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Yosef Nir

Publications and source records attributed to Yosef Nir.

At least 91 records · Page 5Linked to original sources
arXiv2005

The Pattern of CP Asymmetries in $b\to s$ Transitions

New CP violating physics in $b\to s$ transitions will modify the CP asymmetries in B decays into final CP eigenstates ($ϕK_S$, $η^\prime K_S$, $π^0 K_S$, $ωK_S$, $ρ^0 K_S$ and $ηK_S$) from their Standard Model values. In a model independent analysis, the pattern of deviations can be used to probe which Wilson coefficients get a significant contribution from the new physics. We demonstrate this idea using several well-motivated models of new physics, and apply it to current data.

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arXiv2005

SU(3) Relations and the CP Asymmetry in $B \to K_S K_S K_S$

The CP asymmetry in the $B \to K_S K_S K_S$ decay is being measured by the two B factories. A large deviation of the CP asymmetry $S_{K_S K_S K_S}$ from $-S_{ψK_S}$ and/or of $C_{K_S K_S K_S}$ from zero would imply new physics in $b \to s$ transitions. We try to put upper bounds on the Standard Model size of these deviations, using SU(3) flavor relations and experimental data on the branching ratios of various decay modes that proceed via $b \to d$ transitions. We point out several subtleties that distinguish the case of three body final states from two body ones. We present several simple relations that can become useful once all relevant modes are measured accurately enough.

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arXiv2004

New Ways to Soft Leptogenesis

Soft supersymmetry breaking terms involving heavy singlet sneutrinos provide new sources of lepton number violation and of CP violation. In addition to the CP violation in mixing, investigated previously, we find that `soft leptogenesis' can be generated by CP violation in decay and in the interference of mixing and decay. These additional ways to leptogenesis can be significant for a singlet neutrino Majorana mass that is not much larger than the supersymmetry breaking scale, $M < 100 m_{SUSY}$. In contrast to CP violation in mixing, for some of these new contributions the sneutrino oscillation rate can be much faster than the decay rate, so that the bilinear scalar term need not be smaller than its natural scale.

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arXiv2004

The Importance of Being Majorana: Neutrinos versus Charged Fermions in Flavor Models

We argue that neutrino flavor parameters may exhibit features that are very different from those of quarks and charged leptons. Specifically, within the Froggatt-Nielsen (FN) framework, charged fermion parameters depend on the ratio between two scales, while for neutrinos a third scale--that of lepton number breaking--is involved. Consequently, the selection rules for neutrinos may be different. In particular, if the scale of lepton number breaking is similar to the scale of horizontal symmetry breaking, neutrinos may become flavor-blind even if they carry different horizontal charges. This provides an attractive mechanism for neutrino flavor anarchy.

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arXiv2004

The $D^0 - \bar D^0$ mass difference from a dispersion relation

We study the Standard Model prediction for the mass difference between the two neutral D meson mass eigenstates, $Δm$. We derive a dispersion relation based on heavy quark effective theory that relates $Δm$ to an integral of the width difference of heavy mesons, $ΔΓ$, over varying values of the heavy meson mass. Modeling the $m_D$-dependence of certain D decay partial widths, we investigate the effects of SU(3) breaking from phase space on the mass difference. We find that $Δm$ may be comparable in magnitude to $ΔΓ$ in the Standard Model.

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arXiv2004

Baryogenesis from the Kobayashi-Maskawa Phase

The Standard Model fulfills the three Sakharov conditions for baryogenesis. The smallness of quark masses suppresses, however, the CP violation from the Kobayashi-Maskawa phase to a level that is many orders of magnitude below what is required to explain the observed baryon asymmetry. We point out that if, as a result of time variation in the Yukawa couplings, quark masses were large at the time of the electroweak phase transition, then the Kobayashi-Maskawa mechanism could be the source of the asymmetry. The Froggatt-Nielsen mechanism provides a plausible framework where the Yukawa couplings could all be of order one at that time, and settle to their present values before nucleosynthesis. The problems related to a strong first order electroweak phase transition may also be alleviated in this framework. Our scenario reveals a loophole in the commonly held view that the Kobayashi-Maskawa mechanism cannot be the dominant source of CP violation to play a role in baryogenesis.

hep-ph↗
arXiv2003

Comment on extracting alpha from B -> rho rho

Recent experimental results on $B\toρρ$ decays indicate that the CP asymmetry $S_{ρ^+ρ^-}$ will give an interesting determination of $α=\arg[-(V_{td}V_{tb}^*)/(V_{ud}V_{ub}^*)]$. In the limit when the $ρ$ width is neglected, the $B\toππ$ isospin analysis can also be applied to $B\toρρ$, once an angular analysis is used to separate transversity modes. The present bound on the shift of $S_{ρ^+ρ^-}$ from the true $\sin2α$ is already stronger than it is for $S_{π^+π^-}$. We point out a subtle violation of the isospin relations when the two $ρ$ mesons are observed with different invariant masses, and how to constrain this effect experimentally.

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arXiv2003

Leptogenesis from Supersymmetry Breaking

We show that soft supersymmetry breaking terms involving the heavy sneutrinos can lead to sneutrino-antisneutrino mixing and to new sources of CP violation, which are present even if a single generation is considered. These terms are naturally present in supersymmetric versions of leptogenesis scenarios, and they induce indirect CP violation in the decays of the heavy sneutrinos, eventually generating a baryon asymmetry. This new contribution can be comparable to or even dominate over the asymmetry produced in traditional leptogenesis scenarios.

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arXiv2003

SU(3) Relations and the CP Asymmetries in B Decays to $η' K_S$, $ϕK_S$ and $K^+ K^- K_S$

We consider CP asymmetries in neutral $B$ meson decays to $η' K_S$, $ϕK_S$, and $K^+ K^- K_S$. We use SU(3) relations to estimate or bound the contributions to these amplitudes proportional to $V_{ub}^*V_{us}$. Such contributions induce a deviation of the $S_f$ terms measured in these time dependent CP asymmetries from that measured for $ψK_S$. For the $K^+ K^- K_S$ mode, we estimate the deviation to be of order 0.1. For the $η' K_S$ mode, we obtain an upper bound on this deviation of order 0.3. For the $ϕK_S$ mode, we have to add a mild dynamical assumption to the SU(3) analysis due to insufficient available data, yielding an upper bound of order 0.25. These bounds may improve significantly with future data. While they are large at present compared to the usually assumed Standard Model contribution, they are obtained with minimal assumptions and hence provide more rigorous tests for new physics. If measurements yield $|S_f-S_{ψK}|$ that are much larger than our bounds, it would make a convincing case for new physics.

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arXiv2003

CP Violation: The CKM Matrix and New Physics

Recent measurements of CP violating asymmetries have led to a significant progress in our understanding of CP violation. The implications of the experimental results for the Kobayashi-Maskawa mechanism and for new physics are explained.

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arXiv2002

Time Variations in the Scale of Grand Unification

We study the consequences of time variations in the scale of grand unification, $M_U$, when the Planck scale and the value of the unified coupling at the Planck scale are held fixed. We show that the relation between the variations of the low energy gauge couplings is highly model dependent. It is even possible, in principle, that the electromagnetic coupling $α$ varies, but the strong coupling $α_3$ does not (to leading approximation). We investigate whether the interpretation of recent observations of quasar absorption lines in terms of time variation in $α$ can be accounted for by time variation in $M_U$. Our formalism can be applied to any scenario where a time variation in an intermediate scale induces, through threshold corrections, time variations in the effective low scale couplings.

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arXiv2002

Product Groups, Discrete Symmetries, and Grand Unification

We study grand unified theories based on an SU(5)xSU(5) gauge group in which the GUT scale, M_{GUT}, is the VEV of an exact or approximate modulus, and in which fast proton decay is avoided through a combination of a large triplet mass and small triplet couplings. These features are achieved by discrete symmetries. In many of our models, M_{GUT} is generated naturally by the balance of higher dimension terms that lift the GUT modulus potential, and soft supersymmetry breaking masses. The theories often lead to interesting patterns of quark and lepton masses. We also discuss some distinctions between grand unified theories and string unification.

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arXiv2002

Quark-Squark Alignment Revisited

We re-examine the possibility that the solution to the supersymmetric flavor problem is related to small mixing angles in gaugino couplings induced by approximate horizontal Abelian symmetries. We prove that, for a large class of models, there is a single viable structure for the down quark mass matrix with four holomorphic zeros. Consequently, we are able to obtain both lower and upper bounds on the supersymmetric mixing angles and predict the contributions to various flavor changing neutral current processes. We find that the most likely signals for alignment are $Δm_D$ close to the present bound, significant CP violation in $D^0-\bar{D^0}$ mixing, and shifts of order a few percent in various CP asymmetries in $B^0$ and $B_s$ decays. In contrast, the modifications to radiative B decays, to $ε^\prime/ε$ and to $K\toπν\barν$ decays are small. We further investigate a new class of alignment models, where supersymmetric contributions to flavor changing processes are suppressed by both alignment and RGE-induced degeneracy.

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arXiv2002

Implications of the CP asymmetry in semileptonic B decay

Recent experimental searches for $A_{SL}$, the CP asymmetry in semileptonic B decay, have reached an accuracy of order one percent. Consequently, they give meaningful constraints on new physics. We find that cancellations between the Standard Model (SM) and new physics contributions to $B^0 - \bar B^0$ mixing cannot be as strong as was allowed prior to these measurements. The predictions for this asymmetry within the SM and within models of minimal flavor violation (MFV) are below the reach of present and near future measurements. Including order $m_c^2/m_b^2$ and $Λ_{QCD}/m_b$ corrections we obtain the SM prediction: $-1.3 \times 10^{-3} < A_{SL} < -0.5 \times 10^{-3}$. Future measurements can exclude not only the SM, but MFV as well, if the sign of the asymmetry is opposite to the SM or if it is same-sign but much enhanced. We also comment on the CP asymmetry in semileptonic $B_s$ decay, and update the range of the angle $β_s$ in the SM: $0.026 < \sin2β_s < 0.048$.

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arXiv2002

New Physics and Future B Factories

Further experimental and theoretical studies of the physics of flavor and CP violation are well motivated. Within the supersymmetric framework, higher precision measurements will allow to explore classes of models with stronger degree of universality: first, models with no universality, such as alignment or heavy first two squark generations; second, models with approximate universality, such as dilaton dominance or AMSB; and finally models of exact universality, such as GMSB. A broad program, including various rare processes or CP asymmetries in B, D and K decays, will provide detailed information about viable extensions of the Standard Model. Some highlights of future B-physics experiments (the present B-factories with integrated luminosity of 0.5 ab^{-1}, hadron machines, and future high-luminosity B-factories) are described.

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arXiv2001

CP Violation - A New Era

We give a pedagogical review of the theory of CP violation with emphasis on the implications of recent experimental results. The review includes: (i) A detailed description of how CP violation arises in the Standard Model and in its extension that allows for neutrino masses; (ii) The formalism of CP violation in meson decays and its application to various K decays (ε_K, ε^\prime and K\toπνν), D decays (D\to Kπand D\to KK) and B decays (B\to\ellνX, B\toψK_S and B\toππ, including a discussion of the `penguin pollution' problem); (iii) Supersymmetry: the CP problems and the use of CP violation as a probe of the mechanism of dynamical supersymmetry breaking.

hep-ph↗
arXiv2001

CP Violation and the Scale of Supersymmetry Breaking

Supersymmetric models with a high supersymmetry breaking scale give, in general, large contributions to epsilon_K and/or to various electric dipole moments, even when contributions to CP conserving, flavor changing processes are sufficiently suppressed. Some examples are models of dilaton dominance, alignment, non-Abelian flavor symmetries, heavy first two generation sfermions, anomaly mediation and gaugino mediation. There is then strong motivation for `approximate CP', that is a situation where all CP violating phases are small. In contrast, in supersymmetric models with a low breaking scale it is quite plausible that the CKM matrix is the only source of flavor and CP violation. Gauge mediation provides a concrete example. Approximate CP is then unacceptable. Upcoming measurements of the CP asymmetry in B to ψK_S might exclude or support the idea of approximate CP and consequently probe the scale of supersymmetry breaking.

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