Supersymmetric Loop Research Articles

Yukawa coupling unification in an SO(10) model consistent with Fermilab (g \u2212 2)\u03bc result

We investigate the Yukawa coupling unification for the third generation in a class of SO(10) unified models which are consistent with the 4.2 σ deviation from the standard model of the muon g − 2 seen by the Fermilab experiment E989. A recent analysis in supergravity grand unified models shows that such an effect can arise from supersymmetric loops correction. Using a neural network, we further analyze regions of the parameter space where Yukawa coupling unification consistent with the Fermilab result can appear. In the analysis we take into account the contributions to Yukawas from the cubic and the quartic interactions. We test the model at the high luminosity and high energy LHC and estimate the integrated luminosities needed to discover sparticles predicted by the model.

Precise prediction for the W boson mass in the MRSSM

The mass of the W boson, MW, plays a central role for high-precision tests of the electroweak theory. Confronting precise theoretical predictions with the accurately measured experimental value provides a high sensitivity to quantum effects of the theory entering via loop contributions. The currently most accurate prediction for the W boson mass in the Minimal R-symmetric Supersymmetric Standard Model (MRSSM) is presented. Employing the on-shell scheme, it combines all numerically relevant contributions that are known in the Standard Model (SM) in a consistent way with all MRSSM one-loop corrections. Special care is taken in the treatment of the triplet scalar vacuum expectation value vT that enters the prediction for MW already at lowest order. In the numerical analysis the decoupling properties of the supersymmetric loop contributions and the comparison with the MSSM are investigated. Potentially large numerical effects of the MRSSM-specific Λ superpotential couplings are highlighted. The comparison with existing results in the literature is discussed.

Scalar Tensor Cosmology With Kinetic, Gauss-Bonnet and Nonminimal Derivative Couplings and Supersymmetric Loop Corrected Potential

We discuss a particular four-dimensional cosmology based on non-minimal scalar tensor theories characterized by a supersymmetric loop corrected potential and a Hubble parameter defined as a function of the scalar field. Power-law solutions are obtained in the FRW background giving rise to acceleratedly expanding universe characterized by a scale factor and a scalar field depending both on the non-minimal coupling parameter ξ. Based on SNeIa data and on Hubble data X-ray gas mass fraction measurements, we find 0.116 < ξ < 0.225 which results on a universe dominated by vacuum energy.

Supersymmetric partition functions and the three-dimensional A-twist

We study three-dimensional mathcal{N}=2 supersymmetric gauge theories on {mathrm{mathcal{M}}}_{g,p} , an oriented circle bundle of degree p over a closed Riemann surface, Σg. We compute the {mathrm{mathcal{M}}}_{g,p} supersymmetric partition function and correlation functions of supersymmetric loop operators. This uncovers interesting relations between observables on manifolds of different topologies. In particular, the familiar supersymmetric partition function on the round S3 can be understood as the expectation value of a so-called “fibering operator” on S2×S1 with a topological twist. More generally, we show that the 3d mathcal{N}=2 supersymmetric partition functions (and supersymmetric Wilson loop correlation functions) on {mathrm{mathcal{M}}}_{g,p} are fully determined by the two-dimensional A-twisted topological field theory obtained by compactifying the 3d theory on a circle. We give two complementary derivations of the result. We also discuss applications to F-maximization and to three-dimensional supersymmetric dualities.

Neutron electric dipole moment and probe of PeV scale physics

The experimental limit on the neutron electric dipole moment is used as a possible probe of new physics beyond the standard model. Within MSSM we use the current experimental limit on the neutron EDM and possible future improvement as a probe of high scale SUSY. Quantitative analyses show that scalar masses as large as a PeV and larger could be probed in improved experiment far above the scales accessible at future colliders. We also discuss the neutron EDM as a probe of new physics models beyond MSSM. Specifically we consider an MSSM extension with a particle content including a vectorlike multiplet. Such an extension brings in new sources of CP violation beyond those in MSSM. These CP phases contribute to the EDM of the quarks and to the neutron EDM. These contributions are analyzed in this work where we include the supersymmetric loop diagrams involving the neutralinos, charginos, the gluino, squark and mirror squark exchange diagrams at the one loop level. We also take into account the contributions from the $W$, $Z$, quark and mirror quark exchanges arising from the mixings of the vectorlike generation with the three generations. It is shown that the experimental limit on the neutron EDM can be used to probe such new physics models. In the future one expects the neutron EDM to improve an order of magnitude or more allowing one to extend the probe of high scale SUSY and of new physics models. For the MSSM the probe of high scales could go up to and beyond PeV scale masses.

Defect networks and supersymmetric loop operators

We consider topological defect networks with junctions in A N − 1 Toda CFT and the connection to supersymmetric loop operators in $$ \mathcal{N}=2 $$ theories of class $$ \mathcal{S} $$ on a four-sphere. Correlation functions in the presence of topological defect networks are computed by exploiting the monodromy of conformal blocks, generalising the notion of a Verlinde operator. Concentrating on a class of topological defects in A 2 Toda theory, we find that the Verlinde operators generate an algebra whose structure is determined by a set of generalised skein relations that encode the representation theory of a quantum group. In the second half of the paper, we explore the dictionary between topological defect networks and supersymmetric loop operators in the $$ \mathcal{N}={2}^{*} $$ theory by comparing to exact localisation computations. In this context, the the generalised skein relations are related to the operator product expansion of loop operators.

Ω-deformation and quantization

We formulate a deformation of Rozansky-Witten theory analogous to the $\Omega$-deformation. It is applicable when the target space $X$ is hyperk\"ahler and the spacetime is of the form $\mathbb{R} \times \Sigma$, with $\Sigma$ being a Riemann surface. In the case that $\Sigma$ is a disk, the $\Omega$-deformed Rozansky-Witten theory quantizes a symplectic submanifold of $X$, thereby providing a new perspective on quantization. As applications, we elucidate two phenomena in four-dimensional gauge theory from this point of view. One is a correspondence between the $\Omega$-deformation and quantization of integrable systems. The other concerns supersymmetric loop operators and quantization of the algebra of holomorphic functions on a hyperk\"ahler manifold.

Supersymmetric Higgs sector andB−B¯mixing for large tanβ

We match the Higgs sector of the most general flavour breaking and CP violating minimal supersymmetric standard model (MSSM) onto a generic two-Higgs-doublet model, paying special attention to the definition of tan beta in the effective theory. In particular no tan beta-enhanced loop corrections appear in the relation to tan beta defined in the DRbar scheme in the MSSM. The corrections to the Higgs-mediated flavour-changing amplitudes which result from this matching are especially relevant for the B_d and B_s mass differences dM_s,d for minimal flavour violation, where the superficially leading contribution vanishes. We give a symmetry argument to explain this cancellation and perform a systematic study of all Higgs-mediated effects, including Higgs loops. The corrections to dM_s are at most 7% for mu>0 and M_A < 600 if constraints from other observables are taken into account. For mu<0 they can be larger, but are always less than about 20%. Contrary to recent claims we do not find numerically large contributions here, nor do we find any tan beta-enhanced contributions from loop corrections to the Higgs potential in B^+ -> tau^+ nu or B -> X_s gamma. We further update supersymmetric loop corrections to the Yukawa couplings, where we include all possible CP-violating phases and correct errors in the literature. The possible presence of CP-violating phases generated by Higgs exchange diagrams is briefly discussed as well. Finally we provide improved values for the bag factors P^VLL_1, P^LR_2, and P^SLL_1 at the electroweak scale.

Wilson loops in $ \mathcal{N} = 2 $ superconformal Yang-Mills theory

We present a three-loop O(g^6) calculation of the difference between the expectation values of Wilson loops evaluated in N=4 and superconformal N=2 supersymmetric Yang-Mills theory with gauge group SU(N) using dimensional reduction. We find a massive reduction of required Feynman diagrams, leaving only certain two-matter-loop corrections to the gauge field and associated scalar propagator. This "diagrammatic difference" leaves a finite result proportional to the bare propagators and allows the recovery of the zeta(3) term coming from the matrix model for the 1/2 BPS circular Wilson loop in the N=2 theory. The result is valid also for closed Wilson loops of general shape. Comments are made concerning light-like polygons and supersymmetric loops in the plane and on S^2.

Constraining the MSSM sfermion mass matrices with light fermion masses

We study the finite supersymmetric loop corrections to fermion masses and mixing matrices in the generic MSSM. In this context the effects of non-decoupling chirally-enhanced self-energies are studied beyond leading order in perturbation theory. These NLO corrections are not only necessary for the renormalization of the CKM matrix to be unitary, they are also numerically important for the light fermion masses. Focusing on the tri-linear A-terms with generic flavor-structure we derive very strong bounds on the chirality-changing mass insertions delta^{f\,LR,RL}_{IJ} by applying 't Hooft's naturalness criterion. In particular, the NLO corrections to the up quark mass allow us to constrain the unbounded element delta^{u\,RL}_{13} if at the same time $\delta^{u\,LR}_{13}$ is unequal to zero. Our result is important for single-top production at the LHC.

Resummation of tan β-enhanced supersymmetric loop corrections beyond the decoupling limit

We study the Minimal Supersymmetric Standard Model with Minimal Flavour Violation for the case of a large parameter tanbeta and arbitrary values of the supersymmetric mass parameters. We derive several resummation formulae for tanbeta-enhanced loop corrections, which were previously only known in the limit of supersymmetric masses far above the electroweak scale. Studying first the renormalisation-scheme dependence of the resummation formula for the bottom Yukawa coupling, we clarify the use of the sbottom mixing angle in the supersymmetric loop factor Delta_b. As a new feature, we find tan-beta-enhanced loop-induced flavour-changing neutral current (FCNC) couplings of gluinos and neutralinos which in turn give rise to new effects in the renormalisation of the Cabibbo-Kobayashi-Maskawa matrix and in FCNC processes of B mesons. For the chromomagnetic Wilson coefficient C_8, these gluino-squark loops can be of the same size as the known chargino-squark contribution. We discuss the phenomenological consequences for the mixing-induced CP asymmetry in B_d -> phi K_S. We further quote formulae for B_s -> mu^+ mu^- and B_s-B_s-bar mixing valid beyond the decoupling limit and find a new contribution affecting the phase of the B_s-B_s-bar mixing amplitude. Our resummed tan-beta-enhanced effects are cast into Feynman rules permitting an easy implementation in automatic calculations.

Neutralino decay of MSSM neutral Higgs bosons

We compute the one-loop corrected effective Lagrangian for the neutralino-neutralino-neutral Higgs interactions ${\ensuremath{\chi}}_{\ensuremath{\ell}}^{0}{\ensuremath{\chi}}_{k}^{0}{H}_{m}^{0}$. The analysis completes the previous analyses where similar corrections were computed for the $\overline{f}f{H}_{m}^{0}$ couplings, where $f$ stands for standard model quarks and leptons and for the chargino-chargino-neutral Higgs couplings ${\ensuremath{\chi}}_{l}^{+}{\ensuremath{\chi}}_{k}^{\ensuremath{-}}{H}_{m}^{0}$ within the minimal supersymmetric standard model. The effective one-loop Lagrangian is then applied to the computation of the neutral Higgs decays. The sizes of the supersymmetric loop corrections of the neutral Higgs decay widths into ${\ensuremath{\chi}}_{\ensuremath{\ell}}^{0}{\ensuremath{\chi}}_{k}^{0}$ ($\ensuremath{\ell}=1$, 2, 3, 4; $k=1$, 2, 3, 4) are investigated and the supersymmetric loop correction is found to be in the range of $\ensuremath{\sim}10%$ in significant regions of the parameter space. By including the loop corrections of the other decay channels $\overline{b}b$, $\overline{t}t$, $\overline{\ensuremath{\tau}}\ensuremath{\tau}$, $\overline{c}c$, and ${\ensuremath{\chi}}_{i}^{\ensuremath{-}}{\ensuremath{\chi}}_{j}^{+}$ ($i=1$, 2; $j=1$, 2), the corrections to branching ratios for ${H}_{m}^{0}\ensuremath{\rightarrow}{\ensuremath{\chi}}_{\ensuremath{\ell}}^{0}{\ensuremath{\chi}}_{k}^{0}$ can reach as high as 50%. The effects of $CP$ phases on the branching ratio are also investigated. A discussion of the implications of the analysis for colliders is given.

Light Minimal Supersymmetric Standard Model Higgs Boson Scenario and its Test at Hadron Colliders

We show that, in the minimal supersymmetric standard model, the possibility for the lightest CP-even Higgs boson to be lighter than Z boson (as low as about 60 GeV) is, contrary to the usual belief, not yet excluded by the CERN LEP2 Higgs search nor any direct searches for supersymmetric particles at high energy colliders. The characteristic of the light Higgs boson scenario (LHS) is that the ZZh coupling and the decay branching ratio Br(h/A-->bb) are simultaneously suppressed as a result of generic supersymmetric loop corrections. Consequently, the W(+/-)H(-/+)h coupling has to be large due to the sum rule of Higgs couplings to weak gauge bosons. We discuss the potential of the Fermilab Tevatron and B factories to test the LHS, and show that the associated neutral and charged Higgs boson production process, pp-->H(+/-)h(A), can completely probe the LHS at the CERN Large Hadron Collider.

Effective Lagrangian for theχj+χk−Hl0interaction in the minimal supersymmetric standard model and neutral Higgs decays

We extend previous analyses of the supersymmetric loop correction to the neutral Higgs couplings to include the coupling {chi}{sub j}{sup +}{chi}{sub k}{sup -}H{sub l}{sup 0}. The analysis completes the previous analyses where similar corrections were computed for the {tau}{tau}H{sub l}{sup 0}, bbH{sub l}{sup 0}, ccH{sub l}{sup 0} and for ttH{sub l}{sup 0} couplings within the minimal supersymmetric standard model. The effective one-loop Lagrangian is then applied to the computation of the neutral Higgs decays. The sizes of the supersymmetric loop corrections of the neutral Higgs decay widths into {chi}{sub i}{sup +}{chi}{sub j}{sup -} (i=1, 2; j=1, 2) are investigated and the supersymmetric loop correction is found to be in the range of 7{approx}15% in significant regions of the parameter space. By including the loop corrections of the other decay channels bb, tt, {tau}{tau}, cc, and {chi}{sub i}{sup 0}{chi}{sub j}{sup 0} (i=1-4; j=1-4), the corrections to branching ratios for H{sub l}{sup 0}{yields}{chi}{sub i}{sup +}{chi}{sub j}{sup -} can reach as high as 40%. The effects of CP phases on the branching ratio are also investigated.

The seesaw with many right-handed neutrinos

There are no upper limits on the possible number of massive, singlet (right-handed) neutrinos that may participate in the seesaw mechanism, and some string constructions motivate seesaw models with up to O(100) right-handed neutrinos. In this case, the seesaw mass scale can be significantly higher than that in the traditional scheme with just 3 right-handed neutrinos. We consider the possible phenomenological implications of such models, in particular, for lepton-flavour violation and electric dipole moments. Since the neutrino masses depend on the Majorana mass scale linearly, while supersymmetric loop corrections depend on it logarithmically, the magnitude of lepton-flavour- and CP-violating transitions may increase with the multiplicity of the right-handed neutrinos and may be enhanced by orders of magnitude. We also point out that, in the context of leptogenesis, the bounds on the reheating temperature and the lightest neutrino mass get relaxed compared to those in the case of 3 right-handed neutrinos.

Fermionic superstring loop amplitudes in the pure spinor formalism

The pure spinor formulation of the ten-dimensional superstring leads to manifestly supersymmetric loop amplitudes, expressed as integrals in pure spinor superspace. This paper explores different methods to evaluate these integrals and then uses them to calculate the kinematic factors of the one-loop and two-loop massless four-point amplitudes involving two and four Ramond states.

Testing supersymmetry with lepton flavor violatingτandμdecays

In this work the following lepton flavor violating $\ensuremath{\tau}$ and $\ensuremath{\mu}$ decays are studied: ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$, ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{e}^{\ensuremath{-}}{e}^{+}$, ${\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{e}^{\ensuremath{-}}{e}^{+}$, ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}$, ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}\ensuremath{\gamma}$, and ${\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}\ensuremath{\gamma}$. We work in a supersymmetric scenario consisting of the minimal supersymmetric standard model particle content, extended by the addition of three heavy right-handed Majorana neutrinos and their supersymmetric partners, and where the generation of neutrino masses is done via the seesaw mechanism. Within this context, a significant lepton flavor mixing is generated in the slepton sector due to the Yukawa neutrino couplings, which is transmitted from the high to the low energies via the renormalization group equations. This slepton mixing then generates via loops of supersymmetric particles significant contributions to the rates of ${l}_{j}\ensuremath{\rightarrow}3{l}_{i}$ and the correlated ${l}_{j}\ensuremath{\rightarrow}{l}_{i}\ensuremath{\gamma}$ decays. We analyze here in full detail these rates in terms of the relevant input parameters, which are the usual minimal supergravity parameters and the seesaw parameters. For the ${l}_{j}\ensuremath{\rightarrow}3{l}_{i}$ decays, a full one-loop analytical computation of all the contributing supersymmetric loops is presented. This completes and corrects previous computations in the literature. In the numerical analysis compatibility with the most recent experimental upper bounds on all these $\ensuremath{\tau}$ and $\ensuremath{\mu}$ decays, with the neutrino data, and with the present lower bounds on the supersymmetric particle masses are required. Two typical scenarios with degenerate and hierarchical heavy neutrinos are considered. We will show here that the minimal supergravity and seesaw parameters do get important restrictions from these $\ensuremath{\tau}$ and $\ensuremath{\mu}$ decays in the hierarchical neutrino case.

Associated production of a top quark and a charged Higgs boson

We compute the inclusive and differential cross sections for the associated production of a top quark along with a charged Higgs boson at hadron colliders to next-to-leading order (NLO) in perturbative quantum chromodynamics (QCD) and in supersymmetric QCD. For small Higgs boson masses we include top quark pair production diagrams with subsequent top quark decay into a bottom quark and a charged Higgs boson. We compare the NLO differential cross sections obtained in the bottom parton picture with those for the gluon-initiated production process and find good agreement. The effects of supersymmetric loop contributions are explored. Only the corrections to the Yukawa coupling are sizable in the potential discovery region at the CERN Large Hadron Collider (LHC). All expressions and numerical results are fully differential, permitting selections on the momenta of both the top quark and the charged Higgs boson.

Tauonic B Decays in the Minimal Supersymmetric Standard Model

We study new physics effects on B decay processes including a final τ particle, namely B → Dτν and B → τν. An important feature of these processes is that a charged Higgs boson can contribute to the decay amplitude at the tree level in models such as Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model (MSSM). We derive a resummed effective Lagrangian for charged-Higgs mediated interactions in the MSSM with the Minimal Flavor Violation. Including supersymmetric (SUSY) loop corrections for down-type-quark and charged-lepton Yukawa couplings, we calculate the branching ratios of the B → Dτν and B → τν processes. We find that SUSY correction due to gluino-sbottom diagrams can change the Higgs exchange contribution by ±50%, whereas stau-neutralino diagrams can make corrections up to 20%. We also discuss relationship between SUSY corrections in the tauonic decays and flavor changing neutral current processes such as Bs → µ+µ− and b → sγ.

Sensitivity of supersymmetric dark matter to thebquark mass

An analysis of the sensitivity of supersymmetric dark matter to variations in the b quark mass is given. Specifically we study the effects on the neutralino relic abundance from supersymmetric loop corrections to the mass of the b quark. It is known that these loop corrections can become significant for large $\mathrm{tan}\ensuremath{\beta}.$ The analysis is carried out in the framework of MSUGRA and we focus on the region where the relic density constraints are satisfied by resonant annihilation through the s-channel Higgs poles. We extend the analysis to include CP phases taking into account the mixing of the CP-even and CP-odd Higgs boson states which play an important role in determining the relic density. Implications of the analysis for the neutralino relic density consistent with the recent WMAP relic density constraints are discussed.