arXiv subjects

Yosef Nir

Publications and source records attributed to Yosef Nir.

139 records · Page 8Linked to original sources

arXiv1994

Missing (up) Mass, Accidental Anomalous Symmetries, and the Strong CP Problem

We reconsider the massless up quark solution of the strong CP problem. We show that an anomaly free horizontal symmetry can naturally lead to a massless up quark and to a corresponding accidental anomalous symmetry. Reviewing the controversy about the phenomenological viability of $m_u=0$ we conclude that this possiblity is still open and can solve the strong CP problem. To appear in the Proceedings of The Yukawa Couplings and the Origins of Mass Workshop.

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arXiv1994

Naturally Small $x_s$?

Within the Standard Model, $x_s$ (the mixing parameter in the $B_s-\bar B_s$ system) is constrained to the range $7 \leq x_s\leq 40$. We point out that if New Physics contributes significantly to $x_d$ (the mixing parameter in the $B_d-\bar B_d$ system), then $2 \leq x_s\leq 7$ is possible without any fine-tuned cancellations between the Standard Model and the New Physics contributions.

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arXiv1994

Phenomenological Constraints on $\barΛ$ and $λ_1$

Combining the experimental data on the inclusive decays $D\to X\,e\,ν$, $B\to X\,e\,ν$ and $B\to X\,τ\,ν$, we find severe constraints on the $\barΛ$ and $λ_1$ parameters of the Heavy Quark Effective Theory. In particular, we get $\barΛ<0.7\,$GeV. Our constraints further imply $m_c\geq1.43\,$GeV and $m_b\geq4.66\,$GeV. We discuss future prospects of improving these bounds and their phenomenological implications.

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arXiv1994

Heavy Quark Expansion for the Inclusive Decay $\bar B\toτ\,\barν\,X$

We calculate the differential decay rate for inclusive $\bar B\toτ\,\barν\,X$ transitions to order $1/m_b^2$ in the heavy quark expansion, for both polarized and unpolarized tau leptons. We show that using a systematic $1/m_b$ expansion significantly reduces the theoretical uncertainties in the calculation. We obtain for the total branching ratio ${\rm BR}(\bar B\toτ\,\barν\,X)=2.30\pm 0.25\%$, and for the tau polarization $A_{\rm pol}=-0.706\pm0.006$. {}From the experimental measurement of the branching ratio at LEP, we derive the upper bound $\lo\leq 0.8\gev^2$ for one of the parameters of the heavy quark effective theory.

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arXiv1993

Mass Matrix Models: The Sequel

The smallness of the quark sector parameters and the hierarchy between them could be the result of a horizontal symmetry broken by a small parameter. Such an explicitly broken symmetry can arise from an exact symmetry which is spontaneously broken. Constraints on the scales of new physics arise {}from new flavor changing interactions and {}from Landau poles, but do not exclude the possibility of observable signatures at the TeV scale. Such a horizontal symmetry could also lead to many interesting results: (i) quark -- squark alignment that would suppress, without squark degeneracy, flavor changing neutral currents induced by supersymmetric particles, (ii) exact relations between mass ratios and mixing angles, (iii) a solution of the $μ$-problem and (iv) a natural mechanism for obtaining hierarchy among various symmetry breaking scales.

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arXiv1993

New Physics Effects on CP Violation in $B$ Decays

We review new physics effects on CP violation in B decays. We describe the Standard Model predictions for the various types of CP asymmetries and discuss the theoretical cleanliness of these predictions. We point out the ingredients in the analysis that are most sensitive to new physics and deduce the type of new physics that is likely to modify the Standard Model predictions. Several explicit examples are discussed in detail. Finally, we explain how, if deviations from the Standard Model predictions are measured, we will be able to learn detailed features of the new physics involved. Plenary talk presented at the Workshop on B Physics at Hadron Accelerators, Snowmass, Colorado, June 21 - July 2, 1993.

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arXiv1993

The Decay $B\toπ\ellν$ in Heavy Quark Effective Theory

We present a systematic analysis of the $B^{(*)}\toπ\,\ell\,ν$ weak decay form factors to order $1/m_b$ in the heavy quark effective theory, including a discussion of renormalization group effects. These processes are described by a set of ten universal functions (two at leading order, and eight at order $1/m_b$), which are defined in terms of matrix elements of operators in the effective theory. In the soft pion limit, the effective theory yields normalization conditions for these functions, which generalize the well-known current algebra relations derived from the combination of heavy quark and chiral symmetries to next-to-leading order in $1/m_b$. In particular, the effects of the nearby $B^*$-pole are correctly contained in the form factors of the effective theory. We discuss the prospects for a model independent determination of $|V_{ub}|$ and the $B B^*π$ coupling constant from these processes.

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arXiv1993

Constraints on Extended Technicolor Models from B -> mu+ mu- X

A recent study by Randall and Sundrum shows that models of Extended Technicolor (ETC) have interesting implications on rare B decays. We extend their study to the decay B -> mu+ mu- X. ETC models with a GIM mechanism predict a decay rate that is a factor of order 30 above the Standard Model, violating the experimental upper bound by a factor of 2-4. ``Traditional" ETC models predict a decay rate that is a factor of order 4 above the Standard Model, and will be probed when an improvement in the sensitivity of experiments by a factor of order 2-4 is achieved.

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arXiv1993

Implications of $b\rightarrow sγ$ for CP Violation in Charged Scalar Exchange

In models of three or more scalar doublets, new CP violating phases appear in charged scalar exchange. These phases affect CP asymmetries in neutral $B$ decays, even if Natural Flavor Conservation holds. The recent upper bound on the decay $b\rightarrow sγ$ constrains the effect to be at most of order a few percent. Modifications of constraints on the CKM parameters open an interesting new region in the $\sin2α-\sin2β$ plane even in the absence of new phases.

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arXiv1993

Should Squarks Be Degenerate?

For generic squark masses, box diagrams with squarks and gluinos give unacceptably large contributions to neutral meson ($K$, $B$ and $D$) mixing. The standard solution to this problem is to assume that squarks are degenerate to a very good approximation. We suggest an alternative mechanism to suppress squark contributions to flavor changing neutral currents: the alignment of quark with squark mass matrices. This mechanism arises naturally in the framework of Abelian horizontal symmetries.

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arXiv1993

Z\rightarrow A^0 A^0ν\barν$ and $e^+e^-\rightarrow A^0 A^0 Z$ in Two Higgs Doublet Models

In LEP searches for the neutral CP-odd scalar $A^0$ of a multi-Higgs doublet model, experimenters have searched for $Z\rightarrow h^0 A^0$ (where $h^0$ is the lightest CP-even scalar). No model-independent limit on the $A^0$ mass can be deduced from present data if $m_{h^0}>m_Z$. In this paper, we compute the rates for $Z\rightarrow A^0 A^0ν\barν$ and $e^+e^-\rightarrow A^0 A^0 Z$. Assuming that no light CP-even neutral scalars exist, the branching ratio for $Z\rightarrow A^0 A^0ν\barν$ is found to be less than $1.4\times10^{-8}$. At higher $e^+e^-$ center-of-mass energies, $σ(e^+e^-\rightarrow A^0 A^0 Z)$ peaks at $0.5$~fb. A comparison with other direct searches for the $A^0$ is briefly considered.

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arXiv1992

Mass Matrix Models

It is possible that the hierarchy in the masses and mixing of quarks is a result of a horizontal symmetry. The smallness of various parameters is related to their suppression by high powers of a scale of new physics. We analyze in detail the structure of such symmetries in view of new experimental data and present explicit models consistent with all phenomenological constraints. We show that it is possible that the flavor dynamics can be at accessible energies -- as low as a $TeV$.

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arXiv1992

Testing the Standard Model and Schemes for Quark Mass Matrices with CP Asymmetries in B Decays

The values of $\sin (2 α)$ and $\sin (2 β)$, where $α$ and $β$ are angles of the unitarity triangle, will be readily measured in a B factory (and maybe also in hadron colliders). We study the standard model constraints in the $\sin (2 α) - \sin (2 β)$ plane. We use the results from recent analyses of $f_B$ and $τ_b|V_{cb}|^2$ which take into account heavy quark symmetry considerations. We find $\sin (2 β) \geq 0.15$ and most likely $\sin (2 β) \roughly{>} 0.6$, and emphasize the strong correlations between $\sin (2 α)$ and $\sin (2 β)$. Various schemes for quark mass matrices allow much smaller areas in the $\sin (2 α) - \sin (2 β)$ plane. We study the schemes of Fritzsch, of Dimopoulos, Hall and Raby, and of Giudice, as well as the ``symmetric CKM'' idea, and show how CP asymmetries in B decays will crucially test each of these schemes.

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