Abstract
Abstract We show that a large mixing between the right-handed charm and top squarks (i) is allowed by low-energy flavour constraints; (ii) reduces the experimental bound on the stop mass; (iii) has a mild, but beneficial, effect on fine-tuning; (iv) leads to interesting signatures at the LHC not presently investigated by experiments. We estimate the current bound on the stop mass, in presence of flavour mixing, and discuss the new collider signatures. The signal in the "Image missing" channel is large enough that it can be immediately searched for experimentally, while the signature with same-sign tops and "Image missing" requires a luminosity upgrade of the LHC.
Highlights
Λ is the scale of supersymmetry-breaking mediation, Yu is the up-type Yukawa matrix, m Q,U are the left and right up-squark mass matrices, and Au is the matrix of trilinear couplings
We show that a large mixing between the right-handed charm and top squarks (i) is allowed by low-energy flavour constraints; (ii) reduces the experimental bound on the stop mass; (iii) has a mild, but beneficial, effect on fine-tuning; (iv) leads to interesting signatures at the LHC not presently investigated by experiments
One would naively conclude that having no flavour mixing is the most favourable situation to minimise the amount of fine tuning, while satisfying the experimental bounds on stop masses
Summary
For a fixed value of m2 ∼ 550 GeV the exclusion contour in m1 is not single valued This stems from the fact that the bound on the stop cross section (shown by the black curve in figure 1) is steeply falling near stop masses of ∼ 380 GeV, faster than the corresponding theory prediction for the stop pair production. This implies that unlike what one would naively expect, for a fixed m2 value, when the mass of m1 is increased the bound becomes stronger, for this narrow region of m1.
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