arXiv subjects
Publications and source records attributed to Maurizio Piai.
We explore a framework for the computation of quark mass ratios and CKM mixing angles based on an SU(3) family gauge symmetry. The four ratios md/mb, ms/mb, mu/mt, and mc/mt can be fit at one-loop in the family gauge interaction. The same is true of the quark mixing angles theta12 and theta23, although the result for theta13 is too small. The CP violating phase is naturally O(1).
We study the spontaneous breaking of discrete symmetries in theories with broken gauge symmetry. The intended application is to CP breaking in theories with gauged flavor symmetries, but the analysis described here is preliminary. We dispense with matter fields and take the gauge theory to be weakly coupled and broken spontaneously by unspecified, short-distance forces. We develop an effective-field-theory description of the resultant low energy theory, and ask whether this theory by itself can describe the subsequent breaking of discrete symmetries. We conclude that this can happen depending on the parameters of the effective theory, and that the intrinsic violation is naturally of order unity.
I review a technique to embed vector mesons in the chiral Lagrangian of QCD, and apply it to more general coset spaces, relevant for Little Higgs models. The implementation of heavy spin-1 fields in Little Higgs models allows for a better control over previously non calculable, ultra-violate sensitive quantities, such as the Higgs couplings. A relevant application is the study of vacuum alignment in the SU(6)/Sp(6) models.
We analyze constraints on a class of extended technicolor (ETC) models from neutral flavor-changing processes induced by (dimension-six) four-fermion operators. The ETC gauge group is taken to commute with the standard-model gauge group. The models in the class are distinguished by how the left- and right-handed $(L,R)$ components of the quarks and charged leptons transform under the ETC group. We consider $K^{0} - \bar K^0$ and other pseudoscalar meson mixings, and conclude that they are adequately suppressed if the $L$ and $R$ components of the relevant quarks are assigned to the same (fundamental or conjugate-fundamental) representation of the ETC group. Models in which the $L$ and $R$ components of the down-type quarks are assigned to relatively conjugate representations, while they can lead to realistic CKM mixing and intra-family mass splittings, do not adequately suppress these mixing processes. We identify an approximate global symmetry that elucidates these behavioral differences and can be used to analyze other possible representation assignments. Flavor-changing decays, involving quarks and/or leptons, are adequately suppressed for any ETC-representation assignment of the $L$ and $R$ components of the quarks, as well as the leptons. We draw lessons for future ETC model building.
We study diagonal and transition quark dipole operators in a class of extended technicolor (ETC) models, taking account of the multiscale nature of the ETC gauge symmetry breaking and of the mixing among ETC interaction eigenstates. Because of this mixing, terms involving the lowest ETC scale can play an important role in dipole operators, and we focus on these terms. We derive from experiment new correlated constraints on the quark mixing angles and phases. Our bounds yield information on mixing angles individually in the up- and down-sectors, for both left- and right-handed quark fields and thus constrain even quark mixing parameters that do not enter in the CKM matrix. With phases of order unity, we conclude that these mixing angles are small, constraining future ETC model building, but plausibly in the range suggested by the size of the CKM elements. These values still allow substantial deviations from the standard model predictions, in particular for several CP violating quantities, including the asymmetries in $b \to s γ$ and $B_{d} \to ϕK_S$, $Re(ε^\prime/ε)$, and the electric dipole moments of the neutron and the ${}^{199}$Hg atom.
We review how the rho meson can be modeled in an effective theory and discuss the implications of applying this approach to heavier spin-one resonances. Georgi's vector limit is explored, and its relationship to locality in a deconstructed extra-dimension is discussed. We then apply the formalism for rho's to strongly coupled theories of electroweak symmetry breaking, studying the lightest spin-one techni-rho resonances. Understanding these new particles in Little Higgs models can shed light on previously incalculable, ultraviolet sensitive physics, including the mass of the Higgs boson.
We analyze the diagonal and transition magnetic and electric dipole moments of charged leptons in extended technicolor (ETC) models, taking account of the multiscale nature of the ETC gauge symmetry breaking, conformal (walking) behavior of the technicolor theory, and mixing in the charged-lepton mass matrix. We show that mixing effects dominate the ETC contributions to charged lepton electric dipole moments and that these can yield a value of |d_e| comparable to the current limit. The rate for mu to e gamma can also be close to its limit. From these and other processes we derive constraints on the charged lepton mixing angles. The constraints are such that the ETC contribution to the muon anomalous magnetic moment, which includes a significant lepton mixing term, can approach, but does not exceed, the current sensitivity level.
We study fermion masses and mixing angles, including the generation of a seesaw mechanism for the neutrinos, in extended technicolor (ETC) theories. We formulate an approach to these problems that relies on assigning right-handed $Q=-1/3$ quarks and charged leptons to ETC representations that are conjugates of those of the corresponding left-handed fermions. This leads to a natural suppression of these masses relative to the $Q=2/3$ quarks, as well as the generation of quark mixing angles, both long-standing challenges for ETC theories. Standard-model-singlet neutrinos are assigned to ETC representations that provide a similar suppression of neutrino Dirac masses, as well as the possibility of a realistic seesaw mechanism with no mass scale above the highest ETC scale of roughly $10^3$ TeV. A simple model based on the ETC group SU(5) is constructed and analyzed. This model leads to non-trivial, but not realistic mixing angles in the quark and lepton sectors. It can also produce sufficiently light neutrinos, although not simultaneously with a realistic quark spectrum. We discuss several aspects of the phenomenology of this class of models.
We study the behavior of simple models for financial markets with widely spread frequency either in the trading activity of agents or in the occurrence of basic events. The generic picture of a phase transition between information efficient and inefficient markets still persists even when agents trade on widely spread time-scales. We derive analytically the dependence of the critical threshold on the distribution of time-scales. We also address the issue of market efficiency as a function of frequency. In an inefficient market we find that the size of arbitrage opportunities is inversely proportional to the frequency of the events on which they occur. Greatest asymmetries in market outcomes are concentrated on the most rare events. The practical limits of the applications of these ideas to real markets are discussed in a specific example.