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Yasaman Farzan

Publications and source records attributed to Yasaman Farzan.

At least 73 records · Page 4Linked to original sources
arXiv2012

Proceedings of the first workshop on Flavor Symmetries and consequences in Accelerators and Cosmology (FLASY2011)

The main goals of the first "Workshop on FLAvor SYmmetries and consequences in accelerators and cosmology" (FLASY) was to summarize the theoretical status of flavor symmetries, bringing together young researchers in the field to stimulate discussions and new collaborations, with the aim of investigating possible new physics scenarios to be tested at the LHC, as well as in future neutrino, cosmology experiments and dark matter searches.

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arXiv2011

Strategies to link tiny neutrino masses with huge missing mass of the Universe

With the start of the LHC, interest in electroweak scale models for the neutrino mass has grown. In this letter, we review two specific models that simultaneously explain neutrino masses and provide a suitable DM candidate. We discuss the implications of these models for various observations and experiments including the LHC, Lepton Flavor Violating (LFV) rare decays, direct and indirect dark matter searches and Kaon decay.

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arXiv2011

A novel method to extract dark matter parameters from neutrino telescope data

Recently it has been shown that when the Dark Matter (DM) particles captured in the Sun directly annihilate into neutrino pairs, the oscillatory terms in the oscillation probability do not average to zero and can lead to a seasonal variation as the distance between the Sun and Earth changes in time. In this paper, we explore this feature as a novel method to extract information on the properties of dark matter. We show that by studying the variation of the flux over a few months, it would in principle be possible to derive the DM mass as well as new information on the flavor structure of the DM annihilation modes. In addition to analytic analysis, we present the results of our numerical calculations that take into account scattering and regeneration of neutrinos traversing the Sun.

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arXiv2010

AMEND: A Model Explaining Neutrino masses and Dark matter testable at the LHC and MEG

Despite being very successful in explaining the wide range of precision experimental results obtained so far, the Standard Model (SM) of elementary particles fails to address two of the greatest observations of the recent decades: tiny but nonzero neutrino masses and the well-known problem of missing mass in the Universe. Typically the new models beyond the SM explain only one of these observations. Instead, in the present article, we take the view that they both point towards the same new extension of the Standard Model. The new particles introduced are responsible simultaneously for neutrino masses and for the dark matter of the Universe. The stability of dark matter and the smallness of neutrino masses are guaranteed by a U(1) global symmetry, broken to a remnant Z_2. The canonical seesaw mechanism is forbidden and neutrino masses emerge at the loop level being further suppressed by the small explicit breaking of the U(1) symmetry. The new particles and interactions are invoked at the electroweak scale and lead to rich phenomenology in colliders, in lepton flavour violating rare decays and in direct and indirect dark matter searches, making the model testable in the coming future.

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arXiv2010

A minimal model linking two great mysteries: neutrino mass and dark matter

We present an economic model that establishes a link between neutrino masses and properties of the dark matter candidate. The particle content of the model can be divided into two groups: light particles with masses lighter than the electroweak scale and heavy particles. The light particles, which also include the dark matter candidate, are predicted to show up in the low energy experiments such as $(K\to \ell +{\rm missing energy})$, making the model testable. The heavy sector can show up at the LHC and may give rise to Br($\ell_i \to \ell_j γ$) close to the present bounds. In principle, the new couplings of the model can independently be derived from the data from the LHC and from the information on neutrino masses and Lepton Flavor Violating (LFV) rare decays, providing the possibility of an intensive cross-check of the model.

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arXiv2010

SLIM at LHC: LHC search power for a model linking dark matter and neutrino mass

Recently a model has been proposed that links dark matter and neutrino masses. The dark matter candidate which is dubbed as SLIM has a mass of MeV scale and can show up at low energy experiments. The model also has a high energy sector which consists of a scalar doublet, $(ϕ^-, ϕ^0)$. We discuss the potential of the LHC for discovering the new scalars. We focus on the $ϕ^+ϕ^-$ and $ϕ^{\pm} ϕ^0$ production and the subsequent decay of the charged scalar to a charged lepton and the SLIM which appears as missing energy. Identifying the background, we estimate the signal significance and find that it can exceed $5 σ$ at 30 ${\rm fb}^{-1}$ for the 14 TeV run at the LHC. We comment on the possibility of extracting the flavor structure of the Yukawa couplings which also determine the neutrino mass matrix. Finally, we discuss the prospects of this search at the current 7 TeV run of the LHC.

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arXiv2010

A Framework to Simultaneously Explain Tiny Neutrino Mass and Huge Missing Mass Problem of the Universe

Recently a minimalistic scenario has been developed to explain dark matter and tiny but nonzero neutrino masses. In this scenario, a new scalar called SLIM plays the role of the dark matter. Neutrinos achieve Majorana mass through a one-loop diagram. This scenario can be realized for both real and complex SLIM. Simultaneously explaining the neutrino mass and dark matter abundance constrains the scenario. In particular for real SLIM, an upper bound of a few MeV on the masses of the new particles and a lower bound on their coupling are obtained which make the scenario testable. The low energy scenario can be embedded within various $SU(2)\times U(1)$ symmetric models. I shall briefly review the scenario and a specific model that embeds the scenario, with special emphasis on the effects in the charged Kaon decay which might be observable at the KLOE and NA62 experiments.

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arXiv2010

Extracting the CP-violating phases of trilinear R-parity violating couplings from $μ\to eee$

It has recently been shown that by measuring the transverse polarizations of the final particles in $μ^- \to e^- e^+ e^-$, it is possible to extract information on the phases of the effective couplings leading to this decay. We examine this possibility within the context of R-parity violating Minimal Supersymmetric Standard Model (MSSM) in which the $μ^- \to e^- e^+e^-$ process can take place at a tree level. We demonstrate how a combined analysis of the angular distribution of the emitted positrons and their transverse polarization can determine the CP-violating phases of the trilinear R-parity violating Yukawa couplings.

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arXiv2010

On the Oscillation of Neutrinos Produced by the Annihilation of Dark Matter inside the Sun

The annihilation of dark matter particles captured by the Sun can lead to a neutrino flux observable in neutrino detectors. Considering the fact that these dark matter particles are non-relativistic, if a pair of dark matter annihilates to a neutrino pair, the spectrum of neutrinos will be monochromatic. We show that in this case, even after averaging over production point inside the Sun, the oscillatory terms of the oscillation probability do not average to zero. This leads to interesting observable features in the annual variation of the number of muon track events. We show that smearing of the spectrum due to thermal distribution of dark matter inside the Sun is too small to wash out this variation. We point out the possibility of studying the initial flavor composition of neutrinos produced by the annihilation of dark matter particles via measuring the annual variation of the number of muon-track events in neutrino telescopes.

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arXiv2009

An Analysis of Cosmic Neutrinos: Flavor Composition at Source and Neutrino Mixing Parameters

We examine the feasibility of deriving neutrino mixing parameters $δ$ and $θ_{13}$ from the cosmic neutrino flavor composition under the assumption that the flavor ratios of the cosmic neutrinos at the source were $F_{ν_e}+F_{\barν_e}:F_{ν_μ}+F_{\barν_μ}: F_{ν_τ}+F_{\barν_τ}=1:2:0$. We analyze various uncertainties that enter the derivation of $δ$ and $θ_{13}$ from the ratio of the shower-like to $μ$-tracks events which is the only realistic source of information on the flavor composition at neutrino telescopes such as ICECUBE. We then examine to what extent the deviation of the initial flavor ratio from $1:2:0$ can be tested by measurement of this ratio at neutrino telescopes taking into account various sources of uncertainty.

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arXiv2009

A new class of invariants in the lepton sector

We construct a new set of combinations from the mass matrices of the charged leptons and neutrinos that are invariant under basis transformation, hereafter {\it the} invariants. We use these invariants to study various symmetries and neutrino mass textures in a basis independent way. In particular, we show that by using these invariants the ansatz such as $μ-τ$ exchange and reflection symmetries, various texture zeros and flavor symmetries can be expressed in a general basis.

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arXiv2009

A Window on the CP-violating Phases of MSSM from Lepton Flavor Violating Processes

It has recently been shown that by measuring the transverse polarization of the final particles in the LFV processes $μ\to eγ$, $μ\to eee$ and $μN\to e N$, one can derive information on the CP-violating phases of the underlying theory. We derive formulas for the transverse polarization of the final particles in terms of the couplings of the effective potential leading to these processes. We then study the dependence of the polarizations of $e$ and $γ$ in the $μ\to e γ$ and $μN \to e N$ on the parameters of the Minimal Supersymmetric Standard Model (MSSM). We show that combining the information on various observables in the $μ\to eγ$ and $μN\to e N$ search experiments with the information on the electric dipole moment of the electron can help us to solve the degeneracies in parameter space and to determine the values of certain phases.

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arXiv2008

Combined Analysis of Electric Dipole Moments and Lepton Flavor Violating Rare Decays

In the context of general Minimal Supersymmetric Standard Model (MSSM), new sources for Lepton Flavor Violation (LFV) as well as CP-violation appear. We show that in the presence of LFV sources, the electric dipole moment of the electron ($d_e$) can receive new contributions. In particular, $d_e$ can receive a significant contribution at one loop level from the phase of the trilinear $A$-term of the staus, $ϕ_{A_τ}$. We discuss how we can derive information on $ϕ_{A_τ}$ by combining the information on $d_e$ with that on the LFV decay modes of the $τ$ lepton. We then discuss if this approach can be considered as an alternative to the direct measurement of $ϕ_{A_τ}$ at ILC.

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arXiv2008

Coherence and oscillations of cosmic neutrinos

For cosmic neutrinos we study the conditions and the effects of the coherence loss as well as coherent broadening of the spectrum. We evaluate the width of the neutrino wavepacket produced by charged particles under various circumstances: in an interaction-free environment, in a radiation-dominated medium (typical of the sources of the gamma ray bursts) and in the presence of a magnetic field. The effect of the magnetic field on the wavepacket size appears to be more important than the scattering. If the magnetic field at the source is larger than $\sim$10 Gauss, the coherence of neutrinos will be lost while traveling over cosmological distances. Various applications of these results have been considered. We find that for large magnetic fields ($B> 10^9$ Gauss) and high energies ($E_ν>{\rm PeV}$), "coherent broadening" can modify the energy spectrum of neutrinos. In the coherent case, averaging out the oscillatory terms of the probabilities does not induce any statistical uncertainty beyond what expected in the absence of these terms. A deviation from the standard quantum mechanics that preserves average energy and unitarity cannot alter the picture.

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arXiv2008

Reconciling results of LSND, MiniBooNE and other experiments with soft decoherence

We propose an explanation of the LSND signal via quantum-decoherence of the mass states, which leads to damping of the interference terms in the oscillation probabilities. The decoherence parameters as well as their energy dependence are chosen in such a way that the damping affects only oscillations with the large (atmospheric) $Δm^2$ and rapidly decreases with the neutrino energy. This allows us to reconcile the positive LSND signal with MiniBooNE and other null-result experiments. The standard explanations of solar, atmospheric, KamLAND and MINOS data are not affected. No new particles, and in particular, no sterile neutrinos are needed. The LSND signal is controlled by the 1-3 mixing angle $θ_{13}$ and, depending on the degree of damping, yields $0.0014 < \sin^2θ_{13} < 0.034$ at $3σ$. The scenario can be tested at upcoming $θ_{13}$ searches: while the comparison of near and far detector measurements at reactors should lead to a null-result a positive signal for $θ_{13}$ is expected in long-baseline accelerator experiments. The proposed decoherence may partially explain the results of Gallium detector calibrations and it can strongly affect supernova neutrino signals.

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arXiv2007

Electron Electric Dipole Moment from Lepton Flavor Violation

The general Minimal Supersymmetric Standard Model introduces new sources for Lepton Flavor Violation (LFV) as well as CP-violation. In this paper, we show that when both sources are present, the electric dipole moment of the electron, $d_e$, receives a contribution from the phase of the trilinear $A$-term of staus, $ϕ_{A_τ}$. For $ϕ_{A_τ}=π/2$, the value of $d_e$, depending on the ratios of the LFV mass elements, can range between zero and three orders of magnitude above the present bound. We show that the present bound on $d_e$ rules out a large portion of the CP-violating and the LFV parameter space which is consistent with the bounds on the LFV rare decays. We show that studying the correlation between $d_e$ and the P-odd asymmetry in $τ\to eγ$ helps us to derive a more conclusive bound on $ϕ_{A_τ}$ We also discuss the possibility of cancelation among the contributions of different CP-violating phases to $d_e$.

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arXiv2007

Tracing CP-violation in Lepton Flavor Violating Muon Decays

Although the Lepton Flavor Violating (LFV) decay $μ^+\to e^+ γ$ is forbidden in the Standard Model (SM), it can take place within various theories beyond the SM. If the branching ratio of this decay saturates its present bound [{\it i.e.,} Br$(μ^+ \to e^+γ)\sim 10^{-11}$], the forthcoming experiments can measure the branching ratio with high precision and consequently yield information on the sources of LFV. In this letter, we show that for polarized $μ^+$, by studying the angular distribution of the transversely polarized positron and linearly polarized photon we can derive information on the CP-violating sources beyond those in the SM. We also study the angular distribution of the final particles in the decay $μ^+\to e^+_1 e^- e^+_2$ where $e^+_1$ is defined to be the more energetic positron. We show that transversely polarized $e_1^+$ can provide information on a certain combination of the CP-violating phases of the underlying theory which would be lost by averaging over the spin of $e^+_1$.

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