arXiv subjects
Publications and source records attributed to Martin Schmaltz.
We show that the SU(3) little Higgs model has a region of parameter space in which electroweak symmetry breaking is natural and in which corrections to precision electroweak observables are sufficiently small. The model is anomaly free, generates a Higgs mass near 150 GeV, and predicts new gauge bosons and fermions at 1 TeV.
We present an ultra-violet extension of the "simplest little Higgs" model. The model marries the simplest little Higgs at low energies to two copies of the "littlest Higgs'' at higher energies. The result is a weakly coupled theory below 100 TeV with a naturally light Higgs. The higher cutoff suppresses the contributions of strongly coupled dynamics to dangerous operators such as those which induce flavor changing neutral currents and CP violation. We briefly survey the distinctive phenomenology of the model.
We present a model of electroweak symmetry breaking in which the Higgs boson is a pseudo-Nambu-Goldstone boson. By embedding the standard model SU(2) x U(1) into an SU(4) x U(1) gauge group, one-loop quadratic divergences to the Higgs mass from gauge and top loops are canceled automatically with the minimal particle content. The potential contains a Higgs quartic coupling which does not introduce one-loop quadratic divergences. Our theory is weakly coupled at the electroweak scale, it has new weakly coupled particles at the TeV scale and a cutoff above 10 TeV, all without fine tuning. We discuss the spectrum of the model and estimate the constraints from electroweak precision measurements.
Little Higgs theories are an exciting new possibility for physics at TeV energies. In the Standard Model the Higgs mass suffers from an instability under radiative corrections. This ``hierarchy problem'' motivates much of current physics beyond the Standard Model research. Little Higgs theories offer a new and very promising solution to this problem in which the Higgs is naturally light as a result of non-linearly realized symmetries. This article reviews some of the underlying ideas and gives a pedagogical introduction to the Little Higgs. The examples provided are taken from the paper "A Little Higgs from a Simple Group", by D.E. Kaplan and M. Schmaltz.
We define a minimal model with Universal Extra Dimensions, and begin to study its phenomenology. The collider signals of the first KK level are surprisingly similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum. The lightest KK particle (LKP) is neutral and stable because of KK-parity. KK excitations cascade decay to the LKP yielding missing energy signatures with relatively soft jets and leptons. Level 2 KK modes may also be probed via their KK number violating decays to Standard Model particles. In either case we provide initial estimates for the discovery potential of the Tevatron and the LHC.
Extra-dimensional theories contain a number of almost degenerate states at each Kaluza-Klein level. If extra dimensional momentum is at least approximately conserved then the phenomenology of such nearly degenerate states depends crucially on the mass splittings between KK modes. We calculate the complete one-loop radiative corrections to KK masses in general 5 and 6 dimensional theories. We apply our formulae to the example of universal extra dimensions and show that the radiative corrections are essential to any meaningful study of the phenomenology. Our calculations demonstrate that Feynman diagrams with loops wrapping the extra dimensions are well-defined and cut-off independent even though higher dimensional theories are not renormalizable.
We point out that the hierarchy between the measured values of the CKM phase and the strong CP phase has a natural origin in supersymmetry with spontaneous CP violation and low energy supersymmetry breaking. The underlying reason is simple and elegant: in supersymmetry the strong CP phase is protected by an exact non-renormalization theorem while the CKM phase is not. We present explicit examples of models which exploit this fact and discuss corrections to the non-renormalization theorem in the presence of supersymmetry breaking. This framework for solving the strong CP problem has generic predictions for the superpartner spectrum, for CP and flavor violation, and predicts a preferred range of values for electric dipole moments.
We propose Minimal Gaugino Mediation as the simplest known solution to the supersymmetric flavor and CP problems. The framework predicts a very minimal structure for the soft parameters at ultra-high energies: gaugino masses are unified and non-vanishing whereas all other soft supersymmetry breaking parameters vanish. We show that this boundary condition naturally arises from a small extra dimension and present a complete model which includes a new extra-dimensional solution to the mu problem. We briefly discuss the predicted superpartner spectrum as a function of the two parameters of the model. The commonly ignored renormalization group evolution above the GUT scale is crucial to the viability of Minimal Gaugino Mediation but does not introduce new model dependence.
We compute the superpartner masses in a class of models with gaugino mediation (or no-scale) boundary conditions at a scale between the GUT and Planck scales. These models are compelling because they are simple, solve the supersymmetric flavor and CP problems, satisfy all constraints from colliders and cosmology, and predict the superpartner masses in terms of very few parameters. Our analysis includes the renormalization group evolution of the soft-breaking terms above the GUT scale. We show that the running above the GUT scale is largely model independent and find that a phenomenologically viable spectrum is obtained.
We present work in progress on employing domain wall fermions to simulate N=1 supersymmetric Yang-Mills theories on the lattice in d=4 and d=3 dimensions. The geometrical nature of domain wall fermions gives simple insights into how to construct these theories. We also discuss the obstacles associated with simulating the N=2 theory in d=4.
We explore a mechanism for generating the Yukawa hierarchies by displacing the left- and right-handed components of the Standard Model fermions in a higher-dimensional space. We find a unique configuration of displacements which fits all quark and lepton masses and mixing angles, with a prediction for the strange quark mass m_s = 120 MeV.
We propose a new framework for mediating supersymmetry breaking through an extra dimension. It predicts positive scalar masses and solves the supersymmetric flavor problem. Supersymmetry breaks on a ``source'' brane that is spatially separated from a parallel brane on which the standard model matter fields and their superpartners live. The gauge and gaugino fields propagate in the bulk, the latter receiving a supersymmetry breaking mass from direct couplings to the source brane. Scalar masses are suppressed at the high scale but are generated via the renormalization group. We briefly discuss the spectrum and collider signals for a range of compactification scales.
We point out a dramatic new experimental signature for a class of theories with extra dimensions, where quarks and leptons are localized at slightly separated parallel ``walls'' whereas gauge and Higgs fields live in the bulk of the extra dimensions. The separation forbids direct local couplings between quarks and leptons, allowing for an elegant solution to the proton decay problem. We show that scattering cross sections for collisions of fermions which are separated in the extra dimensions vanish exponentially at energies high enough to probe the separation distance. This is because the separation puts a lower bound on the attainable impact parameter in the collision. We present cross sections for two body high energy scattering and estimate the power with which future colliders can probe this scenario, finding sensitivity to inverse fermion separations of order 10-70 TeV.
Recently, a new constraint on the structure of a wide class of strongly coupled field theories has been proposed. It takes the form of an inequality limiting the number of degrees of freedom in the infrared description of a theory to be no larger than the number of underlying, ultraviolet degrees of freedom. Here we apply this inequality to chiral gauge theories. For some models we find that it is always satisfied, while for others we find that the assumption of the validity of the inequality implies a strong additional restriction on the spectrum of massless composite particles.
It is commonly thought that small couplings in a low-energy theory, such as those needed for the fermion mass hierarchy or proton stability, must originate from symmetries in a high-energy theory. We show that this expectation is violated in theories where the Standard Model fields are confined to a thick wall in extra dimensions, with the fermions "stuck" at different points in the wall. Couplings between them are then suppressed due to the exponentially small overlaps of their wave functions. This provides a framework for understanding both the fermion mass hierarchy and proton stability without imposing symmetries, but rather in terms of higher dimensional geography. A model independent prediction of this scenario is non-universal couplings of the Standard Model fermions to the ``Kaluza-Klein'' excitations of the gauge fields. This allows a measurement of the fermion locations in the extra dimensions at the LHC or NLC if the wall thickness is close to the TeV scale.
We propose a new constraint on the structure of strongly coupled field theories. The constraint takes the form of an inequality limiting the number of degrees of freedom in the infrared description of a theory relative to the number of underlying, ultraviolet degrees of freedom. We apply the inequality to a variety of theories (both supersymmetric and nonsupersymmetric), where it agrees with all known results and leads to interesting new constraints on low energy spectra. We discuss the relation of this constraint to Renormalization Group c-theorems.
Dvali and Shifman have proposed a field-theoretic mechanism for localizing gauge fields to "branes" in higher dimensional spaces using confinement in a bulk gauge theory. The resulting objects have a number of qualitative features in common with string theory D-branes; they support a gauge field and flux strings can end on them. In this letter, we explore this analogy further, by considering what happens when N of these "branes" approach each other. Unlike in the case of D-branes, we find a reduction of the gauge symmetry as the "branes" overlap. This can be attributed to a tachyonic instability of the flux string stretching between the branes.
Starting from Seiberg's electric-magnetic duality for supersymmetric QCD, we construct dual pairs of non-supersymmetric gauge theories. This is accomplished by first taking the large N limit of supersymmetric QCD and its dual partner and then performing a special ``orbifold projection'' recently introduced by Kachru and Silverstein. We argue that in the large N limit the two projected theories remain dual. The non-supersymmetric gauge theories which can be studied in this fashion have non-supersymmetric field content, chiral fermions and exactly massless scalar matter.