arXiv subjects

Gilad Perez

Publications and source records attributed to Gilad Perez.

155 records · Page 9Linked to original sources

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.

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arXiv2002

Realistic construction of 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 show that models with two bulk scalars compactified on an orbifold can produce such separations in a natural way. We study the shapes and overlaps of the fermion wave functions. We show that, generically, realistic models of Gaussian overlaps are unnatural since they require very large Yukawa couplings between the fermions and the bulk scalars. We give an example of a five dimensional two scalar model that accounts naturally for the observed quark masses, mixing angles and CP violation.

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arXiv2002

Lepton Masses and Mixing in a Left-Right Symmetric Model with a TeV-scale Gravity

We construct a left-right symmetric (LRS) model in five dimensions which accounts naturally for the lepton flavor parameters. The fifth dimension is described by an orbifold, S_1/Z_2 times Z'_2, with a typical size of order TeV^{-1}. The fundamental scale is of order 25 TeV which implies that the gauge hierarchy problem is ameliorated. In addition the LRS breaking scale is of order few TeV which implies that interactions beyond those of the standard model are accessible to near future experiments. Leptons of different representations are localized around different orbifold fixed points. This explains, through the Arkani-Hamed-Schmaltz mechanism, the smallness of the tau mass compared to the electroweak breaking scale. An additional U(1) horizontal symmetry, broken by small parameters, yields the hierarchy in the charged lepton masses, strong suppression of the light neutrino masses and accounts for the mixing parameters. The model yields several unique predictions. In particular, the branching ratio for the lepton flavor violating process mu^- --> e^+ e^- e^- is comparable with its present experimental sensitivity.

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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

On Neutrino Masses and a Low Breaking Scale of Left-Right Symmetry

In left-right symmetric models (LRSM) the light neutrino masses arise from two sources: the seesaw mechanism and a VEV of an SU(2)$_L$ triplet. If the left-right symmetry breaking, $v_R$, is low, $v_R\lsim15\TeV$, the contributions to the light neutrino masses from both the seesaw mechanism and the triplet Yukawa couplings are expected to be well above the experimental bounds. We present a minimal LRSM with an additional U(1) symmetry in which the masses induced by the two sources are below the eV scale and the two-fold problem is solved. We further show that, if the U(1) symmetry is also responsible for the lepton flavor structure, the model yields a small mixing angle within the first two lepton generations.

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arXiv2001

Constraining Models of New Physics in Light of Recent Experimental Results on $a_{ψK_S}$

We study extensions of the Standard Model where the charged current weak interactions are governed by the CKM matrix and where all tree-level decays are dominated by their Standard Model contribution. We constrain both analytically and numerically the ratio and the phase difference between the New Physics and the Standard Model contributions to the mixing amplitude of the neutral $B$ system using the experimental results on $R_u$, $Δm_{d,s}$, $ε_K$ and $a_{ψK_S}$. We present new results concerning models with minimal flavor violation and update the relevant parameter space. We also study the left-right symmetric model with spontaneously broken CP, probing the viability of this model in view of the recent results for $a_{ψK_S}$ and other observables.

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arXiv2001

Lepton Masses and Mixing Angles with Spontaneously Broken O(3) Flavor Symmetry

We present a model based on an O(3) flavor symmetry and a minimal extension of the scalar sector to induce hierarchical breaking, O(3) -> O(2) -> SO(2) -> nothing. The model naturally accounts for all the known lepton parameters and yields various interesting predictions for others: (i) Neutrinos are nearly degenerate, m_ν\sim 0.1 eV; (ii) The solar neutrino problem is solved by the MSW small mixing angle solution; (iii) The MNS mixing angle theta_{13} is unobservably small, theta_{13} = O(10^{-5}).

hep-ph↗

arXiv2000

Standard Model correlations between K -> πν\barνdecays and observables in B Physics

Including the recent preliminary results of BaBar and BELLE experiments, we update the currently allowed intervals for various CKM parameters: $\barρ$, $\barη$, $\sin2β$, $\sin2α$, $\sin^2γ$. We also update the SM prediction for the rates of the $K_L \to π^0 ν\barν$ and $K^+ \to π^+ ν\barν$ decays, their ratio $a_{πν\barν}$, as well as for certain observables related to $B$ Physics like the CP asymmetries $a_{ψK_S}$ in $B^0_d \to J/ψK_S$ and $a_{ψϕ}$ in $B^0_s \to J/ψϕ$ or the mass differences $Δm_q$ ($q=d,s$) in the $B^0_q-\bar B^0_q$ systems. We investigate the correlations between them. The strongest correlations are between i) $a_{πν\barν}$ and $a_{ψK_S}$, ii) $\BR(K^+ \to π^+ ν\barν)$ and $Δm_d/Δm_s$ and iii) $\BR(K_L \to π^0 ν\barν)$ and $a_{ψϕ}$. These correlations are likely to be violated in the presence of New Physics and therefore provide stringent tests of the Standard Model.

hep-ph↗

arXiv2000

Implications of a Small CP Asymmetry in B->ψK_S

New measurements of the CP asymmetry in B->ψK_S, a_{ψK_S}, by the BABAR and BELLE collaborations are consistent with the Standard Model prediction for sin2β. These measurements, however, leave open the possibility that a_{ψK_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 sin2β. New physics, mainly in B^0-\barB^0 mixing and/or K^0-\barK^0 mixing, can explain low values of a_{ψK_S} in two ways: either by allowing for values of sin2βbelow the Standard Model prediction or by modifying the relation between a_{ψK_S} and sin2β.

hep-ph↗

arXiv2000

The $K_L\toπ^0ν\barν$ Decay in Models of Extended Scalar Sector

We calculate new contributions to the $K_L\toπ^0ν\barν$ decay in models where neutrino Majorana masses require an extension of the scalar sector. First, we study a model where the neutrino mass is induced by the vacuum expectation value of an SU(2)-triplet scalar. Second, we study the Zee model where the Majorana mass comes from one loop diagrams involving a singly charged, SU(2)-singlet scalar. In both models, the Yukawa couplings that involve the new scalar and the neutrinos could be of order one. We find, however, that the contributions to the $K_L\toπ^0ν\barν$ decay mediated by the new scalars depend on the neutrino masses rather than the Yukawa couplings and are, therefore, negligibly small.

hep-ph↗

arXiv1999

Implications of Neutrino Masses on the $K_{L}\toπ^{0}ν\barν$ Decay

We calculate the different contributions to the decay $K_{L}\to π^{0}ν\barν$ that arise if the neutrinos are massive. In spite of a chiral enhancement factor, we find that these contributions are negligibly small. Compared to the CP violating leading contributions, the CP conserving contributions related to Dirac masses are suppressed by a factor of order $(m_K m_ν/m_W^2)^2\lesssim10^{-12}$, and those related to Majorana masses are suppressed by a factor of order $(α_W m_K m_s^2 m_ν/m_W^4)^2\lesssim10^{-29}$. With lepton flavor mixing we find new contributions with a single CP violating coupling leading to a final CP even state or with two CP violating couplings leading to a final CP odd state. These contributions can be of the order of the Standard Model CP conserving contributions to the flavor diagonal modes.

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