arXiv subjects

Sandip Pakvasa

Publications and source records attributed to Sandip Pakvasa.

At least 37 records · Page 2Linked to original sources

arXiv2008

Prospects of neutrino oscillation measurements in the detection of reactor antineutrinos with a medium-baseline experiment

Despite the dramatic progress made in neutrino oscillation studies recently, several fundamental neutrino parameters remain either unknown or poorly measured. We discuss in detail a method for their measurement by precision studies of oscillation-caused neutrino energy spectrum distortions, for which a large underwater inverse beta decay detector appears to be a perfect tool. Results determine optimal baselines and necessary exposures in the presence of systematic uncertainties and the unavoidable background from terrestrial antineutrinos.

hep-ph↗

arXiv2008

Hanohano: A Deep Ocean Anti-Neutrino Detector for Unique Neutrino Physics and Geophysics Studies

The science potential of a 10 kiloton deep-ocean liquid scintillation detector for ~1 MeV energy scale electron anti-neutrinos has been studied. Such an instrument, designed to be portable and function in the deep ocean (3-5 km) can make unique measurements of the anti-neutrinos from radioactive decays in the Earth'.s mantle. Ths information speaks to some of the most fundamental questions in geology about the origin of the Earth, plat e tectonics, the geomagnetic field and even somewhat indirectly to global warming. Measurements in multiple locations will strengthen the potential insights. On the particle physics side, we have identified a unique role in the study of anti-neutrinos from a nuclear power complex, at a range of 55-60 km off shore. Not only can precision measurements be made of most neutrino mixing parameters, including $θ_{13}$ (depending on magnitude), but the neutrino mass hierarchy can be determined in a method not heretofore discussed, and one which does not rely upon matter effects. This detector is under active study on paper, in the laboratory, and at sea. An interdisciplinary and international collaboration is in formation, and plans are in motion for a major proposal, to be followed by construction over several years.

hep-ex↗

arXiv2008

The Cepheid Galactic Internet

We propose that a sufficiently advanced civilization may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. One can construct many scenarios wherein it would be desirable for such a civilization of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar(we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over one hundred years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signaling.

astro-ph↗

arXiv2008

Determination of Neutrino Mass Hierarchy and Theta_13 with a Remote Detector of Reactor Antineutrinos

We describe a method for determining the hierarchy of the neutrino mass spectrum and theta_13 through remote detection of antineutrinos from a nuclear reactor. This method utilizing a single, 10-kt scintillating liquid detector at a distance of 50-64 kilometers from the reactor complex measures mass-squared differences involving nu_3 with a one (ten) year exposure provided sin2(2theta_13)>0.05 (0.02). Our technique applies the Fourier transform to the event rate as a function of neutrino flight distance over energy. Sweeping over a relevant range of delta-m2 resolves separate spectral peaks for delta-m2_31 and delta-m2_32. For normal (inverted) hierarchy the absolute value of delta-m2_31 is greater (lesser) than the absolute value of delta-m2_32. This robust method requires a detector energy resolution of 3.5% divided by the square root of the scintillation energy.

hep-ex↗

arXiv2008

Neutrino Flavor Goniometry by High Energy Astrophysical Beams

It is shown how high energy neutrino beams from very distant sources can be utilized to learn about many properties of neutrinos such as lifetimes, mass hierarchy, mixing, minuscule pseudo-Dirac mass splittings; in addition, the production mechanism of neutrinos in astrophysical sources can also be elucidated.

hep-ph↗

arXiv2008

TriMinimal Parametrization of the Neutrino Mixing Matrix

Current experimental data on neutrino mixing are very well described by TriBiMaximal mixing. Accordingly, any phenomenological parametrization of the MNSP matrix must build upon TriBiMaximal mixing. We propose one particularly natural parametrization, which we call "TriMinimal". The three small deviations of the PDG angles from their TriBiMaximal values, and the PDG phase, parametrize the TriMinimal mixing matrix. As an important example of the utility of this new parametrization, we present the simple resulting expressions for the flavor-mixing probabilities of atmospheric and astrophysical neutrinos. As no foreseeable experiment will be sensitive to more than second order in the small parameters, we expand these flavor probabilities to second order.

hep-ph↗

arXiv2008

SN1987A Pulsar Velocity From Modified URCA Processes and Landau Levels

Using a recent estimate of the velocity of pulsars arising from neutrinos emitted with modified URCA processes with electrons in Landua levels, and the temperture of the protoneutron star created by SN1987A, derived from the energy of the observed neutrinos, we predict the velocity of the resulting pulsar.

astro-ph↗

arXiv2008

Flavor Ratios of Astrophysical Neutrinos: Implications for Precision Measurements

We discuss flavor-mixing probabilities and flavor ratios of high energy astrophysical neutrinos. In the first part of this paper, we expand the neutrino flavor-fluxes in terms of the small parameters U_{e3} and pi/4 - theta_{23}, and show that there are universal first and second order corrections. The second order term can exceed the first order term, and so should be included in any analytic study. We also investigate the probabilities and ratios after a further expansion around the tribimaximal value of sin^2 theta_{12} = 1/3. In the second part of the paper, we discuss implications of deviations of initial flavor ratios from the usually assumed, idealized flavor compositions for pion, muon-damped, and neutron beam sources, viz., (1 : 2 : 0), (0 : 1 : 0), and (1 : 0 : 0), respectively. We show that even small deviations have significant consequences for the observed flavor ratios at Earth. If initial flavor deviations are not taken into account in analyses, then false inferences for the values in the PMNS matrix elements (angles and phase) may result.

hep-ph↗

arXiv2008

Unparticle Induced Baryon Number Violating Nucleon Decays

We study baryon number violating nucleon decays induced by unparticle interactions with the standard model particles. We find that the lowest dimension operators which cause nucleon decays can arise at dimension 6 + (d_s-3/2) with the unparticles being a spinor of dimension d_s=d_\U +1/2. For scalar and vector unparticles of dimension d_\U, the lowest order operatoers arise at 6+d_\U and 7+d_\U dimensions,respectively. Comparing the spinor unparticle induced n \to O^s_\U and experimental bound on invisible decay of a neutron from KamLAND, we find that the scale for unparticle physics is required to be larger than 10^{10} GeV for d_\U < 2 if the couplings are set to be of order one. For scalar and vector unparticles, the dominant baryon number violating decay modes are n\to \bar ν+ O_\U (O^μ_\U) and p \to e^+ + O_\U (O^μ_\U). The same experimental bound puts the scales for scalar and vector unparticle to be larger than 10^{7} and 10^{5} GeV for d_\U <2 with couplings set to be of order one. Data on, p \to e^+ invisible, puts similar constraints on unparticle interactions.

hep-ph↗

arXiv2007

Neutrino time travel

We discuss causality properties of extra-dimensional theories allowing for effectively superluminal bulk shortcuts. Such shortcuts for sterile neutrinos have been discussed as a solution to the puzzling LSND and MiniBooNE neutrino oscillation results. We focus here on the sub-category of asymmetrically warped brane spacetimes and argue that scenarios with two extra dimensions may allow for timelike curves which can be closed via paths in the extra-dimensional bulk. In principle sterile neutrinos propagating in the extra dimension may be manipulated in a way to test the chronology protection conjecture experimentally.

hep-ph↗

arXiv2007

Implications of D^0-\bar D^0 Mixing for New Physics

We provide a comprehensive, up-to-date analysis of possible New Physics contributions to the mass difference $ΔM_D$ in $D^0$-${\bar D}^0$ mixing. We consider the most general low energy effective Hamiltonian and include leading order QCD running of effective operators. We then explore an extensive list of possible New Physics models that can generate these operators, which we organize as including Extra Fermions, Extra Gauge Bosons, Extra Scalars, Extra Space Dimensions and Extra Symmetries. For each model we place restrictions on the allowed parameter space using the recent evidence for observation of $D$ meson mixing. In many scenarios, we find strong constraints that surpass those from other search techniques and provide an important test of flavor changing neutral currents in the up-quark sector. We also review the recent BaBar and Belle findings, and describe the current status of the Standard Model predictions of $D^0$-${\bar D}^0$ mixing.

hep-ph↗

arXiv2007

Accurate measurement of the D0-D0bar mixing parameters

We propose a new method to determine the mass and width differences of the two D meson mass-eigenstates as well as the CP violating parameters associated with D^0-\bar{D}^0 mixing. We show that an accurate measurement of all the mixing parameters is possible for an arbitrary CP violating phase, by combining observables from a time dependent study of D decays to a doubly Cabibbo suppressed mode with information from a CP eigenstate. As an example we consider D^0-> K^{*0} π^0 decays where the K^{*0} is reconstructed in both K^+π^- and K_Sπ^0. We also show that decays to the CP eigenstate D-> K^+K^- together with D-> K^+π^- can be used to extract all the mixing parameters. A combined analysis using D^0-> K^{*0} π^0 and D-> K^+K^- can also be used to reduce the ambiguity in the determination of parameters.

hep-ph↗

arXiv2006

Shortcuts in extra dimensions and neutrino physics

We discuss the possibility of sterile neutrinos taking shortcuts in extra dimensions, and the consequences for neutrino oscillations. This effect influences the active-sterile neutrino mixing and provides a possibility to accommodate the LSND evidence for neutrino oscillations together with bounds from accelerator and reactor experiments. We briefly comment on causality in such schemes.

hep-ph↗

arXiv2006

New Physics contributions to the lifetime difference in D0-anti-D0 mixing

The first general analysis of New Physics contributions to the D0-anti-D0 lifetime difference (equivalently Delta Gamma_D} is presented. The extent to which New Physics (NP) contributions to |Delta C|=1 processes can produce effects in Delta Gamma_D, even if such NP contributions are undetectable in the current round of D0 decay experiments, is studied. New Physics models which do and do not dominate the lifetime difference in the flavor SU(3) limit are identified. Specific examples are provided.

hep-ph↗

arXiv2005

Sterile-active neutrino oscillations and shortcuts in the extra dimension

We discuss a possible new resonance in active-sterile neutrino oscillations arising in theories with large extra dimensions. Fluctuations in the brane effectively increase the path-length of active neutrinos relative to the path-length of sterile neutrinos through the extra-dimensional bulk. Well below the resonance, the standard oscillation formulas apply. Well above the resonance, active-sterile oscillations are suppressed. We show that a resonance energy in the range of 30-400 MeV allows an explanation of all neutrino oscillation data, including LSND data, in a consistent four-neutrino model. A high resonance energy implies an enhanced signal in MiniBooNE. A low resonance energy implies a distorted energy spectrum in LSND, and an enhanced v_mu depletion from a stopped-pion source. The numerical value of the resonance energy may be related back to the geometric aspects of the brane world. Some astrophysical and cosmological consequences of the brane-bulk resonance are briefly sketched.

hep-ph↗

arXiv2005

Measuring Flavor Ratios of High-Energy Astrophysical Neutrinos

We discuss the prospects for next generation neutrino telescopes, such as IceCube, to measure the flavor ratios of high-energy astrophysical neutrinos. The expected flavor ratios at the sources are $ϕ_{ν_e}:ϕ_{ν_μ}:ϕ_{ν_τ} = 1:2:0$, and neutrino oscillations quickly transform these to $1:1:1$. The flavor ratios can be deduced from the relative rates of showers ($ν_e$ charged-current, most $ν_τ$ charged-current, and all flavors neutral-current), muon tracks ($ν_μ$ charged-current only), and tau lepton lollipops and double-bangs ($ν_τ$ charged-current only). The peak sensitivities for these interactions are at different neutrino energies, but the flavor ratios can be reliably connected by a reasonable measurement of the spectrum shape. Measurement of the astrophysical neutrino flavor ratios tests the assumed production mechanism and also provides a very long baseline test of a number of exotic scenarios, including neutrino decay, CPT violation, and small-$δm^2$ oscillations to sterile neutrinos.

hep-ph↗

arXiv2005

Concluding Remarks/Summary

These remarks summarize some of the discussion at the NOW 2004; in addition some topics not touched on at the meeting are reviewed briefly.

hep-ph↗

arXiv2005

QLC relation and neutrino mass hierarchy

Latest measurements have revealed that the deviation from a maximal solar mixing angle is approximately the Cabibbo angle, i.e. QLC relation. We argue that it is not plausible that this deviation from maximality, be it a coincidence or not, comes from the charged lepton mixing. Consequently we have calculated the required corrections to the exactly bimaximal neutrino mass matrix ansatz necessary to account for the solar mass difference and the solar mixing angle. We point out that the relative size of these two corrections depends strongly on the hierarchy case under consideration. We find that the inverted hierarchy case with opposite CP parities, which is known to guarantee the RGE stability of the solar mixing angle, offers the most plausible scenario for a high energy origin of a QLC-corrected bimaximal neutrino mass matrix. This possibility may allow us to explain the QLC relation in connection with the origin of the charged fermion mass matrices.

hep-ph↗