arXiv subjects

Yuval Grossman

Publications and source records attributed to Yuval Grossman.

At least 109 records · Page 6Linked to original sources

arXiv2005

Testing the dynamics of B -> ππand constraints on α

In charmless nonleptonic B decays to ππor ρρ, the "color allowed" and "color suppressed" tree amplitudes can be studied in a systematic expansion in \alphas(mb) and Λ/mb. At leading order in this expansion their relative strong phase vanishes. The implications of this prediction are obscured by penguin contributions. We propose to use this prediction to test the relative importance of the various penguin amplitudes using experimental data. The present B->ππdata suggest that there are large corrections to the heavy quark limit, which can be due to power corrections to the tree amplitudes, large up-quark penguin amplitude, or enhanced weak annihilation. Because the penguin contributions are smaller, the heavy quark limit is more consistent with the B->ρρdata, and its implications may become important for the extraction of αfrom this mode in the future.

hep-ph↗

arXiv2005

Neutrino Constraints on Spontaneous Lorentz Violation

We study the effect of spontaneous Lorentz violation on neutrinos. We consider two kinds of effects: static effects, where the neutrino acquires a Lorentz-violating dispersion relation, and dynamic effects, which arise from the interactions of the neutrino with the Goldstone boson of spontaneous Lorentz violation. Static effects are well detailed in the literature. Here, special emphasis is given to the novel dynamic effect of Goldstone-Cerenkov radiation, where neutrinos moving with respect to a preferred rest frame can spontaneously emit Goldstone bosons. We calculate the observable consequences of this process and use them to derive experimental bounds from SN1987A and the CMBR. The bounds derived from dynamic effects are complementary to - and in many cases much stronger than - those obtained from static effects.

hep-ph↗

arXiv2005

The Effect of $D-\bar D$ Mixing on the Measurement of $γ$ in $B\to D K$ Decays

$D-\bar D$ mixing is the source of the largest theoretical uncertainty in the extraction of $γ$ from $B\to D K$ decays. In the Standard Model, the mixing can have a rate close to its current experimental upper bound and is CP-conserving to an excellent approximation. We show that neglecting CP-conserving $D-\bar D$ mixing leads to an error in the determination of $γ$ only at second order in the small parameters, $Δm_D/Γ_D$ and $ΔΓ_D/Γ_D$, and is therefore very small and can be safely neglected.

hep-ph↗

arXiv2005

Natural soft leptogenesis

Successful soft leptogenesis requires small B-terms for the right-handed sneutrinos and a large CP violating phase between the A- and B-terms. We show that this situation is realized naturally within the framework of gauge mediated supersymmetry breaking. The A-term is dominated by contribution from gauge mediation, while supergravity effects are more important for the B-term. The different origins naturally explain simultaneously the smallness of the B-term and the large CP violating phase. The most stringent bounds on the model come from the cosmological gravitino problem. We find a viable parameter region with very light gravitino $m_{3/2} \lesssim 16 eV$, providing a consistent framework for supersymmetry phenomenology, soft leptogenesis and cosmology.

hep-ph↗

arXiv2004

The photon polarization in B -> X gamma in the standard model

The standard model prediction for the $B\to X_{s,d}γ$ decay amplitude with a right-handed photon is believed to be tiny, suppressed by $m_{s,d}/m_b$, compared to the amplitude with a left-handed photon. We show that this suppression is fictitious: in inclusive decays, the ratio of these two amplitudes is only suppressed by $g_s/(4π)$, and in exclusive decays by $Λ_{QCD}/m_b$. The suppression is not stronger in $B\to X_dγ$ decays than it is in $B\to X_sγ$. We estimate that the time dependent CP asymmetries in $B\to K^*γ$, $ργ$, $K_Sπ^0γ$, and $π^+π^-γ$ are of order 0.1 and that they have significant uncertainties.

hep-ph↗

arXiv2004

Twisted Split Fermions

The observed flavor structure of the standard model arises naturally in "split fermion" models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation coming from the Yukawa couplings to the Higgs. We consider the more natural possibility in which the bulk masses cannot be simultaneously diagonalized, that is, that they are twisted in flavor space. We show that, in general, this does not disturb the natural generation of hierarchies in the flavor parameters. Moreover, it is conceivable that all the flavor mixing and CP-violation in the standard model may come only from twisting, with the five-dimensional Yukawa couplings taken to be universal.

hep-ph↗

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.

hep-ph↗

arXiv2004

Neutrino masses in R-parity violating supersymmetric models

We study neutrino masses and mixing in R-parity violating supersymmetric models with generic soft supersymmetry breaking terms. Neutrinos acquire masses from various sources: Tree level neutrino--neutralino mixing and loop effects proportional to bilinear and/or trilinear R-parity violating parameters. Each of these contributions is controlled by different parameters and have different suppression or enhancement factors which we identified. Within an Abelian horizontal symmetry framework these factors are related and specific predictions can be made. We found that the main contributions to the neutrino masses are from the tree level and the bilinear loops and that the observed neutrino data can be accommodated once mild fine-tuning is allowed.

hep-ph↗

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.

hep-ph↗

arXiv2003

Beyond the standard model with B and K physics

In the first part of the talk the flavor physics input to models beyond the Standard Model is described. One specific example of such a new physics model is given: a model with bulk fermions in one non-factorizable extra dimension. In the second part of the talk we discuss several observables that are sensitive to new physics. We explain what type of new physics can produce deviations from the Standard Model predictions in each of these observables.

hep-ph↗

arXiv2003

Lepton-flavor mixing and $K \to πν\barν$ decays

The impact of possible sources of lepton-flavor mixing on $K \to πν\barν$ decays is analysed. At the one-loop level lepton-flavor mixing originated from non-diagonal lepton mass matrices cannot generate a CP-conserving $K_L \to π^0ν\barν$ amplitude. The rates of these modes are sensitive to leptonic flavor violation when there are at least two different leptonic mixing matrices. New interactions that violate both quark and lepton universalities could enhance the CP-conserving component of $Γ(K_L \to π^0ν\barν)$ and have a substantial impact. Explicit examples of these effects in the context of supersymmetric models, with and without R-parity conservation, are discussed.

hep-ph↗

arXiv2003

Interpreting the time-dependent CP asymmetry in $B^0 \to π^0 K_S$

Flavor SU(3) is used for studying the time-dependent CP asymmetry in $B^0 \to π^0 K_S$ by relating this process to $B^0\to π^0π^0$ and $B^0 \to K^+K^-$. We calculate correlated bounds on $S_{πK} - \sin 2β$ and $C_{πK}$, with maximal magnitudes of 0.2 and 0.3, where $S_{πK}$ and $C_{πK}$ are coefficients of $\sinΔmt$ and $\cosΔmt$ in the asymmetry. Stronger upper limits on $B^0 \to K^+K^-$ are expected to reduce these bounds and to imply nonzero lower limits on these observables. The asymmetry is studied as a function of a strong phase and the weak phase $γ$.

hep-ph↗

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.

hep-ph↗

arXiv2003

Determination of the angle gamma using multibody D decays in B^+- -> D K^+-

We describe a method for determining gamma using B^+- -> D K^+- decays followed by a multibody D decay. In the talk we focus on K_S pi^- pi^+ final state, but other modes such as D -> K_S K^- K^+ and D -> K_S pi^- pi^+ pi^0 can also be used. The main advantages of the method are that it uses only Cabibbo allowed D decays, and that large strong phases are expected due to the presence of resonances. Since no knowledge about the resonance structure is needed, gamma can be extracted without any hadronic uncertainty.

hep-ph↗

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.

hep-ph↗

arXiv2003

TASI 2002 lectures on neutrinos

We present a pedagogical review of neutrino physics. In the first lecture we describe the theoretical motivation for neutrino masses, and explain how neutrino flavor oscillation experiments can probe neutrino masses. In the second lecture we review the experimental data, and show that it is best explained if neutrinos are massive. In the third lecture we explain what are the theoretical implications of the data, in particular, what are the challenges they impose on models of physics beyond the SM. We give examples of theoretical models that cope with some of these challenges.

hep-ph↗

arXiv2003

Realistic split fermion models

The standard model flavor structure can be explained in theories where the fermions are localized on different points in a compact extra dimension. We explain how models with two bulk scalars compactified on an orbifold can produce such separations in a natural way. We show that, generically, models of Gaussian overlaps are unnatural since they require very large Yukawa couplings between the fermions and the bulk scalars. We present a two scalar model that accounts naturally for the quark flavor parameters and in particular yields order one CP violating phase.

hep-ph↗

arXiv2003

Determining $γ$ using $B^\pm \to D K^\pm$ with multibody D decays

We propose a method for determining $γ$ using $B^\pm\to D K^\pm$ decays followed by a multibody $D$ decay, such as $D \to K_S π^-π^+$, $D \to K_S K^-K^+$ and $D \to K_S π^-π^+π^0$. The main advantages of the method is that it uses only Cabibbo allowed $D$ decays, and that large strong phases are expected due to the presence of resonances. Since no knowledge about the resonance structure is needed, $γ$ can be extracted without any hadronic uncertainty.

hep-ph↗