Notable Recent Physics Research

The Muonic Hydrogen Problem

Two recent physics papers address the fact that protons in muonic hydrogen apparently has a different radius than ordinary hydrogen when not quantum electrodynamics effects should make that possible.

One of the papers argues that this flows from failing to consider general and special relativity correctly in the calculations:

M.M. Giannini, E. Santopinto, "On the proton radius problem" (1 Nov 2013)

The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectroscopy are about 4% different from the electron scattering data. It has been suggested that the proton radius is actually measured in different frames and that, starting from a non relativistic quark model calculation, the Lorentz transformation of the form factors accounts properly for the discepancy. We shall show that the relation between the charge radii measured in different frames can be determined on very general grounds by taking into account the Lorentz transformation of the charge density. In this way, the discrepancy between muonic-hydrogen laser spectroscopy and electron scattering data can be removed.

This result is identical to that of a paper earlier this year by D. Robson, but does so in a manner that the authors of the new paper believes is more rigorous and theoretically correct.  As the earlier paper explains:

Associating the muonic-hydrogen data analysis for the proton charge radius of 0.84087 fm with the rest frame and associating the electron scattering with the Breit frame yields a prediction 0f 0.87944 fm for the proton radius in the relativistic frame. The most recent value deduced via electron scattering from the proton is 0.877(6)fm so that the frame dependence used here yields a plausible solution to the proton radius puzzle.

Another paper, using very general realizations from lattice QCD argues that high energy hadrons are more compact than low energy hadrons (contrary to widespread intuition expressed in some QCD effective theories), and that the high energy of hadrons in the muonic hydrogen system may provide a QCD as opposed to a QED explanation:

Tamar Friedmann, "No Radial Excitations in Low Energy QCD. II. The Shrinking Radius of Hadrons" (Submitted on 12 Oct 2009 (v1), last revised 4 Nov 2013 (this version, v4))

We discuss the implications of our prior results obtained in our companion paper [arXiv:0910.2229]. Inescapably, they lead to three laws governing the size of hadrons, including in particular protons and neutrons that make up the bulk of ordinary matter: a) there are no radial excitations in low-energy QCD; b) the size of a hadron is largest in its ground state; c) the hadron's size shrinks when its orbital excitation increases. The second and third laws follow from the first law. It follows that the path from confinement to asymptotic freedom is a Regge trajectory. It also follows that the top quark is a free, albeit short-lived, quark. [For Note Added regarding experimental support, including the experiments studying muonic hydrogen, and other experiments, see last page.]

Gravitational Impacts on Weak Sector Interactions

Along the same lines as Giannini and Santopinto's paper, a recent paper looks at the role of gravity in Higgs boson and weak boson scattering. The paper predicts scattering effects that can be discerned at the TeV scale and hence that should be possible to observe at the LHC.

Warm Dark Matter

A recent paper compares three varieties of sterile neutrino production: non-resonant, oscillation based; non-resonant, non-oscillation based; and resonant. The paper argues that the first method of sterile neutrino production is inconsistent with Milky Way data, while not ruling out the other two. It also compares the conventional way of stating sterile neutrino mass of 2.5 keV is equivalent of a 0.7 keV thermal mass. The paper also engages in some critical analysis of the assumptions that go into sterile neutrino warm dark matter mass boundaries from other kinds of observations.

Snowmass Paper On New Particles

The latest Snowmass white paper on new particles is a disappointingly unimaginative and unpersuasive argument for building new very expensive colliders to detect new supersymmetric or other new particles or extra dimensions.

The discussion of WIMP dark matter in the white paper, for example, fails to meaningfully acknowledge the serious problems presented by astronomy models and observations with very heavy dark matter particles, despite abundant research on the subject that essentially rules out such heavy WIMPs based on observed dark matter phenomenology at galactic and smaller scales. Similarly, the discussion of compositeness fails to really grapple with the very high energy scales at which compositeness by the measures suggested have already been ruled out.

In areas where the paper really needed to be specific, like low energy blind spots at the LHC, or the waning solidity of the motivation for new TeV scale physics in light of the developments of the last couple years, it was decidely vague.

A Low Energy Effective Weak Force Theory

While mostly interesting as a historical novelty, an effective weak force theory for energies well below the W boson small scale, that does not require W bosons, Z bosons, Higgs bosons, or top quarks, that was explored by some of the leading physicists before these high energy particles were discovered (e.g. Fermi, Feynman, Gell-Mann, Marshak, and Sudarshan), is explored and refined in a recent paper.

The theory works at these low energies, and hence could be applied as a way to simplify calculations where the elaborations necessary to handle high energy situations is not required. It also is useful as a way of elaborating in a historically authentic way how a low energy effective theory can be transformed into a more exact higher energy effective theory and to clarify why the paradigm shift to the Standard Model approach was necessary.

Within The Standard Model Neutrino Mixing Parameter Predictions

A recent paper looks at an approach to add additional group symmetries (C₂*D₃) to the Standard Model lepton interactions in a manner that makes it possible to predict the three theta mixing angles of the PMNS matrix from a single parameter (which can be derived from a function of the three charged lepton masses). It also illustrates the interaction of the lepton masses and the neutrino oscillation mixing parameters.