Joel W. Walker

A Higgs mass shift to 125 GeV and a multi-jet supersymmetry signal: Miracle of the flippons at the s=7 TeV LHC

We describe a model named No-Scale F-SU(5) which is simultaneously capable of explaining the dual signals emerging at the LHC of (i) a 124-126 GeV Higgs boson mass m(h), and (ii) tantalizing low-statistics excesses in the multi-jet data which may attributable to supersymmetry. These targets tend to be mutually exclusive in more conventional approaches. The unified mechanism responsible for both effects is the introduction of a rather unique set of vector-like multiplets at the TeV scale, dubbed flippons, which (i) can elevate m(h) by around 3-4 GeV via radiative loop corrections, and (ii) flatten the running of the strong coupling and color-charged gaugino, resulting in a prominent collider signal from production of light gluino pairs. This well-motivated theoretical framework maintains consistency with all key phenomenological constraints, and all residual parameterization freedom may in principle be fixed by a combination of the two experiments described. We project that the already collected luminosity of 5 fb(-1) may be sufficient to definitively establish the status of this model, given appropriate data selection cuts

Phenomenological study of a minimal superstring standard model

Abstract Recently, we demonstrated the existence of heterotic-string solutions in which the observable sector effective field theory just below the string scale reduces to that of the MSSM, with the standard observable gauge group being just SU(3) C ×SU(2) L ×U(1) Y and the SU(3) C ×SU(2) L ×U(1) Y -charged spectrum of the observable sector consisting solely of the MSSM spectrum. Associated with this model is a set of distinct flat directions of vacuum expectation values (VEVs) of non-Abelian singlet fields that all produce solely the MSSM spectrum. In this paper, we study the effective superpotential induced by these choices of flat directions. We investigate whether sufficient degrees of freedom exist in these singlet flat directions to satisfy various phenomenological constraints imposed by the observed standard model data. For each flat direction, the effective superpotential is given to sixth order. The variations in the singlet and hidden sector low energy spectrums are analyzed. We then determine the mass matrices (to all finite orders) for the three generations of MSSM quarks and leptons. Possible Higgs μ -terms are investigated. We conclude by considering generalizations of our flat directions involving VEVs of non-Abelian fields.Recently, we demonstrated the existence of heterotic–string solutions in which the observable sector effective field theory just below the string scale reduces to that of the MSSM, with the standard observable gauge group being just SU(3)C × SU(2)L × U(1)Y and the SU(3)C × SU(2)L × U(1)Y –charged spectrum of the observable sector consisting solely of the MSSM spectrum. Associated with this model is a set of distinct flat directions of vacuum expectation values (VEVs) of non–Abelian singlet fields that all produce solely the MSSM spectrum. In this paper, we study the effective superpotential induced by these choices of flat directions. We investigate whether sufficient degrees of freedom exist in these singlet flat directions to satisfy various phenomenological constraints imposed by the observed Standard Model data. For each flat direction, the effective superpotential is given to sixth order. The variations in the singlet and hidden sector low energy spectrums are analyzed. We then determine the mass matrices (to all finite orders) for the three generations of MSSM quarks and leptons. Possible Higgs μ–terms are investigated. We conclude by considering generalizations of our flat directions involving VEVs of non–Abelian fields. gcleaver@rainbow.physics.tamu.edu faraggi@mnhepw.hep.umn.edu dimitri@soda.physics.tamu.edu jwalker@rainbow.physics.tamu.edu 1 Minimal Superstring Standard Models Recently [1, 2] we demonstrated that it is indeed possible for a string model [3, 4] to have exactly the minimal supersymmetric standard model (MSSM) fields as the SU(3)C × SU(2)L × U(1)Y –charged matter content of its low energy effective field theory. We propose that string models with this property be classified as “Minimal Superstring Standard Models” (MSstrSM ) [2]. In our MSstrSM, , decoupling of all MSSM–charged exotics from the low energy effective field theory was accomplished by sets of vacuum expectation values (VEVs) that eliminate the anomalous U(1)A endemic to several classes of string models (in particular, those of bosonic lattice, orbifold, or free fermionic construction). Besides restoring spacetime supersymmetry through cancellation of the Fayet–Iliopoulos (FI) D–term, these sets of VEVs also give FI–scale (≈ 4 to 7 × 10 GEV) mass to the MSSM exotics. If the underlying “initial” state of the universe truly was an anomalous U(1)A string model, then determination of the specific flat VEV direction chosen to cancel the FI D–term was a result of non–perturbative dynamics. That is, the physically preferred flat direction cannot be identified perturbatively. However, through perturbative means we can locate and classify the possible flat directions most consistent with observed data. Classification of non–Abelian (NA) singlet flat directions that produce the MSSM gauge group and matter fields, while simultaneously decoupling all MSSM exotics, was performed in [2]. Based on our “stringent” F–flatness constraints, we found three directions flat to all order, one direction flat to 12 order, and around 100 remaining directions only flat to seventh order or less. The existence of free fermionic models with solely the MSSM spectrum below the string scale reinforces the motivation to improve our understanding of this particular class of string models. Both from the point of view of understanding the non–perturbative dynamics, as well as improving the techniques that are needed in order to confront the perturbative string models with the low energy experimental data. In this paper we perform studies of the phenomenological features of these first four flat directions of the “FNY” model of [3, 4]. We explore the phenomenology of our MSstrSM flat directions and investigate which (if any) of our four singlet directions appear most consistent with observed phenomenological criteria. We remark that phenomenological studies, similar to the one performed in this paper, were done in the past for other three generation free fermionic models. The new features in this paper are as follows. First, the FNY model is the first known example of a semi–realistic string model, which produces solely the MSSM–charged spectrum just below the string scale. Thus, for the first time such a phenomenological analysis is carried out in a Minimal Superstring Standard Model. Second, and more importantly, in the phenomenological analysis performed in this paper, we implement the systematic techniques for the analysis of F and D flat directions that were developed over the last few years [5, 6, 7, 2]. Relative to the more primitive studies performed in the past, our study here has the advantage that it incorporates

A supersymmetric flipped SU(5) intersecting brane world

Abstract We construct an N = 1 supersymmetric three-family flipped SU ( 5 ) model from type IIA orientifolds on T 6 / ( Z 2 × Z 2 ) with D6-branes intersecting at general angles. The spectrum contains a complete grand unified and electroweak Higgs sector. In addition, it contains extra exotic matter both in bi-fundamental and vector-like representations as well as two copies of matter in the symmetric representation of SU ( 5 ) .

Elements of F-ast Proton Decay

Gauge coupling unification in the Minimal Supersymmetric Standard Model (MSSM) strongly suggests the existence of a Grand Unified Theory (GUT), which could be probed by the observation of proton decay. Proton lifetime in the p -> (e/mu)(+)pi(0) dimension six mode is proportional in the fourth power to the GUT mass scale, and inversely proportional in the fourth power to the GUT coupling. Flipped SU(5) with strict MSSM field content is known to survive existing null detection limits for proton decay approaching 10(34) years, and indeed, the lifetime predicted by prior studies can be so long that successful detection is not currently plausible. We provide an updated dictionary of solutions for the relevant flipped unification parameters with generic beta-function coefficients, significantly upgrading the level of detail with which second order effects are treated, and correcting subtle published errors. Recently studied classes of a-theory derived GUT models postulate additional vector-like multiplets at the TeV scale which modify the renormalization group to yield a substantial increase in the SU(3)(C) x SU(2)(L) unified coupling. In conjunction with the naturally depressed F-lipped SU(5) partial unification mass M(32), the F-resh analysis undertaken predicts comparatively F-ast proton decay which only narrowly evades existing detection limits, and likely falls within the observable range of proposed next generation detectors such as DUSEL and Hyper-Kamiokande. The TeV-scale vector multiplets are themselves suitable for cross correlation by the Large Hadron Collider. Their presence moreover magnifies the gap between the dual mass scales of Flipped SU(5), allowing for an elongated second stage renormalization, pushing the F-inal grand unification to the doorstep of the reduced Planck mass

Phenomenology of non-Abelian flat directions in a minimal superstring standard model

Abstract Recently, we presented the first non-Abelian flat directions that produce from a heterotic string model solely the three-generation MSSM states as the massless spectrum in the observable sector of the low energy effective field theory. In this paper we continue to develop the systematic techniques for the analysis of non-renormalizable superpotential terms and non-Abelian flat direction in realistic string models. Some of our non-Abelian directions were F-flat to all finite orders in the superpotential. We study for the same string model the varying phenomenologies resulting from a large set of such all-order flat directions. We focus on the quark, charged lepton, and Higgs doublet mass matrices resulting for our phenomenologically superior non-Abelian flat direction. We review and apply a string-related method for generating large mass hierarchies between MSSM generations, first discussed in string-derived flipped SU(5) models, when all generational mass terms are of renormalizable or very low non-renormalizable order.

Flipping SU(5) out of trouble

Abstract Minimal supersymmetric SU(5) GUTs are being squeezed by the recent values of αs, sin2θW, the lower limit on the lifetime for p→ ν K decay, and other experimental data. We show how the minimal flipped SU(5) GUT survives these perils, accommodating the experimental values of αs and sin2θW and other constraints, while yielding a p→e/μ+π0 lifetime beyond the present experimental limit but potentially accessible to a further round of experiments. We exemplify our analysis using a set of benchmark supersymmetric scenarios proposed recently in a constrained MSSM framework.

Ultrahigh jet multiplicity signal of stringy no-scale F-SU(5) at the root s=7 TeV LHC

We present the distinctive collider signatures of no-scale F-SU(5), a highly efficient and phenomenologically favored model built on the tripodal foundations of the F-lipped SU(5) x U(1)(X) grand unified theory, extra F-theory derived TeV scale vectorlike particle multiplets, and the dynamic high-scale boundary conditions of no-scale supergravity. The identifying features of the supersymmetric spectrum are a light stop and gluino, with both sparticles much lighter than all the additional squarks. This unique mass hierarchy leads to the enhanced production of events with an ultrahigh multiplicity of hadronic jets, which should be clearly visible to the root s = 7 TeV LHC at only 1 fb(-1) of integrated luminosity. We suggest a modest alternative event cutting procedure based around a reduced minimal transverse momentum per jet (p(T) > 20 GeV), and an increased minimal multiplicity (>= 9) of distinct jets per subscribed event. These criteria optimize the F-SU(5) signal-to-background ratio, while readily suppressing the contribution of all standard model processes, allowing moreover a clear differentiation from competing models of new physics, most notably minimal supergravity. The characteristic no-scale signature is quite stable across the viable parameter space, modulo an overall rescaling of the mass spectrum; detection by the LHC of the ultrahigh jet signal would constitute a suggestive evocation of the intimately linked stringy origins of F-SU(5) and could possibly provide a glimpse into the underlying structure of the fundamental string moduli.

NON-ABELIAN FLAT DIRECTIONS IN A MINIMAL SUPERSTRING STANDARD MODEL

Recently, by studying exact flat directions of non-Abelian singlet fields, we demonstrated the existence of free fermionic heterotic-string models in which the SU(3)C×SU(2)L×U(1)Y-charged matter spectrum reduces to that of the MSSM in the effective field theory. In this letter we generalize the analysis to include vevs of non-Abelian fields. We find MSSM-producing, exact non-Abelian flat directions, which are the first such examples in the literature. We examine the possibility that hidden sector condensates lift the flat directions.

A K-theory anomaly free supersymmetric flipped SU(5) model from intersecting branes

Abstract We construct an N = 1 supersymmetric three-family flipped SU ( 5 ) model from type IIA orientifolds on T 6 / ( Z 2 × Z 2 ) with D6-branes intersecting at general angles. The model is constrained by the requirement that Ramond–Ramond tadpoles cancel, the supersymmetry conditions, and that the gauge boson coupled to the U ( 1 ) X factor does not get a string-scale mass via a generalised Green–Schwarz mechanism. The model is further constrained by requiring cancellation of K-theory charges. The spectrum contains a complete grand unified and electroweak Higgs sector, however the latter in a non-minimal number of copies. In addition, it contains extra matter both in bi-fundamental and vector-like representations as well as two copies of matter in the symmetric representation of SU ( 5 ) .

Dark matter, proton decay and other phenomenological constraints in F-SU(5)

We study gravity mediated supersymmetry breaking in F-SU(5) and its low-energy supersymmetric phenomenology. The gaugino masses are not unified at the traditional grand unification scale, but we nonetheless have the same one-loop gaugino mass relation at the electroweak scale as minimal supergravity (mSUGRA). We introduce parameters testable at the colliders to measure the small second loop deviation from the mSUGRA gaugino mass relation at the electroweak scale. In the minimal SU(5) model with gravity mediated supersymmetry breaking, we show that the deviations from the mSUGRA gaugino mass relations are within 5%. However, in F-SU(5), we predict the deviations from the mSUGRA gaugino mass relations to be larger due to the presence of vector-like particles, which can be tested at the colliders. We determine the viable parameter space that satisfies all the latest experimental constraints and find it is consistent with the CDMS II experiment. Further, we compute the cross-sections of neutralino annihilations into gamma-rays and compare to the first published Fermi-LAT measurement. Finally, the corresponding range of proton lifetime predictions is calculated and found to be within reach of the future Hyper-Kamiokande and DUSEL experiments