Right-handed Scale Research Articles

Comprehensive analysis of charged lepton flavour violation in the symmetry protected type-I seesaw

The type-I seesaw model is probably the most straightforward and best studied extension of the Standard Model that can account for the tiny active neutrino masses determined from neutrino oscillation data. In this article, we calculate the complete set of one-loop corrections to charged lepton flavour violating processes within this model. We give the results both using exact diagonalisation of the neutrino mass matrix, and at leading order in the seesaw expansion (i.e. mathcal{O} (v2/ {M}_R^2 )). Furthermore, we perform the matching onto the SU(2)L invariant Standard Model Effective Field Theory at the dimension 6 level. These results can be used as initial conditions for the renormalisation group evolution from the right-handed neutrino scale down to the scale of the physical processes, which resums large logarithms. In our numerical analysis, we study the inverse seesaw limit, i.e. the symmetry protected type-I seesaw, where the Wilson coefficient of the Weinberg operator is zero such that sizeable neutrino Yukawas are permissible and relevant effects in charged lepton flavour violating observables are possible. We correlate the different charged lepton flavour violating processes, e.g. ℓ → ℓ′γ, ℓ → 3ℓ′, μ → e conversion and Z → ℓℓ′, taking into account the constraints from electroweak precision observables and tests of lepton flavour universality.

Light sterile neutrinos, left-right symmetry, and 0νββ decay

We investigate neutrinoless double beta (0νββ) decay rates in minimal left-right symmetric models in presence of relatively light right-handed neutrinos. By use of an effective field theory approach, we systematically include all contributions in the model as well as the dependence of the decay amplitude on the masses of right-handed neutrinos. In type-I and type-II seesaw scenarios, we analyze the impact of right-handed neutrinos heavier than about 10 MeV, showing that this effect can lead to a detection of 0νββ decay in the next-generation experiments even for the normal hierarchy and a relatively large right-handed scale set by the mass of hypothetical right-handed gauge bosons. Finally, we comment on a possible connection between light right-handed neutrinos and the strong CP problem.

Broken scaling neutrino mass matrix and leptogenesis based on A4 modular invariance

In this work, we have proposed a modular A4 symmetric model of neutrino mass which, simultaneously, explains observed baryon asymmetry of the Universe (BAU). In minimal extension of the standard model (SM) with two right-handed neutrinos we work in a supersymmetric framework. At Type-I seesaw level, the model predicts scaling in the neutrino mass matrix. In order to have correct low energy phenomenology, we propose two possible scenarios of scale-breaking in the neutrino mass matrix emanating from Type-I seesaw. Scenario-1 is based on the dimension-5 Weinberg operator whereas scenario-2 implements Type-II seesaw via scalar triplet Higgs superfields (∆, overline{Delta } ). Interestingly, the breaking patterns in both, otherwise dynamically different scenarios, are similar which can be attributed to the same charge assignments of superfields (∆, overline{Delta } ) and the Higgs superfield Hu under modular A4 symmetry. The breaking is found to be proportional to the Yukawa coupling of modular weight 10 ( {Y}_{1,1prime}^{10} ). We, further, investigates the predictions of the model under scenario-2 (Type-I+II) for neutrino mass, mixings and matter-antimatter asymmetry of the Universe. The model predicts normal hierarchical neutrino masses and provide a robust range (0.05 − 0.08)eV for sum of neutrino masses (Σmi). Lepton number violating 0νββ decay amplitude (Mee) is obtained to lie in the range (0.04 − 0.06)eV. Future 0νββ decay experiments such as NEXT and nEXO shall pose crucial test for the model. Both CP conserving and CP violating solutions are allowed in the model. Interesting correlations are obtained, specially, between Yukawa couplings of modular weight 2 and complex modulus τ. Contrary to {Y}_2^2 and {Y}_3^2 , the Yukawa coupling {Y}_1^2 is found to be insensitive to τ and thus to CP violation because complex modulus τ is the only source of CP violation in the model. We, also, investigate the prediction of the model for BAU. The model exhibit consistent explanation of BAU for right-handed Majorana neutrino mass scale in the range ((1 − 5) × 1013) GeV.

Perturbativity constraints on U(1)B\u2212L and left-right models and implications for heavy gauge boson searches

We derive perturbativity constraints on beyond standard model scenarios with extra gauge groups, such as SU(2) or U(1), whose generators contribute to the electric charge, and show that there are both upper and lower limits on the additional gauge couplings, from the requirement that the couplings remain perturbative up to the grand unification theory (GUT) scale. This leads to stringent constraints on the masses of the corresponding gauge bosons and their collider phenomenology. We specifically focus on the models based on SU{(2)}_L times U{(1)}_{I_{3R}} times U{(1)}_{B-L} and the left-right symmetric models based on SU(2)L × SU(2)R × U(1)B − L, and discuss the implications of the perturbativity constraints for new gauge boson searches at current and future colliders. In particular, we find that the stringent flavor constraints in the scalar sector of left-right model set a lower bound on the right-handed scale vR ≳ 10 TeV, if all the gauge and quartic couplings are to remain perturbative up to the GUT scale. This precludes the prospects of finding the ZR boson in the left-right model at the LHC, even in the high-luminosity phase, and leaves only a narrow window for the WR boson. A much broader allowed parameter space, with the right-handed scale vR up to ≃ 87 TeV, could be probed at the future 100 TeV collider.

Displaced photon signal from a possible light scalar in minimal left-right seesaw model

We point out that in the minimal left-right realization of TeV scale seesaw for neutrino masses, the neutral scalar from the right-handed $SU(2{)}_{R}$ breaking sector could be much lighter than the right-handed scale. We discuss for the first time the constraints on this particle from low-energy flavor observables and find that the light scalar is necessarily long-lived. We show that it can be searched for at the LHC via displaced signals of a collimated photon jet and can also be tested in current and future high-intensity experiments. In contrast to the unique diphoton signal (and associated jets) in the left-right case, a generic beyond-standard-model light scalar decays mostly to leptons or jets. Thus, the diphoton channel proposed here provides a new avenue to test the left-right framework and reveal the underlying neutrino mass generation mechanism.

Left–right model with TeV fermionic dark matter and unification

The ingredients for a model with a TeV right-handed scale, gauge coupling unification, and suitable dark matter candidates lie at the heart of left–right symmetry with broken D-parity. After detailing the contents of such a model, with SU(2)R self-conjugate fermions at the right-handed scale aiding in unification of couplings, we explore its dark matter implications and collider signatures.

StrongPinvariance, neutron electric dipole moment, and minimal left-right parity at LHC

In the minimal left-right model the choice of left-right symmetry is twofold: either generalized parity $\mathcal{P}$ or charge conjugation $\mathcal{C}$. In the minimal model with spontaneously broken strict $\mathcal{P}$, a large tree-level contribution to strong $CP$ violation can be computed in terms of the spontaneous phase $\ensuremath{\alpha}$. Searches for the neutron electric dipole moments then constrain the size of $\ensuremath{\alpha}$. Following the latest update on indirect $CP$ violation in the kaon sector, a bound on ${W}_{R}$ mass at 20 TeV is set. Possible ways out of this bound require a further hypothesis, either a relaxation mechanism or explicit breaking of $\mathcal{P}$. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is recomputed and provides an estimate of the weak contribution. Combining this constraint with other $CP$-violating observables in the kaon sector allows for ${M}_{{W}_{R}}\ensuremath{\gtrsim}3\text{ }\text{ }\mathrm{TeV}$. On the other hand, $\mathcal{C}$ symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.

B cell lymphoma and myeloma in murine Gaucher's disease. J Pathol 2013; 231: 88–97

Figure 1. Conditional deletion of 9–11 exons of GBA1 induces deficiency of acid β-glucosidase and visceral accumulation of glycosphingolipids: ‘‘Gaucher mice’’. (A) High-performance thin-layer chromatography shows increased β-glucosylceramide concentrations in the spleen of a 15 month-old Gaucher mouse compared with a littermate control (induced GCflox/flox Cremouse); glycosphingolipids in spleen samples obtained from a 3 month-old Gaucher mouse and wild type sibling are also displayed. (B) Enzymatic assay of acid β-glucosidase with 4-MUGP as substrate at pH 5.5 showed reduced activity in spleen and liver tissues from Gaucher mice; acid β-glucosidase activity was significantly higher in spleen and liver tissue obtained from animals with lymphoma. (C) Elevation of spleen and liver but not plasma β-glucosylceramide concentrations in Gaucher mice. Unlike the determinations carried out in target viscera in this disease, plasma concentrations of β-glucosylceramide were not significantly different in Gaucher mice and controls. The left-hand scale of the figure denotes median tissue concentrations of β-glucosylceramide quantified as nmol/g wet tissue; the right-hand scale refers to median plasma concentrations of this glycosphingolipid in μM. (D) In Gaucher mice, abundance of β-glucosylsphingosine, the unacylated congener of β-glucosylceramide in tissues and plasma, was markedly greater than in control strains. The left–hand vertical scale of the figure represents median spleen and liver β-glucosylsphingosine concentrations expressed as nmol/g wet tissue; the right-hand scale denotes median plasma concentrations in nM. *p < 0.05 of medians between Gaucher mice and mice with tumours. †p < 0.05 of medians between mice with tumours and control animals.

The structural basis for peptide selection by the transport receptor OppA

Oligopeptide-binding protein A (OppA) from Lactococcus lactis binds peptides of an exceptionally wide range of lengths (4-35 residues), with no apparent sequence preference. Here, we present the crystal structures of OppA in the open- and closed-liganded conformations. The structures directly explain the protein's phenomenal promiscuity. A huge cavity allows binding of very long peptides, and a lack of constraints for the position of the N and C termini of the ligand is compatible with binding of peptides with varying lengths. Unexpectedly, the peptide's amino-acid composition (but not the exact sequence) appears to have a function in selection, with a preference for proline-rich peptides containing at least one isoleucine. These properties can be related to the physiology of the organism: L. lactis is auxotrophic for branched chain amino acids and favours proline-rich caseins as a source of amino acids. We propose a new mechanism for peptide selection based on amino-acid composition rather than sequence.

Constraining the right-handed scale through kaon mixing in the supersymmetric left-right model

We study flavor-changing neutral current and $CP$ violations in the minimal supersymmetric left-right model. We calculate the beyond-standard-model contributions to the neutral kaon mixing $\ensuremath{\Delta}{M}_{K}$ and $ϵ$, and find it is possible to have a numerical cancellation between the contributions from the right-handed gauge boson and supersymmetric box diagram. With the cancellation, the right-handed $W$-boson mass scale can be lowered to about 2 TeV, well within the search limit of LHC.

General CP violation in minimal left–right symmetric model and constraints on the right-handed scale

In minimal left–right symmetric theories, the requirement of parity invariance allows only one complex phase in the Higgs potential and one in the Yukawa couplings, leading to a two-phase theory with both spontaneous and explicit CP violations. We present a systematic way to solve the right-handed quark mixing matrix analytically in this model and find that the leading order solution has the same hierarchical structure as the left-handed CKM matrix with one more CP-violating phase coming from the complex Higgs vev. Armed with this explicit right-handed mixing matrix, we explore its implications for flavor changing and conserving processes in detail, low-energy CP-violating observables in particular. We report an improved lower bound on the W R mass of 2.5 TeV from Δ M K and Δ M B , and a somewhat higher bound (4 TeV) from kaon decay parameters ϵ, ϵ ′ , and neutron electric dipole moment. The new bound on the flavor-changing neutral Higgs mass is 25 TeV.

EV seesaw with four generations

We extend the eV seesaw scenario to four lepton generations. The LSND anomaly is taken as the right-handed seesaw scale, i.e. m_R ~ eV. The fourth generation then gives a heavy pseudo-Dirac neutrino which largely decouples from other generations, and is relatively stable. One effectively has a 3+3 solution to the LSND anomaly, where we illustrate with numerical solutions. Our study indicates that the third mixing angle sin^2(theta13) is likely less than 0.01.

Neutrinos in a left-right model with a horizontal symmetry

We analyze the lepton sector of a Left-Right Model based on the gauge group SU(2)_L x SU(2)_R x U(1), concentrating mainly on neutrino properties. Using the seesaw mechanism and a horizontal symmetry, we keep the right-handed symmetry breaking scale relatively low, while simultaneously satisfying phenomenological constraints on the light neutrino masses. We take the right-handed scale to be of order 10's of TeV and perform a full numerical analysis of the model's parameter space, subject to experimental constraints on neutrino masses and mixings. The numerical procedure yields results for the right-handed neutrino masses and mixings and the various CP-violating phases. We also discuss phenomenological applications of the model to neutrinoless double beta decay, lepton-flavor-violating decays (including decays such as \tau \to 3\mu) and leptogenesis.

Higgs sector of the left-right model with explicitCPviolation

We explore the Higgs sector of the Minimal Left-Right (LR) Model based on the gauge group $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{R}\ifmmode\times\else\texttimes\fi{}U(1{)}_{B\ensuremath{-}L}$ with explicit $CP$ violation in the Higgs potential. Since flavour-changing neutral current experiments and the small scale of neutrino masses both place stringent constraints on the Higgs potential, we seek to determine whether minima of the Higgs potential exist that are consistent with current experimental bounds. We focus on the case in which the right-handed symmetry-breaking scale is only moderately large, of order 15--50 TeV. Unlike the case in which the Higgs potential is $CP$-invariant, the $CP$ noninvariant case does yield viable scenarios, although these require a small amount of fine-tuning. We consider a LR model supplemented by an additional $U(1)$ horizontal symmetry, which results in a Higgs sector consistent with current experimental constraints and a realistic spectrum of neutrino masses.

Neutrino masses and mixing, quark-lepton symmetry, and strong right-handed neutrino hierarchy

Assuming the same form of all mass matrices as motivated by quark-lepton symmetry, we discuss conditions under which bi-large mixing in the lepton sector can be obtained with a minimal amount of fine tuning requirements for possible models. We assume hierarchical mass matrices, dominated by the 3-3 element, with off-diagonal elements much smaller than the larger neighboring diagonal element. Characteristic features of this scenario are strong hierarchy in masses of right-handed neutrinos, and comparable contributions of both lighter right-handed neutrinos to the resulting left-handed neutrino Majorana mass matrix. Due to obvious quark lepton symmetry, this approach can be embedded into grand unified theories. The mass of the lightest neutrino does not depend on details of a model in the leading order. The right-handed neutrino scale can be identified with the GUT scale in which case the mass of the lightest neutrino is given as (m_{top}^2/M_{GUT}) |U_{\tau 1}|^2.

Soft lepton-flavor violation in a multi-Higgs-doublet seesaw model

We consider the Standard Model with an arbitrary number n_H of Higgs doublets and enlarge the lepton sector by adding to each lepton family \ell a right-handed neutrino singlet \nu_{\ell R}. We assume that all Yukawa-coupling matrices are diagonal, but the Majorana mass matrix M_R of the right-handed neutrino singlets is an arbitrary symmetric matrix, thereby introducing an explicit but soft violation of all lepton numbers. We investigate lepton-flavor-violating processes within this model. We pay particular attention to the large-m_R behavior of the amplitudes for these processes, where m_R is the order of magnitude of the matrix elements of M_R. While the amplitudes for processes like tau^- --> mu^- gamma and Z --> tau^+ mu^- drop as 1/m_R^2 for arbitrary n_H, processes like tau^- --> mu^- e^+ e^- and mu^- --> e^- e^+ e^- obey this power law only for n_H = 1. For n_H \geq 2, on the contrary, those amplitudes do not fall off when m_R increases, rather they converge towards constants. This non-decoupling of the right-handed scale occurs because of the sub-process ell^- --> ell'^- {S_b^0}^*, where S_b^0 is a neutral scalar which subsequently decays to e^+ e^-. That sub-process has a contribution from charged-scalar exchange which, for n_H \geq 2, does not decrease when m_R tends to infinity. We also perform a general study of the non-decoupling and argue that, after performing the limit m_R --> \infty and removing the \nu_R from the Lagrangian, our model becomes a multi-Higgs-doublet Standard Model with suppressed flavor-changing Yukawa couplings. Finally, we show that, with the usual assumptions about the mass scales in the seesaw mechanism, the branching ratios of all lepton-flavor-changing processes are several orders of magnitude smaller than present experimental limits.

Phenomenology of left-right supersymmetric models with brokenB−Lsymmetry

We discuss the implications of R parity breaking through spontaneous $B\ensuremath{-}L$ breaking in left--right supersymmetric models. We give expressions for three generations of neutrino--neutralino and charged--lepton--chargino mixings. We find the masses of the light neutrinos at both the tree and one loop levels. We explore the most stringent bounds on the parameters of the LRSUSY model coming from rare leptonic processes. These phenomena severely restrict the parameters in both the R-parity violating and R-parity conserving sectors. We find that such models are likely to produce light doubly charged Higgs bosons and fermions, with masses as low as ${M}_{{\ensuremath{\Delta}}^{++},{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\Delta}}}^{++}}&lt;~200$ GeV for $\mathrm{tan}\ensuremath{\beta}=1;$ however, the right-handed scale is restricted to be heavy, pushing the ${Z}_{R}$ mass above $160$ TeV.

$\mu-e$ conversion in nuclei in the left-right supersymmetric model

We investigate the contributions to $\mu - e $ conversion in nuclei in a supersymmetric model with left-right symmetry, motivated by the new data on neutrino oscillations. We study the dependence of the conversion rate on the various parameters of the model, and show that light-mass or large $\tan \beta$ scenarios are severely restricted. We analyse the effect of several popular mecahnisms of neutrino mixing on the conversion rate as well as the influence of the right-handed scale on the conversion rate. We compare the conversion rate to the branching ratio for $\mu \rightarrow e \gamma$ and discuss their relative accessibility at future experiments, their sensitivity to various parameters of the model, as well as their relative importance in providing signals for new Physics.

A monte carlo approach for simulation of heat flow in sand and metal mold castings (virtual mold modeling)

Fig. 3—Activity coefficients of cuprous sulfide and ferrous sulfide as a function of cation fraction of ferrous sulfide. A plot of the ratio of gFeS / (right-hand scale) shows the relative drop in the two individual gCuS0.5 activity coefficients. cuprous sulfide and ferrous sulfide decrease. To determine the relative decrease of the two activity coefficients, the ratio of the activity coefficient of ferrous sulfide to that of cuprous sulfide is also plotted in Figure 3 (right-hand axis). The ratio increases as ferrous sulfide decreases, implying that the drop in the activity coefficient of cuprous sulfide is greater than that for the activity coefficient of ferrous sulfide as the concentration of aluminum sulfide in the matte increases. For a pure ferrous sulfide flux, the activity coefficient for cuprous sulfide (given in Table I) was found to be 2.87, which compares very well with the 2.6 reported by Wang et al. [3] and is only a bit lower than the 4.1 reported by Jimbo et al. [2] The removal of copper from molten ferrous alloys is possible with the use of a sulfide-based flux, although because of the high sulfur pickup and the added cost of subsequent removal, it is not a very practical solution. Several conclusions can be drawn from the results of this study, in which varying compositions of ferrous sulfide and aluminum sulfide were used as a flux. 1. The presence of aluminum sulfide reduces the activity coefficient of cuprous sulfide because of the effects of the trivalent aluminum ion on the monovalent cuprous cation in the mixture. 2. The distribution coefficient for copper (LCu) varies with flux composition. The maximum value of LCu was ’30 at an initial cation fraction of 0.18 ferrous sulfide. As the ferrous sulfide content of the molten aluminum sulfide increases from zero, the equilibrium concentration of cuprous sulfide increases. However, as the ferrous sulfide concentration increases, the activity coefficient of cuprous sulfide increases faster than that of ferrous sulfide because the effect of the polyvalent cation (Al 3+ )i s greater on the monovalent cuprous cation than on the divalent ferrous cation. Combined, the two competing effects result in maximizing the distribution coefficient. 3. A copper content of ’0.4 wt pct in carbon-saturated iron can be reduced to below 0.10 wt pct (actually, 0.07 wt pct in our experiment at this composition) by using a flux with a cation fraction of 0.18FeS and 0.82AlS 1.5 , with an initial weight one-fourth that of the metal.

FCNCs in left-right symmetric theories and constraints on the right-handed scale

We revise the limits on the FCNC higgses in manifestly left-right symmetric theories. It is shown that the combination of the Kobayashi-Maskawa CP-violation with the tree level $\Delta S=2$ higgs exchange gives very large contribution to the CP-violating $\epsilon$ parameter. It leads to the new strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of the order $\sqrt{m_t/m_c}$. Being addressed to the supersymmetric left-right models, FCNC problem requires both right-handed scale and supersymmetric mass parameters be heavier than 50 TeV for $tan\beta\sim 1$. The most relaxed case corresponds to $tan\beta\sim 20- 30$ where right-handed scale can be of the order of few TeV.