Tuesday, August 11, 2020

You Can't Explain Dark Matter Phenomena Without A Fifth Force Or Gravity Modification

The line between a modifications of gravity including quantum gravity effects, and a fifth force is very thin. 

In the first, it is possible, but not necessary, to have no beyond the Standard Model particles. In the second, you generally assume that existence of beyond the Standard Model dark matter particles (usually, but not always, fermionic) and some sort of carrier boson.

Dark Matter Without An Additional Force

Without such a force, you get some form of collisionless Λ Cold Dark Matter theory, in which the only interaction that cold dark matter particles have in the post-matter creation era is gravitational. In such a model, there are a limited number of variables. 

For each species of dark matter particle you have a mass and a velocity distribution of particles in that species, and then you determine how many species of dark matter there are in the model. In a thermal freezeout scenario, each species as a very specific and narrow velocity distribution that is purely a function of its mass. You also need to determine if each species of dark matter particle is a fermion or boson.

Each dark matter species can basically be divided into truly cold dark matter particle models, with particles of 1 GeV or more of mass, and "warm dark matter" models, with particles on the order of keV in mass (with the masses serving as proxies for mean velocity as determined in a thermal freezeout scenario), with the light dark matter displaying some quantum behavior that influences its distribution.

When I first started looking into this seriously (i.e. when I started reading scientific journal articles on dark matter), the models with only one species of truly collisionless Cold Dark Matter almost always fit the observational data better than those with multiple species. Alas, I haven't been able to find any of those old papers lately since I've looked into again.

But the bottom line is that such simple theories don't do a good job a producing the dark matter phenomena that are observed, for example, in galaxies. The halo shapes observed from gravitational lensing are the wrong shape (especially for cold as opposed to warm dark matter) and the correspondence between baryonic (i.e. ordinary) matter distributions and dark matter effects are too closely aligned.

Footnote: The Gravity Only Condition

The condition that dark matter particles only interact via gravity is stronger than it needed to actual match observations. Dark matter needs to be "almost collisionless" for purposes of cosmology applications, for example, by not completely collisionless.

Astronomy observations, for example, don't rule out dark matter particles that have the same weak force charge as Standard Model fundamental fermions, but don't have electromagnetic charge.

But direct dark matter detection experiments have ruled out dark matter particles with a weak force charge as strong as that of neutrinos over a wide range of dark matter particle masses: roughly 1 GeV to 1 TeV. Dark matter particles with masses of 1 TeV or more would have mean velocities too low to fit observations in thermal freezeout scenarios.

So, the original supersymmetric WIMP (weakly interacting massive particle) candidate for dark matter, which would be stable, interact via the weak force and gravity only, be formed in thermal freezeout, and have a mass in the 1 GeV to 1 TeV range, has been ruled out pretty definitively.

Footnote: True One Species Dark Matter Particle Models Are Almost Indistinguishable From One Dominant Species Models.

This wouldn't imply that there was actually only one kind of dark matter particle. It could just mean that one kind of stable particle is dominant for cosmology applications.

By analogy, there are hundreds of possible ground state hadrons (i.e. possible composite particles made of quarks and/or gluons bound by gluons), but the longest lived mesons (the charged pion and the K-long meson) have mean lifetimes on the order of 10^-8 seconds, and there are only two baryons with mean lifetimes on the order of more than 10^-10 seconds: the proton (which is stable) and the neutron (which is stable when bound and has a mean lifetime of about 880 seconds when bound in an atom). 

Likewise, for many applications you can ignore the existence of muons which have a mean lifetime of 10^-6 seconds and tau leptons with a mean lifetime on the order of 10^-13 seconds, and can ignore the fact that there are distinct electron neutrinos, muon neutrinos and tau neutrinos, and act as if there are only electrons.

For most purposes, a protons, neutrons, electron model in which protons and neutrons are the only hadrons, neutrons are composite particles made up of a proton, electron and an electron neutrino that decays when free of the nuclear binding force with a mean lifetime of 880 seconds, and and there is an additional nuclear force binding protons and neutrons whose behavior is described by a phenomenologically determined formula works just fine, because those hadrons are dominant. For example,  this simplified model is more than sufficient for even sophisticated nuclear physics applications like building nuclear weapons and designing and operating nuclear power plants.

Moreover, while there are hundreds of stable or metastable atomic elements, some of which have several stable or metastable isotopes, the baryonic mass of the universe is roughly 73.9% hydrogen, 24.6% helium, and 1.5% "metals" (i.e. all atoms other than hydrogen and helium). Two atomic element baryonic matter model can give you something quite close to the truth for astronomy purposes, and a three atomic element baryonic matter model in which a single particle statistically blending the properties of oxygen, carbon and neon.
Table via Wikipedia.

The reason I detour at length to recognize the possibility of a rich number of species of dark matter with a dominant species (possibly even a composite one, rather than a fundamental one) is because it is important not to rule out theoretically complex models that may be a better fit to the Standard Model in some respects merely because the observed phenomena are best described by one to three dominant particles from within a richer array of possibilities.

Self-Interacting Dark Matter (SIDM) v. Fifth Forces

Once you've reconciled yourself to the idea that a pure collisionless dark matter particle theory doesn't work, a modified gravity theory that adds no new dark matter particles but modifies (at least) the weak field behavior of general relativity, possibly via a quantum gravity effect, becomes the most conservative option, i.e. it changes core theory the least.

The possibility of a new force that operates only within the dark sector, allowing dark matter particles to interact with each other, but not with Standard Model particles, is addressed by self-interacting dark matter theories, with the carrier boson (often a light boson with some rest mass giving rise to a Yukawa force) of the self-interaction force sometimes called a "dark photon".

The main benefit of SIDM is that it fixes the discrepancy between the observed shape of inferred dark matter halos based upon gravitational lensing observations, and the NFW halo shape predicted in the case of truly collisionless dark matter.

There are observational bounds on the strength and nature of a self-interaction force from astronomy observations, which suggest a medium range, medium strength force with a strength roughly on the order of strength of the electromagnetic force if we were carried by a carrier boson with a mass on the order of tens or hundreds of MeVs.

The trouble with SIDM theories is that they don't explain the tight match between baryonic matter distributions and dark matter phenomena. To get that, you need a "fifth force" between dark matter and ordinary matter. 

Of course, by the time you have added both new particles and a new force that interacts with Standard Model particles and has never been seen, the special case of modified gravity without dark matter particles starts to look more conservative and more favored by Occam's Razor.

A new pre-print concludes (not for the first time that someone has done so) that you can't explain dark matter phenomena without a fifth force within the dark matter particle paradigm.

Paradigms and Scenarios for the Dark Matter~Phenomenon

Well known scaling laws among the structural properties of the dark and the luminous matter in disc systems are too complex to be arisen by two inert components that just share the same gravitational field. This brings us to critically focus on the 30-year-old paradigm, that, resting on a priori knowledge of the nature of Dark Matter (DM), has led us to a restricted number of scenarios, especially favouring the collisionless Λ Cold Dark Matter one. 
Motivated by such observational evidence, we propose to resolve the dark matter mystery by following a new Paradigm: the nature of DM must be guessed/derived by deeply analyzing the properties of the dark and luminous mass distribution at galactic scales. The immediate application of this paradigm leads us to propose the existence of a direct interaction between Dark and Standard Model particles, which has finely shaped the inner regions of galaxies.
Comments:16 pages, 8 figures , in print. Comments wellcome
Subjects:Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as:arXiv:2008.04052 [astro-ph.CO]
 (or arXiv:2008.04052v1 [astro-ph.CO] for this version)
From the body text:
The mass distribution in Spirals is largely dominated by a dark component as it is evident from their kinematics and their other tracers of the mass distribution (e.g., see [1]). More in general, many other observations indicate the presence of such “substance” in the Universe. Among those, the gravitational lensing of background objects, the extraordinary Bullet Cluster [2], the temperature distribution in Clusters of galaxies (e.g., [3]) and, more recently, the pattern of anisotropies in the cosmic microwave background (CMB) radiation ([4]). Furthermore, the theory of Big Bang nucleosynthesis indicates that the vast majority of dark matter in the Universe cannot be made by baryons. With the caveat of an (exotic) population of primordial Black Holes, the Dark Matter is therefore thought to be made of massive particles that interact with Standard Model particles and with themselves mainly via Gravitation: the non-gravitational interactions are believed to have cross sections very small (for WIMPS: 10−26 cm2 ) and no role in the building of the cosmological structures. Noticeably, the current belief is that such DM-Luminous Matter (hereafter LM) interactions provide us with messengers of the dark particle. 
In the past 30 years, the leading approach to the ’DM mystery’ has not been astrophysical or experimental but has followed a particular route that in Physics has often been successful. Everything starts by adopting the Paradigm according to which strong theoretical arguments on how nature could be made lead us to the correct cosmological scenario and, in turn, to the actual dark particle in which the detectability via experiments and astrophysical observations results as a bonus of the same arguments above. This Paradigm has pointed especially to a stable Weakly Interacting Massive Particle (WIMP), likely coming from SuperSymmetric extensions of the Standard Model of Elementary Particles [5,6] and has opened the way for the collisionless ΛCDM scenario. In spite of a good agreement of its predictions with many cosmological observations, at galactic scales, the above scenario runs in serious problems including the well known one for which the predicted structural properties of DM halos result in strong disagreement with respect to those inferred from the internal motions of galaxies (see, e.g., [1]). It has been claimed that these strong discrepancies could be eliminated by astrophysical processes (e.g., [7]) in which supernovae explosions eventually flatten the originally cusped DM density profiles, however, as new data come in, the DM halos density profiles appear to be always more difficult to be accounted by such processes (e.g., [8,9]). As an example of this, the presence of very large DM halo core radii in Low Surface Brightness galaxies [8]. Furthermore, it is important to stress that, despite the large efforts made in searching for them, the WIMP particles have not turned up in direct, indirect and LHC collider searches (see, e.g., [10,11]).1 . . . .  
The three features reported and the three newly presented in this section, that ultimately stem from the entangled dark-luminous mass distribution in galaxies, strongly suggest that some non gravitational energy has been directly exchanged between atoms (or photons and/or neutrinos) and DM particles via processes currently unknown and seemingly not explainable within the First Principles underlying the ongoing Paradigm for the Dark Matter Phenomenon. More specifically,5 the DM–LM entanglement in galaxies presented in previous sections works as a strong motivation for advocating a change of Paradigm, in the direction in which the nature of the dark particle and its related Cosmological Scenario are determined from reverse-engineering the galactic observations characterizing the DM Phenomenon.


neo said...

"Of course, by the time you have added both new particles and a new force that interacts with Standard Model particles and has never been seen, the special case of modified gravity without dark matter particles starts to look more conservative and more favored by Occam's Razor."

how does X17, if proven to exist, fit in this discussion?

i did find this paper,

Interpretation of the Galactic gamma-ray excess with the dark matter indicated by 8Be and 4He anomalous transitions
Lian-Bao Jia, Tong Li

The long-standing Galactic center gamma-ray excess could be explained by GeV dark matter (DM) annihilation, while the DM interpretation seems in tension with recent joint limits from different astronomical scale observations, such as dwarf spheroidal galaxies, the Milky Way halo and galaxy groups/clusters. Motivated by 8Be and 4He anomalous transitions with possible new interactions mediated by a vector boson X, we consider a small fraction of DM mainly annihilating into a pair of on-shell vector boson XX followed by X→e+e− in this paper. The Galactic center gamma-ray excess is explained by this DM cascade annihilation. The gamma rays are mainly from Inverse Compton Scattering emission, and the DM cascade annihilation could be compatible with joint astrophysical limits and meanwhile be allowed by the AMS-02 positron observation. The direct detection of this model is also discussed.

Comments: 14 pages, 3 figures
Subjects: High Energy Physics - Phenomenology (hep-ph)
Cite as: arXiv:2006.13357 [hep-ph]

andrew said...

The X17 interaction shouldn't be sufficient to account for the ordinary matter-dark matter correlations observed that cannot be explained by gravity alone, a factor that proponents of this as a DM candidate have not evaluated.

Yukawa forces carried by massive bosons of the type hypothesized in the X17 proposal, in general, do not have infinite spatial range. The range of a force mediated by a 17 MeV boson should be about 4.8 proton radii. See http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/exchg.html A force that mediates dark matter to ordinary matter interactions should have a range on the order of millions of kilometers or even light years or parsecs. Indeed, the expected mass of the hypothetical boson was probably estimated in part based upon the range at which it appeared to operate.

andrew said...

The mediator of the nuclear binding force between atoms which is derivative of the Standard Model strong force is primarily the pion which we have now measured to have a mass of 135 MeV for the neutral pion and 139.6 MeV for the charged pion (other non-fundamental bosons that are more massive have second and third order contributions to this emergent force). In preliminary estimates of the target carrier boson by Yukawa himself, the prediction was that the carrier boson would have a mass on the order of 100 MeV, which was order of magnitude correct (and not made more precisely than a one significant digit order of magnitude estimate in the first place).

andrew said...

A carrier boson with a mass of 1 meV (i.e. 10^-3 electron volts, which is on the same order of magnitude as the lightest neutrino mass) would give rise to a force with an effective range of about 0.1 millimeters.

So, a fifth Yukawa force with a massive carrier boson which would explain the correlation observed between dark matter and ordinary matter distributions would need to have a mass on the order of the masses being considered for axion-like particles (ALPs) of much less than the massive neutrinos, which are the lightest of the massive Standard Model particles (fundamental or otherwise). In the Standard Model the photon and gluon have zero rest mass, and the hypothetical graviton of quantum gravity theories would also have zero rest mass (except in non-canonical "massive gravity" theories in which the mass of the graviton would still be very small. The Particle Data Group limits the mass of the graviton based on observations and model dependent Yukawa force analysis at less than 6*10^-32 eV. https://pdglive.lbl.gov/Particle.action?node=G033&init=0 A fifth force boson wouldn't have to be that low in mass, but it would have to have a mass many orders of magnitude less than 1 eV. By comparison the X17 has an estimated mass of 17,000,000 eV.

andrew said...

Discussion of axion and axion-like particle dark matter can be found at https://arxiv.org/pdf/1407.0546.pdf and https://en.wikipedia.org/wiki/Axion The axion was originally hypothesized as a way to explain the lack of CP violation in the strong force (which arguably is unnecessary to explain).

andrew said...

To be clear, the X17 particle, if it existed, would be perfectly capable of being a bosonic dark matter candidate. But the upshot of the analysis of the article in the original post and previous articles cited at this blog, is that you need a fifth force giving rise to interactions between ordinary matter and dark matter that interacts at long range in order to explain observations of correlations of ordinary matter and dark matter distributions in galaxies. It doesn't have to be (and indeed cannot be) terribly strong. But a carrier boson for such a force would need to either have zero rest mass or to have a rest mass of many orders of magnitude less than 1 eV. So, while X17 could be a bosonic dark matter candidate, there would have to be some additional force mediated by a massless or ALP or massive graviton order of magnitude mass carrier boson in addition to the X17 to fit the data. So, in the case of X17 which is purported to give rise to a fifth nuclear scale force, you'd also need a sixth force to explain DM-ordinary matter correlations.

andrew said...

The complete X17 literature at arXiv: arXiv:2008.02733 [pdf, other] hep-ph nucl-th
Neutron star structure with nuclear force mediated by hypothetical X17 boson

Authors: Vlasios Petousis, Martin Veselsky, Jozef Leja

Abstract: The reported 17 MeV boson - which has been proposed as an explanation to the 8Be and 4He anomaly - investigated in the context of its possible influence to the neutron stars structure. Implementing the mv=17 MeV to the nuclear equation of state using different incompressibility values K0=245 MeV and K0=260 MeV and solving the Tolman-Oppenheimer-Volkoff equations, we es… ▽ More
Submitted 5 August, 2020; originally announced August 2020.

Comments: 5 pages, 3 figures

arXiv:2006.01018 [pdf, other] hep-ph
Is the X17 composed of four bare quarks?

Authors: Hua-Xing Chen

Abstract: …contribute much to them. This indicates the possible existence of tetraquark states composed of bare quarks with abnormally small masses. We study the possible assignment of the X17 as such a state. We argue that the Atomki experiments might observe a new type of nuclear decay process, where sea quarks take away the extra energy of the nucleus. A unique fe… ▽ More
Submitted 3 June, 2020; v1 submitted 1 June, 2020; originally announced June 2020.

Comments: 16 pages, 8 figures, revised version with several typos fixed

arXiv:2005.10643 [pdf, ps, other] nucl-th
Anomalous Internal Pair Creation

Authors: Péter Kálmán, Tamás Keszthelyi

Abstract: …boson called X17 particle. In this paper it is brought up that such enhancements can be generated by higher order processes. It is found that nuclear transitions, the transition energy of which is significantly lower than the whole transition energy, can cause peaked angle dependence in electron-positron angular correlation. ▽ More
Submitted 23 April, 2020; originally announced May 2020.

arXiv:2003.07207 [pdf, ps, other] hep-ph physics.atom-ph
Fifth Force and Hyperfine Splitting in Bound Systems

Authors: Ulrich D. Jentschura

Abstract: …pairs from nuclear transitions from excited states in 8Be and 4He) indicate the possible existence of a particle of a rest mass energy of roughly 17 MeV. The so-called X17 particle constitutes a virtual state in the process, preceding the emission of the electron-positron pair. Based on the symmetry of the nuclear transitions (1+ to 0+ and 0− to… ▽ More
Submitted 2 June, 2020; v1 submitted 12 March, 2020; originally announced March 2020.

Comments: 14 pages; RevTeX

Journal ref: Phys. Rev. A 101, 062503 (2020)

arXiv:2003.05722 [pdf, other] hep-ph hep-ex nucl-th
X17: A new force, or evidence for a hard γ+γ process?
Authors: Benjamin Koch
Abstract: It is pointed out that the "X17 puzzle" is likely to be explained by a nuclear decay chain and a conversion of the two resulting highly energetic γs into an electron-positron pair.
Submitted 24 March, 2020; v1 submitted 12 March, 2020; originally announced March 2020.

arXiv:2002.07496 [pdf, other] hep-ph
Implication of the hidden sub-GeV bosons for the (g−2)μ, 8Be-4He anomaly, proton charge radius, EDM of fermions and dark axion portal
Authors: D. V. Kirpichnikov, Valery E. Lyubovitskij, Alexey S. Zhevlakov

arXiv:2001.08995 [pdf, ps, other] nucl-th nucl-ex
Evidence of quantum phase transition in carbon-12 in a 3α model and the problem of hypothetical X17 boson
Authors: E. M. Tursunov

arXiv:2001.04864 [pdf, other] nucl-th astro-ph.HE hep-ph nucl-ex
Open string QED meson description of the X17 particle and dark matter
Authors: Cheuk-Yin Wong

arXiv:1910.10459 [pdf, ps, other] nucl-ex
New evidence supporting the existence of the hypothetic X17 particle
Authors: A. J. Krasznahorkay, M. Csatlos, L. Csige, J. Gulyas, M. Koszta, B. Szihalmi, J. Timar, D. S. Firak, A. Nagy, N. J. Sas, A. Krasznahorkay

arXiv:1907.04517 [pdf, other] hep-ph hep-th
Extra dimension of space-time exposed by anomalies at low energy
Authors: Nguyen Ai Viet

neo said...

"To be clear, the X17 particle, if it existed, would be perfectly capable of being a bosonic dark matter candidate."

even with a half life of 10-14 s?

what do you know about U(1)B and U(1) B-L gauge theory that X17 is based on?

of all the BSM physics, this one could be confirmed or refuted in the next couple of years via ep collisions and it is being actively searched by multiple research teams already looking for dark photons.

i suspect dark matter, MOND, SUSY, proton decay, EDM, string theory will not be resolved within our lifetime

andrew said...

@neo A new X17 article from me is scheduled to publish late tonight.