Questions tagged [cosmology]
The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.
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questions with no upvoted or accepted answers
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750 GeV diphoton resonance: KK graviton?
As everybody of you may know at LHC they found this probable resonance (https://cds.cern.ch/record/2114808, https://cds.cern.ch/record/2114853?ln=en). It may be a scalar or a KK graviton mode. Now, ...
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Poincare recurrence and the multiverse
In this paper Susskind claims that a stable de Sitter universe is problematic (among other things) due to the existence of Poincare recurrence, which happen because of finite entropy. I disagree that ...
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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 ...
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What is torsion physically in the Einstein-Cartan theory?
In Einsteins theory of gravity the metric gives a unique torsion free connection called the Levi-Civita connection.
In the Einstein-Cartan theory we allow any connection compatible with the metric ...
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Sterile (4th) neutrino and cosmological bound
Recent results by MicroBoone seems to give support to old LSND experiment in favor of a fourth neutrino (sterile). How does it fit with the current cosmological bound for neutrinos?
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Adiabatic fluctuations
In Baumann's cosmology lecture, chapter 4, page 89, he defines adiabatic perturbation as:
Adiabatic perturbations have the property that the local state of matter (determined, for example, by the ...
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In a perturbative FRW cosmology, why do constant-density hypersurfaces define a good gauge?
It appears to be common in the discussion of perturbative FRW cosmologies to choose a gauge using hypersurfaces for special values of some quantity, like surfaces of constant density $\rho$, constant ...
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$f_{NL}$ non-Gaussianity in cosmology
In the context of cosmology, what is meant by "..arbitrary quadratic non-Gaussianity i.e non-Gaussianity that is described to leading order by a 3-point function.."? (.."quadratic non-Gaussianity" ...
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Status of large-scale structure formation within cosmology today
Since the CMB results of the past decade, would it be fair to say that the consensus among cosmologists is that cosmic strings are no longer considered as a (major) source for density perturbations?
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EB95
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How do you explain cosmological red shifting in terms of gravitons?
We know that the photons from the big bang are continually being red shifted and losing more and more energy. In terms of the graviton view, how would you explain that? Where is the energy going?
Are ...
user84158
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Bargmann–Wigner equations in NP formalism
Bargmann-Wigner equations describe free particles of arbitrary spin $j$, namely
$$(-\gamma^{\mu}\partial_{\mu}+m)_{\alpha_r \alpha_{r’}}\Psi_{\alpha_1,..,\alpha_{r’},...,\alpha_{2j}}=0$$
where we have ...
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Wheeler-deWitt equation in words?
Looking at the Wheeler-deWitt equation. My attempt to describe it in words is this:
"For each 3d-manifold given by metric tensor field $\gamma$, associate a complex number $\Psi$. The Wheeler-de-Witt ...
user84158
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Why is the relation between luminosity distance $d_L$ and comoving distance $\chi$ $d_L=\chi/a$?
The textbook (Scott Dodelson, Modern Cosmology, Section 2.2 Distance, Page 35-36) states the following:
Another way of inferring distances in astronomy is to measure the flux from
an object of known ...
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Meaning of the simplest potential of quintessence models. Fields in denominator?
I am reading Sec. 1.12 of the Cosmology book by Weinberg.
In this section he explains the very simple model of quintessence which attempts to provide a dynamical explanation of the smallness of the ...
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A question from cosmological perturbation theory
We consider the following scalar perturbation on the FRW metric
$$ds^2=-(1+2\Phi)dt^2+2a(\partial_iB)dx^idt+a^2[(1-2\Psi)\delta_{ij}+2\partial_{ij}E]dx^idx^j,$$
where $\Phi$, $B$, $\Psi$ and $E$ are ...
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