Search

The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of $^{136}$Xe. Out of its 50$\,$t total natural xenon inventory, 40$\,$t will be the active target of a time projection chamber which thus contains about 3.6 t of $^{136}$Xe. Here, we show that its projected half-life sensitivity is $2.4\times10^{27}\,$yr, using a fiducial volume of 5t of natural xenon and 10$\,$yr of operation with a background rate of less than 0.2$~$events/(t$\cdot$yr) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in $^{136}$Xe., 12 pages, 9 figures

We detail the sensitivity of the liquid xenon (LXe) DARWIN observatory to solar neutrinos via elastic electron scattering. We find that DARWIN will have the potential to measure the fluxes of five solar neutrino components: $pp$, $^7$Be, $^{13}$N, $^{15}$O and $pep$. The precision of the $^{13}$N, $^{15}$O and $pep$ components is hindered by the double-beta decay of $^{136}$Xe and, thus, would benefit from a depleted target. A high-statistics observation of $pp$ neutrinos would allow us to infer the values of the weak mixing angle, $\sin^2\theta_w$, and the electron-type neutrino survival probability, $P_e$, in the electron recoil energy region from a few keV up to 200 keV for the first time, with relative precision of 5% and 4%, respectively, at an exposure of 300 ty. An observation of $pp$ and $^7$Be neutrinos would constrain the neutrino-inferred solar luminosity down to 0.2%. A combination of all flux measurements would distinguish between the high (GS98) and low metallicity (AGS09) solar models with 2.1-2.5$\sigma$ significance, independent of external measurements from other experiments or a measurement of $^8$B neutrinos through coherent elastic neutrino-nucleus scattering in DARWIN. Finally, we demonstrate that with a depleted target DARWIN may be sensitive to the neutrino capture process of $^{131}$Xe., Comment: 9 pages, 4 figures; for associated data files, see https://github.com/Physik-Institut-UZH/DARWIN-Sensitivity-Studies/tree/master/solar_neutrinos_electron_scattering

Die unmittelbar auf den Urknall folgende Phase der kosmischen Inflation erzeugte Gravitationswellen, die im kosmischen Strahlungshintergrund feinste Spuren hinterliesen. Die kurzlich beobachtete „Verwirbelung“ der kosmischen Mikrowellenstrahlung wird allerdings grostenteils vom Staub in der Milchstrase erzeugt. Schon bald sollen prazisere Messungen aus den galaktischen Staubsignalen die Spur der kosmischen Inflation herausfiltern (aus Spektrum der Wissenschaft 3/2015).

Gravitinos are a fundamental prediction of supergravity, their mass (${m}_{G}$) is informative of the value of the SUSY breaking scale, and, if produced during reheating, their number density is a function of the reheating temperature (${T}_{\mathrm{rh}}$). As a result, constraining their parameter space provides, in turn, significant constraints on particle physics and cosmology. We have previously shown that for gravitinos decaying into photons or charged particles during the ($\ensuremath{\mu}$ and $y$) distortion eras, upcoming CMB spectral distortions bounds are highly effective in constraining the ${T}_{\mathrm{rh}}\ensuremath{-}{m}_{G}$ space. For heavier gravitinos (with lifetimes shorter than a few $\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{sec}$), distortions are quickly thermalized and energy injections cause a temperature rise for the CMB bath. If the decay occurs after neutrino decoupling, its overall effect is a suppression of the effective number of relativistic degrees of freedom (${N}_{\mathrm{eff}}$). In this paper, we utilize the observational bounds on ${N}_{\mathrm{eff}}$ to constrain gravitino decays and, hence, provide new constraints on gravitinos and reheating. For gravitino masses less than $\ensuremath{\approx}{10}^{5}\text{ }\text{ }\mathrm{GeV}$, current observations give an upper limit on the reheating scale in the range of $\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{10}--5\ifmmode\times\else\texttimes\fi{}{10}^{11}\text{ }\text{ }\mathrm{GeV}$. For masses greater than $\ensuremath{\approx}4\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }\mathrm{GeV}$, this can be more stringent than previous bounds from BBN constraints, coming from photodissociation of deuterium, by almost 2 orders of magnitude.

The author explores the reasons why scientists such as Albert Einstein, Richard Feynman, Carl Sagan, Stephen Hawking, and Neil deGrasse Tyson became celebrities, as well as sharing his own experience. He describes how public acclaim is often uncorrelated to scientific accomplishment and depends more on communication skills and personality traits. Nevertheless, he argues that the entire scientific community benefits when credible scientists gain a wider audience, and that celebrity is an opportunity that should not be squandered. Scientists who become recognizable have a chance and perhaps even a responsibility, which they have often exploited, to promote science literacy, combat scientific nonsense, motivate young people, and steer public policy discussions toward sound decision making.

If local supersymmetry is the correct extension of the standard model of particle physics, then following Inflation the early universe would have been populated by gravitinos produced from scatterings in the hot plasma during reheating. Their abundance is directly related to the magnitude of the reheating temperature. The gravitino lifetime is fixed as a function of its mass, and for gravitinos with lifetimes longer than the age of the universe at redshift $z\simeq 2\times 10^{6}$ (or roughly $6\times 10^6{\rm s}$), decay products can produce spectral distortion of the cosmic microwave background. Currently available COBE/FIRAS limits on spectral distortion can, in certain cases, already be competitive with respect to cosmological constraints from primordial nucleosynthesis for some gravitino decay scenarios. We show how the sensitivity limits on $\mu$ and $y$ distortions that can be reached with current technology would improve constraints and possibly rule out a significant portion of the parameter space for gravitino masses and Inflation reheating temperatures., Comment: submitted to Phys. Rev D., 8 pages, 4 figs (1 new figure added, references updated)

Generalized fluid equations, using sound speed $c_{\rm eff}^2$ and viscosity $c_{\rm vis}^2$ as effective parameters, provide a convenient phenomenological formalism for testing the relic neutrino "null hypothesis," i.e. that that neutrinos are relativistic and free-streaming prior to recombination. In this work, we relax the relativistic assumption and ask "to what extent can the generalized fluid equations accommodate finite neutrino mass?" We consider both the mass of active neutrinos, which are largely still relativistic at recombination $m^2 / T^2 \sim 0.2$, and the effect of a semi-relativistic sterile component. While there is no one-to-one mapping between mass/mixing parameters and $c_{\rm eff}^2$ and $c_{\rm vis}^2$, we demonstrate that the existence of a neutrino mass could induce a bias to measurements of $c_{\rm eff}^2$ and $c_{\rm vis}^2$ at the level of $0.01 m^2 / T^2 \sim 10^{-3}$., Comment: 20 pages, 3 figs; v2 -- references added, matches JCAP version

In this brief review of recent theoretical developments associated with the search for dark matter I describe the following: why baryons are now ruled out as dark matter candidates; SUSY WIMPS and signatures in the MSSM and NMSSM why claimed indirect signatures are probably not WIMP related, why axions may be of new interest, how WIMP detection might tell us about the galactic halo, and how theorists are preparing to avoid the next generation of experimental constraints., Comment: 6 pages, Invited Review talk, Neutrino 2006. To appear in Proceedings

The surprisingly large value of $r$, the ratio of power in tensor to scalar density perturbations in the CMB reported by the BICEP2 Collaboration, if confirmed, provides strong evidence for Inflation at the GUT scale. While the Inflationary signal remains the best motivated source, a large value of $r$ alone would still allow for the possibility that a comparable gravitational wave background might result from a self ordering scalar field (SOSF) transition that takes place later at somewhat lower energy. We find that even without detailed considerations of the predicted BICEP signature of such a transition, simple existing limits on the isocurvature contribution to CMB anisotropies would definitively rule out a contribution of more than $5\%$ to $r \approx 0.2$,. We also present a general relation for the allowed fractional SOSF contribution to $r$ as a function of the ultimate measured value of $r$. These results point strongly not only to an inflationary origin of the BICEP2 signal, if confirmed, but also to the fact that if the GUT scale is of order $10^{16} GeV$ then either the GUT transition happens before Inflation or the Inflationary transition and the GUT transition must be one and the same., 3 pages 2 figures, accepted for publication in Physics Letters B . Accepted version revised slightly in response to referee's comments

The observation of primordial gravitational waves could provide a new and unique window on the earliest moments in the history of the universe, and on possible new physics at energies many orders of magnitude beyond those accessible at particle accelerators. Such waves might be detectable soon in current or planned satellite experiments that will probe for characteristic imprints in the polarization of the cosmic microwave background (CMB), or later with direct space-based interferometers. A positive detection could provide definitive evidence for Inflation in the early universe, and would constrain new physics from the Grand Unification scale to the Planck scale., Comment: 12 pages. 4 figures

Cosmological discoveries over the past century have completely changed our picture of our place in the universe. New observations have a realistic chance of probing nature on heretofore unimaginable scales, and as a result are changing the nature of fundamental science. Perhaps no other domain of science has an equal capacity to completely change our perspective of the world in which we live., Invited Lecture, UNESCO/IAU Meeting: The Role of Astronomy in Society and Culture Jan 2009, to appear, IAU Proceedings, D. Valls-Gaubaud and A. Boksenberg, eds.. (Several typos removed in this version)

This article offers a debate on how scientists ought to approach religion and its followers. Lawrence M. Krauss of Case Western Reserve University says the goal is to teach people about science and that to do that it is important to know about them. Teaching is seduction and telling people that their deepest beliefs are silly is no way to educate them. Richard Dawkins presents an opposing view saying that dishonesty is also not a strong educational technique. INSET: EDITORS' INTRODUCTION.

The research projects described in our original proposal are continuing, with completion of several of the envisaged projects, and several new related projects underway. Research of each of the Investigators and the postdocs supported by the grant are summarized in attached report.

The article presents an overview of several conceptual mistakes of the 20th-century physicist Albert Einstein and discussion of their implications on advanced scientific research. Examples include how Einstein incorrectly predicted, misunderstood or disregarded phenomena such as gravitational lensing, gravitational waves, and the cosmological constant.

Beginning with a set of simplified models for spin-0, spin-$\half$, and spin-1 dark matter candidates using completely general Lorentz invariant and renormalizable Lagrangians, we derive the full set of non-relativistic operators and nuclear matrix elements relevant for direct detection of dark matter, and use these to calculate rates and recoil spectra for scattering on various target nuclei. This allows us to explore what high energy physics constraints might be obtainable from direct detection experiments, what degeneracies exist, which operators are ubiquitous and which are unlikely or sub-dominant. We find that there are operators which are common to all spins as well operators which are unique to spin-$\half$ and spin-1 and elucidate two new operators which have not been previously considered. In addition we demonstrate how recoil energy spectra can distinguish fundamental microphysics if multiple target nuclei are used. Our work provides a complete roadmap for taking generic fundamental dark matter theories and calculating rates in direct detection experiments. This provides a useful guide for experimentalists designing experiments and theorists developing new dark matter models., Comment: 37 pages, six figures, submitted to Phys. Rev. D

Reheating is a transition era after the end of inflation, during which the inflaton is converted into the particles that populate the Universe at later times. No direct cosmological observables are normally traceable to this period of reheating. Indirect bounds can however be derived. One possibility is to consider cosmological evolution for observable CMB scales from the time of Hubble crossing to the present time. Depending upon the model, the duration and final temperature after reheating, as well as its equation of state, may be directly linked to inflationary observables. For single-field inflationary models, if we approximate reheating by a constant equation of state, one can derive relations between the reheating duration (or final temperature), its equation of state parameter, and the scalar power spectrum amplitude and spectral index. While this is a simple approximation, by restricting the equation of state to lie within a broad physically allowed range, one can in turn bracket an allowed range of $n_s$ and $r$ for these models. The added constraints can help break degeneracies between inflation models that otherwise overlap in their predictions for $n_s$ and $r$., 32 pages, 15 figures. Revised in response to comments on the original version, and in preparation for submission for publication. More references and a new figure were added

We initially consider two simple situations where inflationary slow roll parameters are large and modes no longer freeze out shortly after exiting the horizon, treating both cases analytically. We then consider applications to transient phases where the slow roll parameters can become large, especially in the context of the common `fast-roll' inflation frequently used as a mechanism to explain the anomalously low scalar power at low $l$ in the CMB. These transient cases we treat numerically. We find when $\epsilon$, the first slow roll parameter, and only $\epsilon$ is large, modes decay outside the horizon, and when $\delta$, the second slow roll parameter, is large, modes grow outside the horizon. When multiple slow roll parameters are large the behavior in general is more complicated, but we nevertheless show in the 'fast-roll' inflation case, modes grow outside the horizon., Comment: 21 pages, 11 figures

We compare the sensitivity of WIMP detection via direct separation of possible signal vs. background to WIMP detection via detection of an annual modulation, in which signal and background cannot be separated on an event-by-event basis. In order to determine how the constraints from the two different types of experiments might be combined an adequate incorporation of uncertainties due to galactic halo models must be made. This issue is particularly timely in light of recent direct detection limits from Edelweiss and CDMS, which we now demonstrate cannot be made consistent with the most recent claimed DAMA annual modulation observation, even by including halo uncertainties for spin-independent interactions. On the other hand, we demonstrate that a combination of these two techniques, in the event of any positive direct detection signal, could ultimately allow significant constraints on anisotropic halo models even without directional sensitivity in these detectors. For direction-sensitive detectors we derive a new formalism to calculate angular event rates, and present the predicted angular signal for a variety of halo models and calculate the number of events needed to distinguish a dark matter signal from an isotropic background.

A new incarnation of Einstein's cosmological constant may point the way beyond general relativity

Cosmology, the field that focuses on the origin and evolution of the universe on its largest scales, is undergoing what many have called a “golden era.” New observations, on the ground, in the air, and in space, combined with exciting new theoretical insights, have, over the past decade or two, literally revolutionized our picture of the universe in which we live. Ideas that were essentially pure speculation 20 years ago now rest firmly on the bedrock of experiment. At the same time, many new questions have arisen, and some once firmly held notions about the future of the universe have been displaced. In this article I present a guide to our current understanding of the history and fate of the universe to parallel and supplement the overview presented in the Contemporary Physics Education Project Cosmology Chart.

The article discusses the discovery of gravitational waves from the early universe by a team of astrophysicists working with the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) telescope at the Amundsen-Scott South Pole Station. Topics include probing inflation by the observation of gravitational waves, the implications for science if the BICEP2 cosmic microwave background (CMB) polarization signal is confirmed, and the multiverse theory.

We consider the status of Higgs inflation in light of the recently announced detection of B modes in the polarization of the cosmic microwave background radiation by the BICEP2 Collaboration. In order for the primordial B-mode signal to be observable by BICEP2, the energy scale of inflation must be high: ${V}_{\text{inf}}\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}1{0}^{16}\text{ }\text{ }\mathrm{GeV}$. Higgs inflation generally predicts a small amplitude of tensor perturbations, and therefore it is natural to ask if Higgs inflation might accommodate this new measurement. We find that the answer is essentially no, unless one considers either extreme fine-tuning or possibly adding new beyond the Standard Model fields, which remove some of the more attractive features of the original idea. We also explore the possible importance of a factor that has not previously been explicitly incorporated, namely the gauge dependence of the effective potential used in calculating inflationary observables (e.g., ${n}_{S}$ and $r$), to see if this might provide additional wiggle room. Such gauge effects are comparable to the effects of Higgs mass uncertainties and other observables already considered in the analysis, and therefore they are relevant for constraining models. However, they are therefore too small to remove the apparent incompatibility between the BICEP2 observation and the predictions of Higgs inflation.

It is commonly anticipated that gravity is subject to the standard principles of quantum mechanics. Yet some (including Einstein) have questioned that presumption, whose empirical basis is weak. Indeed, recently Freeman Dyson has emphasized that no conventional experiment is capable of detecting individual gravitons. However, as we describe, if inflation occurred, the Universe, by acting as an ideal graviton amplifier, affords such access. It produces a classical signal, in the form of macroscopic gravitational waves, in response to spontaneous (not induced) emission of gravitons. Thus recent BICEP2 observations of polarization in the cosmic microwave background will, if confirmed, provide empirical evidence for the quantization of gravity. Their details also support quantitative ideas concerning the unification of strong, electromagnetic, and weak forces, and of all these with gravity., 4 pages, no figures. v2: minor typos corrected, reference added. v3: very minor typo corrected. Winning entry in Gravity Research Foundation essay competition

While many aspects of general relativity have been tested, and general principles of quantum dynamics demand its quantization, there is no direct evidence for that. It has been argued that development of detectors sensitive to individual gravitons is unlikely, and perhaps impossible. We argue here, however, that measurement of polarization of the Cosmic Microwave Background due to a long wavelength stochastic background of gravitational waves from Inflation in the Early Universe would firmly establish the quantization of gravity., Comment: 4 pages, no figures, revised in response to referee's reports. Accepted for publication in PRD

We have selected 42 elliptical galaxies from the literature and estimated their velocity dispersions at the effective radius ($\sigma_{\re}$) and at 0.54 effective radii ($\vff$). We find by a dynamical analysis that the normalized velocity dispersion of the dark halo of an elliptical galaxy $\vdm$ is roughly $\sigma_{\re}$ multiplied by a constant, which is almost independent of the core radius or the anisotropy parameter of each galaxy. Our sample analysis suggests that $\vdm^{*}$ lies in the range 178-198 km s$^{-1}$. The power law relation we find between the luminosity and the dark matter velocity dispersion measured in this way is $(L/L^{*}) = (\vdm/\vdm^{*})^\gamma$, where $\gamma$ is between 2-3. These results are of interest for strong gravitational lensing statistics studies. In order to determine the value of $\vdm^{*}$, we calculate $\mstar$ in the same $\bt$ band in which $\vdm^{*}$ has been estimated. We select 131 elliptical galaxies as a complete sample set with apparent magnitudes $\bt$ between 9.26 and 12.19. We find that the luminosity function is well fitted to the Schechter form, with parameters $\mstar$ = -19.66 + 5$\cdot\log_{10}h \pm 0.30$, $\alpha = 0.15 \pm 0.55$, and the normalization constant $\phi^{*} = (1.34 \pm 0.30) \times 10^{-3} h^{3}$ Mpc$^{-3}$, with the Hubble constant $\hnot$ = 100 $h$ km s$^{-1}$ Mpc$^{-1}$. This normalization implies that morphology type E galaxies make up (10.8 $\pm$ 1.2) per cent of all galaxies., Comment: 18 pages latex, with ps figs included. accepted by New Astronomy (revised to incorporate referees comments)

Current evidence suggests that the cosmological constant is not zero, or that we live in an open universe. We examine the implications for the future under these assumptions, and find that they are striking. If the Universe is cosmological constant-dominated, our ability to probe the evolution of large scale structure will decrease with time ---presently observable distant sources will disappear on a time-scale comparable to the period of stellar burning. Moreover, while the Universe might expand forever, the integrated conscious lifetime of any civilization will be finite, although it can be astronomically long. We find that this latter result is far more general. In the absence of possible exotic and uncertain strong gravitational effects, the total information recoverable by any civilization over the entire history of our universe is finite, and assuming that consciousness has a physical computational basis, life cannot be eternal., 23 pages, latex, submitted to Ap.J

Distinguishing the signals due to scattering of WIMP dark matter off of nuclear targets from those due to background noise is a major challenge. The Earth's motion relative to the galactic halo should produce halo-dependent seasonal modulation in the event rate, but it also should produce an angular signal that is both far stronger and less ambiguous. Distinct patterns in the recoil spectrum can reflect the details of the galactic halo. We derive a new formalism to calculate angular event rates, and present the predicted angular signal for a variety of halo models and calculate the number of events needed to distinguish a dark matter signal from an isotropic background., 4 pages revtex, submitted to PRL

Recent evidence for oscillations of atmospheric neutrinos at Super-Kamiokande suggest, in the simplest see-saw interpretation, neutrino masses such that `just so' vacuum oscillations can explain the solar neutrino deficit. Super-K solar neutrino data provide preliminary support for this interpretation. We describe how the just-so signal---an energy dependent seasonal variation of the event rate, might be detected within the coming years and provide general arguments constraining the sign of the variation. The expected variation at radiochemical detectors may be below present sensitivity, but a significant modulation in the $^7$Be signal could shed light on the physics of the solar core---including a direct measure of the solar core temperature., Comment: 4 pages, revtex, 4 ps figs: new refs added, and Super-K energy resolution function incorporated

A decade before Alan Sokal’s famous hoax was published in Social Text, a thinly veiled spoof was submitted to Physical Review Letters. But in that case the editors gave as good as they got.

Perturbations due to the planets combined with the non-Coulomb nature of the gravitational potential in the Sun imply that weakly interacting massive particles (WIMPs) that are gravitationally captured by scattering in surface layers of the Sun can evolve into orbits that no longer intersect the Sun. For orbits with a semimajor axis $l1/2$ of Jupiter's orbit, such WIMPs can persist in the solar system for $g{10}^{9}$ years, leading to a previously unanticipated population intersecting Earth's orbit. For WIMPs detectable in the next generation of detectors, this population can provide a complementary signal, in the keV range, to that of galactic halo dark matter.

I first outline new results on the angular modulation of WIMP dark matter scattering on targets in terrestrial laboratories, based on our uncertainties of the WIMP halo distribution, I then outline an exciting new result which indicates that for the high end of allowed SUSY WIMP scattering cross sections there exists a new distribution of WIMP dark matter in our solar system which could produce a dramatically different signal from halo WIMP dark matter in terrestrial detectors.

The lower limit on the age of the universe derived from globular cluster dating techniques, which previously strongly motivated a non-zero cosmological constant, has now been dramatically reduced, allowing consistency for a flat matter dominated universe with a Hubble Constant, $H_0 \le 66 km s^{-1} Mpc^{-1}$. The case for an open universe versus a flat universe with non-zero cosmological constant is reanalyzed in this context, incorporating not only the new age data, but also updates on baryon abundance constraints, and large scale structure arguments. For the first time, the allowed parameter space for the density of non-relativistic matter appears larger for an open universe than for a flat universe with cosmological constant, while a flat universe with zero cosmological constant remains strongly disfavored. Several other preliminary observations suggest a non-zero cosmological constant, but a definitive determination awaits refined measurements of $q_0$, and small scale anisotropies of the Cosmic Microwave background. I argue that fundamental theoretical arguments favor a non-zero cosmological constant over an open universe. However, if either case is confirmed, the challenges posed for fundamental particle physics will be great., Comment: 15 pages, Latex, including 2 eps figs, submitted to Science