arXiv subjects

M. Raidal

Publications and source records attributed to M. Raidal.

At least 37 records · Page 2Linked to original sources

arXiv2006

Les Houches "Physics at TeV Colliders 2005'' Beyond the Standard Model working group: summary report

The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as computational tools designed in order to facilitate their phenomenology.

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arXiv2004

Leptogenesis in the minimal supersymmetric triplet seesaw model

In the supersymmetric triplet (type-II) seesaw model, in which a single SU(2)_L-triplet couples to leptons, the high-energy neutrino flavour structure can be directly determined from the low-energy neutrino data. We show that even with such a minimal triplet content, leptogenesis can be naturally accommodated thanks to the resonant interference between superpotential and soft supersymmetry breaking terms.

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arXiv2004

Seesaw mechanism and the baryon asymmetry

I review the present understanding of connection between the non-zero neutrino masses and the baryon asymmetry of the Universe. The state-of-art results are presented for the standard thermal leptogenesis.

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arXiv2003

Sneutrino Inflation in the Light of WMAP: Reheating, Leptogenesis and Flavour-Violating Lepton Decays

We reconsider the possibility that inflation was driven by a sneutrino - the scalar supersymmetric partner of a heavy singlet neutrino - in the minimal seesaw model of neutrino masses. We show that this model is consistent with data on the cosmic microwave background (CMB), including those from the WMAP satellite. We derive and implement the CMB constraints on sneutrino properties, calculate reheating and the cosmological baryon asymmetry arising via direct leptogenesis from sneutrino decays following sneutrino inflation, and relate them to light neutrino masses. We show that this scenario is compatible with a low reheating temperature that avoids the gravitino problem, and calculate its predictions for flavour-violating decays of charged leptons. We find that $μ\to e γ$ should occur close to the present experimental upper limits, as might also $τ\to μγ$.

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arXiv2002

Predictions of the most minimal see-saw model

We derive the most minimal see-saw texture from an extra-dimensional dynamics. It predicts theta_13 = 0.078 \pm 0.015 and m_ee = 2.6 \pm 0.4 meV. Assuming thermal leptogenesis, the sign of the CP-phase measurable in neutrino oscillations, together with the sign of baryon asymmetry, determines the order of heavy neutrino masses. Unless heavy neutrinos are almost degenerate, successful leptogenesis fixes the lightest mass. Depending on the sign of the neutrino CP-phase, the supersymmetric version of the model with universal soft terms at high scale predicts BR(mu --> e gamma) or BR(tau --> mu gamma), and gives a lower bound on the other process.

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arXiv2002

Higgs-Mediated $B_{s,d}^0\toμτ, eτ$ and $τ\to3μ, eμμ$ Decays in Supersymmetric Seesaw Models

We study the rates allowed for the Higgs-mediated decays $B_{s,d}^0\toμτ, eτ$ and $τ\to μμμ, eμμ$ in supersymmetric seesaw models, assuming that the only source of lepton flavour violation (LFV) is the renormalization of soft supersymmetry-breaking terms due to off-diagonal singlet-neutrino Yukawa interactions. These decays are strongly correlated with, and constrained by, the branching ratios for $B_{s,d}^0\toμμ$ and $τ\to μ(e)γ.$ Parametrizing the singlet-neutrino Yukawa couplings $Y_ν$ and masses $M_{N_i}$ in terms of low-energy neutrino data, and allowing the flavour-universal soft masses for sleptons and for squarks, as well as those for the two Higgs doublets, to be different at the unification scale, we scan systematically over the model parameter space. Neutrino data and the present experimental constraints set upper limits on the Higgs-mediated LFV decay rates $Br(B_{s}^0\toμτ, eτ)\lsim 4\times 10^{-9}$ and $Br(τ\toμμμ, eμμ)\lsim 4\times 10^{-10}$.

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arXiv2000

Testing Left-Right Symmetric Gauge Theories at e^+e^- Colliders

If the Standard Model is embedded in a left-right symmetric gauge theory at the TeV scale, the pair production of light W-bosons in e^+e^- collisions, e^+e^- -> W^+W^-, will be affected by mixings in the gauge and neutrino sectors, and by the t-channel exchange of a heavy right-handed neutrino. The modification of the cross section by these new effects is studied for high--energy e^+e^- colliders.

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arXiv2000

Flavour Violation in SUSY SU(5) GUT at Large tan beta

We study flavour violation in the minimal SUSY SU(5) GUT assuming all the third generation Yukawa couplings to be due to the renormalizable physics above GUT scale. At large $\tanβ,$ as suggested by Yukawa unification in SU(5), sizable flavour violation in the left (right) slepton (down squark) sector is induced due to renormalization effects of down type Yukawa couplings between GUT and Planck scales in addition to the flavour violation in the right slepton sector. The new flavour physics contribution to $K-\bar K,$ $B-\bar B$ mixing is small but might be of phenomenological interest in the case of $b\to sγ.$ The sign of the latter contribution is the same as the sign of the dominant chargino contribution, thus making the constraints on SUSY scale coming from $b\to sγ$ somewhat more restrictive. The most important feature of the considered scenario is the large rate of lepton flavour violation. Given the present experimental constraints, the $μ\to eγ$ and $μ-e$ conversion branching ratios are above the sensitivity of the planned experiments unless the SUSY scale is pushed above one TeV.

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arXiv1999

Tests of the left-right electroweak model at linear collider

The left-right model is a gauge theory of electroweak interactions based on the gauge symmetry SU(2)_R . The main motivations for this model are that it gives an explanation for the parity violation of weak interactions, provides a mechanism (see-saw) for generating neutrino masses, and has B-L as a gauge symmetry. The quark-lepton symmetry in weak interactions is also maintained in this theory. The model has many predictions one can directly test at a TeV-scale linear collider. We will consider here two processes (e,e -> q, q, barQ, barQ and e,e ->mu, nu, q, barQ) testing the lepton flavour violation predicted by the model. We will also discuss constraints on supersymmetric versions of the model.

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arXiv1999

CP Asymmetries in B_s Decays and Spontaneous CP violation

We study possible effects of new physics in CP asymmetries in two-body $B_s$ decays in left-right models with spontaneous CP violation. Considering the contributions of new CP phases to the $B_s$ mixing as well as to the penguin dominated decay amplitudes we show that, with the present constraints, large deviations from the standard model predictions in CP asymmetries are allowed in both cases. Detection of the new physics can be done by measuring non-zero asymmetries which are predicted to vanish in the standard model or by comparing two measurements which are predicted to be equal in the standard model. In particular, we show that the measurement of the CKM angle $γ$ in electroweak penguin dominated processes $B_s^0\toρ^0η^{(')}, ρ^0ϕ$ can largely be affected by the new physics.

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arXiv1999

Supersymmetry and CP Violating Asymmetries in $B_{d,s}$ Decays

We study possible effects of supersymmetry (SUSY) in CP asymmetries in non-leptonic $B_{d,s}$ decays in a variety of SUSY flavour models considered in literature. We use both mass insertion and vertex mixing methods to calculate squark-gluino box diagrams contribution to $B_{d,s} - \bar{B}_{d,s}$ mixings. With the squark mixing parameter $η=0.22$, and with large new CP phases, it turns out that the CP asymmetries to be measured in upcoming B-factories, HERA-B and LHC-B, can be completely dominated by the SUSY contribution in almost every considered model. Discrimination between the different models can be done by comparing experimental results in different decay modes. In some models squark masses up to $\sim 5$ TeV can be probed through these experiments provided the SUSY contribution to $B - \bar{B}$ mixing is at 10% level, $|M^{SUSY}_{12}/M_{12}^{SM}|\sim 0.1.$ This implies that models with heavy squarks have a fair chance to be tested in the future CP experiments before LHC.

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arXiv1998

Doubly Charged Higgsino Pair Production and Decays in e+e- Collisions

In supersymmetric grand unified theories, light higgsino multiplets generally exist in addition to the familiar chargino/neutralino multiplets of the minimal supersymmetric extension of the Standard Model. The new multiplets may include doubly charged states $\tildeΔ^{\pm\pm}$ and $\tildeδ^{\pm\pm}$. We study the properties and the production channels of these novel higgsinos in $e^+e^-$ and $γγ$ collisions, and investigate how their properties can be analyzed experimentally.

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arXiv1998

CP asymmetries in B0 decays in the left-right model

We study time dependent CP asymmetries in B^0_{d,s} decays in the left-right model with spontaneous breakdown of CP. Due to the new contributions to B^0-\bar B^0 mixing the CP asymmetries can be substantially modified. Moreover, there can be significant new contributions to the $B$-meson decay amplitudes from the magnetic penguins. Most promising for detection of the new physics in the planned $B$ factories is that the CP asymmetries in the decays B--> J/ψK_S and B--> ϕK_S which are supposed to be equal in the standard model can differ significantly in this class of models independently of the results in the measurements of B--> X_s γ.

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arXiv1998

μ-e conversion in nuclei versus μ-->e γ: an effective field theory point of view

Using an effective lagrangian description we analyze possible new physics contributions to the most relevant muon number violating processes: $μ\to e γ$ and $μ$--$e$ conversion in nuclei. We identify a general class of models in which those processes are generated at one loop level and in which $μ$--$e$ conversion is enhanced with respect to $μ\to e γ$ by a large $\ln(m^2_μ/Λ^2),$ where $Λ$ is the scale responsible for the new physics. For this wide class of models bounds on $μ$--$e$ conversion constrain the scale of new physics more stringently than $μ\to e γ$ already at present and, with the expected improvements in $μ$--$e$ conversion experiments, will push it upwards by about one order of magnitude more. To illustrate this general result we give an explicit model containing a doubly charged scalar and derive new bounds on its couplings to the leptons.

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arXiv1997

New constraints on R-parity violation from μ-e conversion in nuclei

We derive new constraints on the products of explicitly R-parity violating couplings $λ$ and $λ'$ in MSSM from searches for μ-e conversion in nuclei. We concentrate on the loop induced photonic coherent conversion mode. For the combinations $|λλ|$ which in μ-e conversion can be probed only at loop level our constraints are in many cases more stringent than the previous ones due to the enhancement of the process by large $\ln(m^2_f/m^2_{\tilde f}).$ For the combinations of $|λ'λ'|$ the tree-level μ-e conversion constraints are usually more restrictive than the loop ones except for two cases which involve the third generation. With the expected improvements in the experimental sensitivity, the μ-e conversion will become the most stringent test for all the involved combinations of couplings.

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arXiv1997

Lower Bounds on Bilepton Processes at e-e- and mu-mu- Colliders

We show that the cross section of at least one of the s-channel processes e-e- (mu-mu-) --> l_i^- l_i^-, i=e,mu,tau, mediated by a doubly-charged scalar triplet bilepton is bounded from below and observable at a linear or muon collider if one of the light neutrinos has a mass in the range where it is required to be unstable by cosmological considerations. The result is model independent. We therefore stress the importance of the e-e- and mu-mu- collision modes of the future colliders for discovering new physics.

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arXiv1997

Mass of tau neutrino in SO(10) GUT-s

We investigate the allowed ranges of masses for an unstable tau neutrino in the context of SO(10) GUT-s. In light of the new nucleosynthesis results we obtain that there is a narrow window for m_{ν_τ} where the LEP, neutrino oscillation and nucleosynthesis data are compatible. This window, which depends on the effective number of neutrinos contributing to nucleosynthesis, has important cosmological consequences and will be tested by ongoing neutrino oscillation and LEP II experiments.

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arXiv1997

Heavy neutrino mixing and single production at Linear Collider

We study the single production of heavy neutrinos via the processes $e^-e^+ \to νN$ and $e^-γ\to W^- N$ at future linear colliders. As a base of our considerations we take a wide class of models, both with vanishing and non-vanishing left-handed Majorana neutrino mass matrix $m_L$. We perform a model independent analyses of the existing experimental data and find connections between the characteristic of heavy neutrinos (masses, mixings, CP eigenvalues) and the $m_L$ parameters. We show that with the present experimental constraints heavy neutrino masses almost up to the collision energy can be tested in the future experiments.

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