arXiv subjects

Mihir P. Worah

Publications and source records attributed to Mihir P. Worah.

At least 19 recordsLinked to original sources

arXiv1999

Baryogenesis and Low Energy CP Violation

CP violation is a crucial component in the creation of the matter - anti matter asymmetry of the universe. An important open question is whether the CP violating phenomena observeable in terrestrial experiments have any relation with those responsible for baryogenesis. We discuss two mechanisms of baryogenesis where this question can be meaningfully posed: ``electroweak baryogenesis'' and ``baryogenesis via leptogenesis''. We show how these scenarios can be constrained by existing and forthcoming experimental data. We present a specific example of both these scenarios where the CP violating phase in the Cabbibo Kobayashi Maskawa matrix is related in a calculable way to the CP violating phase responsible for baryogenesis.

hep-ph↗

arXiv1999

New Physics in CP Violating B Decays

We discuss the sensitivity of the CP violating measurements at the upcoming B factories to the presence of physics beyond the Standard Model. We review the three manifestations of CP violation possible in the B meson system. We give examples of decay modes for each of these which are sensitive to new physics, are experimentally feasible, and theoretically clean. Finally, we present techniques to extract Standard Model parameters in the presence of new physics.

hep-ph↗

arXiv1999

Constraining the CKM Parameters using CP Violation in semi-leptonic B Decays

We discuss the usefulness of the CP violating semi-leptonic asymmetry a_{SL} not only as a signal of new physics, but also as a tool in constraining the CKM parameters. We show that this technique could yield useful results in the first years of running at the B factories. We present the analysis graphically in terms of M_{12}, the dispersive part of the B-Bbar mixing amplitude. This is complementary to the usual unitarity triangle representation and often allows a cleaner interpretation of the data.

hep-ph↗

arXiv1998

Atmospheric ν_μDeficit from Decoherence

The simplest explanation for the observed deficit of atmospheric muon neutrinos is that they have oscillated into tau or sterile neutrinos with an oscillation length of the order of the Earth diameter. In order to confirm this hypothesis, all other possible explanations should be ruled out. We propose that a viable alternative hypothesis is that the muon neutrino deficit is caused by flavor sampling events that result in a loss of coherence. The coherence length of the muon neutrinos is expected to be approximately one Earth diameter. We give predictions and experimental tests of this scenario.

hep-ph↗

arXiv1998

Fast CP Violation

$B$ flavor tagging will be extensively studied at the asymmetric $B$ factories due to its importance in CP asymmetry measurements. The primary tagging modes are the semileptonic decays of the $b$ (lepton tag), or the hadronic $b \to c (\to s)$ decays (kaon tag). We suggest that looking for time dependent CP asymmetries in events where one $B$ is tagged leptonically and the other one is tagged with a kaon could result in an early detection of CP violation. Although in the Standard Model these asymmetries are expected to be small, $\sim 1%$, they could be measured with about the same amount of data as in the ``gold-plated'' decay $B_d \to ψK_S$. In the presence of physics beyond the Standard Model, these asymmetries could be as large as $\sim 5%$, and the first CP violation signal in the $B$ system may show up in these events. We give explicit examples of new physics scenarios where this occurs.

hep-ph↗

arXiv1998

Probing the Flavor and CP Structure of Supersymmetric Models with K --> pi nu nubar Decays

We study the implications of various supersymmetric models on the rare $K^+ \to π^+ ν\barν$ and $K_L \to π^0 ν\barν$ 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 $K \to πν\barν$ 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 $K \to πν\barν$ decays with that from $B-\bar B$ and $D-\bar D$ mixing.

hep-ph↗

arXiv1997

Searching for New Physics with CP Violating B Decays

We explore the possibility of using CP violation in B decays to detect the presence of physics beyond the Standard Model. We first study the possibility of new physics in the $B-\bar B$ mixing amplitude. We discuss a construction to extract information about the phase and magnitude of the new physics contribution, as well as the CKM parameters in a model independent way. We point out the difficulty of carrying through this program induced by hadronic uncertainties and discrete ambiguities, and suggest additional measurements to overcome these problems. We then study the possibility of new physics contributions to the B meson decay amplitudes. We emphasize the sensitivity of the $B\to ϕK_S$ decay to these new contributions, and explain how this sensitivity can be quantified using experimental data on SU(3) related decays. Finally, we analyse a number of models where the B decay amplitudes are modified.

hep-ph↗

arXiv1997

Supersymmetric Baryogenesis and Flavor Physics

We study the flavor physics implications of baryogenesis in the Minimal Supersymmetric Standard Model. Enhanced $B-\bar B$ mixing and $b \to s γ$ rates are generic to all scenarios. Depending on the origin of the CP violating phase responsible for baryogenesis there could be a large neutron electric dipole moment, large CP violating $D-\bar D$ mixing or CP violation in top quark production. We discuss how the combination of these measurements with the requirement of baryogenesis shed light on the MSSM parameter space and the source of CP violation.

hep-ph↗

arXiv1997

CP Asymmetry in B_d --> phi K_S: Standard Model Pollution

The difference in the time dependent CP asymmetries between the modes $B --> psi K_S$ and $B --> phi K_S$ is a clean signal for physics beyond the Standard Model. This interpretation could fail if there is a large enhancement of the matrix element of the $b --> u ubar s$ operator between the $B_d$ initial state and the $phi K_S$ final state. We argue against this possibility and propose some experimental tests that could shed light on the situation.

hep-ph↗

arXiv1997

Supersymmetric Baryogenesis at the Electroweak Phase Transition

We study the possibility of baryogenesis in the case of supersymmetry breaking with large mixing between the right-handed scalar charm and right-handed scalar top or right-handed scalar up and right-handed scalar top squarks resulting in one light right-handed up-type squark mass eigenstate. We argue that in this case the electroweak phase transition will be first order, and that large phases already present in the quark mass matrices can generate a baryon asymmetry of the correct magnitude without introducing any new phases specifically for this purpose. We study in detail a particular ansatz for supersymmetry breaking and CP violation where there is only one CP violating phase in the theory: in the up-type quark mass matrix. We study the constraints placed on this model by baryogenesis and flavor physics. This scenario has robust implications for low energy flavor phsyics including D-Dbar mixing and an electric dipole moment for the neutron that are close to the experimental bounds, and CP violation in the B-Bbar system that is different from that in the Standard Model.

hep-ph↗

arXiv1997

CP Violation due to new Delta B =1 Amplitudes

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arXiv1997

A Model Independent Construction of the Unitarity Triangle

In a large class of models, the only significant new physics effect on the CP asymmetries in $B \to ψK_S$ and $B \to ππ$ 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.

hep-ph↗

arXiv1996

CP Asymmetries in B Decays with New Physics in Decay Amplitudes

We make a systematic analysis of the effects of new physics in the B decay amplitudes on the CP asymmetries in neutral B decays. Although these are expected to be smaller than new physics effects on the mixing amplitude, they are easier to probe in some cases. The effects of new contributions to the mixing amplitude are felt universally across all decay modes, whereas the effects of new decay amplitudes could vary from mode to mode. In particular the prediction that the CP asymmetries in the B_d decay modes with $b\to c\bar c s, b \to c\bar c d, b\to c \bar u d$ and $ b\to s \bar s s$ should all measure the same quantity ($sin2β$ in the Standard Model) could be violated. Since the above Standard Model prediction is very precise, new decay amplitudes which are a few percent of the Standard Model amplitudes can be probed. Three examples of models where measurable effects are allowed are given: effective supersymmetry, models with enhanced chromomagnetic dipole operators, and supersymmetry without R parity.

hep-ph↗

arXiv1996

A New Supersymmetric CP Violating Contribution to Neutral Meson Mixing

We study the contribution to flavor changing neutral current processes from box diagrams with light higgsinos and squarks. Starting with just the Cabbibo Kobayashi Maskawa (CKM) phase, we find contributions to the $K^0$ and $B^0$ meson mass matrices that are out of phase with the Standard Model contributions in the case of substantial mixing between the up-type squarks. This difference in phase could be large enough to be detected at the proposed $B$ factories, with interesting implications for the unitarity triangle of CKM matrix elements.

hep-ph↗

arXiv1995

Cosmological Baryon Asymmetry and Kaon CP Violation from a Common Source

We extend an earlier model for radiatively generated fermion masses based on the Pati-Salam group to include CP violation. Spontaneous CP violation in the early universe gives rise to a complex mass matrix for heavy sterile neutrinos. The out-of-equilibrium decay of these neutrinos generates a $B-L$ asymmetry. The sterile neutrinos also act as a mass seed in generating one-loop (complex) mass matrices for the quarks. Thus, the two low energy manifestations of CP violation -- the CKM phase and the baryon number asymmetry -- can both be traced in a calculable way to a common source.

hep-ph↗

arXiv1995

Radiatively Generated Fermion Masses In $SU(4)\times SU(2)_L\times SU(2)_R$

We propose a model based on the gauge group $SU(4)\times SU(2)_L\times SU(2)_R$ where the Dirac masses of all the known fermions are generated as one-loop radiative corrections. We are able to generate realistic quark and lepton masses and mixings without a large hierarchy of Yukawa couplings or extra symmetries. The neutrino masses, which are see-saw suppressed, lie in the mass range favored to solve the solar neutrino problem. The importance of threshold corrections to tree-level mass relations in certain non-supersymmetric GUTs is demonstrated.

hep-ph↗

arXiv1995

The difficulties involved in calculating $δρ$

We discuss the difficulties that arise when one tries to calculate $δρ$ using dispersion relations.

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arXiv1994

Comment on the Dispersion Relations used to Calculate $Δρ$

We use the operator product expansion (OPE) to show that non-perturbative QCD corrections to $Δρ$ can be calculated using unsubtracted dispersion relations for either the transverse or the longitudinal vacuum polarization functions. Recent calculations of the non-perturbative contribution to $Δρ$ based on a non-relativistic calculation of corrections to the $\ttbar$ threshold are inconsistent with this result.

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