Contrarian Astronomy Results

One recent paper makes the case that one fairly small spiral galaxy has considerable unaccounted for apparent mass in its central region, contrary to the predictions of MOND in a system well within its range of applicability and also demonstrating an unusual cuspy dark matter profile in a Cold Dark Matter paradigm, unlike most observed galaxies, despite the fact that the NFW dark matter halo distribution which an analytical treatment of collisionless CDM should produce.

It isn't at all clear why this galaxy is an outlier.

(I am short for time today, so I will cut corners in presenting the underlying paper and abstracts.)

Dark Matter in the Central Region of the Spiral Galaxy NGC 4321

Israa Abdulqasim Mohammed Ali, Chorng-Yuan Hwang, Zamri Zainal Abidin

(Submitted on 13 Dec 2018)

We present our results of 12 CO(1-0) transition in the central region of NGC 4321 using the Atacama Large Millimeter and Sub-millimeter Array (ALMA). We found an unaccounted mass of 2.3×109M⊙ within the central 0.7 kpc of this galaxy. The expected mass of the supermassive black hole (SMBH) in this galaxy is much smaller than the unaccounted mass. The invisible mass is likely caused by dark matter in the central region of the galaxy, indicating a cuspy dark matter profile. We also investigated the Modified Newtonian Dynamics (MOND) as an alternative mechanism to explain the invisible mass. We noted that at the radius of 0.7 kpc of the galaxy, the acceleration is about 1.04×10−7 cm s−2, which is much larger than the critical acceleration a0∼1.2×10−8 cm s−2 in the MOND theory, suggesting that theory might not be able explain the unseen mass problem in central region of this galaxy.

Another new paper seeks to explain the discrepancies between two different Hubble constant measurements by different methods by assuming contrary to the Plank experiment's conclusions, that there are four, rather than three kinds of neutrinos. The Plank experiment has favored three neutrino types (which implies a 3.045 effective number of neutrino types, Neff) on a 5 sigma basis, which turns out to be model dependent, while the contrarian view interpreting the data with a different model, favors four neutrino types over three on a 3 sigma basis. The stark contrast from more or less the same input data, demonstrates well the limits of statistical significance in the face of large theoretical uncertainties.

Is the H0 tension suggesting a 4th neutrino's generation?

S. Carneiro, P. C. de Holanda, C. Pigozzo, F. Sobreira

(Submitted on 14 Dec 2018)

Flavour oscillations experiments are suggesting the existence of a sterile, 4th neutrino's generation with a mass of an eV order. This would mean an additional relativistic degree of freedom in the cosmic inventory, in contradiction with recent results from the Planck satellite, that have confirmed the standard value Neff≈3 for the effective number of relativistic species. On the other hand, the Planck best-fit for the Hubble-Lemaître parameter is in tension with the local value determined with the Hubble Space Telescope, and adjusting Neff is a possible way to overcome such a tension. In this paper we perform a joint analysis of three complementary cosmological distance rulers, namely the CMB acoustic scale measured by Planck, the BAO scale model-independently determined by Verde {\it et al.}, and luminosity distances measured with JLA and Pantheon SNe Ia surveys. Two Gaussian priors were imposed to the analysis, the local expansion rate measured by Riess {\it et al.}, and the baryon density parameter fixed from primordial nucleosynthesis by Cooke {\it et al.}. For the sake of generality, two different models are used in the tests, the standard ΛCDM model and a generalised Chaplygin gas. The best-fit gives Neff≈4 in both models, with a Chaplygin gas parameter slightly negative, α≈−0.04. The standard value Neff≈3 is ruled out with ≈3σ.

Two other recent papers also consider Neff. One does so in the context of lepton number asymmetry and also seeks to resolve the tension in the measurements of the Hubble constant.

Lepton Number and Expansion of the Universe

Cheng Tao Yang, Jeremiah Birrell, Johann Rafelski

(Submitted on 12 Dec 2018)

We show that the non-integer effective number of neutrinos Neffν can be understood as an effect of lepton L asymmetry in the early Universe carried by the Dirac neutrino cosmic background. We show that Neffν=3.36±0.34 (CMB only) and Neffν=3.62±0.25 (CMB and H0) require a ratio between baryon number B and lepton number to be 1.16×10−9⩽B/|L|⩽1.51×10−9. These values are close to the baryon-to-photon ratio 0.57×10−9⩽B/Nγ⩽0.67×10−9. Thus instead of the usual |L|≪Nγ and B≃|L|, we propose to use 0.4⩽|L|/Nγ⩽0.52 and B≪|L| as another natural choice, which resolves the tension between Planck-CMB and H0 and leads to a non-integer value of Neffν>3.

The other tries to link the dark matter aspects of the Concordance Cosmology model use MeV (lukewarm dark matter?) mass dark matter particles with the effective neutrino number.

Neutrino Decoupling Beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation

Miguel Escudero

(Submitted on 13 Dec 2018)

The number of effective relativistic neutrino species represents a fundamental probe of the thermal history of the early Universe, and as such of the Standard Model of Particle Physics. Traditional approaches to the neutrino decoupling are either very technical and computationally expensive, or assume that neutrinos decouple instantaneously. In this work, we aim to fill the gap between these two approaches by modelling the neutrino decoupling in terms of two simple coupled differential equations for the electromagnetic and neutrino sector temperatures, in which all the relevant interactions are taken into account and which allows for a straightforward implementation of BSM species. Upon including finite temperature QED corrections we reach an accuracy on Neff in the SM of 0.01. We illustrate the usefulness of this approach to the neutrino decoupling by considering, in a model independent manner, the impact of MeV thermal dark matter on Neff. We show that Planck rules out electrophilic and neutrinophilic thermal dark matter particles of m<4.4MeVregardless of their spin, and of their annihilation being s-wave or p-wave. We point out that thermal dark matter particles with non-negligible interactions with both electrons and neutrinos are more elusive to CMB observations than purely electrophilic or neutrinophilic ones. In addition, assisted by the accuracy of our approach, we show that CMB Stage-IV experiments will generically test thermal dark matter particles with m≲20MeV. We make publicly available the codes developed for this study at this https URL. 

Finally, a new paper rehashes the warm dark matter paradigm considering self-interacting MeV dark matter particles (lukewarm dark matter?), and finds that the results don't differ greatly from keV mass particle warm dark matter models.

KeV Scale Frozen-in Self-Interacting Fermionic Dark Matter

Haipeng An, Ran Huo, Wanqiang Liu

(Submitted on 13 Dec 2018)

We present a model in which the dark matter particle is frozen-in at MeV scale. In this model, the mediator between the standard model sector and the dark sector can automatically provide a self-interaction for dark matter. The interaction strength is naturally to be the in the region in favor of the cluster mass deficit anomaly. Due to the self-scattering, the Lyman-α constraint can be relaxed to mD≳2 keV. In this region the self-interaction and the Fermi pressure both play roles on forming a dark matter core at the center of the dwarf galaxies.

Yet another new paper evaluates how gravity wave telescope may make it possible to evaluate the "no hair theorem" about black holes observationally.

Hair loss in parity violating gravity

Pratik Wagle, Nicolas Yunes, David Garfinkle, Lydia Bieri

(Submitted on 13 Dec 2018)

The recent detection of gravitational waves by the LIGO/VIRGO collaboration has allowed for the first tests of Einstein's theory in the extreme gravity regime, where the gravitational interaction is simultaneously strong, non-linear and dynamical. One such test concerns the rate at which the binaries inspiral, or equivalently the rate at which the gravitational wave frequency increases, which can constrain the existence of hairy black holes. This is because black holes with scalar hair typically excite dipole radiation, which in turn leads to a faster decay rate and frequency chirping. In this paper, we present a mathematical proof that scalar hair is not sourced in vacuum, spherically symmetric spacetimes when considering extensions of Einstein's theory that break parity in gravity, focusing on dynamical Chern-Simons theory as a particular toy model. This result implies that the observational confirmation of the baldness of black holes cannot be used to constrain parity violation in gravity, unless the black holes observed are also spinning.

In other physics news, there is a new paper from ATLAS and CMS combined regarding the top quark's properties.

Top quark properties

Petra Van Mulders (on behalf of the ATLAS and CMS Collaborations)

(Submitted on 14 Dec 2018)

The multi-purpose experiments at CERN's Large Hadron Collider have a very rich programme in top quark physics. The large amount of data allows for measuring the top quark properties with an unprecedented precision. This document presents some of the properties that have been measured using top quark pair events produced in proton-proton collisions with a centre-of-mass energy of 13 TeV. The focus lies on the measurements of the colour flow, the charge asymmetry and spin correlations in top quark pair events.

A counterpart to the W boson that interacts only with right handed parity particles rather than left handed ones like the ordinary W boson is excluded experimentally up to masses of more than 3 TeV.

Relaxing LHC constraints on the WR mass

Mariana Frank, Özer Özdal, Poulose Poulose

(Submitted on 13 Dec 2018)

We study mass bounds of the WR gauge boson in generic left-right symmetric models. Assuming that the gauge bosons couple universally to quarks and leptons, we allow different gauge couplings gR≠gL and mass mixing, VLCKM≠VRCKM in the left and right sectors. Imposing constraints from collider experiments and K0, Bd, Bs physics, we investigate scenarios where WR is lighter, or heavier than the right handed neutrino νR. In these scenarios, WRmass bounds can be considerably relaxed, while ZR mass bounds are much more stringent. In the case where MWR≤MνR, the experimental constraints come from WR→tb and WR→jj channels, while if MWR≥MνR, the dominant constraints come from WR→ℓℓjj. The observed (expected) limits in the two-dimensional (MWR, MνR) mass plane excluded at 95\% confidence level extend to approximately MWR= 3.1 (3.3) TeV in the ee channel and 3.3 (3.4) TeV in the (μμ) channel, for a large range of right-handed neutrino masses up to MνR= 2.1 (2.1) TeV in the ee channel and 2.6 (2.5) in the (μμ) channel, representing a significant relaxation of the mass bounds.