arXiv subjects

B. Dutta

Publications and source records attributed to B. Dutta.

At least 55 records · Page 3Linked to original sources

arXiv2005

Theory of Neutrinos: A White Paper

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

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arXiv2004

Theory of Neutrinos

After a brief overview of the present knowledge of neutrino masses and mixing, we summarize what can be learned about physics beyond the standard model from the various proposed neutrino experiments. We also comment on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe as well as what can be learned from some experiments outside the domain of neutrinos.

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arXiv2004

Five Dimensional Cosmology in Horava-Witten M-Theory

The cosmology in the Hubble expansion era of the Horava-Witten M-theory compactified on a Calabi-Yau threefold is studied in the reduction to five-dimensions where the effects of the Calabi-Yau manifold are summarized by the volume modulus, and all perturbative potentials are included. Matter on the branes are treated as first order perturbations of the static vacuum solution, and all equations in the bulk and all boundary conditions on both end branes are imposed. It is found that for a static volume modulus and a static fifth dimension, y, one can recover the four dimensional Robertson Friedmann Walker cosmology for relativistic matter on the branes, but not for non-relativistic matter. In this case, the Hubble parameter H becomes independent of y to first order in matter density. This result holds also when an arbitrary number of 5-branes are included in the bulk. The five dimensional Horava-Witten model is compared with the Randall Sundrum phenomenology with a scalar field in the bulk where a bulk and brane potential are used so that the vacuum solutions can be rigorously obtained. (In the Appendix, the difficulty of obtaining approximate vacuum solutions for other potentials is discussed.) In this case non-relativistic matter is accommodated by allowing the distance between the branes to vary. It is suggested that non-perturbative potentials for the vacuum solution of Horava-Witten theory are needed to remove the inconsistency that non-relativistic matter creates.

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arXiv2004

Yukawa Textures, Neutrino Masses and Horava-Witten M-Theory

We consider the Horava-Witten based model with 5-branes situated near the distant orbifold plane and with vanishing instanton numbers on the physical plane. This model has a toric fibered Calabi-Yau with del Pezzo base dP_7 which allows three generations with Standard Model gauge group at the GUT scale. Previous analysis showed that the quark hierarchy at the electroweak scale could be achieved qualitatively without undue fine tuning due to the effects of the 5-branes on the Kahler potential. We extend here this analysis to include the leptons. A new mechanism is introduced to obtain neutrino masses by assuming massless right handed neutrinos exist in the particle spectrum, which allows a cubic holomorphic term to exist in the Kahler metric, l_L*H_2*nu_R, scaled by the 11D Planck mass. After transferring this term to the superpotential, this term gives rise to neutrino masses of the correct size at the electroweak scale. With natural choices of the Yukawa and Kahler matrix entries, it is possible to fit all mass, CKM and MNS experimental data. The model predicts mu -> e + gamma decay at a rate that should be detectable for much of the SUSY parameter space in the next round of experiments.

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arXiv2003

Dark Matter, Muon g-2 and Other SUSY Constraints

Recent developments constraining the SUSY parameter space are reviewed within the framework of SUGRA GUT models. The WMAP data is seen to reduce the error in the density of cold dark matter by about a factor of four, implying that the lightest stau is only 5 -10 GeV heavier than the lightest neutralino when m_0, m_{1/2} < 1 TeV. The CMD-2 re-analysis of their data has reduced the disagreement between the Standard Model prediction and the Brookhaven measurement of the muon magnetic moment to 1.9 sigma, while using the tau decay data plus CVC, the disagreement is 0.7 sigma. (However, the two sets of data remain inconsistent at the 2.9 sigma level.) The recent Belle and BABAR measurements of the B -> phi K CP violating parameters and branching ratios are discussed. They are analyzed theoretically within the BBNS improved factorization method. The CP parameters are in disagreement with the Standard Model at the 2.7 sigma level, and the branching ratios are low by a factor of two or more over most of the parameter space. It is shown that both anomalies can naturally be accounted for by adding a non-universal cubic soft breaking term at M_G mixing the second and third generations.

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arXiv2003

Horava-Witten Cosmology

We consider the cosmology of the reduced 5D Horava-Witten M-Theory (HW) with volume modulus and treating matter on the orbifold planes to first order. It is seen that one can recover the FRW cosmology in the Hubble expansion era with relativistic matter, but if a solution exist with non-relativistic (massive) matter it must be non-static with a Hubble constant that depends on the fifth dimension. (The same result holds when 5-branes are present.) This difficulty is traced to the fact that in HW, the volume modulus couples to the bulk and brane cosmological constants (so that the net 4D constant vanishes naturally). This situation is contrasted with the Randall-Sundrum 1 model (which is here treated without making the stiff potential approximation) where the radion field does not couple to the cosmological constants (and so one must instead fine tune the net constant to zero). One finds that non-relativistic matter is accommodated there by changing the distance between the end branes.

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arXiv2003

B^0 -> phi K_S in SUGRA models with CP violations

We examine the B -> phi K decays within the framework of SUGRA models making use of the improved QCD factorization method of Beneke et al. which allows calculations of non-factorizable contributions. All other experimental constraints (B -> X_S gamma, neutron and electron electric dipole moments, dark matter constraints, etc.) are imposed. We calculate the CP violating parameters S_{phi K_S}, C_{phi K_S} and A_{phi K^{-+}} as well as the branching ratios (BR) of B^0 and B^{+-}, Br[B -> phi K]. We find for the Standard Model(SM) and mSUGRA it is not possible to account for the observed 2.7 sigma deviation between S_{phi K_S} and S_{J/Psi K_S}. In general the BRs are also in 3 sigma disagreement with experiment, except in the parameter region where the weak annihilation terms dominate the decay (and hence where the theory is least reliable). Thus if future data confirm the current numbers, this would represent the first significant breakdown of both the SM and mSUGRA. We show then that adding a SUGRA non-universal A soft breaking left-right term mixing the second and third generations in either the down or up quark sector, all data can be accommodated for a wide range of parameters. The full 6x6 quark mass matrices are used and the SUSY contributions calculated without approximation.

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arXiv2003

mSUGRA At A 500-GeV Linear Collider

A study is made of what SUSY signals would be observable for mSUGRA models in a 500-GeV linear collider. All current experimental bounds on the mSUGRA parameter space are imposed. For m_0 < 1 TeV (or alternately if the current g_μ- 2 anomaly maintains) the only observable signals that remain are slepton pair production and neutralino production of {\tildeχ^0_2}+{\tildeχ^0_1}. Slepton pair production can occur for masses < 250 GeV which for the selectron and smuon pairs require tanbeta < 40. In this domain very accurate selectron and smuon masses could be measured. Light staus, \tildeτ_1, with mass < 250 GeV can be pair produced for any tanbeta and the neutralino signal can be seen provided m_{1/2}<~400 GeV. However, the detection of these requires a much more complicated analysis due to the fact that the dark matter co-annihilation constraint requires that the \tildeτ_1 and {\tildeχ^0_1} mass difference be <~ 15 GeV. The point m_{1/2} = 360 GeV, A_0 = 0, μ>0 is analyzed in detail, and it is shown that the stau and neutralino signals can be detected provided an active mask down to 2^o is used. However, large parts of the mSUGRA parameter space exists where a 500-GeV machine would not be able to see any SUSY signal.

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arXiv2003

Probing mSUGRA Models at Linear Colliders

A feasibility study of a 500-GeV linear collider is presented for mSUGRA models in co-annihilation region. We find an active mask is critical to suppress $e^+ e^- \to e^+ e^- τ^+ τ^-$ events to probe the models.

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arXiv2003

Lepton Flavor Violation and Neutrino Mixings in a 3X2 Seesaw Model

We study the predictions for BR(mu-> e+gamma) and BR(tau-> e,mu+gamma) in a class of recently proposed horizontal SU(2) model that leads to a 3 X 2 seesaw model for neutrino masses. We consider two such models and obtain the correct bi-large mixing pattern for neutrinos. In these models, the effective low energy theory below the SU(2)_H scale is the MSSM. Assuming a supersymmetry breaking pattern as in the minimal SUGRA models, we find that consistent with present g-2, b->s+gamma and WMAP dark matter constraints on the parameters of the model, the BR(mu-> e+gamma) prediction is accessible to the proposed MEG experiment at PSI making this class of models testable in the near future.

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arXiv2003

Dark Matter, Muon g - 2 And Other Accelerator Constraints

We review the current status of the Brookhaven muon g - 2 experiment, and it's effects on the SUSY parameter space when combined with dark matter relic density bounds, b->sγand Higgs mass constraints. If the 3σdeviation of g - 2 from the Standard Model value is correct, these data constrain the mSUGRA parameter space strongly, i.e. 300 GeV <~m_{1/2}<~850 GeV, and m_0 (at fixed \tanβ, A_0) is tightly constrained (except at very large \tanβ). Dark matter detection cross sections lie within the range accessible to future planned experiments. A non-universal gluino soft breaking mass however can greatly reduce the lower bound on m_{1/2} (arising from the b->sγconstraint) allowing for relatively light neutralinos, while non-universal Higgs H_2 mass can lead to new regions of allowed relic density where the detection cross sections can be increased by a factor of 10 or more.

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arXiv2002

A Consistent Resolution of Possible Anomalies in B^0 --> phi K_S and B^+ --> eta' K^+ Decays

In the framework of R-parity violating (\rpv) supersymmetry, we try to find a consistent explanation for both recently measured CP asymmetry in B^0 --> phi K_S decay and the large branching ratio of B^{+/-} --> eta' K^{+/-} decay, which are inconsistent with the Standard Model (SM) prediction. We also investigate other charmless hadronic B --> PP and B --> VP decay modes whose experimental data favor the SM: for instance, recently measured CP asymmetries in B^0 --> eta^{prime} K_S and B^0 --> J / Psi K_S. We find that all the observed data can be accommodated for certain values of \rpv couplings.

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arXiv2002

Cosmology in Horava-Witten M-Theory

The cosmology of the Horava-Witten M-Theory reduced to five dimensions retaining the volume modulus is considered. Brane matter is considered as a perturbation on the vacuum solution, and the question of under what circumstances does the theory give rise to the standard RWF cosmology is examined. It is found that for static solutions, one obtains a consistent solution of the bulk field equations and the brane boundary conditions only for pure radiation on the branes. (A similar result holds if additional 5-branes are added in the bulk.) If one stabilizes the fifth dimension in an ad hoc manner, a similar inconsistency still occurs (at least for a Hubble constant that has no dependence on y, the fifth dimension.) Within this framework, the possibility of recovering the RWF cosmology still remains if the volume modulus and /or the distance between branes becomes time dependent, under which circumstances the Hubble constant must then depend on y (unless the fifth dimension and volume modulus expand at precisely the same rate).

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arXiv2002

Quark, Lepton and Neutrino Masses In Horava-Witten Inspired Models

Horava-Witten M-Theory offers new ways in achieving the quark and lepton mass hierarchies not naturally available in supergravity unified models. In previous work, based on a torus fibered Calabi-Yau manifold with a del Pezzo base dP_7,a three generation SU(5)model with Wilson line breaking to the Standard Model was constructed. It was seen that if the additional 5- branes clustered near the distant orbifold plane, it was possible that such models could generate the observed hierarchies of quark masses without undue fine tuning. We update these results here and extend them to include the charged leptons. A new mechanism for generating small neutrino masses (different from the ususal seesaw mechanism)arises naturally from a possible cubic holomorphic term in the Kahler potential when supersymmetry is broken. We show that the LMA solution to neutrino masses can occur, with a good fit to all neutrino oscillation data. The model implies the existance of the μ-> e γdecay even for universal slepton soft breaking masses, at rates accessible to the next round of experiments.

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arXiv2002

Lepton Flavor Violation and the Origin of the Seesaw Mechanism

The right--handed neutrino mass matrix that is central to the understanding of small neutrino masses via the seesaw mechanism can arise either (i) from renormalizable operators or (ii) from nonrenormalizable or super-renormalizable operators, depending on the symmetries and the Higgs content of the theory beyond the Standard Model. In this paper, we study lepton flavor violating (LFV) effects in the first class of seesaw models wherein the ν_R Majorana masses arise from renormalizable Yukawa couplings involving a B-L = 2 Higgs field. We present detailed predictions for τ-> μ+ γand μ-> e + γbranching ratios in these models taking the current neutrino oscillation data into account. Focusing on minimal supergravity models, we find that for a large range of MSSM parameters suggested by the relic abundance of neutralino dark matter and that is consistent with Higgs boson mass and other constraints, these radiative decays are in the range accessible to planned experiments. We compare these predictions with lepton flavor violation in the second class of models arising entirely from the Dirac Yukawa couplings. We study the dependence of the ratio r \equiv B(μ-> e+γ)/B(τ->μ+γ) on the MSSM parameters and show that measurement of r can provide crucial insight into the origin of the seesaw mechanism.

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arXiv2002

Dark matter and Consequences of SUSY

We examine here the constraints from the amount of relic density of neutralino dark matter and other experiments have on the SUSY parameter space for the mSUGRA model and for models with non-universal soft breaking at the GUT scale. In mSUGRA, the allowed amount of dark matter restricts the SUSY parameter space to a narrow band in m_0 - m_{1/2} (except at very large \tanβ). The Higgs mass and b-> sγconstraints produce a lower bound of m_{1/2}>~{\sim} 300GeV and if the muon magnetic moment anomaly can be interpreted as a 3σdeviation from the Standard Model, one also obtains an upper bound of m_{1/2} <~900 GeV, making the SUSY spectrum well accessible to the LHC. The B_s->μμdecay is seen to be accessible to the Tevatron Run2B with 15 fb^{-1} for \tanβ>~30. However, only parts of the spectrum will be accessible to the NLC if it's energy is below 800GeV. Non-universal soft breaking opens new regions of parameter space. Thus the m_{1/2} lower bound constraint of b->sγand also the Higgs mass can be reduced greatly if the gluino mass is assumed larger at the GUT scale (allowing for a lighter gaugino spectrum), and non-universal Higgs soft breaking masses at the GUT scale can open new allowed regions at relatively low m_{1/2} and high m_0 where dark matter detection cross sections may be increased by a factor of ten or more.

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arXiv2002

SUSY Dark Matter: Closing The Parameter Space

We consider here the constraints in SUGRA models on the SUSY parameter space due to current experimental bounds on the light Higgs mass m_h, the b-> s gamma decay, the amount of neutralino cold dark matter Omega h^2, and the muon magnetic moment. Models with universal soft breaking (mSUGRA) and non-universal gaugino or Higgs masses at M_G are examined. For mSUGRA, the m_h, b->s gamma and Omega h^2 constraints imply a lower bound on the gaugino mass of m_{1/2}>~300GeV implying the gluino and squarks have mass >~700GeV, and the neutralino >~120GeV. The current status of the Brookhaven muon g - 2 experiment is reviewed, and if the Standard Model (SM) contribution evaluated using the e^+ + e^- data is correct, a 2 sigma bound on the deviation of experiment from the SM produces an upper bound on m_{1/2} that eliminates the "focus point" regions of parameter space. Dark matter (DM) detection cross sections range from 5\times10^{-8} pb to 5\times10^{-10} pb which would be accessible to future planned detectors. The SUSY decay B_s->μ^+ +μ^- is seen to be accessible to the Tevatron Run 2B with 15 fb^{-1} luminosity for tanbeta >~30. The most favorable signals of SUSY for linear colliders are stau pair production and neutralino pair production, though it will require an 800GeV machine to cover the full parameter space. Non-universal models can modify some of the above results. Thus a non-universal (heavier) gluino mass at M_G can significantly reduce the lower bound constraints of b\to s gamma and m_h giving rise to a lighter SUSY spectrum. A heavier up Higgs mass can open an additional region with allowed relic density arising from annihilation via the s-channel Z diagram with an O(10) larger DM detector cross section.

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arXiv2002

Decays $B \to η^{\prime} K$ in R-parity violating supersymmetry

In light of the recent experimental data from $B$ factories, We try to explain the large branching ratio (compared to the Standard Model prediction) of the decay $B^{\pm}\to η' K^{\pm}$ in the context of R-parity violating ($\rpv$) supersymmetry. We investigate other observed $η^{(\prime)}$ modes and find that only two pairs of $\rpv$ coupling can satisfy the requirements without affecting the other $B \to PP$ and $B \to VP$ decay modes except the mode $B \to ϕK$. We also calculate the CP asymmetry for the observed decay modes affected by the new couplings.

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