LHC Physics Mini Workshop

LHC is coming soon, every one in particle physics is excited. And you can smell in the air how crazily LHC-driven they are. The mini workshop of LHC physics was held at UMD, for model builders to discuss the phenomenology of some model which are expected to be tested on LHC.

Quirks:
Markus Luty and Roni Harnik
Both of them talked about “quirk”(sounds like the bird who calls “quark, quark, quark” catches a cold). Quirk is the simplest extension of SM gauge symmetry. It’s a QCD inspired SU(N) field, with it’s strong coupling scale . So if you stretch a quirk-antiquirk pair, the energy reserved in a unit length is , unlike QCD, it is less than the energy required for producing another quirk-antiquirk pair, so the string will never broken. It can be stretched to macro scale, depending on the cutoff. Because of the string, this pair can oscillate like a spring. This gives the quirk very rich phenomenology. The two talks focused on the detection signal of quirks, they argued about different life time of the string before it annihilates and the stuff shaken off during the oscillation.
Markus’ quirks also carry QCD colors. So they will be surrounded by quarks and gluons to form a so called “brown muck”. When the string is oscillating, soft pions are the dominating shaken off particles. They lifetime of the string is estimated by using WKB approximation of the wave function of a quantum oscillator, and then considering the energy and angular momentum change by shaking off pions
Roni actually studied squirks, which are superpartners of quirks. They are uncolored under QCD. And in his “folded SUSY” model, squarks and quirks are orbifolded out by symmetry, leaving quark and uncolored squirks to be superpartners. This scenario can be realized in extra dimension. Since the squirks are uncolored, the dominating shaken off stuff are soft photons and glueballs(I do not understand why there are still gluons even though they are not colored.). And the life time is longer since the energy taken away by photons are much lower.

Loopy fermion mass:
Patrick Fox
This is most precise “posdiction” of fermion mass I have ever seen, which is too good to be true. But it’s interesting and maybe useful to my project. In this model, it assumes that only top quark (or one quark which we call “top”) gets mass at tree level, and all the other uptype fermions get their mass at loop level.
The conventional yukawa term is forbidden by a new U(1) symmetry of Higgs, so another U(1) charged scalar field is introduced to form a 5 dimensional operator, whose UV completion is the propagator of a massive U(1) charged fermion . The UV completion allows only one type of quark coupled to and , so after this U(1) symmetry is broken by vev of , only one type of quark obtain mass. But my question is, is there any symmetry to forbid other types of fermions in this coupling?
The next work is more generic. By introducing a QCD and EW charged scalar field r and a set of coupling constants, the following fermions get mass at 1,2,3,4,5 loops level respectively: . The generated mass are very close to the real values, by varying the couplings only between 0.3 and 3. This is the most beautiful part of the model.
The down type masses are much more messier. They have to introduce several weird fields and coupling terms, but the couplings are still order one. And the CKM matrix is in the right form. Neutrino mass is not explained in this model. But it can be done via seesaw mechanism.
The most intriguing LHC signals will be those colored and charged scalar fields. The constrain of available data is , which gives no hope to see them at LHC. But the constrain for a scalar field for downtype mass is .