Grand unification of quark and lepton flavor changing neutral currents

In the context of supersymmetric grand unified theories with soft breaking terms arising at the Planck scale, it is generally possible to link flavor changing neutral current and CP violating processes occurring in the leptonic and hadronic sectors. We study the correlation between flavor changing squark and slepton mass insertions in models à la SU(5). We show that the constraints coming from lepton flavor violation exhibit a strong impact on CP-violating B decays.     

Radiative corrections to the scalar Higgs masses in a non-minimal supersymmetric Standard Model

We calculate the dominant one-loop radiative corrections arising from quark-squark loops to the mass squared matrix of theCP-even Higgs bosons in a non-minimal supersymmetric Standard Model containing two Higgs doublets and a Higgs singlet chiral superfield using one-loop effective potential approximation. We use this result to evaluate upper and lower bounds on the radiatively corrected masses of all the scalar Higgs bosons as a function of the parameters of the model. We find that the one-loop radiative corrections are substantial only for the lightest Higgs boson of the model and can push its mass beyond the reach of LEP. We also calculate an absolute upper bound on the mass of the radiatively corrected lightest Higgs boson and compare it with the corresponding bound in the minimal supersymmetric Standard Model.     

Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries

In a class of supersymmetric flavor models predictions are based on residual symmetries of some subsectors of the theory such as those of the charged leptons and neutrinos. However, the vacuum expectation values of the so-called flavon fields generally modify the Kähler potential of the setting, thus changing the predictions. We derive simple analytic formulae that allow us to understand the impact of these corrections on the predictions for the masses and mixing parameters. Furthermore, we discuss the effects on the vacuum alignment and on flavor changing neutral currents. Our results can also be applied to non-supersymmetric flavor models.     

\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998     

B → X_sγ in BLMSSM

Applying the effective Lagrangian method,we study the flavor changing neutral current process b→ sγwithin the minimal supersymmetric extension of the Standard Model,where baryon and lepton numbers are local gauge symmetries.Constraints on the parameters are investigated numerically with the experimental data for the branching ratio of B→ X_sγ.Additionally,we present the corrections to direct CP-violation in B→ X_sγ and time-dependent CP-asymmetry in B→K~*γ.With appropriate assumptions on the parameters,we find the direct CP-violation Acp is very small,while one-loop contributions to S_(K~*_γ) can be significant.     

Effects of Complex Parameters on t→ch0 in Supersymmetric QCD

We investigate the leading SUSY-QCD contributions to the branch ratio (BR) of t → ch⁰ within the context of the minimal supersymmetric standard model (MSSM) with complex parameters, assuming more generally that there is a misalignment between the squark and quark that leads to a flavor non-diagonal squark mass matrix. We introduce complex phases only in μ and A_t, namely φ_μ and φ_Aq, for simplicity, and study the dependence of the BR of t → ch⁰ on these phase parameters. Our calculations show that these CP-violation phases and the flavor mixing parameter λ influence the BR of t → ch⁰ considerably, and the effect induced by φ_At is much larger than that by φ_μ and φ_Ac,u . For different values of the complex parameters μ and A_t that are set in this paper, the BR of t → ch⁰ is in the range of 10^-7 ～ 10^-6, depending mainly on the value of the trilinear coupling A_t.     

Search for flavor lepton number violation in slepton decays at LHC

We show that in supersymmetric models with explicit flavor lepton number violation due to soft supersymmetry breaking mass terms there could be detectable flavor lepton number violation in slepton decays. We estimate the potential for discovery of lepton flavor number violation in slepton decays at LHC. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 139–144 (25 January 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Supersymmetry breaking in warped geometry

We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS₅ which generate the hierarchical Yukawa couplings by dynamically quasi-localizing the bulk matter fields in an extra dimension. Such models can be regarded as the AdS dual of the recently studied 4-dimensional models which contain a supersymmetric CFT to generate the hierarchical Yukawa couplings. In such models, if supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous flavor-violating soft parameters are suppressed with an appropriate correlation with the Yukawa coupling suppression, thereby avoiding the SUSY flavor problem in a natural manner. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework, and discuss the constraints from flavor-changing rare processes. Most of the discussions in this paper can be applied also to models with a flat extra dimension in which the Yukawa hierarchy is generated by quasi-localizing the bulk matter fields in the extra dimension.Received: 21 October 2003, Revised: 12 January 2004, Published online: 5 May 2004     

Anomaly constraints on supersymmetric effective lagrangians

In this paper we set constraints on the possible effective-lagrangian representations of supersymmetric gauge theories with spontaneously broken chiral flavor symmetries, by finding the conditions under which a Wess-Zumino term to represent the anomalous interactions can be constructed. We find that effective lagrangians for such theories are possible only for nonlinear sigma models defined on noncompact manifolds, and demonstrate the realization of this result in supersymmetric QCD. We also consider the Wess-Zumino term in the nonlinear realization of broken supersymmetry.     

Renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking

The renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking is presented using spurion fields for introducing the breaking terms. It is proven that renormalization of the fields and parameters in the classical action yields precisely the correct counterterms to cancel all divergences. In the course of the construction of higher orders additional independent parameters appear, but they can be shown to be irrelevant in physics respects. Thus, the only parameters with influence on physical amplitudes are the supersymmetric and the well-known soft breaking parameters. Received: 19 December 2001 / Published online: 15 March 2002     

Supersymmetry and proton decay

Using supergraph techniques it is shown that all one-loop contributions to the proton decay amplitude, which are suppressed by only one power of the unification mass and are not of fourth order in Higgs couplings, vanish in a general supersymmetric grand unification setting. Corrections to this statement due to soft supersymmetry breaking are analysed.     

General issues connecting flavor symmetry and supersymmetry

We motivate and construct supersymmetric theories with continuous flavor symmetry, under which the electroweak Higgs doublets transform non-trivially. Flavor symmetry is spontaneously broken at a large mass scale in a sector of gauge-singlet fields; the light Higgs multiplets naturally emerge as special linear combinations that avoid acquiring the generic large mass. Couplings of the light Higgs doublets to light moduli fields from the singlet sector could lead to important effects in the phenomenology of the Higgs sector.     

Supersymmetry beyond minimal flavor violation

We review the sources and phenomenology of non-minimal flavor violation in the MSSM. We discuss in some detail the most important theoretical and experimental constraints, as well as promising observables to look for supersymmetric effects at the LHC and in future experiments. We emphasize the sensitivity of flavor physics to the mechanism of supersymmetry breaking and to new degrees of freedom present at fundamental scales, such as the grand unification scale. We include a discussion of present data that may hint at departures from the standard model.     

Analytical Designing of Two-Aspherical-Mirror Anastigmats Permitting Practical Misalignments in a Soft-X-Ray Optics

A new analytical method of designing two-aspherical-mirror anastigmats was developed and applied to searching solution groups of soft X-ray microscopes of a large misalignment tolerance. The two-mirror anastigmat configurations were expressed by a practical variable related to pupil obstruction limiting the system throughput. Axial coma and other aberrations caused by a slight decenter of the system were then formulated to represent sensitivity to misalignment. These formulations enabled a global survey of solution groups as demonstrated by a designing example of soft X-ray microscopes with a magnification m = −1/50, which resulted in four solutions more insensitive to misalignment than a standard Schwarzschild optics in the soft X-ray region. Some solutions were also found to have much larger fields of view suitable for high resolution imaging as confirmed by computer ray tracing.     

Anomaly,gauge and gaugino mediation in brane worlds with messenger matter

Theories in which supersymmetry is broken on another brane, which is separated from the minimal supersymmetry standard model (MSSM) matter fields in an extra dimension, are attractive because they may solve the supersymmetric flavor problem. We consider the effects in such theories of new messenger fields with standard model gauge charges and with direct couplings to the supersymmetry breaking sector. The effect on the masses of the MSSM superpartners can be dramatic. In particular, the tachyonic slepton problem of anomaly mediation and the stable slepton problem of gaugino mediation can be cured.     

Soft gluon radiation in Higgs boson production at the LHC

We examine the contributions of soft gluons to the Higgs production cross section at the LHC in the Standard Model and its minimal supersymmetric extension. The soft gluon radiation effects of this reaction share many features with the Drell-Yan process, but arise at lowest order from a purely gluonic initial state. We provide an extension of the conventional soft gluon resummation formalism to include a new class of contributions which we argue to be universal, and resum these and the usual Sudakov effects to all orders. The effect of these new terms is striking: only if they are included, does the expansion of the resummed cross section to next-to-leading order reproduce the exact result to within a few percent for the full range of Higgs boson masses. We use our resummed cross section to derive next-to-next-to-leading order results, and their scale dependence. Moreover, we demonstrate the importance of including the novel contributions in the resummed Drell-Yan process.     

Probing Topcolor-Assisted Technicolor Models from Like-Sign τ Pair Production in eγ Collisions

We consider the contributions of the extra gauge boson Z' to the like sign τ production processes e^{-γ _→} e⁺(μ⁺)τ^-τ^-, induced by the tree-level flavor changing interactions. Since these rare production are far below theobservable level in the Standard Model and other popular new physics models such as the minimal supersymmetric model, we find that, inthe topcolor-assisted technicolor models, the Z' can give significant contributions to these processes, and with reasonable values of the parameters, the cross section σ can reach several tens of fb and may be detected at the eγ collisions.     

The Effects from the Complex Parameters on t→ch^0 Within the Minimal Supersymmetric Standard Model

We investigate the effects from complex parameters on the branching ratio (BR) of the flavor changing rare decay t→ch^0 contributed by the electroweak interactions in the framework of the minimal supersymmetric standard model with complex parameters. We study the dependence of the BR on the possible relevant additional parameter swhich could be the originalsources inducing CP-violation, i.e., the complex phase angles φμ and φAb in squark and chargino sectors and δ13 appearing in Cabibbo-Kobayashi-Maskawa matrix. We find that these parameters influence the BR obviously and the effects induced by φμ and φAb are much larger than by δ13. With the different chosen values of the complex parameters, the BR is in the range between 10^-10 and 10^-8, depending mainly on the phase angles of the higgsino mass parameter μ and the trilinear coupling Ab.     

Some phenomenological implications of string loop effects

We investigate low energy implications of string loop corrections to supergravity couplings which break a possible flavor universality of the tree level. If supersymmetry is broken by the dilaton F-term, universal soft scalar masses arise at the leading order but string loop corrections generically induce flavor-non-diagonal soft terms. Constraints from flavor changing neutral currents (FCNC) and CP violation then require a large supersymmetry breading scale and thus heavy gluinos and squarks. If supersymmetry is broken by moduli F-terms, universality at the string tree level can only be guaranteed by extra conditions on the Kahler potential. A large hierarchy between the gluino and squark masses ensures that FCNC and CP-violation constraints are satisfied. If the soft scalar masses vanish at the string tree level, the cosmological problems related to light moduli can be evaded. However, generic string loop corrections violate FCNC bounds and require very heavy squark masses (∼ 100 TeV).     

Proton decay and flavor violating thresholds in SO(10) models

Discovery of neutrino mass has put the spotlight on the supersymmetric (SUSY) SO(10) model as a natural candidate for grand unification of forces and matter. However, the suppression of proton decay is a major problem in such SUSY grand unified models. In this Letter we show how to alleviate this problem by simple threshold effects which raise the colored Higgsino masses and the grand unification scale to greater than or similar to 10(17) GeV. There exist only four types of fields arising from different SO(10) representations which can generate this kind of threshold effect. Some of these fields also generate a sizable flavor violation in the quark sector compared to the lepton sector. The b-tau unification can work in these types of models even for intermediate values of tanbeta.