distance during inflation? [closed]

I'm trying to find a relationship between two points that are $\ell$ distance apart $N_0$ e-folds into inflation, assuming there are 60 e-folds total and inflation starts at 60 and ends at 0, and ...
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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). 1) Do you have any good reviews on the topic? I saw both the ...
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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 ...
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If energy is neither created nor destroyed, where is the extra space coming from? [duplicate]

I've been learning about many aspects of science all of my life, and have come to understand the following: Energy is neither created, nor destroyed. (Classical Physics) Space is expanding. (...
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Swampland conjectures and $f(R)$ gravity

Why the swampland conjectures should be satisfied even in backgrounds with the $f(R)$ gravitational model, if the gradient energy (or the kinetic term of the scalar fields) are negligible for the ...
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Does “inflation” eliminate the requirement that the big bang distributed an infinitely dense kernel of mass?

My admittedly limited understanding of the big bang is that it was an event that expanded spacetime itself along with the kernel of infinitely dense material that coexisted at the moment of the big ...
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Indications on the axion symmetry breaking scale

The production of cold dark matter axions can be provided for by multiple mechanisms which in turn depend on whether the breaking of the $U(1)_{pq}$ symmetry occurs before or after the inflationary ...
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Gravity against dark energy

If inflation of space makes stars and galaxies move apart from each other and gravity does the oposite, what happen to clusters of galaxies that aten't so close to get no effect of dark energy but ...
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How inflation explains the missing monopole? [duplicate]

I read that Alan Guth used phase transition model of early universe to dilute the monopole so that nowadays we don't get to see any of them? I know there is no monopole in nature but I am interested ...
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Flat inflationary spectrum

As far as I know, any successful model of inflation must predict an almost flat spectrum of primordial perturbations ($n_s$ close to one). However, according to some reviews: http://pdg.lbl.gov/2019/...
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Time between Big Bang and 'now'

To point at first my question has a part of trying to make a concept and is not about was there a Big Bang or not. We accept expansion so it is right to think about a starting point of expansion and I ...
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1answer
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Why inflation give rises to gravitational wave?

GR predicts accelerated expansion of spacetime should create gravitational wave, how? I thought universe does not have a center and the big bang happens everywhere so then where do these early ...
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Early Universe Flatness Problem

My question is about the curvature of spacetime in the early universe (Plank era) https://en.wikipedia.org/wiki/Flatness_problem Based on data from Wilkinson Microwave Anisotropy Probe, in order to ...
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Are quantum fields such as electron field fundamental? [closed]

I am wondering do quantum fields transform into other different fields? I came across a hypothetical inflaton field which is suggested to decay into every quantum fields we see today, however most ...
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realistic string cosmology and cosmological constant

Apparently one can recover the Friedman Equations from String Cosmology where the critical dimensions is lowered (from 26) to four. If this is the case, is the bosonic partition function (~ ...
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Observers frame of reference for history / chronolgy of very early universe [duplicate]

What is the observers frame of reference when discussing t=0 the instant of the big bang, or the Plank epoch, or the Grand Unification Epoch, or the Inflation, or the Electroweak Epoch?
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Is eternal inflation compatible with inflation starting at $10^{-34}$ second after the big bang?

Eternal inflation is taking place in an eternally inflating 4-d spacetime. It is "commonly" assumed that inflation (whatever its cause may be) took off (big bang) at about $10^{-34}$ second. Then ...
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Deriving the correct expression for the action of the scalar field at the time of inflation

In its matrix form, the FRW metric is $$g^{\rm FRW}_{\mu\nu}=\begin{pmatrix}1 & 0 & 0 & 0\\ 0 & -\frac{a^2}{1-kr^2} & 0 & 0\\0 & 0 & -a^2r^2 & 0\\0 & 0 & 0 &...
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Is gravitational field disrupted by exponential expansion during Inflationary epoch?

I have seen references to gravity not being able to keep pace during the Inflationary epoch, as gravitational field is only able to propagate at the speed of light. This was an explanation for why the ...
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Why does inflationary expansion of the very early universe require time duration?

If the grand unified force symmetry breaking separation into the strong force and electroweak force leads to a change in scale of the metric that defines distance within space is the cause of the ...
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Is there any other explanation for the expansion of the universe other than dark energy? [closed]

Why did the universe expand from the Big Bang singularity? If gravity was a separate force and in its current form by 1 Plank time, would not have gravity prevented expansion, unless there was some ...
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Why is the homogeneity problem actually a problem?

I don't mean to be flippant but I have never understood why the homogeneity in the universe needs.explaining. I have searched other questions on stack exchange and they don't really address the ...
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Does eternal inflation predate big bang and big bang is only where it partially stops OR does big bang start it and inflation only stops partially?

I am aware eternal inflation could also be infinite to the past, but if it had a beginning, is that beginning the big bang we observe using the cosmic microwave background? Did the big bang start the ...
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How did the Universe thermalize to the same temperature before inflation?

Inflation is speculated to take place at about $10^{-35}$ seconds after BigBang. The idea is that at that moment the universe was small enough so that photons could thermalize to reach the same ...
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The nature of cosmological inflation — unfolding dimensions?

While the paradigm of cosmological inflation is well established, the nature of the inflation is not known and is tackled by introduction of a hypothetical "inflaton" field. I was wondering if there ...
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What is meant by “Big Bang” in expressions like “$10^{-36}$ seconds after the Big Bang”?

Sometimes I find expressions like "The inflationary epoch lasted from $10^{−36}$ seconds after the conjectured Big Bang singularity [...]". What is meant by "the Big Bang" in this context? I ...

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