arXiv subjects

D. Marfatia

Publications and source records attributed to D. Marfatia.

At least 37 records · Page 2Linked to original sources

arXiv2011

Dark matter at DeepCore and IceCube

With the augmentation of IceCube by DeepCore, the prospect for detecting dark matter annihilation in the Sun is much improved. To complement this experimental development, we provide a thorough template analysis of the particle physics issues that are necessary to precisely interpret the data. Our study is about nitty-gritty and is intended as a framework for detailed work on a variety of dark matter candidates. To accurately predict the source neutrino spectrum, we account for spin correlations of the final state particles and the helicity-dependence of their decays, and absorption effects at production. We fully treat the propagation of neutrinos through the Sun, including neutrino oscillations, energy losses and tau regeneration. We simulate the survival probability of muons produced in the Earth by using the Muon Monte Carlo program, reproduce the published IceCube effective area, and update the parameters in the differential equation that approximates muon energy losses. To evaluate the zenith-angle dependent atmospheric background event rate, we track the Sun and determine the time it spends at each zenith angle. Throughout, we employ neutralino dark matter as our example.

hep-ph↗

arXiv2009

Generic dark matter signature for gamma-ray telescopes

We describe a characteristic signature of dark matter (DM) annihilation or decay into gamma-rays. We show that if the total angular momentum of the initial DM particle(s) vanishes, and helicity suppression operates to prevent annihilation/decay into light fermion pairs, then the amplitude for the dominant 3-body final state f^+f^-γhas a unique form dictated by gauge invariance. This amplitude and the corresponding energy spectra hold for annihilation of DM Majorana fermions or self-conjugate scalars, and for decay of DM scalars, thus encompassing a variety of possibilities. Within this scenario, we analyze Fermi LAT, PAMELA and HESS data, and predict a hint in future Fermi gamma-ray data that portends a striking signal at atmospheric Cherenkov telescopes (ACTs).

hep-ph↗

arXiv2009

Dark matter and pulsar signals for Fermi LAT, PAMELA, ATIC, HESS and WMAP data

We analyze new diffuse gamma-ray data from the Fermi Gamma-ray Space Telescope, which do not confirm an excess in the EGRET data at galactic mid-latitudes, in combination with measurements of electron and positron fuxes from PAMELA, Fermi and HESS within the context of three possible sources: dark matter (DM) annihilation or decay into charged leptons, and a continuum distribution of pulsars. We allow for variations in the backgrounds, consider several DM halo profiles, and account for systematic uncertainties in data where possible. We find that all three scenarios represent the data well. The pulsar description holds for a wide range of injection energy spectra. We compare with ATIC data and the WMAP haze where appropriate, but do not fit these data since the former are discrepant with Fermi data and the latter are subject to large systematic uncertainties. We show that for cusped halo profiles, Fermi could observe a spectacular gamma-ray signal of DM annihilation from the galactic center while seeing no excess at mid-latitudes.

hep-ph↗

arXiv2008

PAMELA and dark matter

Assuming that the positron excess in PAMELA satellite data is a consequence of annihilations of cold dark matter, we consider from a model-independent perspective if the data show a preference for the spin of dark matter. We then perform a general analysis of annihilations into two-body final states to determine what weighted combination of channels best describes the data.

hep-ph↗

arXiv2008

DUSEL Theory White Paper

The NSF has chosen the site for the Deep Underground Science and Engineering Laboratory (DUSEL) to be in Lead, South Dakota. In fact, the state of South Dakota has already stepped up to the plate and contributed its own funding for the proposed lab, see http://www.sanfordlaboratoryathomestake.org/index.html. The final decision by NSF for funding the Initial Suite of Experiments for DUSEL will be made early in 2009. At that time the NSF Science Board must make a decision. Of order 200 experimentalists have already expressed an interest in performing experiments at DUSEL. In order to assess the interest of the theoretical community, the Center for Cosmology and Astro-Particle Physics (CCAPP) at The Ohio State University (OSU) organized a 3-day DUSEL Theory Workshop in Columbus, Ohio from April 4 - 6, 2008. The workshop focused on the scientific case for six proposed experiments for DUSEL: long baseline neutrino oscillations, proton decay, dark matter, astrophysical neutrinos, neutrinoless double beta decay and N-Nbar oscillations. The outcome of this workshop is the DUSEL Theory White paper addressing the scientific case at a level which may be useful in the decision making process for policy makers at the NSF and in the U.S. Congress. In order to assess the physics interest in the DUSEL project we have posted the DUSEL Theory White paper on the following CCAPP link http://ccapp.osu.edu/whitepaper.html . Please read the white paper and, if you are interested, use the link to show your support by co-signing the white paper.

hep-ph↗

arXiv2008

Upward shower rates at neutrino telescopes directly determine the neutrino flux

We show that the rate for upward showers from an isotropic cosmic neutrino flux at neutrino telescopes like IceCube is independent of the neutrino-nucleon cross section. For bins that span a relatively narrow range in energy, neither scaling the cross section, nor changing its power-law energy behavior affects the upward shower rate, which depends only on the flux. The neutrino flux can be completely known since its spectral shape can be determined by comparing the rates in neighboring bins. We also show that the downward shower rate varies linearly with cross section with a proportionality constant determined by the energy-dependence of the cross section, independent of the power-law behavior of the flux. The normalization and energy dependence of the cross section can be known by comparing the downward rates in neighboring bins.

hep-ph↗

arXiv2008

Phase transition in the fine structure constant

Within the context of mass-varying neutrinos, we construct a cosmological model that has a phase transition in the electromagnetic fine structure constant αat a redshift of 0.5. The model accommodates hints of a time variable αin quasar spectra and the nonobservance of such an effect at very low redshifts. It is consistent with limits from the recombination and primordial nucleosynthesis eras and is free of instabilities.

hep-ph↗

arXiv2007

Which long-baseline neutrino experiments are preferable?

We discuss the physics of superbeam upgrades, where we focus on T2KK, a NuMI beam line based experiment NOvA*, and a wide band beam (WBB) experiment independent of the NuMI beam line. For T2KK, we find that the Japan-Korea baseline helps resolve parameter degeneracies, but the improvement due to correlated systematics between the two detectors (using identical detectors) is only moderate. For an upgrade of NOvA with a liquid argon detector, we demonstrate that the Ash River site is preferred compared to alternatives, such as at the second oscillation maximum, and is the optimal site within the U.S. For a WBB experiment, we find that high proton energies and long decay tunnels are preferable. We compare water Cherenkov and liquid argon technologies, and find the break-even point in detector cost at about 4:1. In order to compare the physics potential of the different experimental configurations, we use the concept of exposure to normalize the performance. We find that experiments with WBBs are the best experimental concept. NOvA* could be competitive with sufficient luminosity. If $\sin^2 2θ_{13}$ > 0.01, a WBB experiment can perform better than a neutrino factory.

hep-ph↗

arXiv2007

Challenging Lorentz noninvariant neutrino oscillations without neutrino masses

We show that the combined data from solar, long-baseline and reactor neutrino experiments can exclude the generalized bicycle model of Lorentz noninvariant direction-dependent and/or direction-independent oscillations of massless neutrinos. This model has five parameters, which is more than is needed in standard oscillation phenomenology with neutrino masses. Solar data alone are sufficient to exclude the pure direction-dependent case. The combination of solar and long-baseline data rules out the pure direction-independent case. With the addition of KamLAND data, a mixture of direction-dependent and direction-independent terms in the effective Hamiltonian is also excluded.

hep-ph↗

arXiv2007

Report of the US long baseline neutrino experiment study

This report provides the results of an extensive and important study of the potential for a U.S. scientific program that will extend our knowledge of neutrino oscillations well beyond what can be anticipated from ongoing and planned experiments worldwide. The program examined here has the potential to provide the U.S. particle physics community with world leading experimental capability in this intensely interesting and active field of fundamental research. Furthermore, this capability could be unique compared to anywhere else in the world because of the available beam intensity and baseline distances. The present study was initially commissioned in April 2006 by top research officers of Brookhaven National Laboratory and Fermi National Accelerator Laboratory and, as the study evolved, it also provided responses to questions formulated and addressed to the study group by the Neutrino Scientific Advisory Committee (NuSAG) of the U.S. DOE and NSF. The participants in the study, its Charge and history, plus the study results and conclusions are provided in this report and its appendices. A summary of the conclusions is provided in the Executive Summary.

hep-ph↗

arXiv2007

Accelerating cosmologies tested by distance measures

We test if the latest Gold set of 182 SNIa or the combined "Platinum" set of 192 SNIa from the ESSENCE and Gold sets, in conjunction with the CMB shift parameter show a preference between the LambdaCDM model, three wCDM models, and the DGP model of modified gravity as an explanation for the current accelerating phase of the universe's expansion. We consider flat wCDM models with an equation of state w(a) that is (i) constant with scale factor $a$, (ii) varies as w(a)=w_0+w_a(1-a) for redshifts probed by supernovae but is fixed at -1 at earlier epochs and (iii) varies as w_0+w_a(1-a) since recombination. We find that all five models explain the data with comparable success.

astro-ph↗

arXiv2007

Proposal for an Experimental Program in Neutrino Physics and Proton Decay in the Homestake Laboratory

This report is intended to describe first, the principal physics reasons for an ambitious experimental program in neutrino physics and proton decay based on construction of a series of massive water Cherenkov detectors located deep underground (4850 ft) in the Homestake Mine of the South Dakota Science and Technology Authority (SDSTA); and second, the engineering design of the underground chambers to house the Cherenkov detector modules; and third, the conceptual design of the water Cherenkov detectors themselves for this purpose. Included in this document are preliminary costs and time-to-completion estimates which have been exposed to acknowledged experts in their respective areas. We have included some contingency factors. Nevertheless, we recognize that much more extensive documentation and contingency estimates will be needed for a full technical design report. In this proposal we show the event rates and physics sensitivity for beams from both FNAL (1300 km distant from Homestake) and BNL (2540 km distant from Homestake). The program we propose will benefit from a beam from FNAL because of the high intensities currently available from the Main Injector with modest upgrades. The possibility of tuning the primary proton energy over a large range from 30 to 120 GeV also adds considerable flexibility to the program from FNAL.

hep-ex↗

arXiv2006

Precision physics with a wide band super neutrino beam

We carry out a state-of-the-art assessment of long baseline neutrino oscillation experiments with wide band beams. We describe the feasibility of an experimental program using existing high energy accelerator facilities, a new intense wide band neutrino beam (0-6 GeV) and a proposed large detector in a deep underground laboratory. We find that a decade-long program with 1 MW operation in the neutrino mode and 2 MW operation in the antineutrino mode, a baseline as long as the distance between Fermilab and the Homestake mine (1300 km) or the Henderson mine (1500 km), and a water Cherenkov detector with fiducial mass of about 300 kT has optimum sensitivity to θ_{13}, the mass hierarchy and to neutrino CP violation at the 3σC.L. for \sin^22θ_{13}>0.008. This program is capable of breaking the eight-fold degeneracy down to the octant degeneracy without additional external input.

hep-ph↗

arXiv2006

Cross section dependence of event rates at neutrino telescopes

We examine the dependence of event rates at neutrino telescopes on the neutrino-nucleon cross section for neutrinos with energy above 1 PeV, and contrast the results with those for cosmic ray experiments. Simple scaling of the Standard Model cross sections leaves the rates of upward events essentially unchanged. Details, such as detector depth and cross section inelasticity, can influence rates. Numerical estimates of upward shower, muon and tau event rates in the IceCube detector confirm these results.

hep-ph↗

arXiv2006

Confronting mass-varying neutrinos with MiniBooNE

We study the proposal that mass-varying neutrinos could provide an explanation for the LSND signal for \barν_mu to \barν_e oscillations. We first point out that all positive oscillation signals occur in matter and that three active mass-varying neutrinos are insufficient to describe all existing neutrino data including LSND. We then examine the possibility that a model with four mass-varying neutrinos (three active and one sterile) can explain the LSND effect and remain consistent with all other neutrino data. We find that such models with a 3+1 mass structure in the neutrino sector may explain the LSND data and a null MiniBooNE result for 0.10 < \sin^2 2θ_x < 0.30. Predictions of the model include a null result at Double-CHOOZ, but positive signals for underground reactor experiments and for ν_μto ν_e oscillations in long-baseline experiments.

hep-ph↗

arXiv2005

Testing the LMA solution with solar neutrinos independently of solar models

We perform a comparative study of two methods of determining the survival probabilities of low, intermediate, and high energy solar neutrinos that emphasizes the general agreement between the Large Mixing Angle (LMA) solution and extant solar neutrino data. The first analysis is oscillation parameter-independent and the second analysis involves an approximate calculation of the survival probabilities in the three energy ranges that depends only on oscillation parameters. We show that future experiments like BOREXino, CLEAN, Heron, LENS and MOON, that measure $pp$ and $^7$Be neutrinos, will facilitate a stringent test of the LMA solution independently of the Standard Solar Model (SSM), without recourse to earth-matter effects. Throughout, we describe the role of SSM assumptions on our results. If the LMA solution passes the test without needing to be modified, it may be possible to establish that $θ_x$ is nonzero at more than $2σ$ assuming the SSM prediction for the $pp$ flux is correct.

hep-ph↗

arXiv2005

Neutrino physics from new SNO and KamLAND data and future prospects

We analyze the cumulative data from the latest SNO, KamLAND and other solar neutrino experiments in the standard scenario of three oscillating active neutrinos. We determine the solar neutrino oscillation parameters and obtain new bounds on $θ_x$. We also place constraints on the fraction of oscillating solar neutrinos that transform to sterile neutrinos with the $^8$B flux normalization left free. Concomitantly, we assess the sensitivity of future data from the SNO and KamLAND experiments to $θ_x$ and to the sterile neutrino content of the solar flux.

hep-ph↗

arXiv2003

Progress in the physics of massive neutrinos

The current status of the physics of massive neutrinos is reviewed with a forward-looking emphasis. The article begins with the general phenomenology of neutrino oscillations in vacuum and matter and documents the experimental evidence for oscillations of solar, reactor, atmospheric and accelerator neutrinos. Both active and sterile oscillation possibilities are considered. The impact of cosmology (BBN, CMB, leptogenesis) and astrophysics (supernovae, highest energy cosmic rays) on neutrino observables and vice versa, is evaluated. The predictions of grand unified, radiative and other models of neutrino mass are discussed. Ways of determining the unknown parameters of three-neutrino oscillations are assessed, taking into account eight-fold degeneracies in parameters that yield the same oscillation probabilities, as well as ways to determine the absolute neutrino mass scale (from beta-decay, neutrinoless double-beta decay, large scale structure and Z-bursts). Critical unknowns at present are the amplitude of ν_μto ν_e oscillations and the hierarchy of the neutrino mass spectrum; the detection of CP violation in the neutrino sector depends on these and on an unknown phase. The estimated neutrino parameter sensitivities at future facilities (reactors, superbeams, neutrino factories) are given. The overall agenda of a future neutrino physics program to construct a bottom-up understanding of the lepton sector is presented.

hep-ph↗