A New Year has arrived and will have much to offer the field of fundamental physics (predictions are in italics):
* The Planck satellite group will issue a final report addressing the discrepancy between the BICEP-2 results and its own on the value of the tensor mode constant r, which is material to primordial gravitational waves and evidence of inflation, based upon its polarization data (which has been otherwise fully analyzed) and unpublished dust observations in the location where the BICEP-2 group focused their observations. These are expected this month and are expected to largely refute the BICEP-2 claim that they had observed primordial gravitational waves providing strong evidence for particular kinds of inflation theories. Results in addition to Planck and BICEP-2 from other experiments will be announced in 2015 and confirm this conclusion, forcing theorists into the more boring and straightforward inflation models by default.
* The hunt for dark matter will continue, probably inconclusively as it did in 2014, in 2015. Fundamentally, the problem is that the interpretation of any signals or dark matter exclusions is highly model dependent, and we don't know enough about background processes intergalactic space or even in our own Sun's nuclear dynamics and atmospheric physics, to rule out non-dark matter alternatives to observational results.
Particularly notable will be the extent to which claims of cold dark matter theorists that feedback effects from baryonic matter can solve that theory's failure to reproduce a universe like the one observed can be convincingly supported without self-interacting dark matter. I expect that they will fail. Another worry in the cold dark matter camp is that the Bullet Cluster data is incompatible with many versions of this theory. Cold dark matter proponents may start to migrate into the warm dark matter camp at the margins.
Warm dark matter theorists, in contrast, face renewed arguments that the narrow parameter space of this theory is over constrained by Lyman alpha data and other data points, but proponents will ignore or theorize around this limitations.
DAMA is claiming a seasonal direct dark matter detection signal in the warm dark matter mass range in a late December pre-print, but I suspect that upon further inspection, this will turn out to be merely seasonal variation in the solar neutrino background. DAMA has cried wolf before and been disproved by LUX and others.
It also remains to be seen if the 3.5 keV X-ray signal touted this year, which could be a warm dark matter annihilation signal, will really turn out to be something more than emissions of potassium atoms as the "banana camp" has argued. I suspect that either the banana camp will ultimately win this argument, or that the signal will ultimately prove to be too inconsistent across different galaxies to fit a dark matter annihilation interpretation. Fortunately for warm dark matter proponents, the loss of this piece of evidence is not fatal to warm dark matter in general, since its annihilation properties are model dependent.
Modified gravity proponents have marshaled some arguments such as those related to the tightness of fit of galactic rotation curves to MOND predictions with a couple of minor well reasoned adjustments that are inconsistent with both of those theories. But, the leading MOND theory itself, of course, has always underestimated dark matter in galactic clusters and is missing a theoretically well motivated mechanism. Notably, MOND does particularly poorly in the case of non-spherical galactic clusters. And, it can't explain the Bullet cluster.
I am currently inclined to believe that Deur is right in attributing all dark matter phenomena and much or all of dark energy phenomena to non-linear self-interactions of canonical spin-2 gravitons, and that general relativity theorists have failed to correctly model the self-interaction terms of gravitional fields (a quantum gravity analysis using analogies to QCD highlights this conclusions although it isn't an inherently quantum gravitational observation and could be reproduced in a less transparent way with classical GR equations). If Deur is right, we have already discovered all particles that exist except the graviton and all forces that exist. Basically, GR math has had the right basic axioms, but not quite the right mathematical implementation in complex non-spherically symmetric cases, for a century. But, I don't think that this will gain wide acceptance or even recognition in 2015. Certainly, some researchers disagree (and here). Correspondence with Deur indicates that he has limited resources in the next year to devote to this not part of the day job project, and there isn't yet a critical mass of investigators coordinated in investigating this class of non-linear evaluations of GR axioms with gravitons. Others have also noted the critical role that assumptions other than spherical symmetry have on the non-linear effects in GR.
A scalar theory of gravity with a coupling dependent upon the tightness of matter-clustering produces similar results for similar reasons. Others also note that only mild modifications to GR are necessary to eliminate the need for dark matter.
In general, there is not a strong consensus on the way that the non-linear aspects of GR play out in all but the simplest matter distributions. There are strong suggestions that important, but largely unmodeled configurations like the multi-level cellular structure that seems to characterize the actual distribution of matter in the universe, can amplify these non-linear effects to orders of magnitude sufficient to account for a material share of dark matter and dark energy phenomena (see also here arguing that slight inhomogenities in matter-energy density in the radiation density can replicate the effect of dark matter in the lamda CDM model).
Moffat's MOG theory arguably outperforms MOND and has a larger domain of applicability, but like MOND and unlike Deur's analysis, is a purely phenomenological theory without a solid theoretical basis behind it. The formulas derived by each of the investigators is not all that different, which is reassuring (and, of course, necessary for the formulas to match reality). There has been at least one serious effort, however, to reproduce MOG in a manner with a more solid theoretical basis that is generalized to address dark energy as well.
One powerful new dark matter data point we are likely to get in 2015 is increasingly precise data on Milky Way dynamics in previously unobservable parts of our galaxy that can be used to more precisely model a hypothetical Milky Way dark matter halo, and to fine tune modified gravity model parameters.
* The LHC will begin operating again in 2015, but I suspect that the new data will merely confirm what was found in the first run, with greater precision and stronger exclusions for BSM physics. I expect no new physics from the second run. Increased precision in the top quark and Higgs boson mass measurements would be particularly useful in gaining an understanding of the inner workings of the Standard Model by providing data sufficiently precise to rule out many competing within the Standard Model theories.
The most interesting thing that this run of the LHC could (and is likely to) reveal is that the running of the Standard Model coupling constants confirms the Standard Model and contradicts SUSY models up to a significantly higher energy scale than previously expected, effectively adding a death knell to low energy SUSY theories beyond the damage already done so far.
Another new experiment is in the works to measure the weak mixing angle with vast improvements in accuracy, but may take a decade to provide a result.
* Both modified gravity (also here)and loop quantum gravity theories have only relatively meager cosmology work done in those paradigms. The year 2015 will not be the year that either of these theories are used to reconcile these theories to the data supporting the dominant lamda CDM cosmology model.
* Increasingly precise neutrinoless double beta decay experiments will continue to not observe neutrinoless double beta decay with more strict exclusions, but not enough to rule out the Majorana neutrino mass hypothesis (which is probably false in my opinion) yet in 2015.
* Neutrino physics experiments may give us as much as a two sigma insight into the unknown neutrino oscillation and mass hierarchy issues which are currently known only at about a one sigma level, and will add a bit more precision into the PMNS and mass difference constants of the three known neutrinos. A fourth light sterile neutrino will increasingly be recognized as experimentally ruled out.
Precision data from Planck with polarization data has already ruled out a fourth light neutrino species, as reactor data tend to confirm, and strongly bounded the sum of the neutrino masses, which may be the last deep space astronomy contribution to neutrino physics for a while despite efforts to pin it down with supernova and neutron star data.
* New muon anomalous magnetic moment (muon g-2) and muonic hydrogen work in 2015 is likely to tend to resolve the tensions in the existing data with a combination of more rigorous theoretical analysis and increased experimental precision, but may not do so sufficiently to convince everyone that there is no new physics lurking there.
* Short range gravity experiments will be conducted and will find nothing anomalous. The year 2014 did close, however, with a notable new measurement of Newton's constant to high precision by a novel method (about 1.5 sigma different from the current most precise measurement) that makes the combined estimate robust for systemic errors common to other methods. The new cold atom laser measurement method produced a value of G=6.67191(99) x 10^(-11) m^3 kg^(-1) s^(-2), although the four significant digit accuracy still pales in precision compared to many other fundamental physical constant measurements.
* Some new predicted but undiscovered hadrons will likely be detected in 2015, just as they were in 2014. But, there is no good reason to expect breakthroughs in understanding true scalar mesons, axial vector mesons, tetraquarks, pentaquarks, or glueballs. It is unlikely that any of the latter three will be observed definitively in 2015. But, some progress on the front of understanding meson molecules, and baryon molecules involving particles other than protons and neutrons, is likely.
* Efforts to get a next generation collider going will stall in the face of hard economic times and the lack of a compelling scientific reason to build one right away until we know what we are looking for more clearly in light of more LHC and dark matter data.
* There is an outside chance that we could get a data point on a key cosmology and neutrino physics question - the relative proportions of neutrinos and anti-neutrinos in space. This data point is key to understanding and modeling B and L number conservation and violations in cosmology models. If it is very close to 50-50, it could allow for a B-L number conservation theory to solve the baryon asymmetry by bleeding it into an excess of antineutrinos. But, if anti-neutrinos very greatly outnumber "ordinary" neutrinos as widely suspected, then even B-L number conservation can't solve the asymmetry problem even with the help of dark matter, and we need either a non-zero starting point at the Big Bang, or a B-L violating process. On the other hand, if large numbers of black holes have strong magnetic fields as the Milky Way's does, a completely different and novel solution to baryon asymmetry could present itself (i.e. excess matter or anti-matter is inside black holes).
* Another possible dark horse for new interesting physics would be to corroborate a variety of couple of data points suggesting that lepton universality is violated either at the LHC or in neutrino physics experiments.
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