arXiv subjects
Publications and source records attributed to G. Barenboim.
The Standard Model has been incredibly successful in predicting the outcome of almost all the experiments done up so far. In it, neutrinos are mass-less. However, in recent years we have accumulated evidence pointing to tiny masses for the neutrinos (as compared to the charged leptons). These masses allow neutrinos to change their flavour and oscillate. In these lectures I review the properties of neutrinos in and beyond the Standard Model.
In this work, we use the results from Higgs searches in the $γγ$ and $ττ$ decay channels at LHC and indirect bounds as BR$(B \to X_s γ)$ to constrain the parameter space of a generic MSSM Higgs sector. In particular, we include the latest CMS results that look for additional Higgs states with masses up to 1 TeV. We show that the $ττ$ channel is the best and most accurate weapon in the hunt for new Higgs states beyond the Standard Model. We obtain that present experimental results rule out additional neutral Higgs bosons in a generic MSSM below 300 GeV for any value of $\tan β$ and, for instance, values of $\tan β$ above 30 are only possible for Higgs masses above 600 GeV. ATLAS stored data has the potential to render this bound obsolete in the near future.
We prove that the present experimental constraints are already enough to rule out the possibility of the ~125 GeV Higgs found at LHC being the second lightest Higgs in a general MSSM context, even with explicit CP violation in the Higgs potential. Contrary to previous studies, we are able to eliminate this possibility analytically, using simple expressions for a relatively small number of observables. We show that the present LHC constraints on the diphoton signal strength, tau-tau production through Higgs and BR(B -> X_s gamma) are enough to preclude the possibility of H_2 being the observed Higgs with m_H~125 GeV within an MSSM context, without leaving room for finely tuned cancellations. As a by-product, we also comment on the difficulties of an MSSM interpretation of the excess in the gamma-gamma production cross section recently found at CMS that could correspond to a second Higgs resonance at m_H~136 GeV.
This white paper addresses the hypothesis of light sterile neutrinos based on recent anomalies observed in neutrino experiments and the latest astrophysical data.
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d_A(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Omega_k in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d_A(z) up to sufficiently high redshifts around z = 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)-Omega_k degeneracy.
In this work we perform global fits of microscopic decoherence models of neutrinos to all available current data, including LSND and KamLAND spectral distortion results. In previous works on related issues the models used were supposed to explain LSND results by means of quantum gravity induced decoherence. However those models were purely phenomenological without any underlying microscopic basis. It is one of the main purposes of this article to use detailed microscopic decoherence models with complete positivity, to fit the data.The decoherence in these models has contributions not only from stochastic quantum gravity vacua operating as a medium, but also from conventional uncertainties in the energy of the (anti)neutrino beam. All these contributions lead to oscillation-length independent damping factors modulating the oscillatory terms from which one obtains an excellent fit to all available neutrino data, including LSND and Kamland spectral distortion.
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.
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.
We show that a hierarchical CPT violating neutrino spectrum can simultaneously accommodate all published neutrino data, including the LSND result, with a total chi^2 which is almost identical to the CPT conserving best fit. In our scenario the oscillation signal seen by the KamLAND experiment in antineutrinos is independent of the LMA solar oscillation signal seen in neutrinos. A larger antineutrino mass splitting accounts for the LSND signal and also contributes to atmospheric oscillations. Because of this feature, there is some tension between our model and certain Super-K atmospheric results. Thus, if LSND did not exist, our model would survive only at the 99% confidence level; with LSND, our model is (essentially) statistically equivalent to the CPT conserving best fit.
A report to the Fermilab Director from the Study Group on Future Neutrino Experiments at Fermilab
Any local relativistic quantum field theory of Dirac-Weyl fermions conserves CPT. Here we examine whether a simple nonlocal field theory can violate CPT. We construct a new relativistic field theory of fermions, which we call ``homeotic'', which is nonlocal but causal and Lorentz invariant. The free homeotic theory is in fact equivalent to free Dirac theory. We show that a homeotic theory with a suitable nonlocal four-fermion interaction is causal and as a result has a well-defined perturbative S-matrix. By coupling a right-handed homeotic fermion to a left-handed Dirac-Weyl fermion, we obtain a causal theory of CPT-violating neutrino oscillations.
This document is the second in a series of reports on the exciting physics that would be accessible at Fermilab in the event of an upgraded proton source. Where the first report covered a broad range of topics, this report focuses specifically on three areas of study: there are brief discussions on the new measurements one could make in both the neutron and anti-proton sectors, and then a detailed discussion of what could be achieved in the neutrino oscillation sector using an upgraded proton source to supply the NuMI beamline with more protons. If one places a new detector optimized for $ν_e$ appearance at a new location slightly off the axis defined by the MINOS experiment, that new experiment would be ideal for making the next important steps in lepton flavor studies, namely, the search for $ν_μ\to ν_e$ at the atmospheric mass splitting, and CP violations. The report concludes with a summary of proton economics and demands for increased proton intensity for the Booster and Main Injector: what the proton source at Fermilab can currently supply, and what adiabatic changes could be implemented to boost the proton supply on the way from here to a proton driver upgrade.
In order to accommodate the neutrino oscillation signals from the solar, atmospheric, and LSND data, a sterile fourth neutrino is generally invoked, though the fits to the data are becoming more and more constrained. However, it has recently been shown that the data can be explained with only three neutrinos, if one invokes CPT violation to allow different masses and mixing angles for neutrinos and antineutrinos. We explore the nature of neutrinos in such CPT-violating scenarios. Majorana neutrino masses are allowed, but in general, there are no longer Majorana neutrinos in the conventional sense. However, CPT-violating models still have interesting consequences for neutrinoless double beta decay. Compared to the usual case, while the larger mass scale (from LSND) may appear, a greater degree of suppression can also occur.
Recently we proposed a framework for explaining the observed evidence for neutrino oscillations without enlarging the neutrino sector, by introducing CPT violating Dirac masses for the neutrinos. In this paper we continue the exploration of the phenomenology of CPT violation in the neutrino sector. We show that our CPT violating model fits the existing SuperKamiokande data at least as well as the standard atmospheric neutrino oscillation models. We discuss the challenge of measuring CP violation in a neutrino sector that also violates CPT. We point out that the proposed off-axis extension of MINOS looks especially promising in this regard. Finally, we describe a method to compute CPT violating neutrino effects by mocking them up with analog matter effects.
CPT violation has the potential to explain all three existing neutrino anomalies without enlarging the neutrino sector. CPT violation in the Dirac mass terms of the three neutrino flavors preserves Lorentz invariance, but generates independent masses for neutrinos and antineutrinos. This specific signature is strongly motivated by braneworld scenarios with extra dimensions, where neutrinos are the natural messengers for Standard Model physics of CPT violation in the bulk. A simple model of maximal CPT violation is sufficient to explain the exisiting neutrino data quite neatly, while making dramatic predictions for the upcoming KamLAND and MiniBooNE experiments. Furthermore we obtain a promising new mechanism for baryogenesis.
In this work, we update the constraints on tree level FCNC couplings in the framework of a theory with n isosinglet vector-like down quarks. In this context, we emphasize the sensitivity of the B -> J/psi K_S CP asymmetry to the presence of new vector-like down quarks. This CP asymmetry, together with the rare decays B -> X_{s,d} l bar{l} and K -> pi nu bar{nu} are the best options to further constrain the FCNC tree level couplings or even to point out, in the near future, the possible presence of vector-like quarks in the low energy spectrum, as suggested by GUT theories or models of large extra dimensions at the TeV scale.
We investigate the three-neutrino mixing scheme for solving the atmospheric and LSND anomalies. We find the region in the parameter space that provides a good fit to the LSND and the SK atmospheric data, taking into account the CHOOZ constraint. We demonstrate that the goodness of this fit is comparable to that of the conventional fit to the solar and atmospheric data. Large values of the LSND angle are favoured and $\sin^2(2θ_{\rm LSND})$ can be as high as 0.1. This can have important effects on the atmospheric electron neutrino ratios as well as on down-going multi-GeV muon neutrino ratios. We examine the possibility of distinguishing this scheme from the conventional one at the long baseline experiments. We find that the number of electron neutrino events observed at the CERN to Gran Sasso experiment may lead us to identify the scheme, and hence the mass pattern of neutrinos.
Tree-level Flavor-Changing Neutral Currents (FCNC) are characteristic of models with extra vector-like quarks. These new couplings can strongly modify the B^0 CP asymmetries without conflicting with low--energy constraints. In the light of a low CP asymmetry in B --> J/ψK_{S}, we discuss the implications of these contributions. We find that even these low values can be easily accommodated in these models. Furthermore, we show that the new data from B factories tend to favor an O(20) enhancement of the b --> d l \bar{l} transition over the SM expectation.