Questions tagged [dark-matter]

Questions about astrophysical observations, experimental searches, and theoretical models related to dark matter and its quanta.

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Is there an acknowledged unsolved problem in some cosmological theories with respect to "dark" matter and general relativity?

Some mainstream cosmological hypotheses hold both that: general relativity is correct and universal; and a form of "dark" matter exists that is, in somewhat of a misnomer, "non-...
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Normal positive matter interacts with negative matter repulsively?

What's wrong with the following idea: This is too simple. There must be something wrong with it. What's wrong with it?
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Does dark matter act gravitationaly to itself. If Yes, why does not form more compact objects? [duplicate]

Does dark matter act gravitationaly to itself.If Yes, why does not form more compact objects? Can this be explained as its components have enough kinetic energy to overcome the collapse?
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Could dark matter be explained by the fact of empty space expanding much faster than space inside galaxies?

We know the expansion of the universe is accelerating and mass slows time. So pockets of empty space experienced more time since the big bang. That mean the current expansion rate of empty space is ...
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Is the particle labelled $\chi$ a specific spin of dark matter particle? Or is it a non-specified spin?

In supersymmetry, the particle labelled $\chi^0$ is the neutralino. Its spin its 1/2. In dark matter scenarios, some analyses search for various types of candidates for the dark matter : it could be ...
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Can a Higgs boson decay into dark matter?

I've a couple of questions around the title, all closely related. Assuming dark matter is composed of particles outside of the standard model, is it possible that a Higgs could decay into some dark ...
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Could dark matter be made of particles that interact only gravitationally?

Are current observations consistent with the hypothesis that dark matter is entirely composed of one or more types of particles that interact only gravitationally with each other and the usual matter? ...
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Dark matter and the gravitational constant

I am not a real physicist, so please bear with me if my question sounds stupid to all experts around here. What I have learned about the dark matter is, that objects behave as if there was more mass ...
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Rotation of galaxies and gravitomagnetism [duplicate]

Can we explain the bigger speed of rotation of the galaxies from gravitomagnetic field acting from the "inner layers" of the galaxy to the "outer layers" of the galaxy?
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Is it true that frame-dragging (as applied to galactic rotation curves) goes as second order in $v/c$ rather than $(GM/Rc²)(v/R)$?

I have seen various people (see e.g. comments here) dismissing this article using the argument that GR frame-dragging is second order in $v/c$ and therefore insignificant because $v << c$ for ...
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Mass of All the Neutrinos

I have read that the Sun produces $2 \times 10^{38}$ Neutrinos per second weighing in at approximately 8 MeV. I have 2 questions. Is there any way to calculate how many neutrinos have been produced ...
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Could Dark Matter imply the existence of Dark energy? [closed]

This is admittedly a simple example, but it seems to check out. Consider the standard metric for the Schwarzschild solution in coordinates $(t, r,\theta,\phi)$: $$ g_{oo} = U, \ g_{11} = V, \ g_{22} = ...
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If dark matter can't interact electromagnetically, then how can it annihilate into photons?

I have read this question: As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, ...
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What is the dark energy & dark matter? [duplicate]

Can anyone explain to me simply what is the dark energy or what is the dark matter. I have been trying to understand it deeply. but I somehow failed.
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If dark matter can't lose kinetic energy, then why is it not traveling at relativistic speeds?

I have read this question: The only way you can do this is to remove kinetic energy from the system. With normal matter this is done through electromagnetic interactions, which turn the kinetic ...
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If dark matter can't clump together, then where was it when the observable universe was much smaller at the beginning of the universe?

I have read this question: To zeroth order, dark matter can only 'clump' as much as its initial energy (obtained soon after the big-bang) allows. One example of such a 'clump' is a 'Dark Matter Halo' ...
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Can Integrating out Dark Matter give Modified Gravity?

I'm sure I misunderstood something obvious, but reading this question, I wondered what philosophically is the difference between modified gravity (like TeVeS, f(R), etc.) and dark matter, if/since we ...
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Given current densities of dark energy, dark matter and normal matter in universe currently, calculate ratio of density of dark matter at CMB to now? [closed]

I stumbled upon this question while preparing for the astronomy Olympiad. It is question #17 in this pdf. Given that dark energy is vacuum energy, and that the densities of dark energy, dark matter ...
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How can we calculate formula for effective coupling constant in spin independent direct detection of dark matter?

At tree level, the spin independent (SI) direct-detection cross section includes effective coupling constant. How to calculate effective coupling constant? There is always a mandelstram variable in it....
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Could dark matter be ultra-long wavelength photons?

Photons produced during inflation, e.g. by annihilation of antimatter and matter, and not somehow reabsorbed would presumably have been highly redshifted by the end of the inflationary epoch and even ...
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What are the exclusion limits on WIMPs?

As I understand the way dark matter WIMP exclusion plots work, they are cross-sections (usually 2D) of the fuzzy boundary surface of a hyperdimensional property space, defining a fuzzy volume of that ...
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Could Hawking radiation have a lot of neutrinos and dark matter?

Up till now I have thought that Hawking radiation would be mostly photons, since the temperatures are typically small. However, a comment on another question (thanks to John Doty) suggested that we ...
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Galactic rotation curves question

I think I need to ask this question now, because it's in my mind for several years and I just can't find an answer to it. After observations of those galaxtic rotation curves, it's pretty clear, that ...
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Annihilation Scattering Cross-Section $N_{n}+N_{n} \rightarrow \nu_{i} + \nu_{j}$ [closed]

I'm calculating the annihilation scattering cross section for fermionic dark matter candidate. I got the following result for the squared amplitude, $|\mathcal{M}|^2= \frac{h_{ji}f^{*}_{ij}}{(m^{2}_{{...
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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 ...
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Why are wide binary systems assumed to contain negligible dark matter?

I'm doing a project that simulates wide binaries to do gravity tests, specifically a dark matter vs MOND test. I've come across similar papers, and their justification for using wide binaries for this ...
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Does dark matter exist or not?

I've seen articles in recent days (e.g. https://physics.aps.org/articles/v14/s71) about an experiment in Spain possibly disproving the precedent finding by DAMA/LIBRA. At the same time there are new ...
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Gondolo-Gelmini Change of Variables

In the article Cosmic abundances of stable particles: Improved analysis, P. Gondolo and G. Gelmini, Nucl. Phys. B 360 (1991), p. 145-179, they convert $\rm{d}^3p_1\rm{d}^3p_2=2\pi^2p_1p_2\rm{d}E_1\rm{...
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Is it possible that dark matter and dark energy come from the same dark particle?

I've skimmed articles/blogs and watched videos around this issue, and the universal consensus is that dark matter and dark energy are two different things >> DM is attractive while DE is ...
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Forces besides gravity acting at astronomical distances?

It seems like all one reads about is gravity affecting planets and stars whereas at the atomic level there are other forces and gravity is unimportant. How do we know there are not other forces ...
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Fully General Relativistic treatment of Galaxy Rotation Curve

Over the years I have seen several approaches to this problem in the GR context: perturbations around a flat-spacetime, cancelation by hand of $\mathcal{O}(\partial_{\mu}\textbf{g}^{2})$ terms on the ...
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Number of interaction of early universe

I am reading An introduction to particle dark matter by Stefano Profumo. I am struggling on a derivation. As given from the text, in the early universe $\frac{\dot{T}}{T}=-\frac{\dot{a}}{a}=-H$, ...
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Can interstellar, intergalactic particles be Dark Matter?

As per my knowledge the particle density of interstellar space and intergalactic space is not zero. And, there is much more space than the groups/blobs of mass (stars, planets, nebulas etc.) I am ...
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How are the hypothetical intermediate "dark photons" bosons theorized to couple dark matter with normal matter?

I believe that dark matter is said to couple with normal matter only gravitationally? Do these relatively new, hypothetical so far, "dark photons" suggest that there can be also an unknown ...
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What is meant by dark matter being non-relativistic and why is this?

What does it mean by dark matter being non-relativistic and why is it non-relativistic?
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Is there software to calculate/plot decomposed rotation curves from observational data (FITS, etc)?

I have observation data of galaxies (in FITS format). From the FITS data, I want to calculate & plot the decomposed rotation curves as pictured below. Is there a software package that will do that ...
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Assuming the announced $g-2$ experiment αμ discrepancy is mainly because a dark matter candidate, is this a quantum gravity induced effect?

The possible effectively extra added vacuum polarization by a dark matter candidate could account for the recently announced anomalous magnetic moment αμ measured discrepancy from the theoretical ...
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Fermilab's results and a fifth force [duplicate]

On today's news, it says that Fermilab have done measurements on the spin of muons and that they are measured to wobble faster than expected according to current physics theories. Apparently this may ...
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How much faster are the stars on the outskirts of galaxies going than they are 'meant' to as predicted by general relativity?

this is in reference to dark matter. I've look on the internet for this but I can't find precisely what I am looking for.
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What does it mean for CDM to "decouple from baryons"

I am currently working on my Final Year Project as an undergraduate, mostly intended to be a review of $\Lambda$CDM model and some of its modern challenges. When talking about Cold Dark Matter I ...
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Dark matter ... could it be somehow be sound waves? [closed]

I know that this sounds like a ridiculous question, silly even. But as they say, the only truly stupid question is the one not asked ! So how did I get to this thought. Well I was reading stuff and ...
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How to understand the derivation of thermally averaged cross sections?

$$ \frac{d\langle\sigma_\text{ion}^{nl} v\rangle}{d\ln E_\text{er}}=\frac{\bar\sigma_e}{8\mu^2_{\chi e}}\int q|f_\text{ion}^{nl}(k',q)|^2|F_\text{DM}(q)|^2\eta(v_\text{min})\ dq $$ How do I understand ...
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Has frame dragging been accounted for in galactic rotation curves?

This article explicitly takes frame dragging into account in calculating expected galactic rotation curves in the absence of dark matter, and appears to obtain very close matches to observed curves. ...
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Problem with the MadAnalysis

So I am trying to reproduce the result of arXiv:1404.1918 page 12, top-left figure 7 (attached figure) for signal-background of DM via top portal. In the paper the writers said that they use MadGraph ...
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Why is the distribution of Dark Matter in the Universe inhomogeneous?

As far as I know, there exist galaxies containing lots of DM and other galaxies with almost no DM at all. This implies that the distribution of DM in the Universe is inhomogeneous. Do we have any idea ...
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Is there a theory of "dark mass" similar to but different from existing theories of "dark matter"? I.e. gravity without matter?

I'm curious to know if any mainstream theoretical physicists have theorized or spoken about the possibility of a theory of dark matter that doesn't involve any actual matter like hypothesized MACHOs ...
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Why a decaying dark matter?

I'm reading some papers (model, exp and model) that are dealing with decaying models of DM, why is it interesting? What are the signatures that this type of model can give to observe DM? I am ...
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Is galactic gravitational lensing self-magnification big enough to contribute noticeably to the galaxy rotation curve problem?

Gravitational lenses magnifies the appearance of themselves, so in the case of a galaxy it looks bigger than it is. Thus the outer stars in a galaxy seems to have a higher tangential velocity. For ...
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How are matter, dark matter and dark energy compared?

Matter, dark matter and dark energy "make up" 5%, 27% and 68% of the Universe. I can understand that matter and dark matter are comparable, but what does it mean that there is more than ...
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Isn't dark matter just another fancy name and explanation for aether? [closed]

I always get crucified by this, but it is something that has intrigued me for a lot of time, before Michelson Moorley and Einstein there was this idea that there was an invisible "substance" ...

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