Top 2014: Theory Summary

This write-up is the summary of the theoretical presentations at the Top 2014 Workshop held in Mandelieu France from September 29 to October 3, 2014.Comment: 7 page

Dark Matter from Unification of Color and Baryon Number

We analyze a recently proposed extension of the Standard Model based on the SU(4) x SU(2)_L x U(1)_X gauge group, in which baryon number is interpreted as the fourth color and dark matter emerges as a neutral partner of the ordinary quarks under SU(4). We show that under well-motivated minimal flavor-violating assumptions the particle spectrum contains a heavy dark matter candidate which is dominantly the partner of the right-handed top quark. Assuming a standard cosmology, the correct thermal relic density through freeze-out is obtained for dark matter masses around 2 - 3 TeV. We examine the constraints and future prospects for direct and indirect searches for dark matter. We also briefly discuss the LHC phenomenology, which is rich in top quark signatures, and investigate the prospects for discovery at a 100 TeV hadron collider.Comment: 6 pages, 5 figure

A Fat Higgs with a Fat Top

A new variant of the supersymmetric Fat Higgs model is presented in which the MSSM Higgses as well as the top quark are composite. The underlying theory is an s-confining SU(3) gauge theory with the MSSM gauge groups realized as gauged sub-groups of the chiral flavor symmetries. This motivates the large Yukawas necessary for the large top mass and SM-like Higgs of mass>>M_Z in a natural way as the residual of the strong dynamics responsible for the composites. This removes fine-tuning associated with these couplings present in the original Fat Higgs and New Fat Higgs models, respectively.Comment: 17 pages, 4 figures, Latex2e, uses JHEP3.cls and youngtab.sty, new references adde

Extended MSSM Neutralinos as the Source of the PAMELA Positron Excess

We consider a scenario within the Minimal Supersymmetric Standard Model extended by a singlet chiral superfield, in which neutralino dark matter annihilates to light singlet-like Higgs bosons, which proceed to decay to either electron-positron or muon-antimuon pairs. Unlike neutralino annihilations in the MSSM, this model can provide a good fit to the PAMELA cosmic ray positron fraction excess. Furthermore, the singlet-like scalar Higgs can induce a large Sommerfeld enhancement and provide an annihilation rate sufficient to accommodate the observed positron excess

A High Quality Composite Axion

The strong CP problem is a compelling motivation for physics beyond the Standard Model. The most popular solutions invoke a global Peccei-Quinn symmetry, but are challenged by quantum gravitational corrections which are thought to be incompatible with global symmetries, arguing that realistic theories contain additional structure. We explore a construction in which the Peccei-Quinn symmetry is protected to arbitrary order by virtue of a supersymmetric, confining $SU(N)_L \times SU(N) \times SU(N)_R \times U(1)_X$ product gauge group, achieving $\bar\theta < 10^{-11}$ for an $SU(5)$ model with $f_a \lesssim 3 \times 10^{11}$ GeV. This construction leads to low energy predictions such as a $U(1)_X$ gauge symmetry, and for $X = B-L$ engineers a naturally order ~TeV value for the $\mu$ parameter of the MSSM.Comment: 17 pages, 2 figures, 3 table

Top Spin and Experimental Tests

We examine pair mass dependence near threshold as a means to measure the spin of the top quark in hadron collisions, and we discuss the possibility that a top squark signal could be hidden among the top events.Comment: 9 pages, RevTeX, 3 figures. Contribution to the Thinkshop on Top-Quark Physics for the Tevatron Run II, Fermilab, October 16 - 18, 199

Triplet-Quadruplet Dark Matter

We explore a dark matter model extending the standard model particle content by one fermionic $SU(2)_L$ triplet and two fermionic $SU(2)_L$ quadruplets, leading to a minimal realistic UV-complete model of electroweakly interacting dark matter which interacts with the Higgs doublet at tree level via two kinds of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum of the dark sector consists of three Majorana fermions, three singly charged fermions, and one doubly charged fermion, with the lightest neutral fermion $\chi_1^0$ serving as a dark matter candidate. A typical spectrum exhibits a large degree of degeneracy in mass between the neutral and charged fermions, and we examine the one-loop corrections to the mass differences to ensure that the lightest particle is neutral. We identify regions of parameter space for which the dark matter abundance is saturated for a standard cosmology, including coannihilation channels, and find that this is typically achieved for $m_{\chi_1^0}\sim 2.4~\mathrm{TeV}$. Constraints from precision electroweak measurements, searches for dark matter scattering with nuclei, and dark matter annihilation are important, but leave open a viable range for a thermal relic.Comment: 27 pages, 6 figures. v2: minor revisions to match published versio