arXiv subjects

Alexander Friedland

Publications and source records attributed to Alexander Friedland.

At least 37 records · Page 2Linked to original sources

arXiv2013

Integrating In Dark Matter Astrophysics at Direct Detection Experiments

We study the capabilities of the MAJORANA DEMONSTRATOR, a neutrinoless double-beta decay experiment currently under construction at the Sanford Underground Laboratory, as a light WIMP detector. For a cross section near the current experimental bound, the MAJORANA DEMONSTRATOR should collect hundreds or even thousands of recoil events. This opens up the possibility of simultaneously determining the physical properties of the dark matter and its local velocity distribution, directly from the data. We analyze this possibility and find that allowing the dark matter velocity distribution to float considerably worsens the WIMP mass determination. This result is traced to a previously unexplored degeneracy between the WIMP mass and the velocity dispersion. We simulate spectra using both isothermal and Via Lactea II velocity distributions and comment on the possible impact of streams. We conclude that knowledge of the dark matter velocity distribution will greatly facilitate the mass and cross section determination for a light WIMP.

hep-ph↗

arXiv2013

Halo Modification of a Supernova Neutronization Neutrino Burst

We give the first self-consistent calculation of the effect of the scattered neutrino halo on flavor evolution in supernovae. Our example case is an O-Ne-Mg core collapse supernova neutronization neutrino burst. We find that the addition of the halo neutrinos produces qualitative and quantitative changes in the final flavor states of neutrinos. We also find that the halo neutrinos produce a novel distortion of the neutrino flavor swap. Our results provide strong motivation for tackling the full multidimensional and composition-dependent aspects of this problem in the future.

astro-ph.HE↗

arXiv2012

Constraining the Axion-Photon Coupling with Massive Stars

We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{Aγγ}. Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate the blue loop phase of the evolution. This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars. Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g_{Aγγ} <~ 0.8 * 10^{-10} GeV^{-1}, which compares favorably with the existing bounds.

hep-ph↗

arXiv2012

Searching for Novel Neutrino Interactions at NOvA and Beyond in Light of Large theta_13

We examine the prospects of probing nonstandard interactions (NSI) of neutrinos in the e-tau sector with upcoming long-baseline nu_mu -> nu_e oscillation experiments. First conjectured decades ago, neutrino NSI remain of great interest, especially in light of the recent 8B solar neutrino measurements by SNO, Super-Kamiokande, and Borexino. We observe that the recent discovery of large theta_13 implies that long-baseline experiments have considerable NSI sensitivity, thanks to the interference of the standard and new physics conversion amplitudes. In particular, in some parts of NSI parameter space, the upcoming NOvA experiment will be sensitive enough to see ~ 3sigma deviations from the SM-only hypothesis. On the flip side, NSI introduce important ambiguities in interpreting NOvA results as measurements of CP-violation, the mass hierarchy and the octant of theta_23. In particular, observed CP violation could be due to a phase coming from NSI, rather than the vacuum Hamiltonian. The proposed LBNE experiment, with its longer ~ 1300 km baseline, may break many of these interpretative degeneracies.

hep-ph↗

arXiv2012

Probing Nonstandard Standard Model Backgrounds with LHC Monojets

Monojet events at colliders have been used to probe models of dark matter and extra dimensions. We point out that these events also probe extensions of the Standard Model modifying neutrino-quark interactions. Such nonstandard interactions (NSI) have been discussed in connection with neutrino oscillation experiments. Assuming first that NSI remain contact at LHC energies, we derive stringent bounds that approach the levels suggested by the Boron-8 solar data. We next explore the possibility that the mediators of the NSI can be produced at colliders. The constraints are found to be strongest for mediator masses in the 10^2-10^3 GeV range, with the best bounds above ~ 200 GeV coming from ATLAS and below from CDF. For mediators with masses below 30 GeV the monojet bounds are weaker than in the contact limit. These results also directly apply to light dark matter searches. Lastly, we discuss how neutrino NSI can be distinguished from dark matter or Kaluza-Klein states with charged lepton searches.

hep-ph↗

arXiv2012

Neutrino scattering and flavor transformation in supernovae

We argue that the small fraction of neutrinos that undergo direction-changing scattering outside of the neutrinosphere could have significant influence on neutrino flavor transformation in core-collapse supernova environments. We show that the standard treatment for collective neutrino flavor transformation is adequate at late times, but could be inadequate in the crucial shock revival/explosion epoch of core-collapse supernovae, where the potentials that govern neutrino flavor evolution are affected by the scattered neutrinos. Taking account of this effect, and the way it couples to entropy and composition, will require a new paradigm in supernova modeling.

hep-ph↗

arXiv2011

Self-induced suppression of collective neutrino oscillations in a supernova

We investigate collective flavor oscillations of supernova neutrinos at late stages of the explosion. We first show that the frequently used single-angle (averaged coupling) approximation predicts oscillations close to, or perhaps even inside, the neutrinosphere, potentially invalidating the basic neutrino transport paradigm. Fortunately, we also find that the single-angle approximation breaks down in this regime; in the full multiangle calculation, the oscillations start safely outside the transport region. The new suppression effect is traced to the interplay between the dispersion in the neutrino-neutrino interactions and the vacuum oscillation term.

hep-ph↗

arXiv2010

The influence of collective neutrino oscillations on a supernova r-process

Recently, it has been demonstrated that neutrinos in a supernova oscillate collectively. This process occurs much deeper than the conventional matter-induced MSW effect and hence may have an impact on nucleosynthesis. In this paper we explore the effects of collective neutrino oscillations on the r-process, using representative late-time neutrino spectra and outflow models. We find that accurate modeling of the collective oscillations is essential for this analysis. As an illustration, the often-used "single-angle" approximation makes grossly inaccurate predictions for the yields in our setup. With the proper multiangle treatment, the effect of the oscillations is found to be less dramatic, but still significant. Since the oscillation patterns are sensitive to the details of the emitted fluxes and the sign of the neutrino mass hierarchy, so are the r-process yields. The magnitude of the effect also depends sensitively on the astrophysical conditions - in particular on the interplay between the time when nuclei begin to exist in significant numbers and the time when the collective oscillation begins. A more definitive understanding of the astrophysical conditions, and accurate modeling of the collective oscillations for those conditions, is necessary.

astro-ph.SR↗

arXiv2010

Self-refraction of supernova neutrinos: mixed spectra and three-flavor instabilities

Neutrinos in a core-collapse supernova undergo coherent flavor transformations in their own background. We explore this phenomenon during the cooling stage of the explosion. Our three-flavor calculations reveal qualitatively new effects compared to a two-flavor analysis. These effects are especially clearly seen for the inverted mass hierarchy: we find a different pattern of spectral "swaps" in the neutrino spectrum and a novel "mixed" spectrum for the antineutrinos. A brief discussion of the relevant physics is presented, including the instability of the two-flavor evolution trajectory, the 3-flavor pattern of spectral "swaps," and partial nonadiabaticity of the evolution.

hep-ph↗

arXiv2009

Vector Bosons in the Randall-Sundrum 2 and Lykken-Randall models and unparticles

Unparticle behavior is shown to be realized in the Randall-Sundrum 2 (RS 2) and the Lykken-Randall (LR) brane scenarios when brane-localized Standard Model currents are coupled to a massive vector field living in the five-dimensional warped background of the RS 2 model. By the AdS/CFT dictionary these backgrounds exhibit certain properties of the unparticle CFT at large N_c and strong 't Hooft coupling. Within the RS 2 model we also examine and contrast in detail the scalar and vector position-space correlators at intermediate and large distances. Unitarity of brane-to-brane scattering amplitudes is seen to imply a necessary and sufficient condition on the positivity of the bulk mass, which leads to the well-known unitarity bound on vector operators in a CFT.

hep-th↗

arXiv2009

On the RS2 realization of unparticles

To facilitate the study of the unparticle scenario it is very desirable to have a treatable model realizing it in four dimensions. Motivated by the general idea of the AdS/CFT correspondence, we consider a simple construction: the Randall-Sundrum 2 (single brane) setup with the Standard Model fields on the brane and a massive vector field in the warped bulk. We show that in this model the known properties of vector unparticles -- the nontrivial phase of the CFT propagator, the necessity and dominance of contact interactions, the unitarity constraint on the conformal dimension of the operator, and the tensor structure dictated by conformal symmetry -- follow by simple inspection of the brane-to-brane propagator. The phase has a physical interpretation as controlling the rate of escape of unparticles into the extra dimension. Requiring the correct sign for the imaginary part of the longitudinal polarization of the propagator, we obtain the unitarity condition m_5^2 >= 0, which, unlike in the scalar case, is unchanged from flat space. This condition results in the unitarity bound d_V >= 3, or, more generally, d_V >= D-1 for a vector unparticle in D-dimensional space. It is instructive to consider the RS 2 propagator in (Euclidean) position space: at large distances it behaves as a pure CFT propagator, while at short distances it turns into the 5d flat space propagator. The latter is softer than the former, thus regulating the would-be divergences of the spectral integral and turning the "contact" terms seen at low energies into finite-range interactions. Upon Fourier transforming to momentum space, one finds that at low momenta the CFT piece is subdominant to the "contact" interactions.

hep-th↗

arXiv2008

The Impact of Neutrino Magnetic Moments on the Evolution of Massive Stars

We explore the sensitivity of massive stars to neutrino magnetic moments. We find that the additional cooling due to the neutrino magnetic moments bring about qualitative changes to the structure and evolution of stars in the mass window 7 Msun < M < 18 Msun, rather than simply changing the time scales for the burning. We describe some of the consequences of this modified evolution: the shifts in the threshold masses for creating core-collapse supernovae and oxygen-neon-magnesium white dwarfs and the appearance of a new type of supernova in which a partial carbon-oxygen core explodes within a massive star. The resulting sensitivity to the magnetic moment is at the level of (2-4) * 10^{-11} μ_B.

astro-ph↗

arXiv2007

Extra dimensions, orthopositronium decay, and stellar cooling

In a class of extra dimensional models with a warped metric and a single brane the photon can be localized on the brane by gravity only. An intriguing feature of these models is the possibility of the photon escaping into the extra dimensions. The search for this effect has motivated the present round of precision orthopositronium decay experiments. We point out that in this framework a photon in plasma should be metastable. We consider the astrophysical consequences of this observation, in particular, what it implies for the plasmon decay rate in globular cluster stars and for the core-collapse supernova cooling rate. The resulting bounds on the model parameter exceed the possible reach of orthopositronium experiments by many orders of magnitude.

hep-ph↗

arXiv2007

Constraining Models of Neutrino Mass and Neutrino Interactions with the Planck Satellite

In several classes of particle physics models -- ranging from the classical Majoron models, to the more recent scenarios of late neutrino masses or Mass-Varying Neutrinos -- one or more of the neutrinos are postulated to couple to a new light scalar field. As a result of this coupling, neutrinos in the early universe instead of streaming freely could form a self-coupled fluid, with potentially observable signatures in the Cosmic Microwave Background and the large scale structure of the universe. We re-examine the constraints on this scenario from the presently available cosmological data and investigate the sensitivity expected from the Planck satellite. In the first case, we find that the sensitivity strongly depends on which piece of data is used. The SDSS Main sample data, combined with WMAP and other data, disfavors the scenario of three coupled neutrinos at about the 3.5$σ$ confidence level, but also favors a high number of freely streaming neutrinos, with the best fit at 5.2. If the matter power spectrum is instead taken from the SDSS Large Red Galaxy sample, best fit point has 2.5 freely streaming neutrinos, but the scenario with three coupled neutrinos becomes allowed at $2σ$. In contrast, Planck alone will exclude even a single self-coupled neutrino at the $4.2σ$ confidence level, and will determine the total radiation at CMB epoch to $ΔN_ν^{eff} = ^{+0.5}_{-0.3}$ ($1σ$ errors). We investigate the robustness of this result with respect to the details of Planck's detector. This sensitivity to neutrino free-streaming implies that Planck will be capable of probing a large region of the Mass-Varying Neutrino parameter space. Planck may also be sensitive to a scale of neutrino mass generation as high as 1 TeV.

astro-ph↗

arXiv2006

MSW Oscillations - LMA and Subdominant Effects

New physics near the TeV scale could modify neutrino-matter interactions or generate a relatively large neutrino magnetic (transition) moment. Both types of effects have been discussed since the 1970's as alternatives to mass-induced neutrino flavor oscillations. Nowadays, the availability of high-statistics data makes it possible to turn the idea around and ask: How well do the simple mass-induced oscillations describe solar neutrinos? At what level are the above-mentioned nonstandard effects excluded? Can we use solar neutrinos to constrain physics beyond the Standard Model? These notes review the sensitivity of the present-day solar neutrino experiments to the nonstandard neutrino interactions and transition moment and outline progress that may be expected in the near future. Based on a talk given at the Neutrino 2006 conference.

hep-ph↗

arXiv2006

Neutrino signatures of supernova turbulence

Convection that develops behind the shock front during the first second of a core-collapse supernova explosion is believed to play a crucial role in the explosion mechanism. We demonstrate that the resulting turbulent density fluctuations may be directly observable in the neutrino signal starting at t>~ 3-4 s after the onset of the explosion. The effect comes from the modulation of the MSW flavor transformations by the turbulent density fluctuations. We derive a simple and general criterion for neutrino flavor depolarization in a Kolmogorov-type turbulence and apply it to the turbulence seen in modern numerical simulations. The turbulence casts a "shadow", by making other features, such as the shock front, unobservable in the density range covered by the turbulence.

astro-ph↗

arXiv2006

Two modes of searching for new neutrino interactions at MINOS

The SuperKamiokande atmospheric neutrino measurements leave substantial room for nonstandard interactions (NSI) of neutrinos with matter in the nu_e- nu_tau sector. Large values of the NSI couplings are accommodated if the vacuum oscillation parameters are changed from their standard values. Short and medium baseline neutrino beams can break this degeneracy by measuring the true vacuum oscillation parameters with the muon neutrino disappearance mode, for which the matter effects are negligible or subdominant. These experiments can also search for the nu_e-nu_tau flavor changing effects directly, by looking for nu_mu->nu_e conversion caused by the intervening matter. We discuss both of these methods for the case of MINOS. We find that, while the present MINOS data on nu_mu disappearance induce only minor changes on the constraints on the NSI parameters, the situation will improve markedly with the planned increase of the statistics by an order of magnitude. In that case, the precision will be enough to distinguish certain presently allowed NSI scenarios from the no-NSI case. NSI per quark of about 10% the size of the standard weak interaction could give a nu_mu - nu_e conversion probability of the order ~ 10^{-2}, measurable by MINOS in the same high statistics scenario. In this nu_mu - nu_e channel, the small effects of NSI could be comparable or larger than the vacuum contribution of the small angle theta_{13}. The expected theta_{13} bound at MINOS should be more properly interpreted as a bound in the theta_{13}-NSI parameter space.

hep-ph↗

arXiv2006

Construction and analysis of a simplified many-body neutrino model

In dense neutrino systems, such as found in the early Universe, or near a supernova core, neutrino flavor evolution is affected by coherent neutrino-neutrino scattering. It has been recently suggested that many-particle quantum entanglement effects may play an essential role in these systems, potentially invalidating the traditional description in terms of a set of single-particle evolution equations. We model the neutrino system by a system of interacting spins, following an earlier work which showed that such a spin system can in some cases be solved exactly. We extend this work by constructing an exact analytical solution to a more general spin system, including initial states with asymmetric spin distribution and, moreover, not necessarily aligned along the same axis. Our solution exhibits a rich set of behaviors, including coherent oscillations and dephasing and a transition from the classical to quantum regimes. We argue that the classical evolution of the spin system captures the entire coherent behavior of the neutrino system, while the quantum effects in the spin system capture some, but not all, of the neutrino incoherent evolution. By comparing the spin and neutrino systems, we find no evidence for the violation of the accepted one-body description, though the argument involves some subtleties not appreciated before. The analysis in this paper may apply to other two-state systems beyond the neutrino field.

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