Searcharxiv⌕ Search

arXiv subjects

G. L. Kane

Publications and source records attributed to G. L. Kane.

At least 19 recordsLinked to original sources
arXiv2005

Twenty-five Questions for String Theorists

In an effort to promote communication between the formal and phenomenological branches of the high-energy theory community, we provide a description of some important issues in supersymmetric and string phenomenology. We describe each within the context of string constructions, illustrating them with specific examples where applicable. Each topic culminates in a set of questions that we believe are amenable to direct consideration by string theorists, and whose answers we think could help connect string theory and phenomenology.

hep-th↗
arXiv2005

Study of theory and phenomenology of some classes of family symmetry and unification models

We review and compare theoretically and phenomenologically a number of possible family symmetries, which when combined with unification, could be important in explaining quark, lepton and neutrino masses and mixings, providing new results in several cases. Theoretical possibilities include Abelian or non-Abelian, symmetric or non symmetric Yukawa matrices, Grand Unification or not. Our main focus is on anomaly-free U(1) family symmetry combined with SU(5) unification, although we also discuss other possibilities. We provide a detailed phenomenological fit of the fermion masses and mixings for several examples, and discuss the supersymmetric flavour issues in such theories, including a detailed analysis of lepton flavour violation. We show that it is not possible to quantitatively and decisively discriminate between these different theoretical possibilities at the present time.

hep-ph↗
arXiv2005

Massive Neutrinos and (Heterotic) String Theory

String theories in principle address the origin and values of the quark and lepton masses. Perhaps the small values of neutrino masses could be explained generically in string theory even if it is more difficult to calculate individual values, or perhaps some string constructions could be favored by generating small neutrino masses. We examine this issue in the context of the well-known three-family standard-like Z_3 heterotic orbifolds, where the theory is well enough known to construct the corresponding operators allowed by string selection rules, and analyze the D- and F-flatness conditions. Surprisingly, we find that a simple see-saw mechanism does not arise. It is not clear whether this is a property of this construction, or of orbifolds more generally, or of string theory itself. Extended see-saw mechanisms may be allowed; more analysis will be needed to settle that issue. We briefly speculate on their form if allowed and on the possibility of alternatives, such as small Dirac masses and triplet see-saws. The smallness of neutrino masses may be a powerful probe of string constructions in general. We also find further evidence that there are only 20 inequivalent models in this class, which affects the counting of string vacua.

hep-th↗
arXiv2004

An Approach to the Cosmological Constant Problem(s)

We propose an approach to explaining why naive large quantum fluctuations are not the right estimate for the cosmological constant. We argue that the universe is in a superposition of many vacua, in such a way that the resulting fluctuations are suppressed by level repulsion to a very small value. The approach combines several aspects of string theory and the early history of the universe, and is only valid if several assumptions hold true. The approach may also explain why the effective cosmological constant reamins small as the universe evolves though several phase transitions. It provides a non-anthropic mechansim leading to a small, non-zero cosmological constant.

hep-ph↗
arXiv2004

Theoretical Implications of the LEP Higgs Search

We study the implications for the minimal supersymmetric standard model (MSSM) of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. For each of these cases -- as well as the case that the lightest Higgs eigenstate is at, or slightly above, the current LEP limit -- we provide explicit sample configurations of the Higgs sector as well as the soft supersymmetry breaking Lagrangian parameters necessary to generate these outcomes. We argue that all of the cases seem fine-tuned, with the least fine-tuned outcome being that with Higgs mass near 115 GeV. Seeking to minimize this tuning we investigate ways in which the ``maximal-mixing'' scenario with large top-quark trilinear A-term can be obtained from simple string-inspired supergravity models. We find these obvious approaches lead to heavy gauginos and/or problematic low-energy phenomenology with minimal improvement in fine-tuning.

hep-ph↗
arXiv2003

The Soft Supersymmetry-Breaking Lagrangian: Theory and Applications

After an introduction recalling the theoretical motivation for low energy (100 GeV to TeV scale) supersymmetry, this review describes the theory and experimental implications of the soft supersymmetry-breaking Lagrangian of the general minimal supersymmetric standard model (MSSM). Extensions to include neutrino masses and nonminimal theories are also discussed. Topics covered include models of supersymmetry breaking, phenomenological constraints from electroweak symmetry breaking, flavor/CP violation, collider searches, and cosmological constraints including dark matter and implications for baryogenesis and inflation.

hep-ph↗
arXiv2003

Relating Incomplete Data and Incomplete Theory

Assuming string theorists will not soon provide a compelling case for the primary theory underlying particle physics, the field will proceed as it has historically: with data stimulating and testing ideas. Ideally the soft supersymmetry breaking Lagrangian will be measured and its patterns will point to the underlying theory. But there are two new problems. First a matter of principle: the theory may be simplest at distance scales and in numbers of dimensions where direct experiments are not possible. Second a practical problem: in the foreseeable future (with mainly hadron collider data) too few observables can be measured to lead to direct connections between experiment and theory. In this paper we discuss and study these issues and consider ways to circumvent the problems, studying models to test methods. We propose a semi-quantitative method for focusing and sharpening thinking when trying to relate incomplete data to incomplete theory, as will probably be necessary.

hep-ph↗
arXiv2003

A Possible Mechanism for Generating a Small Positive Cosmological Constant

We argue that in the context of string theory a large number N of connected degenerate vacua that mix will lead to a ground state with much lower energy, essentially because of the standard level repulsion of quantum theory for the wavefunction of the Universe. We imagine a history where initial quantum fluctuations give an energy density $\sim m_{susy}^2m_{Pl}^2$, but the universe quickly cascades to an energy density $\sim m_{susy}^2m_{Pl}^2/N$. Then at various phase transitions there are large contributions to the energy density and rearrangement of levels, followed again by a rapid cascade to the ground state or near it. If this mechanism is correct, the ground state of the theory describing our world would be a superposition of a large number of connected string vacua,with shared superselection sets of properties such as three families etc. The observed value of the cosmological constant in terms of the Planck mass, the scale of supersymmetry breaking and the number of connected string vacua.

hep-th↗
arXiv2003

B --> Phi K_S and Supersymmetry

The rare decay B --> Phi K_S is a well-known probe of physics beyond the Standard Model because it arises only through loop effects yet has the same time-dependent CP asymmetry as B --> Psi K_S. Motivated by recent data suggesting new physics in B --> Phi K_S, we look to supersymmetry for possible explanations, including contributions mediated by gluino loops and by Higgs bosons. Chirality-preserving LL and RR gluino contributions are generically small, unless gluinos and squarks masses are close to the current lower bounds. Higgs contributions are also too small to explain a large asymmetry if we impose the current upper limit on B(B_s --> mu mu). On the other hand, chirality-flipping LR and RL gluino contributions can provide sizable effects and while remaining consistent with related results in B --> Psi K_S, Delta M_s, B --> X_s gamma and other processes. We discuss how the LR and RL insertions can be distinguished using other observables, and we provide a string-based model and other estimates to show that the needed sizes of mass insertions are reasonable.

hep-ph↗
arXiv2003

B_s -> mu mu as a Probe of Tan(beta) at the Tevatron

Recently it has been understood that flavor-changing processes mediated by Higgs bosons could be a new and powerful tool for discovering supersymmetry. In this paper we show that they may also provide an important method for constraining the parameters of the minimal supersymmetric standard model (MSSM). Specifically, we show that observation of B_s -> mu mu at the Tevatron implies a significant, model-independent lower bound on tan(beta) in the MSSM. This is very important because tan(beta) enters crucially in predictions and interpretations of the MSSM, though it is difficult to measure. Within specific models, or with other data, the bound becomes significantly stronger.

hep-ph↗
arXiv2003

Phenomenology and Theory of Possible Light Higgs Bosons

We study the implications of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. In the minimal supersymmetric standard model (MSSM) all of these, as well as the cases where the Higgs mass equals or exceeds 115 GeV, seem fine-tuned. We examine some interpretations of the fine tuning in high scale theories. The least fine-tuned MSSM outcome will have a Higgs mass at 115 GeV, while approaches that extend the MSSM at the weak scale can naturally have larger Higgs masses.

hep-ph↗
arXiv2003

B(d) --> phi K(S) CP asymmetries as an important probe of supersymmetry

The decay $B_d \to ϕK_S$ is a special probe of physics beyond the Standard Model (SM), since it has no SM tree level contribution. Motivated by recent data suggesting a deviation from the SM for its time-dependent CP asymmetry, we examine supersymmetric explanations. Chirality preserving contributions are generically small, unless gluino is relatively light. Higgs contributions are also too small to explain a large asymmetry. Chirality flipping $LR$ and $RL$ gluino contributions actually can provide sizable effects without conflict with all related results. We discuss how various insertions can be distinguished, and argue the needed sizes of mass insertions are reasonable.

hep-ph↗
arXiv2003

Theory-Motivated Benchmark Models and Superpartners at the Tevatron

Recently published benchmark models have contained rather heavy superpartners. To test the robustness of this result, several benchmark models have been constructed based on theoretically well-motivated approaches, particularly string-based ones. These include variations on anomaly and gauge-mediated models, as well as gravity mediation. The resulting spectra often have light gauginos that are produced in significant quantities at the Tevatron collider, or will be at a 500 GeV linear collider. The signatures also provide interesting challenges for the LHC. In addition, these models usually account for electroweak symmetry breaking with relatively less fine-tuning than previous benchmark models.

hep-ph↗
arXiv2002

Connecting String Theory and Phenomenology

To make progress in learning the underlying fundamental theory, it will be necessary to combine bottom-up phenomenology and top-down analysis -- in particular, top-down is unlikely to succeed alone. Here I elaborate on the role of both, and describe obstacles that need to be overcome to help data point toward the underlying theory, as well as approaches that might help to bypass full systematic treatments. I also summarize arguments that superpartners are probably being produced at the Tevatron Collider.

hep-ph↗
arXiv2002

Re-examination of Electroweak Symmetry Breaking in Supersymmetry and Implications for Light Superpartners

We examine arguments that could avoid light superpartners as an implication of supersymmetric radiative electroweak symmetry breaking. We argue that, from the point of view of string theory and standard approaches to generating the mu-term, cancellations among parameters are not a generic feature. While the coefficients relating the Z-mass to parameters in the soft supersymmetry breaking Lagrangian can be made smaller, these same mechanisms lead to lighter superpartner masses at the electroweak scale. Consequently we strengthen the implication that gluinos, neutralinos, and charginos are light and likely to be produced at the Fermilab Tevatron and a linear collider.

hep-ph↗
arXiv2002

Supersymmetric Pati-Salam Models from Intersecting D-Branes

We explore supersymmetric Type I string-motivated three-family scenarios in which the Standard Model is embedded within two sets of intersecting D branes with U(1)-extended Pati-Salam gauge groups. We study a model inspired by the Shiu-Tye Type IIB orientifold, in which a three-family scenario is obtained by assuming that the gauge symmetry breaking takes place in two stages; the Pati-Salam group arises from diagonal breaking of the U(N) gauge groups, which is then broken to the SM gauge group. We investigate the diagonal breaking scenario in detail and find that generically there are difficulties involved in decoupling the exotic Higgs remnants. On the phenomenological side, proper low energy gauge coupling predictions effectively lead to a ``single brane'' scenario for M_string of order 10^16 GeV. The soft parameters in this limit are constrained by a well-known sum rule, leading to a distinctive phenomenological pattern for the low energy mass spectrum.

hep-ph↗
arXiv2001

Alternative approach to $b->s γ$ in the uMSSM

The gluino contributions to the $C'_{7,8}$ Wilson coefficients for $b->s γ$ are calculated within the unconstrained MSSM. New stringent bounds on the $δ^{RL}_{23}$ and $δ^{RR}_{23}$ mass insertion parameters are obtained in the limit in which the SM and SUSY contributions to $C_{7,8}$ approximately cancel. Such a cancellation can plausibly appear within several classes of SUSY breaking models in which the trilinear couplings exhibit a factorized structure proportional to the Yukawa matrices. Assuming this cancellation takes place, we perform an analysis of the $b->s γ$ decay. We show that in a supersymmetric world such an alternative is reasonable and it is possible to saturate the $b->s γ$ branching ratio and produce a CP asymmetry of up to 20%, from only the gluino contribution to $C'_{7,8}$ coefficients. Using photon polarization a LR asymmetry can be defined that in principle allows for the $C_{7,8}$ and $C'_{7,8}$ contributions to the $b->s γ$ decay to be disentangled. In this scenario no constraints on the ``sign of $μ$'' can be derived.

hep-ph↗