Observablen−n¯oscillations with new physics at the LHC

Abstract

We explore extensions of the MSSM in which TeV scale vector-like multiplets can mediate observable n − n oscillations, without causing conflict with the proton decay experiments, with a U(1) symmetry playing an important role. The colored vector-like particles, in particular, may be found at the LHC through some decay modes arising from their direct couplings to quarks.Low energy supersymmetry (SUSY) provides one of the most compelling extensions of the standard model (SM). In particular, the minimal supersymmetric standard model (MSSM) with unbroken 'matter' parity offers an attractive resolution of the gauge hierarchy problem, delivers a compelling cold dark matter candidate, and nicely implements gauge coupling unification. It also predicts that the lightest CP-even Higgs mass, assuming TeV scale soft SUSY breaking parameters, cannot be much heavier than about 130 GeV. It is gratifying to note that the MSSM predictions will be tested at the soon to be launched Large Hadron Collider (LHC).Possible extensions of the MSSM have been frequently discussed in the literature. In a recent paper [1] it was shown that by adding new TeV scale vector-like particles, it is possible to increase the upper bound on the mass of the lightest CP-even Higgs boson to 160 GeV, provided there exists a direct coupling between the new vector-like particles and the MSSM Higgs fields. To retain gauge coupling unification it is helpful that the new particles comprise the same particle content as the complete SU(5) multiplets such as 5 + 5 and 10 + 10.Since LHC is a hadron collider, it is expected that the colored components of these vectorlike fields can be produced there. In general, these colored particles will couple to quarks and leptons, which makes the discussion of the creation and decay modes of the vector-like matter quite interesting [2]. In addition to the direct creation of the new particles in LHC, the new couplings with the new colored particles can generate, as we will see, exotic phenomena related to baryon number violation. Indeed, it has been noted in the past that n − n oscillations [3,4,5,6,7,8,9,10,11] can be experimentally accessible if there exist TeV scale colored particles with appropriate baryon number violating couplings to the known particles [8]. Baryon number B is conserved to all orders in perturbation theory in the standard model, up to Planck scale suppressed operators. On the other hand, a naive SUSY extension of the SM leads to rapid nucleon decay via renormalizable couplings. This disaster is usually prevented by introducing a discrete Z 2 'matter' (or R) parity. This version of the MSSM with unbroken matter parity allows nucleon decay to proceed via Planck scale suppressed dimensionfive operators. With the current proton lifetime limit τ p 5 × 10 33 yrs., this implies that the dimensionless coefficients accompanying these operators must be tiny, of order 10 −7 or less. The coefficients can usually be arranged to be tiny by a flavor structure similar to the small Yukawa couplings for the first generatio...

Phenomenology ofn−n¯oscillations revisited

“…[1]. Although particular |∆B| = 1 operators, such as those that mediate n → e − π + , e.g., can also give rise to n-n oscillations, Mohapatra and others have emphasized that the origin of nucleon decay and n-n oscillations can be completely different [2][3][4][5][6][7][8]. Recently, moreover, simple models that give rise to n-n oscillations but not nucleon decay have been enumerated [7].…”

Dark side of Higgs diphoton decays and muong−2

“…However, if the new fermions are vector-like doublets and singlets, the existence of heavy gauge invariant masses combined with mixing induced by the Higgs-singlet-doublet Yukawa couplings can change the sign of the new fermion loop contribution and actually enhance the Higgs diphoton branching ratio. Variants of that possibility have been suggested by a number of authors [9][10][11][12][13][14][15][16] who have discussed such scenarios in detail, including experimental constraints on properties of new vector-like fermions [17].…”

“…(15) and (16). For example, in a 2-generation extension of the model, the charged leptons carrying opposite dark charges are likely to cancel partially and somewhat reduce the rate of H → γZ d (Fig.…”

Revisit to non-decoupling MSSM

“…For example, b → s transition mediated by the scalar top quark (stop) loop in MSSM may cancel the top quark loop in SM and 2HDM in some parameter region. One can thus expect that light stop in MSSM may significantly reduce the flavor violation [24]. In this Letter, we start with this argument and study whether scenarios with light stop can resolve the tension in flavor physics due to the light charged Higgs H ± .…”