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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What would the wavelength of the Cosmic Background Gravitational Wave radiation be?

Considering electromagnetic CMB can only see light as old as 380,000 years after the Big Bang, whilst theoretically those being gravitational should be formed from the beginning, what would their ...
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What is the nature of inflatons being the particles of the inflaton field?

It is thought that the inflationary expansion of the universe is driven by an inflaton field. A scalar field with negative energy. Today, the observed accelerated expansion of the universe is thought ...
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Cosmological models of the expansion of the universe for different curvatures

My question refers to page 38 of Tong's Notes on Cosmology. Here we consider a matter dominated universe and derive the equation $$2h^\prime + h^2 + k = 0$$ for $h = a^\prime/a$, where $^\prime$ ...
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What inflation theories can be considered viable?

Observations made by the Planck consortium excluded many potentials relevant to inflation theories. What inflation theories are still considered viable at the present date?
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Slow-roll approximation for $a^{\prime\prime}/a$

I am currently reading this paper entitled 'Primordial Gravitational Waves From Cosmic Inflation' by M. Wang and would appreciate a complete derivation of the following result found on page 2: $$\frac{...
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What caused the universe to expand in the epoch right after inflation?

I hope this exact question is not a duplicate. I have looked into some high rated answers/questions, but found no satisfying/understandable answer. This is my current line of throught: In the ...
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Confusing index notation in cosmological perturbation theory

On page 24 of the report 'Inflation and Cosmological Perturbation Theory' by S. Auddy (available here), the concept of a perturbed metric tensor is discussed. In this text, a vector is decomposed as $...
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64 views

How does a quantum field spread over time?

Im having trouble knowing how this works, so far online all I’m getting is complex math equations explaining this and I would love if someone out there can give me an explanation on how a quantum ...
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Visualising the Comoving Hubble Sphere

I am currently reading Baumann's Cambridge lecture slides on cosmology and am confused on the notion of the Hubble radius. In particular, on page 12 is the following diagram. I would really appreciate ...
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Comoving Hubble radius in terms of expansion scale factor

I am currently reading Baumann's Cambridge lecture slides on cosmology and am confused on the notion of the Hubble radius. On page 10 it is stated that for a perfect fluid with constant equation of ...
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Why are not quadratic potentials suitable for simple inflationary models?

I am trying to understand why the simple inflationary model with potential $V(\phi) \propto \phi^2$ is disfavored compared to models predicting a smaller tensor-to-scalar ratio. To do so I am reading ...
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Low temperature reheating

I have a question about the Low reheating temperature. [https://arxiv.org/pdf/1406.0012.pdf] I'm confused about the order of the events and maybe in their definitions. Everything is summarized in this ...
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Are the unification of spacetime and the warping of space in general relativity real, or mathematical convenience?

It is known that Einstein was impressed with the elegance of Maxwell’s Equations for electromagnetism, and that he was striving for something similar for gravity in his General Theory of Relativity. ...
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Friedmann equation of motion w.r.t Number of E-folds

So the number of e-folds is given by $N=\ln(a)$ which can act as a substitute for time variable. So I would like to use the fact that $H = \dot{a}/a$ in order to derive the equation of motions for $\...
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If the universe is infinite, then how can we tell it's expanding? [duplicate]

I understand that our universe is finite to a point that we can see it expand but if that's the case, how is it also frequently called 'infinite'. While there are similar questions out there I would ...
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Hybrid Inflation of Two Scalar Fields

Considering the slow-roll regime of a two scalar field inflationary model characterized by the following potential: $$V(\phi, s) = \lambda(\phi^2 - \mu^2)^2 + gs^2\phi^2,$$ where $g$ and $\lambda$ are ...
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Why would a gravity wave signature in CMB favour inflationary cosmology?

I was reminded recently of the BICEP2 experiment which seeks to discover B mode signature in the CMB, indicating early-universe gravitational waves. I noticed that when there was, briefly, a flurry of ...
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References on Cosmic Inflation and CMB fluctuations [without QFT]

I'm making my final seminar for a Cosmology class I am taking as an undergraduate, and I'm going to talk about how quantum fluctuatuions during the inflation period are a reason for the anisotropic ...
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Indirectly breaking the speed of light through inflationary phase

How do you define velocity? Rate of change of "space" between two objects-and that will give relative velocity between them. Now in inflationary phase the universe expanded faster than light ...
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Scale invariant spectrum

In the context of cosmology I often read that "the spectrum is scale invariant". I guess they mean the spectrum of density (etc.) perturbations from inflation? What do they mean exactly with ...
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Is the simplest model of eternal inflation with a minimal landscape viable?

It is believed that much of the string theory landscape is not physically realizable. This creates problems for the usual picture of eternal inflation, in which vacuum transitions fill the entire ...
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Is there any inflationary model or any string theory model that does not assume any symmetries as fundamental?

If I understand them right, in usual chaotic inflationary models or in string theory some symmetries are assumed as fundamental and therefore some fundamental laws of physics are assumed. But, in some ...
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What would slow-roll inflation with $\eta >1$ look like?

In studying slow-roll inflation, the two slow-roll inflation parameters $\epsilon$ and $\eta$ are usually assumed to be small. However, strictly speaking only $\epsilon$ needs to be small to have ...
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When an object crosses the future horizon, what do you see? [closed]

First, there should be a redshift due to the velocity of the object before it crosses the horizon. And then, does the object's light just shut off? Note: There are several cosmological horizon that we ...
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How do you relate the number densities of neutrinos and photons soon after the positron–electron annihilation?

I found this equation: $n_\nu = \frac{3}{4} \frac{g_\nu T_\nu^3}{g_\gamma T_\gamma^3} n_\gamma$ Where does it come from?
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How do you know that objects are accelerating from each other in space?

I know that Hubble redshift comes from the relation between the distances of objects and the Hubble parameter: $$H_0 = \frac{\dot{R}}{R}.$$ But how we differentiate between redshifts effects from the ...
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Can vacuum cause something similar to the Hawking radiation?

If my understanding is correct, Hawking radiation is caused by two virtual photons separated by the event horizon of the black hole. Then, if the universe expands fast enough, (probably faster than ...
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Multiverse theory VS Conformal Cyclic Cosmology (CCC)

Multiverse theory describes that there are many singularities taking birth and then based on their properties (like dark matter content), these may pop in and out of existence. While on the other hand,...
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Power spectrum enhancement in primodial black hole

To produce a primordial Black Hole in in the inflationary epoch, there should be enhancement in the power spectrum. Both the slow roll approximation and exact solution show this feature. My question ...
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If the universe is expanding at an accelerated rate, was it stationary at some point in time and contracting before that?

If the universe is expanding at an accelerated rate it would mean that the more we go in the past, the slower the speed of expansion must have been. Provided the acceleration was always non-zero and ...
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“Law without law” in inflation?

John Wheeler proposed that the fundamental laws of physics actually were emergent from a primordial random/chaotic underlying state. According to this view, every physical law is actually emergent. Is ...
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Are the different fields in multi-field inflation described by different Lagrangians?

The most simple models of cosmological inflation consider only one scalar field. However, there are more complex models (like hybrid inflation or multi-field inflation) which consider more than one ...
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Vacuum expectation vs ensemble average

On p.169 of Dodelson's Modern Cosmology, the following is stated: "We can compute the quantum fluctuations of the operator $\hat{x}$ in the ground state $|0\rangle$: $$ \big \langle |\hat{x}|^2 \...
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Gaussianity of single-field inflation

I have read in multiple sources (i.e. Baumann's TASI lectures on inflation, Dodelson's Modern Cosmology) that single-field inflation is supposed to produce 'nearly Gaussian perturbations'. As far as I ...
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Changes to an EM-wave that is propagating in an inflating space

I am trying to get an easier picture of what happens to an em-wave considering space expansion. My question is: If a star in a non-inflating space emits light recorded at a certain distance of the ...
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Confusion about the shrinking Hubble volume

The particle horizon is given by \begin{equation} \chi_p(\eta) = \int_{t_i}^{t}\frac{dt}{a} = \int_{a_i}^{a}\frac{da}{a\dot{a}} = \int_{\ln a_i}^{\ln a} (aH)^{-1}\ d\ln a . \end{equation} For a ...
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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 ...
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Slow-roll parameter in Inflation

What is the definition of slow-roll parameter? What equation that these parameters are showed up? I read a book "Modern Cosmology" by Scott Dodelson. In chapter 6, it is just given the ...
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2answers
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Physical intuition for negative pressure

Ordinarily, we think of pressure, such as the pressure of a gas as an outward push exerted on the walls of the gas container. In nonequilibrium, the pressure tries to make the volume expand. But the ...
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Is primordial power spectrum $P(k) \propto k^n$ or $P(k) \propto k^{n-1}$?

I am reading in Ryden that $P(k) \propto k^n$, where $n \approx 1$ for the primordial power spectrum. However, I read here that $P_s(k)^{n-1}$. I am confused on the differences between the different $...
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Is there a Friedmann equation form with inflation?

I have been unable to find on the Internet any form of GR similar to the 4 Omegas Friedmann equation that includes a transition from an inflation era back to a radiation era. Is it known whether or ...
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How are the alpha vacua, the Bunch Davies vacuum and Adiabatic vacuum different in context of inflationary cosmology?

I do understand that the Bunch-Davies is the most standard vacuum to consider as an initial condition, but what if there are deviations from a de Sitter spacetime that do not generically reduce the ...
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How did the Universe behave just at the end of inflation?

Edit When the inflaton field $\phi$ rolls down the potential $V(\phi)$ to the value $\phi=\phi_f$ where the slow-roll parameter $\epsilon(\phi_f)\to 1$, inflation ends. By calculating the behaviour of ...
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Has any result of Hubble parameter been obtained by observing SN UDS10Wil?

I am simply asking the question after reading Wikipedia because I am confused about the historical change of the parameter during the cosmic inflation. Knowing that as far a supernova is the more in ...
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Is it realistic for an unstable vacuum to have an infinite past, but a finite future?

Is it realistic for an unstable vacuum to have an infinite past, but a finite future? In other words, can there be a plausible scenario in which an unstable vacuum did not have a beginning, but ...
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Do cosmological event horizon evaporates like black-hole horizon?

While the inflation phase of the universe, expansion was exponential and so the universe was de Sitter-like. So, for a point-like observer, there was a cosmological event horizon. Do this horizon ...
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In Eternal Inflation Theory, what is the average distance between bubble universes?

Patches of normal space randomly condense out of the false vacuum of inflating space. What is the average distance between these patches? Another words, what is the average number of bubble patches ...
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How to calculate cosmological parameters such as scalar spectrum index and the tensor-to-scalar ratio in constant-roll method?

As we know, the scalar spectrum index and the ratio of tensor-to-scalar in the slow-roll method are obtained with a certain relation according to the parameters of the slow-roll. Now I want to ...
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1answer
147 views

Exact solution of scalar field cosmology with exponential potential [closed]

Considering a homogenious and isotropic universe described by the Robertson-Walker metric: $$ ds^2= dt^2-a^2(t)\left[\frac{dr^2}{1-kr^2}+r^2(d\theta^2+\sin^2(\theta)d \phi ^2)\right]$$ and also ...
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What is brane inflation, and can it be eternal?

What is Brane Inflation and how does it describe inflation process? Can it be eternal?

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