Search

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., Comment: 4 pages

Recent experimental results on $B\to\rho\rho$ decays indicate that the CP asymmetry $S_{\rho^+\rho^-}$ will give an interesting determination of $\alpha=\arg[-(V_{td}V_{tb}^*)/(V_{ud}V_{ub}^*)]$. In the limit when the $\rho$ width is neglected, the $B\to\pi\pi$ isospin analysis can also be applied to $B\to\rho\rho$, once an angular analysis is used to separate transversity modes. The present bound on the shift of $S_{\rho^+\rho^-}$ from the true $\sin2\alpha$ is already stronger than it is for $S_{\pi^+\pi^-}$. We point out a subtle violation of the isospin relations when the two $\rho$ mesons are observed with different invariant masses, and how to constrain this effect experimentally., Comment: 12 pages, minor changes

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., Comment: 4 pages; An improved discussion of the relevant numerical range of the soft breaking terms (in agreement with hep-ph/0308031)

We consider CP asymmetries in neutral $B$ meson decays to $\eta' K_S$, $\phi K_S$, 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 $\psi K_S$. For the $K^+ K^- K_S$ mode, we estimate the deviation to be of order 0.1. For the $\eta' K_S$ mode, we obtain an upper bound on this deviation of order 0.3. For the $\phi K_S$ 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 $|S_f-S_{\psi K}|$ that are much larger than our bounds, it would make a convincing case for new physics., Comment: 24 pages; corrections in Sec. III.A and V, results hardly affected, to appear in Phys Rev D

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 $\alpha$ varies, but the strong coupling $\alpha_3$ does not (to leading approximation). We investigate whether the interpretation of recent observations of quasar absorption lines in terms of time variation in $\alpha$ 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., Comment: 14 pages, revtex4; Updated observational results and improved statistical analysis (section IV); added references

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., Comment: 16 pages, 14 postscript figures, uses espcrc2.sty; Plenary talk given at the 31st international conference on high energy physics (ICHEP 2002), Amsterdam, 24-31 July 2002. v2: Typos (signs) in eqs. 27, 28 corrected; v3: Reference for the measurement of B to D*D* (eq. 31) corrected

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., Comment: 23 pages; no figures; revtex4

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 $\Delta m_D$ 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 $\epsilon^\prime/\epsilon$ and to $K\to\pi\nu\bar\nu$ 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., Comment: 20 pages, 3 figures

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., Comment: 16 pages; An extended version of the contribution to the proceedings of the fifth KEK topical conference `Frontiers in Flavor Physics', KEK, Tsukuba, Japan, November 2001; Talk at the conference given by YN

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 $\Lambda_{QCD}/m_b$ 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 $\beta_s$ in the SM: $0.026 < \sin2\beta_s < 0.048$., Comment: 16 pages, a sign typo in eq.(11) fixed, to appear in Phys. Rev. D

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 (\epsilon_K, \epsilon^\prime and K\to\pi\nu\nu), D decays (D\to K\pi and D\to KK) and B decays (B\to\ell\nu X, B\to\psi K_S and B\to\pi\pi, 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., Comment: 58 pages, 1 Postscript figure, lectures at the 55th Scottish Universities Summer School in Physics, St. Andrews, Scotland, August 7-23, 2001

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 \psi K_S might exclude or support the idea of approximate CP and consequently probe the scale of supersymmetry breaking., Comment: 22 pages, harvmac

We review various implications of recent experimental results concerning CP violation and mixing in $K\to\pi\pi$, $B\to\psi K_S$, $D\to K\pi$ and $D\to KK$ decays., Comment: 14 pages latex using JHEP.cls, contribution to the proceedings of SILAFAE III, Cartagena de Indias, Colombia, April 2-8, 2000

New measurements of the CP asymmetry in B->\psi K_S, a_{\psi K_S}, by the BABAR and BELLE collaborations are consistent with the Standard Model prediction for sin2\beta. These measurements, however, leave open the possibility that a_{\psi K_S} is well below the Standard Model prediction. We identify deviations from the `reasonable ranges' of hadronic parameters that can lead to low values of sin2\beta. New physics, mainly in B^0-\barB^0 mixing and/or K^0-\barK^0 mixing, can explain low values of a_{\psi K_S} in two ways: either by allowing for values of sin2\beta below the Standard Model prediction or by modifying the relation between a_{\psi K_S} and sin2\beta., Comment: 14 pages

If the true values of the D0-anti-D0 mixing parameters lie within the one sigma ranges of recent measurements, then there is strong evidence for a large width difference, y > 0.01, and large SU(3) breaking effects in strong phases, \delta > pi/4. These constraints are model independent, and would become stronger if M_{12}/Gamma_{12} << 1 in the D0-anti-D0 system. The interesting fact that the FOCUS result cannot be explained by a large mass difference is not trivial and depends on the small D0-anti-D0 production asymmetry in FOCUS and the bounds on CP violating effects from CLEO. The large value of \delta might help explain why y ~ sin^2(theta_c)., Comment: 15 pages, harvmac

Three of the viable solutions of the solar neutrino problem are consistent with close to maximal leptonic mixing: $\sin^2\theta_{12}={1\over2}(1-\epsilon_{12})$ with $|\epsilon_{12}|\ll1$. Flavor models can naturally explain close to maximal mixing if approximate horizontal symmetries force a pseudo-Dirac structure on the neutrino mass matrix. An experimental determination of $|\epsilon_{12}|$ and sign($\epsilon_{12}$) can constrain the structure of the lepton mass matrices and consequently provide stringent tests of such flavor models. If both $|\epsilon_{12}|$ and $\Delta m^2_{21}$ are known, it may be possible to estimate the mass scale of the pseudo-Dirac neutrinos. Radiative corrections to close to maximal mixing are negligible. Subtleties related to the kinetic terms in Froggatt-Nielsen models are clarified., Comment: 24 pages; v3: significant improvements and modifications, particularly in the three generation analysis

We argue that there could be large, SU(3) violating resonance contributions to D -> K pi decays which would affect the extraction of the D0-anti-D0 mixing parameters from experiment. Such contributions can induce a large strong phase in the interference between the doubly Cabibbo suppressed and the mixing induced Cabibbo favored contributions to the D0 -> K^+ pi^- and anti-D0 -> K^- pi^+ decays. Consequently, the interpretation of a large, CP conserving interference term can involve a large mass difference Delta M rather than a large width difference Delta Gamma., Comment: 9 pages, 1 figure, RevTeX; discussion clarified, qualitative and quantitative conclusions unchanged, version to appear in JHEP

Neutrino masses and mixings have important implications for models of fermion masses, and, most directly, for the charged lepton sector. We consider supersymmetric Abelian flavor models, where neutrino mass parameters are related to those of charged leptons and sleptons. We show that processes such as \tau to \mu\gamma, \mu to e\gamma and \mu-e conversion provide interesting probes. In particular, some existing models are excluded by current bounds, while many others predict rates within reach of proposed near future experiments. We also construct models in which the predicted rates for charged lepton flavor violation are below even the proposed experimental sensitivities, but argue that such models necessarily involve loss of predictive power., Comment: 27 pages, refs added, published version

The special features of CP violation in the Standard Model are presented. The significance of measuring CP violation in B, K and D decays is explained. The predictions of the Standard Model for CP asymmetries in B decays are analyzed in detail. Then, four frameworks of new physics are reviewed: (i) Supersymmetry provides an excellent demonstration of the power of CP violation as a probe of new physics. (ii) Left-right symmetric models are discussed as an example of an extension of the gauge sector. CP violation suggests that the scale of LRS breaking is low. (iii) The variety of extensions of the scalar sector are presented and their unique CP violating signatures are emphasized. (iv) Vector-like down quarks are presented as an example of an extension of the fermion sector. Their implications for CP asymmetries in B decays are highly interesting., Comment: 85 pages, harvmac, Lectures given in the XXVII SLAC Summer Institute on Particle Physics, July 7 - 16, 1999. v2: references added

The most sensitive experimental searches for $D-\bar D$ mixing use $D^0 \to K^+ \pi^-$ decays. It is often assumed that effects of New Physics and, in particular, CP violation, can appear through the mixing, while the $c \to d u \bar s$ decay amplitude cannot have significant contributions from New Physics and is, therefore, CP conserving to a good approximation. We examine this assumption in two ways. First, we calculate the contributions to the decay in various relevant models of New Physics: Supersymmetry without R-parity, multi-scalar models, left-right symmetric models, and models with extra quarks. We find that phenomenological constraints imply that the New Physics contributions are indeed small compared to the standard model doubly Cabibbo suppressed amplitude. Second, we show that many of our constraints hold model-independently. We find, however, one case where the model-independent bound is rather weak and a CP violating contribution of order 30% is not excluded., Comment: 12 pages, no figures, Latex

Models with extended quark sector affect the CP asymmetry in the $B\to \psi K_{S}$ decay, $a_{\psi K_{S}}$, in two ways: First, the top-mediated box diagram is not necessarily the only important contribution to $B-\bar{B}$ mixing. Second, the $3\times 3$ CKM matrix is no longer unitary. We analyze the constraints that follow from the CDF measurement, $a_{\psi K_{S}} =0.79^{+0.41}_{-0.44}$, on the mixing parameters of extended quark sectors. Most noticeably, we find significant constraints on the phase of the relevant flavor changing $Z$ coupling in models with extra down quarks in vector-like representations. Further implications for the CP asymmetry in semileptonic $B$ decays are discussed., Comment: 12 pages, LaTeX, 3 figures

Recently, the CDF collaboration has reported a measurement of the CP asymmetry in the $B\to\psi K_S$ decay: $a_{\psi K_S}=0.79^{+0.41}_{-0.44}$. We analyze the constraints that follow from this measurement on the size and the phase of contributions from new physics to $B-\barB$ mixing. Defining the relative phase between the full $M_{12}$ amplitude and the Standard Model contribution to be $2\theta_d$, we find a new bound: $\sin2\theta_d\gsim-0.6 (-0.87)$ at one sigma (95% CL). Further implications for the CP asymmetry in semileptonic B decays are discussed., Comment: 13 pages, harvmac, 3 figures; v2: a discussion of new physics effects on tree level decays added; references added; accepted for publication in Physical Review Letters

We investigate supersymmetric models where neither R-parity nor lepton number nor baryon number is imposed. The full high energy theory has an exact horizontal U(1) symmetry that is spontaneously broken. Quarks and Higgs fields carry integer horizontal charges but leptons carry half integer charges. Consequently, the effective low energy theory has two special features: a U(1) symmetry that is explicitly broken by a small parameter, leading to selection rules, and an exact residual Z_2 symmetry, that is lepton parity. As concerns neutrino parameters, the Z_2 symmetry forbids contributions from R_p-violating couplings and the U(1) symmetry induces the required hierarchy. As concerns baryon number violation, the Z_2 symmetry forbids proton decay and the U(1) symmetry provides sufficient suppression of double nucleon decay and of neutron - antineutron oscillations., Comment: 12 pages, harvmac

In the near future, we will have the first significant experimental measurements of CP violation in B decays. These measurements will easily test crucial questions such as whether the Standard Model Kobayashi-Maskawa phase plays a dominant role in CP violation or whether CP is an approximate symmetry in nature. We explain the different types of CP violation in B decays, and the usefulness of measuring them. We use the same formalism to describe the epsilon and epsilon(prime) parameters of the neutral K system and to explain the terms direct and indirect CP violation. We present the Standard Model predictions for the various asymmetries. We argue that certain CP asymmetries in B decays are subject to a very clean theoretical interpretation in terms of fundamental Lagrangian parameters. Within the Standard Model, these asymmetries will provide very accurate measurements of the CKM parameters. In case that deviations from the Standard Model predictions will be found, there is enough information to understand the nature of New Physics that is required to explain them. We demonstrate this statement by analyzing the impact of various Supersymmetric flavor models on CP violation., Comment: 50 pages, 2 figures, LaTeX, lectures given at the school on Flavour and Gauge Hierarchies, NATO Advanced Study Institute, Cargese, Corsica, July 20 - August 1, 1998, and at the First Particle Physics Winter School, KIAS, Seoul, Korea, February 22 - 26, 1999

The experimental data on atmospheric and solar neutrinos are used to test the framework of non-anomalous Abelian horizontal gauge symmetries with only three light active neutrinos. We assume that the hierarchy in mass-squared splittings is not accidental and that the small breaking parameters are not considerably larger than 0.2. We find that the small angle MSW solution of the solar neutrino problem can only be accommodated if the $\nu_\mu-\nu_\tau$ mass hierarchy depends on the charges of at least three sterile neutrinos. The large angle MSW solution can be accommodated in simpler models if $\nu_e$ and $\nu_\mu$ form a pseudo-Dirac neutrino, but it is difficult to induce large enough deviation from maximal mixing. The vacuum oscillation solution can be accommodated rather simply. We conclude that it is possible to accommodate the neutrino parameters in the framework of Abelian horizontal symmetries, but it seems that these parameters by themselves will not provide convincing evidence for this framework., Comment: 19 pages, harvmac; Significant changes in the text, some conclusions changed, a reference added

This is a written version of a series of three lectures aimed at graduate students in the field of experimental high energy physics. The emphasis is on physics that is relevant to $B$-factories. The main topics covered are: (i) The flavor sector of the Standard Model; (ii) Determination of the mixing parameters; (iii) CP violation in meson decays (a model independent description); (iv) CP violation in the Standard Model; (v) CP violation as a probe of new physics., Comment: 49 pages, harvmac, no figures, lectures given at the 1998 European School of High Energy Physics, University of St. Andrews, Scotland, August 23 - September 5, 1998

Moduli are generic in string (M) theory. In a large class of gauge-mediated Supersymmetry breaking models, the fermionic components of such fields have very light masses, around the eV scale, and non-negligible mixing with active neutrinos, of order $10^{-4}$. Consequently, these fermions could play the role of sterile neutrinos to which active neutrinos oscillate, thus affecting measurements of solar neutrinos or of atmospheric neutrinos. They could also provide warm dark matter, thus affecting structure formation., Comment: 12 pages, harvmac; added references

The experimental data on atmospheric and solar neutrinos suggest that there is near-maximal mixing between \nu_\mu and \nu_\tau but that their masses are hierarchically separated. In models of Abelian horizontal symmetries, mixing of O(1) generically implies that the corresponding masses are of the same order of magnitude. We describe two new mechanisms by which a large hierarchy between strongly mixed neutrinos can be achieved in this framework. First, a discrete Abelian symmetry can give the desired result in three ways: mass enhancement, mixing enhancement and mass suppression. Second, holomorphic zeros can give mass suppression., Comment: 18 pages, uses harvmac, reference added

We construct phenomenologically viable supersymmetric models where CP is an approximate symmetry. The full high energy theory has exact CP and horizontal symmetries that are spontaneously broken with a naturally induced hierarchy of scales, $\Lambda_{CP}\ll\Lambda_H$. Consequently, the effective low energy theory, that is the supersymmetric Standard Model, has CP broken explicitly but by a small parameter. The $\epsilon_K$ parameter is accounted for by supersymmetric contributions. The predictions for other CP violating observables are very different from the Standard Model. In particular, CP violating effects in neutral B decays into final CP eigenstates such as $B\ra\psi K_S$ and in $K\ra\pi\nu\bar\nu$ decays are very small., Comment: 19 pages, harvmac

Within the Standard Model, and if one assumes that soft rescattering effects are negligible, the CP asymmetry A^dir_CP (B^\pm -> \pi^\pm K) is predicted to be very small and the ratio R = BR(B_d -> \pi^\mp K^\pm)/BR(B^\pm -> \pi^\pm K) provides a bound on the angle \gamma of the unitarity triangle, sin^2 \gamma \leq R. We estimate the corrections from soft rescattering effects using an approach based on Regge phenomenology, and find effects of order 10% with large uncertainties. In particular, we conclude that A^dir_CP \sim 0.2 and sin^2 \gamma \sim 1.2 R could not be taken unambiguously to signal New Physics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of New Physics on A^dir_CP and on R., Comment: 20 pages, RevTex, no figures; a few typos corrected, references added, brief additional discussion of uncertanties is added

We study the implications of various supersymmetric models on the rare $K^+ \to \pi^+ \nu \bar\nu$ and $K_L \to \pi^0 \nu \bar\nu$ decays. Although large effects are possible in generic supersymmetric models, most of the known supersymmetric flavor models lead to negligible effects. Thus, it is likely that one can get information about CKM matrix elements from these decays even in the presence of supersymmetry. Moreover, the possibility of large contributions to $K \to \pi \nu \bar\nu$ in generic supersymmetric models can be constrained by improved bounds on $D-\bar D$ mixing. We show that it may be possible to distinguish between different supersymmetric flavor models by combining the information from the $K \to \pi \nu \bar\nu$ decays with that from $B-\bar B$ and $D-\bar D$ mixing., Comment: 17 pgs Revtex, 1 fig. Uses epsf. Constraints in Table 1 and related text changed due to previously overlooked SU(2) relations; references updated; conclusions unchanged. Version to be published in PLB.

Four topics in theory of CP violation are reviewed. (a) CP violation in $B$ decays: We describe a new clean way of constraining the angle $\gamma$ of the unitarity triangle and how new CP violation in decay amplitudes can signal new physics. (b) CP violation in $K$ decays: We explain the special features of the decay $K_L\ra\pi^0\nu\bar\nu$ both as a measurement of Standard Model CP violating parameters and as a probe of new physics. (c) CP violation in $D$ decays: We describe the consequences of CP violation from new physics in $D-\bar D$ mixing. (d) CP violation in Supersymmetry: We explain how a combination of measurements of CP violating processes will give insight into the flavor and CP structure of supersymmetry., Comment: 29 pages, LaTeX, Invited plenary talk given at the 18th International Symposium on Lepton Photon Interactions, Hamburg, Germany, July 28 -- August 1 1997. To appear in the proceedings

Fleischer and Mannel (FM) have shown that it may become possible to constrain the angle $\gamma$ of the unitarity triangle from measurements of various $B\to\pi K$ decays. This constraint is independent of hadronic uncertainties to the few percent level. We show that, within the Standard Model, the FM bound gives strong constraints on the CKM parameters. In particular, it could predict a well defined sign for $\sin2\gamma$ and $\sin2\alpha$. In a class of extensions of the Standard Model, where the New Physics affects only $\Delta B=2$ (and, in particular, not $\Delta B=1$) processes, the FM bound can lead to constraints on CP asymmetries in $B$ decays into final CP eigenstates even if $B-\bar B$ mixing is dominated by unknown New Physics. In our analysis, we use a new method to combine in a statistically meaningful way the various measurements that involve CKM parameters., Comment: 24 pages, revtex, 6 figures included using psfig

CP asymmetries in $B$ decays into final CP eigenstates are in many cases theoretically clean. In particular, they do not depend on the values of hadronic parameters. The sign of the asymmetries, however, does depend on the sign of the $B_B$ parameter. Furthermore, the information from $\epsilon_K$ that all angles of the unitarity triangles lie in the range $\{0,\pi\}$ depends on the sign of the $B_K$ parameter. Consequently, in the (unlikely) case that the vacuum insertion approximation is such a poor approximation that either $B_B$ or $B_K$ is negative, the sign of CP asymmetries in neutral $B$ decays will be opposite to the standard predictions. Various subtleties concerning the role of $K-\bar K$ mixing in the case of final states with a single $K_S$ or $K_L$, such as the $B\to\psi K_S$ decay, are clarified., Comment: 14 pages, TeX (harvmac)

In a large class of models, the only significant new physics effect on the CP asymmetries in $B \to \psi K_S$ and $B \to \pi\pi$ decays is a new contribution to the $B-\bar B$ mixing amplitude. This allows a model independent construction of the CKM Unitarity Triangle (up to hadronic uncertainties). Furthermore, the contributions to the mixing from the Standard Model and from the new physics can be disentangled. A serious obstacle to this analysis is an eightfold discrete ambiguity in solving for the angles of the triangle. Several ways to reduce the ambiguity either by making further measurements, or by making further assumptions about the nature of the new physics are described., Comment: 14 pages, harvmac, 2 figures uses epsf

We analyze the decay $K_L \to \pi^0 \nu \bar \nu$ in a model independent way. If lepton flavor is conserved the final state is (to a good approximation) purely CP even. In that case this decay mode goes mainly through CP violating interference between mixing and decay. Consequently, a theoretically clean relation between the measured rate and electroweak parameters holds in any given model. Specifically, $\Gamma(K_L \to \pi^0 \nu \bar \nu)/\Gamma(K^+ \to \pi^+ \nu \bar \nu)= \sin^2\theta$ (up to known isospin corrections), where $\theta$ is the relative CP violating phase between the $K-\bar K$ mixing amplitude and the $s\to d\nu\bar\nu$ decay amplitude. The experimental bound on $BR(K^+ \to \pi^+ \nu \bar \nu)$ provides a model independent upper bound: $BR(K_L \to \pi^0 \nu \bar \nu) < 1.1 \times 10^{-8}$. In models with lepton flavor violation, the final state is not necessarily a CP eigenstate. Then CP conserving contributions can dominate the decay rate., Comment: 12 pages, revtex, no figures

We review CP violation in various extensions of the electroweak sector of the Standard Model. A particular emphasis is put on supersymmetric models. We describe the two CP problems of supersymmetry, concerning $d_N$ and $\epsilon_K$. We critically review the various mechanisms that have been suggested to solve these problems: exact universality, approximate CP symmetry, alignment, approximate universality and heavy squarks. We explain how future measurements of CP violation will test these mechanisms. We describe extensions of the quark sector and their implications on CP asymmetries in neutral B decays, on the $K_L \to \pi \nu \bar\nu$ decay and on $\Delta\Gamma(B_s)$. We discuss CP violation in charged scalar exchange in models with natural flavor conservation and explain how transverse lepton polarization in meson decays can probe such models. CP violation in neutral scalar exchange arises in models of horizontal symmetries and may be manifest in heavy quark (b and t) physics. We describe the implications of Left-Right Symmetric models on $d_N$, $\epsilon_K$, $\epsilon'/\epsilon$ and CP asymmetries in B decays. Finally, we briefly discuss the potential of future measurements of CP violation to discover New Physics., Comment: 50 pages, harvmac, 1 figure. To appear in the Review Volume "Heavy Flavours II", eds. A.J. Buras and M. Lindner, Advanced Series on Directions in High Energy Physics, World Scientific Publishing Co., Singapore

We discuss the discovery potential for New Physics of various measurements of CP violation. If nature is supersymmetric, then the flavor problem is even more mysterious than in the standard model. We show how we can learn about the mechanism that solves the supersymmetric flavor problem from measurements of mixing and CP violation in $K$, $D$ and $B$ decays. (Invited talk given at the Workshop on K Physics, Orsay, France, May 30 - June 4, 1996.), Comment: 16 pages, uses harvmac

We study various modifications to the minimal models of gauge mediated supersymmetry breaking. We argue that, under reasonable assumptions, the structure of the messenger sector is rather restricted. We investigate the effects of possible mixing between messenger and ordinary squark and slepton fields and, in particular, violation of universality. We show that acceptable values for the $\mu$ and $B$ parameters can naturally arise from discrete, possibly horizontal, symmetries. We claim that in models where the supersymmetry breaking parameters $A$ and $B$ vanish at tree level, $\tan\beta$ could be large without fine tuning. We explain how the supersymmetric CP problem is solved in such models., Comment: 22 pages, 1 Postscript figure included, uses harvmac, epsf. Two references corrected

We study neutrino masses and mixing in Supersymmetric Models without $R$ parity and with generic soft Supersymmetry breaking terms. Neutrinos acquire mass from various sources: tree level neutrino--neutralino mixing, loop effects and non--renormalizable operators. Abelian horizontal symmetries (invoked to explain the smallness and hierarchy in quark parameters) replace $R$ parity in suppressing neutrino masses. We find lower bounds on the mixing angles: $\sin\theta_{ij} \gsim m(\ell_i^-)/m(\ell_j^-)$ ($i

Models that combine Abelian horizontal symmetries and spontaneous CP violation can (i) explain the smallness and hierarchy in quark parameters; (ii) satisfactorily suppress supersymmetric contributions to flavor changing neutral current processes; (iii) solve the $\mu$-problem; and (iv) suppress supersymmetric contributions to CP violating observables to an acceptable level. The CKM phase is $\O(1)$ and responsible, through Standard Model box diagrams, to $\epsilon_K$. The supersymmetric CP violating phases are suppressed, $\phi_A\sim\lambda^6$ and $\phi_B\sim\lambda^{8}$ ($\lambda\sim0.2$), leading to an electric dipole moment of the neutron that is about 2--3 orders of magnitude below the experimental bound., Comment: 11 pages, harvmac, no figures

We report the construction of large new classes of models which break supersymmetry dynamically. We then turn to model building. Two of the principal obstacles to constructing simple models of dynamical supersymmetry breaking are the appearance of Fayet-Iliopoulos D terms and difficulties in generating a $\mu$ term for the Higgs fields. Among the new models are examples in which symmetries prevent the appearance of Fayet-Iliopoulos terms. A gauge singlet field, that may play a role in explaining the hierarchy in quark and lepton parameters, can generate a suitable $\mu$ term. The result is a comparatively simple model, with a low energy structure similar to that of the MSSM, but with far fewer arbitrary parameters. We begin the study of the phenomenology of these models., Comment: 32 pages and one figure; compressed post script