arXiv subjects

Alfredo Aranda

Publications and source records attributed to Alfredo Aranda.

63 records · Page 4Linked to original sources

arXiv2001

U(2)-like Flavor Symmetries and Approximate Bimaximal Neutrino Mixing

Models involving a U(2) flavor symmetry, or any of a number of its non-Abelian discrete subgroups, can explain the observed hierarchy of charged fermion masses and CKM angles. It is known that a large neutrino mixing angle connecting second and third generation fields may arise via the seesaw mechanism in these models, without a fine tuning of parameters. Here we show that it is possible to obtain approximate bimaximal mixing in a class of models with U(2)-like Yukawa textures. We find a minimal form for Dirac and Majorana neutrino mass matrices that leads to two large mixing angles, and show that our result can quantitatively explain atmospheric neutrino oscillations while accommodating the favored, large angle MSW solution to the solar neutrino problem. We demonstrate that these textures can arise in models by presenting a number of explicit examples.

hep-ph↗

arXiv2001

Orthogonal U(1)'s, Proton Stability and Extra Dimensions

In models with a low quantum gravity scale, one might expect that all operators consistent with gauge symmetries are present in the low-energy effective theory. If this is the case, some mechanism must be present to adequately suppress operators that violate baryon number. Here we explore the possibility that the desired suppression is a consequence of an additional, spontaneously-broken, non-anomalous U(1) symmetry that is orthogonal to hypercharge. We show that successful models can be constructed in which the additional particle content necessary to cancel anomalies is minimal, and compatible with the constraints from precision electroweak measurements and gauge unification. If unification is sacrificed, and only the new U(1) and its associated Higgs fields live in the bulk, it is possible that the gauge field zero mode and first few Kaluza-Klein excitations lie within the kinematic reach of the Tevatron. For gauge couplings not much smaller than that of hypercharge, we show that these highly leptophobic states could evade detection at Run I, but be discovered at Run II. Our scenario presents an alternative to the `cartographic' solution to baryon number violation in which leptons and quarks are separated in an extra dimension.

hep-ph↗

arXiv2000

Bosonic Topcolor

A topcolor model is presented that contains both composite and fundamental scalar fields. Strong dynamics accounts for most of the top quark mass and part of the electroweak symmetry breaking scale. The fundamental scalar is weakly coupled and transmits its share of electroweak symmetry breaking to the light fermions. The model is allowed by the current experimental bounds, and can give a potentially large contribution to $D^0-\bar{D^0}$ mixing.

hep-ph↗

arXiv2000

A Lot of Flavor Physics from a Little Symmetry

Recent neutrino parameter measurements place increasingly stringent constraints on acceptable supersymmetric theories of flavor. A very fruitful approach is the application of non-Abelian discrete gauged flavor symmetries G_f. We discuss a highly successful model using G_f = T' x Z_3, where T' is a non-Abelian group based on the symmetries of a tetrahedron. This model reproduces the basic features of the U(2) model, and also predicts neutrino masses and mixing angles consistent with either the SMA or LMA solutions.

hep-ph↗

arXiv2000

Generations of Higgs Bosons in Supersymmetric Models

We examine extensions of the MSSM with more than one generation of Higgs bosons. If one assumes that a symmetry eliminates the tree-level FCNC, then the extra scalar bosons do not acquire VEVs, do not couple to fermions and do not mix with the ordinary Higgs bosons; the lightest is absolutely stable. The two lightest neutral scalars, $ϕ_S$, and $ϕ_P$, are degenerate in mass, and the mass difference between those and the lightest charged scalar, $ϕ_+$, is calculated. For most of the parameter space, the charged scalar is between a hundred MeV and a few GeV heavier than the neutral scalars. The $ϕ_+$ will decay at the vertex; the signature for this decay will be like that of a chargino with a nearly degenerate undetected neutralino. Next, the possibility that the symmetry that eliminates FCNC is a flavor symmetry is discussed. In an example, the U(2) model, tree-level FCNC processes can be calculated in terms of quark masses. The strongest constraint on this model is from $D-\bar{D}$ mixing, which should be within an order of magnitude of the current bound.

hep-ph↗

arXiv2000

Bounds on Bosonic Topcolor

We consider the phenomenology of models in which electroweak symmetry breaking is triggered by new strong dynamics affecting the third generation and is transmitted to the light fermions via a fundamental Higgs doublet. While similar in spirit to the old bosonic technicolor idea, such `bosonic topcolor' models are allowed by current phenomenological constraints, and may arise naturally in models with large extra dimensions. We study the parameter space of a minimal low-energy theory, including bounds from Higgs boson searches, precision electroweak parameters, and flavor changing neutral current processes. We show that the model can provide a contribution to D0-D0-bar mixing as large as the current experimental bound.

hep-ph↗

arXiv2000

Maximal Neutrino Mixing from a Minimal Flavor Symmetry

We study a number of models, based on a non-Abelian discrete group, that successfully reproduce the simple and predictive Yukawa textures usually associated with U(2) theories of flavor. These models allow for solutions to the solar and atmospheric neutrino problems that do not require altering successful predictions for the charged fermions or introducing sterile neutrinos. Although Yukawa matrices are hierarchical in the models we consider, the mixing between second- and third-generation neutrinos is naturally large. We first present a quantitative analysis of a minimal model proposed in earlier work, consisting of a global fit to fermion masses and mixing angles, including the most important renormalization group effects. We then propose two new variant models: The first reproduces all important features of the SU(5)xU(2) unified theory with neither SU(5) nor U(2). The second demonstrates that discrete subgroups of SU(2) can be used in constructing viable supersymmetric theories of flavor without scalar universality even though SU(2) by itself cannot.

hep-ph↗

arXiv2000

U(2) Flavor Physics without U(2) Symmetry

We present a model of fermion masses based on a minimal, non-Abelian discrete symmetry that reproduces the Yukawa matrices usually associated with U(2) theories of flavor. Mass and mixing angle relations that follow from the simple form of the quark and charged lepton Yukawa textures are therefore common to both theories. We show that the differing representation structure of our horizontal symmetry allows for new solutions to the solar and atmospheric neutrino problems that do not involve modification of the original charged fermion Yukawa textures, or the introduction of sterile neutrinos.

hep-ph↗

arXiv1998

Limits on a Light Leptophobic Gauge Boson

We consider the phenomenology of a naturally leptophobic $Z$-prime boson in the 1 to 10 GeV mass range. The $Z$-prime's couplings to leptons arise only via a radiatively-generated kinetic mixing with the $Z$ and photon, and hence are suppressed. We map out the allowed regions of the mass-coupling plane and show that such a $Z$-prime that couples to quarks with electromagnetic strength is not excluded by the current data. We then discuss possible signatures at bottom and charm factories.

hep-ph↗