Recent papers on particle masses

[mitchell porter]

http://arxiv.org/abs/1612.03825
Towards a new paradigm for quark-lepton unification
Christopher Smith
(Submitted on 12 Dec 2016)

The quark and lepton mass patterns upset their naive unification. In this paper, a new approach to solve this problem is proposed. Model-independently, we find that a successful unification can be achieved. A mechanism is identified by which the large top quark mass renders its third-generation leptonic partner very light. This state is thus identified with the electron. We then provide a generic dynamical implementation of this mechanism, using tree-level exchanges of vector leptons to relate the quark and lepton flavor structures. In a supersymmetric context, this same mechanism splits the squark masses, and third generation squarks end up much lighter than the others. Finally, the implementation of this mechanism in SU(5) GUT permits to avoid introducing any flavor structure beyond the two minimal Yukawa couplings, ensuring the absence of unknown mixing matrices and their potentially large impact on FCNC.

My comments: This is my favorite. It is a modification of Minimal Flavor Violation (MFV), a popular philosophy which posits that any BSM couplings may only involve powers of the yukawa matrices. Here the author instead supposes the existence of some functional relation connecting quark and lepton yukawas, and devises criteria for producing desired effects. The standouts for me are (1) connecting the heavy top quark to light leptons (2) the relationship between MFV and holomorphy.

http://arxiv.org/abs/1612.03069
Gauge hierarchy problem in asymptotically safe gravity--the resurgence mechanism
Christof Wetterich, Masatoshi Yamada
(Submitted on 9 Dec 2016)

The gauge hierarchy problem could find a solution within the scenario of asymptotic safety for quantum gravity. We discuss a "resurgence mechanism" where the running dimensionless coupling responsible for the Higgs scalar mass first decreases in the ultraviolet regime and subsequently increases in the infrared regime. A gravity induced large anomalous dimension plays a crucial role for the required "self-tuned criticality" in the ultraviolet regime beyond the Planck scale.

My comments: In a way this is a sequel to the famous 2006 paper which predicted the Higgs boson mass. Here the topic is the hierarchy problem, the smallness of the Higgs mass relative to the Planck scale. Warning, what the authors call "resurgence" has no connection to the concept of resurgence from complex analysis, recently a hot topic in quantum field theory.

http://arxiv.org/abs/1611.09797
Radiatively generated hierarchy of lepton and quark masses
A. E. Cárcamo Hernández, Sergey Kovalenko, Ivan Schmidt
(Submitted on 29 Nov 2016)

We propose a model for radiatively generating the hierarchy of the Standard Model (SM) fermion masses: tree-level top quark mass; 1-loop bottom, charm, tau and muon masses; 2-loop masses for the light up, down and strange quarks as well as for the electron; and 4-loop masses for the light active neutrinos. Our model is based on a softly-broken S3×Z2 discrete symmetry. Its scalar sector consists only of one SM Higgs doublet and three electrically neutral SM-singlet scalars. We do not need to invoke neither electrically charged scalar fields, nor an extra SU2L scalar doublet, nor the spontaneous breaking of the discrete group, which are typical for other radiative models in the literature. The model features a viable scalar dark matter candidate.

My comments: In this paper, a judicious choice of symmetries and representations ensures that only the top quark has a tree-level mass. All other fermions get their masses from loop effects. It is not elegant, but it is a proof of concept.

 

[kodama]

mitchell porter

if LHC reports no evidence of SUSY in 2016 run or compositeness in the higgs, or extra dimensions, does this support http://arxiv.org/abs/1612.03069
Gauge hierarchy problem in asymptotically safe gravity--the resurgence mechanism
Christof Wetterich, Masatoshi Yamada

as the solution to the hiearchy problem?

 

[mitchell porter]

There is a mildly notorious paper (Bardeen 1995) which introduced the idea that there is no finetuning problem for the standard model Higgs, because the problematic quadratic divergences that have to be cancelled, can be made to look tamely logarithmic in a different series expansion. I am wondering if Wetterich has something similar in mind - in section IV, when this issue is finally addressed, the authors just blithely say "no fine-tuning problem exists from the point of view of the renormalization group" and cite a bunch of old papers by Wetterich. I can't really judge this paper until I understand exactly what the argument is.