We revisit the issue of the limit on the scale of left-right symmetry breaking. We focus on the minimal SUð2ÞL SUð2ÞR Uð1ÞBL gauge theory with the seesaw mechanism and discuss the two possibilities of defining left-right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, MWR > 2:5 TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on MWR is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the standard model and CP violation in the B sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation.We revisit the issue of the limit on the scale of left-right symmetry breaking. We focus on the minimal SU(2)(L) x SU(2)(R) x U(1)(B-L) gauge theory with the seesaw mechanism and discuss the two possibilities of defining left-right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, M(WR) > 2.5 TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on M(WR) is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the standard model and CP violation in the B sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation
We revisit the ∆F = 2 transitions in the K and B d,s neutral meson systems in the context of the minimal Left-Right symmetric model. We take into account, in addition to up-to-date phenomenological data, the contributions related to the renormalization of the flavor-changing neutral Higgs tree-level amplitude. These contributions were neglected in recent discussions, albeit formally needed in order to obtain a gauge independent result. Their impact on the minimal LR model is crucial and twofold. First, the effects are relevant in B meson oscillations, for both CP conserving and CP violating observables, so that for the first time these imply constraints on the LR scenario which compete with those of the K sector (plagued by long-distance uncertainties). Second, they sizably contribute to the indirect kaon CP violation parameter ε. We discuss the bounds from B and K mesons in both cases of LR symmetry: generalized parity (P) and charge conjugation (C). In the case of P, the interplay between the CP-violation parameters ε and ε leads us to rule out the regime of very hierarchical bidoublet vacuum expectation values v2/v1 < m b /mt 0.02. In general, by minimizing the scalar field contribution up to the limit of the perturbative regime and by definite values of the relevant CP phases in the charged right-handed currents, we find that a right-handed gauge boson WR as light as 3 TeV is allowed at the 95% CL. This is well within the reach of direct detection at the next LHC run. If not discovered, within a decade the upgraded LHCb and Super B factories may reach an indirect sensitivity to a Left-Right scale of 8 TeV.
In the minimal Left-Right model the choice of left-right symmetry is twofold: either generalized parity P or charge conjugation C. In the minimal model with spontaneously broken strict P, a large tree-level contribution to strong CP violation can be computed in terms of the spontaneous phase α. Searches for the neutron electric dipole moments then constrain the size of α. Following the latest update on indirect CP violation in the kaon sector, a bound on WR mass at 20 TeV is set. Possible ways out of this bound require a further hypothesis, either a relaxation mechanism or explicit breaking of P. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is re-computed and provides an estimate of the weak contribution. Combining this constraint with other CP violating observables in the kaon sector allows for MW R 3 TeV. On the other hand, C-symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.
We show that within the Left-Right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs with the triplet that breaks parity. As a result, the Higgs can act as a gateway to the origin of heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign di-leptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches.PACS numbers: 14.80. Bn, 13.35.Hb The discovery of the Higgs boson [1,2] allows to test the mechanism of elementary particle mass generation at the LHC [3]. Compared to this success, the problem of neutrino mass in the Standard Model (SM) appears acute. Neutrinos may be their own antiparticles [4], and lead to lepton number violation (LNV). The canonical way of searching for LNV, neutrino-less double beta decay (0ν2β) [5], can be induced by light Majorana neutrinos or by new physics [6]. The latter, needed for neutrino mass, can be provided by the celebrated seesaw mechanism [7][8][9][10][11]. In particular, Left-Right symmetric models (LRSM) [12], designed to explain parity violation of weak interactions [13], embed naturally the seesaw [7,8].With the left-right (LR) scale in the TeV range, 0ν2β may be dominated by heavy Majorana neutrino (N ) exchange [14,15], which may become favored in view of the cosmological bound on light neutrino masses.A direct strategy for LNV searches at hadron colliders was suggested in [16] by Keung and Senjanović (KS) [17]. The KS production of heavy Majorana neutrinos would reveal LNV and relate directly to 0ν2β [15,18] and lepton flavor violation (LFV) [19,20]. The Dirac mass is predicted [21] and may be tested at the LHC through LNV decays, uncovering the underlying seesaw mechanism and connecting to electric dipole moments [21,22]. Indirect constraints [23][24][25][26][27] played an important role and comprehensive analyses [28,29] allow the LR scale well within the ∼ 6 TeV reach of the LHC [30].In this Letter we show that LHC can probe a new channel, connecting Higgs physics to restoration of parity. We exploit the fact that the SM Higgs can have a sizeable mixing with the triplet that breaks spontaneously LR symmetry and provides a mass to N . Through this mixing the Higgs can decay to a pair of N [31]. Therefore, it can probe their Yukawa couplings via a LNV final state with two same or opposite sign charged leptons and four jets, as shown on Fig. 1. The relevant range of N masses * amaiezza@ific.uv.es † miha.nemevsek@ijs.si ‡ fabrizio.nesti@irb.hr FIG. 1. Dominant diagram leading to LNV Higgs decay.typically leads to displaced vertices. Higgs decay to RH neutrinos was mentioned in [32] and studied in [33] with effective operators, pointing out the LNV character and vertex displacement. Here, in the LRSM, the LNV decay is probing the origin of N masses, just as the standard decays te...
The scalar sector of the minimal Left-Right model at TeV scale is revisited in light of the large quartic coupling needed for a heavy flavor-changing scalar. The stability and perturbativity of the effective potential is discussed and merged with constraints from low-energy processes. Thus the perturbative level of the Left-Right scale is sharpened. Lower limits on the triplet scalars are also derived: the left-handed triplet is bounded by oblique parameters, while the doubly-charged right- handed component is limited by the h → γγ, Zγ decays. Current constraints disfavor their detection as long as WR is within the reach of the LHC
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