SUSY Flavor Problem Research Articles

Semidirect product groups, vacuum alignment, and tribimaximal neutrino mixing

The neutrino oscillation data are in very good agreement with the tribimaximal mixing pattern: \sin^2\theta_{23}=1/2, \sin^2\theta_{12}=1/3, and \sin^2\theta_{13}=0. Attempts to generate this pattern based on finite family symmetry groups typically assume that the family symmetry is broken to different subgroups in the charged lepton and the neutrino mass matrices. This leads to a technical problem, where the cross-couplings between the Higgs fields responsible for the two symmetry breaking chains force their vacuum expectation values to align, upsetting the desired breaking pattern. Here, we present a class of models based on the semidirect product group (S_3)^4 \rtimes A_4, where the lepton families belong to representations which are not faithful. In effect, the Higgs sector knows about the full symmetry while the lepton sector knows only about the A_4 factor group. This can solve the alignment problem without altering the desired properties of the family symmetry. Inclusion of quarks into the framework is straightforward, and leads to small and arbitrary CKM mixing angles. Supersymmetry is not essential for our proposal, but the model presented is easily supersymmetrized, in which case the same family symmetry solves the SUSY flavor problem.

Effective supersymmetry at the LHC

We investigate the phenomenology of Effective Supersymmetry (ESUSY) models wherein electroweak gauginos and third generation scalars have masses up to about 1~TeV while first and second generation scalars lie in the multi-TeV range. Such models ameliorate the SUSY flavor and CP problems via a decoupling solution, while at the same time maintaining naturalness. In our analysis, we assume independent GUT scale mass parameters for third and first/second generation scalars and for the Higgs scalars, in addition to m_{1/2}, \tan\beta and A_0, and require radiative electroweak symmetry breaking as usual. We analyse the parameter space which is consistent with current constraints, by means of a Markov Chain Monte Carlo scan. The lightest MSSM particle (LMP) is mostly, but not always the lightest neutralino, and moreover, the thermal relic density of the neutralino LMP is frequently very large. These models may phenomenologically be perfectly viable if the LMP before nucleosynthesis decays into the axino plus SM particles. Dark matter is then an axion/axino mixture. At the LHC, the most important production mechanisms are gluino production (for m_{1/2} ~<700~GeV) and third generation squark production, while SUSY events rich in b-jets are the hallmark of the ESUSY scenario. We present a set of ESUSY benchmark points with characteristic features and discuss their LHC phenomenology.

The SUSY CP problem and the MFV principle

We address the SUSY CP problem in the framework of Minimal Flavor Violation (MFV), where the SUSY flavor problem finds a natural solution. By contrast, the MFV principle does not solve the SUSY CP problem as it allows for the presence of new flavor blind CP-violating phases. Then, we generalize the MFV ansatz accounting for a natural solution of it. The phenomenological implications of the generalized MFV ansatz are explored for MFV scenarios defined both at the electroweak (EW) and at the GUT scales.

FCNC and CP violation observables in an [formula omitted]-flavoured MSSM

A non-Abelian flavour symmetry in a minimal supersymmetric standard model can explain the flavour structures in the Yukawa couplings and simultaneously solve the SUSY flavour problem. Similarly the SUSY CP problem can be solved if CP is spontaneously broken in the flavour sector. In this work, we present an explicit example of these statements with an SU ( 3 ) flavour symmetry and spontaneous CP violation. In addition, we show that it is still possible to find some significant deviation from the SM expectations as far as FCNC and CP violation are concerned. We find that large contributions can be expected in lepton flavour violating decays, as μ → e γ and τ → μ γ , electric dipole moments, d e and d n and kaon CP violating processes as ϵ K . We also show that without further modifications, it is unlikely for these models to solve the Φ B s anomaly at low-moderate tan β . Thus, these flavoured MSSM realizations are phenomenologically sensitive to the experimental searches in the realm of flavor and CP violation physics.

On the phenomenology of strongly coupled hidden sectors

In models of supersymmetry (SUSY) breaking and mediation, strongly coupled SUSY-breaking sectors can play a significant role in determining the low-energy spectrum of the model. For example, strong dynamics may provide a natural solution to both the SUSY flavor problem and the mu / B mu problem. Recently, it has been suggested that a large class of these models lead to identical boundary conditions at the SUSY breaking scale. These boundary conditions would severely constrain the models' viability. We demonstrate that the boundary conditions are instead sensitive to the details of the hidden sector, so that only specific hidden sectors may be ruled out by phenomenological considerations. We determine the high scale boundary conditions using the operator product expansion of the hidden sector. The techniques used to determine the beta functions are generally applicable to the RG flow of any approximately conformal hidden sector. The discrepancy with previously proposed boundary conditions can be traced to the fact that the renormalization group (RG) flow involves multiple fixed points.

Electric dipole moments from spontaneous CP violation in SU(3)-flavoured SUSY

The SUSY flavour problem is deeply related to the origin of flavour and hence to the origin of the SM Yukawa couplings themselves. Since all CP-violation in the SM is restricted to the flavour sector, it is possible that the SUSY CP problem is related to the origin of flavour as well. In this work, we present three variations of an SU(3) flavour model with spontaneous CP violation. Such models explain the hierarchy in the fermion masses and mixings, and predict the structure of the flavoured soft SUSY breaking terms. In such a situation, both SUSY flavour and CP problems do not exist. We use electric dipole moments and lepton flavour violation processes to distinguish between these models, and place constraints on the SUSY parameter space.

Flavor and CP conserving moduli mediated SUSY breaking in flux compactification

In certain class of flux compactification, moduli mediated supersymmetry (SUSY) breaking preserves flavor and CP at leading order in the perturbative expansion controlled by the vacuum expectation value of the messenger modulus. Nevertheless there still might be dangerous flavor or CP violation induced by higher order Kahler potential. We examine the constraints on such SUSY breaking scheme imposed by low energy flavor and/or CP violating observables. It is found that all phenomenological constraints can be satisfied even for generic form of higher order Kahler potential and sparticle spectra in the sub-TeV range, under plausible assumptions on the size of higher order correction and flavor mixing angles. This implies for instance that mirage mediation scheme of SUSY breaking, which involves such modulus mediation together with an anomaly mediation of comparable size, and also the modulus-dominated mediation realized in flux compactification can be free from the SUSY flavor and CP problems, while giving gaugino and sfermion masses in the sub-TeV range.

Revisiting signature of minimal gauge mediation

We revisit phenomenology of the minimal gauge-mediated model. This model is motivated from the SUSY CP and flavor problems. A specific feature of this model is that tanβ is naturally large, since the B term in the Higgs potential is zero at the messenger scale. This leads to significant SUSY contributions to various low-energy observables. We evaluate the anomalous magnetic moment of the muon and the branching ratio of B¯→Xsγ taking account of recent theoretical and experimental developments. We find that the current experimental data prefer a low messenger scale (∼ 100 TeV) and gluino mass around 1 TeV. We also calculate the branching ratios of B¯→Xsl+l−, Bs→μ+μ−, and B−→τ−ν¯, and show that these observables are strongly correlated with each other in this model.

Gauge mediated supersymmetry breaking without exotics in orbifold compactification

We suggest SU(5)′ in the hidden sector toward a possible gauge mediated supersymmetry breaking scenario for removing the SUSY flavor problem, with an example constructed in Z12−I with three families. The example we present has the Pati–Salam type classification of particles in the observable sector and has no exotics at low energy. We point out that six or seven very light pairs of 5′ and 5¯′ out of ten vectorlike 5′ and 5¯′ pairs of SU(5)′ is achievable, leading to a possibility of an unstable supersymmetry breaking vacuum. The possibility of different compactification radii of three two tori toward achieving the needed coupling strength is also suggested.

Field theory on multithroat backgrounds

We consider extra dimensional field theory descriptions of backgrounds with N different throats where one of the extra dimensions in each throat is much larger than the others. Such backgrounds can be described by field theory on N 5D warped spaces which intersect on a ultraviolet (UV) brane. Given a field that propagates in all N throats there are N boundary conditions on the UV brane (which are determined by the effective Lagrangian on the UV brane) in addition to the boundary conditions on the N infrared branes. We derive a general set of UV boundary conditions and give examples of how they are applied to particular situations. Three simple example applications are given: in the first the number of families is determined by the number of throats and the SUSY flavor problem is solved via an S_3 symmetry of the throats; in the second we embed this scenario in a SUSY GUT with a solution of the doublet-triplet splitting problem based on the product group approach; while in the final example we show a simple geometric implementation of a SUSY trinification model on three throats.

Non-Abelian discrete family symmetry to soften the SUSY flavor problem and to suppress proton decay

Family symmetry could explain large mixing of the atmospheric neutrinos. The same symmetry could explain why the flavor changing current processes in supersymmetric standard models can be so suppressed. It also may be able to explain why the proton is so stable. We investigate these questions in a supersymmetric, renormalizable extension of the standard model, which possess a family symmetry based on a binary dihedral group Q 6 . We find that the amplitude for μ → e + γ enjoys a suppression factor proportional to | ( V MNS ) e 3 | ≃ m e / ( 2 m μ ) ≃ 3.4 × 10 −3 , and that B ( p → K 0 μ + ) / B ( p → K 0 e + ) ≃ | ( V MNS ) e 3 | 2 ≃ 10 −5 , where V MNS is the neutrino mixing matrix.

Gauge-mediated supersymmetry breaking in string compactifications

We provide string theory examples where a toy model of a SUSY GUT or the MSSM is embedded in a compactification along with a gauge sector which dynamically breaks supersymmetry. We argue that by changing microscopic details of the model (such as precise choices of flux), one can arrange for the dominant mediation mechanism transmitting SUSY breaking to the Standard Model to be either gravity mediation or gauge mediation. Systematic improvement of such examples may lead to top-down models incorporating a solution to the SUSY flavor problem.

Model independent approach to focus point supersymmetry: from dark matter to collider searches

The focus point region of supersymmetric models is compelling in that it simultaneously features low fine-tuning, provides a decoupling solution to the SUSY flavor and CP problems, suppresses proton decay rates and can accommodate the WMAP measured cold dark matter (DM) relic density through a mixed bino-higgsino dark matter particle. We present the focus point region in terms of a weak scale parameterization, which allows for a relatively model independent compilation of phenomenological constraints and prospects. We present direct and indirect neutralino dark matter detection rates for two different halo density profiles, and show that prospects for direct DM detection and indirect detection via neutrino telescopes such as IceCube and anti-deuteron searches by GAPS are especially promising. We also present LHC reach prospects via gluino and squark cascade decay searches, and also via clean trilepton signatures arising from chargino-neutralino production. Both methods provide a reach out to m ∼ 1.7 TeV. At a TeV-scale linear e+e− collider (LC), the maximal reach is attained in the 12 or 13 channels. In the DM allowed region of parameter space, a (s)1/2 = 0.5 TeV LC has a reach which is comparable to that of the LHC. However, the reach of a 1 TeV LC extends out to m ∼ 3.5 TeV.

Soft SUSY breaking and family symmetry

A spontaneously broken non-Abelian SU(3) family symmetry can generate a realistic form for quark, charged lepton and neutrino masses and mixing angles. It also gives a new solution to the SUSY flavour problem by ensuring near family degeneracy of the soft mass SUSY breaking terms. However the need to generate large third generation fermion masses means that the group must be strongly broken to SU(2) giving significant corrections to the third family squark and slepton masses. We investigate the phenomenological implications of such breaking and show that it leads to new solutions capable of fitting all present experimental measurements and bounds as well as the dark matter abundance.

Supersymmetric unification without low energy supersymmetry and signatures for fine-tuning at the LHC

The cosmological constant problem is a failure of naturalness and suggests that a fine-tuning mechanism is at work, which may also address the hierarchy problem. An example -- supported by Weinberg's successful prediction of the cosmological constant -- is the potentially vast landscape of vacua in string theory, where the existence of galaxies and atoms is promoted to a vacuum selection criterion. Then, low energy SUSY becomes unnecessary, and supersymmetry -- if present in the fundamental theory -- can be broken near the unification scale. All the scalars of the supersymmetric standard model become ultraheavy, except for a single finely tuned Higgs. Yet, the fermions of the supersymmetric standard model can remain light, protected by chiral symmetry, and account for the successful unification of gauge couplings. This framework removes all the difficulties of the SSM: the absence of a light Higgs and sparticles, dimension five proton decay, SUSY flavor and CP problems, and the cosmological gravitino and moduli problems. High-scale SUSY breaking raises the mass of the light Higgs to about 120-150 GeV. The gluino is strikingly long lived, and a measurement of its lifetime can determine the ultraheavy scalar mass scale. Measuring the four Yukawa couplings of the Higgs to the gauginos and higgsinos precisely tests for high-scale SUSY. These ideas, if confirmed, will demonstrate that supersymmetry is present but irrelevant for the hierarchy problem -- just as it has been irrelevant for the cosmological constant problem -- strongly suggesting the existence of a fine-tuning mechanism in nature.

Phenomenology of Twisted Moduli in Type I String Inspired Models

We make a first study of the phenomenological implications of twisted moduli in type I intersecting D5-brane models, focussing on the resulting predictions at the LHC using SOFTSUSY to estimate the Higgs and sparticle spectra. Twisted moduli can play an important role in giving a viable string realisation of sequestering in the limit where supersymmetry breaking comes entirely from the twisted moduli. We focus on a particular string inspired version of gaugino mediation in which the first two families are localised at the intersection between D5-branes, whereas the third family and Higgs doublets are allowed to move within the world-volume of one of the branes. The soft supersymmetry breaking third family sfermion mass terms are then in general non-degenerate with the first two families. We place constraints upon parameter space and predictions of flavour changing neutral current effects. Twisted moduli domination is studied and, as well as solving the most serious part of the SUSY flavour problem, is shown to be highly constrained. The constraints are weakened by switching on gravity-mediated contributions from the dilaton and untwisted T-moduli sectors. In the twisted moduli domination limit we predict a stop-heavy MSSM spectrum and quasi-degenerate lightest neutralino and chargino states with wino-dominated mass eigenstates.

Supersymmetry breaking in warped geometry

We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS_5 which generate the hierarchical Yukawa couplings by dynamically localizing the bulk matter fields in 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 can be naturally suppressed, thereby avoiding the SUSY flavor problem. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework.

E6 Unification, Large Neutrino Mixings and SUSY Flavor Problem

This study indicates that in E6 grand unified theories (GUTs), once a hierarchical structure of up-quark-type Yukawa couplings is given as a basic structure of flavor, larger lepton mixings than the quark mixings and milder down-quark-type (and charged-lepton-type) mass hierarchies than up-quark-type mass hierarchy can generically be obtained under a few natural assumptions. The basic flavor structure is compatible with non-Abelian horizontal symmetry, which can solve the SUSY flavor problem. It is shown that in solving the SUSY flavor problem, the E6 structure, which realizes bi-large neutrino mixings, also solves a problem that results from the large neutrino mixing angles.

Towards 5D Grand Unification without SUSY Flavor Problem

We consider the renormalization group approach to the SUSY flavor problem in the supersymmetric SU(5) model with one extra dimension. In higher dimensional SUSY gauge theories, it has been recently shown that power corrections due to the Kaluza-Klein states of gauge fields run the soft masses generated at the orbifold fixed point to flavor conserving values in the infra-red limit. In models with GUT breaking at the brane where the GUT scale can be larger than the compactification scale, we show that the addition of a bulk Higgs multiplet, which is necessary for the successful unification, is compatible with the flavor universality achieved at the compactification scale.

Finite theories and the supersymmetry flavor problem

We study a finite SU(5) grand unified model based on the non-Abelian discrete symmetry A_4. This model leads to the democratic structure of the mass matrices for the quarks and leptons. In the soft supersymmetry breaking sector, the scalar trilinear couplings are aligned and the soft scalar masses are degenerate, thus solving the SUSY flavor problem.