KICP Friday Noon Seminars: 2006
DateTalk TitleSpeaker
January 6, 2006 cancelledTBAJeremy Tinker, KICP, University of Chicago
January 13, 2006SNO and Solar Neutrinos: Beyond the Solar Neutrino ProblemKathryn Miknaitis, University of Chicago
January 20, 2006Detecting Cosmic SuperstringsMark G. Jackson, Fermilab
January 27, 2006Identifying Dark MatterJonathan Feng, University of California, Irvine
February 3, 2006Baryon Accoustic OscillationsAlexia Schulz, University of California , Berkeley
February 10, 2006Dark Matter and New Physics Searches at hadron and lepton collidersCarlos Wagner, Argonne National Laboratory and University of Chicago
February 17, 2006On the luminosity dependence of quasar clusteringPeder Norberg, University of Edinburgh
February 24, 2006Racetrack InflationJose Blanco-Pillado, New York University
March 3, 2006Neutrino astronomy with IceCube and AMANDAGary Hill, University of Wisconsin, Madison
March 10, 2006Constraining Cosmology with the South Pole TelescopeTom Crawford, University of Chicago
March 17, 2006How I Learned to Like w<-1 Dark EnergyNemanja Kaloper, University of California, Davis
March 31, 2006Modeling Galaxy Clustering with the Halo Occupation DistributionJeremy Tinker, University of Chicago
April 7, 2006Major mergers and the assembly of massive elliptical galaxiesMichael Boylan-Kolchin, UC, Berkeley
April 14, 2006The Cosmological Information Content of the Halo-Model Dark-Matter PowerMark Neyrinck, University of Hawaii
April 21, 2006Tests of Newton's Inverse Square Law to Short DistancesDan Kapner, KICP
April 28, 2006Galaxy Mergers: Simulations, Observations, and Active Galactic NucleiJoel Primack, University of California, Santa Cruz
May 5, 2006Neutrino Physics Beyond SNOMark Chen, Queen's University
May 19, 2006Mapping the Polarized Sky with WMAP: Methods and Cosmological ImplicationsOlivier Dore, CITA
May 26, 2006The Star Formation and Metallicity History of Disk Galaxies: 0Lisa Kewley, University of Hawaii
June 2, 2006High Resolution Imaging of Cerenkov Light from Air ShowersElizabeth Hays, The University of Chicago and Argonne National Laboratory
June 9, 2006Digging for new (Astro-)Physics in the old CMBNiayesh Afshordi, Harvard University
September 29, 2006The Photometric Properties of the Most Massive, High-Redshift GalaxiesBrant Robertson, KICP
October 6, 2006Dark Matter in the Neutrino Sector: Sterile NeutrinosKevork Abazajian, UMD College Park
October 13, 2006Can We See Gravitational Waves from the End of Inflation?Eugene Lim, Yale University
October 27, 2006The XENON10 Dark Matter Search and the Promise of Noble Liquids for a Very Large Scale Dark Matter ExperimentTom Shutt, Case Western Reserve University
November 3, 2006Motion of Satellites and Structure of Outer Parts of GalaxiesAnatoly Klypin, New Mexico State University
November 10, 2006Shooting the Moon: Getting Serious About GravityTom Murphy, University of California, San Diego
November 17, 2006New Views of the High-Redshift UniversePeng Oh, University of California, Santa Barbara
December 1, 2006 cancelledImprints of Tachyonic Preheating on the CMBJames M. Cline, McGill University

January 6, 2006 cancelled | LASR Conference Room | 12:00 PM
Jeremy Tinker, KICP, University of Chicago


SNO and Solar Neutrinos: Beyond the Solar Neutrino Problem
January 13, 2006 | LASR Conference Room | 12:00 PM
Kathryn Miknaitis, University of Chicago

In 2001 (and more definitively in 2002), the Sudbury Neutrino Observatory (SNO) experiment demonstrated that electron neutrinos produced in the solar interior were changing flavor prior to reaching the earth. SNO's measurements of solar neutrino flavor change conclusively solved the long-standing "Solar Neutrino Problem" and provided evidence for the existence of neutrino mass. Far from being the end of the story, these and other recent neutrino physics results have opened up a rich field of fundamental questions to be probed by current and future experiments. I will give an overview of several of the major open questions in neutrino physics and discuss how SNO's recent and ongoing measurements fit into the bigger project of unraveling the neutrino's mysteries.

Detecting Cosmic Superstrings
January 20, 2006 | LASR Conference Room | 12:00 PM
Mark G. Jackson, Fermilab

I will discuss the recent developments suggesting that cosmic superstrings are theoretically possible, and observationally distinct from conventional cosmic strings. First reviewing the appearance of cosmic strings in string theory and some models of inflation therein, I show how their formation can still be consistent with existing CMB/pulsar bounds. I then profile methods by which cosmic strings can be detected. Finally I will explain how to differentiate cosmic superstrings from conventional vortex cosmic strings, and how this can be used to extract information about string parameters and extra dimensions.

Identifying Dark Matter
January 27, 2006 | LASR Conference Room | 12:00 PM
Jonathan Feng, University of California, Irvine

Recent breakthroughs in cosmology indicate that a quarter of the Universe is composed of dark matter, but the microscopic identity of dark matter remains a deep mystery. I will review recent progress in resolving this puzzle, focusing on two well- motivated classes of dark matter candidates: WIMPs and superWIMPs. In each of these classes, stable particles are naturally produced in the early Universe with the right relic density to contribute to dark matter, and dark matter particles have mass around 100 GeV, the energy scale soon to be probed in detail at particle colliders. I will discuss the theoretical motivations for these possibilities, their diverse implications at the interface of particle physics, astroparticle physics, and cosmology, and the prospects for identifying dark matter in the coming years.

Baryon Accoustic Oscillations
February 3, 2006 | LASR Conference Room | 12:00 PM
Alexia Schulz, University of California , Berkeley

Baryon oscillations in the matter power spectrum, used as a standard ruler, have the potential to strongly constrain the expansion history of the universe and the nature of the dark energy. Localizing the features in the galaxy power spectrum and relating them to features predicted in the dark matter spectrum necessitates a theoretical understanding of such complex issues as galaxy bias, non-linear evolution, and redshift space distortions. Using the halo model to analytically investigate these effects, we have identified trends that relate the scale dependance of the galaxy bias to the halo occupation distribution (HOD). These trends reveal a natural parametrization of the galaxy power spectrum. Combining this parametrization with the results of N-body simulations, we have quantified the impact of the HOD parameters on the scale dependance of the galaxy bias. We show that the bias in real space is less profoundly affected by shifts in the HOD parameters, which suggests that baryon oscillation measurments in the correlation function may prove to be more robust to the theoretical uncertainties that are baryon oscillation measurments in the galaxy power spectrum.

Dark Matter and New Physics Searches at hadron and lepton colliders
February 10, 2006 | LASR Conference Room | 12:00 PM
Carlos Wagner, Argonne National Laboratory and University of Chicago

Dark Matter candidates abound in models of new physics. The best motivated candidates are associated with extensions of the Standard Model (SM) that provide a natural mechanism for electroweak symmetry breaking. Production of a weakly interacting, neutral, dark matter candidate at hadron and lepton colliders will lead to events with missing energy. In this talk I will discuss the prospects of detecting such dark matter candidates at the Tevatron, the LHC and the ILC.

On the luminosity dependence of quasar clustering
February 17, 2006 | LASR Conference Room | 12:00 PM
Peder Norberg, University of Edinburgh

We present detailed clustering measurements for a flux limited sample of ~14,000 quasars extracted from the 2dF QSO Redshift Survey(2QZ) in the redshift range 0.810^12 M_sun and that the mean mass of their host haloes is of the order of 10^13 M_sun. We then split each redshift interval into several luminosity intervals, for which we estimate the quasar projected auto and cross-correlation functions. Fitting the data with a biased CDM model and using several statistical tests, we find that models with luminosity dependent clustering tend to be statistically favoured. However, the quality of the data is not good enough to accurately quantify how quasar biasing depends on luminosity. We critically discuss the limitations of our dataset, as well as the method, and show that a much larger sample is needed to rule out current models for luminosity segregation.

Racetrack Inflation
February 24, 2006 | LASR Conference Room | 12:00 PM
Jose Blanco-Pillado, New York University

Four dimensional effective actions of many of the currently studied extra-dimensional theories seem to contain massless scalar fields called moduli. Giving these fields a potential is crucial to make these theories compatible with observations. It is therefore natural to explore the possibility that before they settle down to the true minimum of their potentials these fields could be relevant for cosmology, in particular they could be the source of an inflationary expansion period of the universe. In this talk, I will review ealier attempts to follow these ideas and present a new model of topological modular inflation in the context of the recently develop flux compactifications within string theory.

Neutrino astronomy with IceCube and AMANDA
March 3, 2006 | RI 480 | 12:00 PM
Gary Hill, University of Wisconsin, Madison

Since the early 1990's, the South Pole station in Antarctica has been the site of the development and operation of the world's first ice-Cherenkov neutrino telescopes, AMANDA and IceCube. The AMANDA telescope was completed in 2000 and has been used to search for the first high-energy neutrinos from beyond the earth. The successor to AMANDA, IceCube, will be a kilometre-scale neutrino and air shower detector with unprecedented sensitivity to astrophysical sources of neutrinos. In this talk, a summary of the results from AMANDA and report on the first two construction seasons of the IceCube telescope will be given. The prospects for extraterrestrial neutrino observation with the full IceCube array, slated for completion in 2010, will be discussed.

Constraining Cosmology with the South Pole Telescope
March 10, 2006 | LASR Conference Room | 12:00 PM
Tom Crawford, University of Chicago

A new millimeter/submillimeter-wave telescope is being constructed for deployment at the NSF South Pole research station. This telescope, with a 10-meter clear aperture, is designed for conducting large area surveys with unprecedented sensitivity to low surface brightness emission such as primary and secondary CMB anisotropy. The first camera for the new South Pole Telescope (SPT) will be a 1000-element bolometer array designed to conduct a blind survey over a few thousand square degrees, searching for galaxy clusters through their Sunyaev-Zel'dovich Effect. The survey should find many thousands of clusters with a selection criterion that is remarkably uniform with redshift. Armed with redshifts obtained from optical/IR follow-up, the survey yields should allow tight constraints to be placed on the equation of state of the dark energy. The cluster survey data will also be used to measure the small-scale primary and secondary CMB power spectra well beyond current limits of sensitivity and resolution, improving our knowledge of the spectrum of primordial fluctuations, the mass of the neutrino, and other cosmological measurables. Finally, a planned polarimeter for the SPT will have the statistical power to constrain the energy scale of inflation through measurement of the B-mode power spectrum of the polarized CMB.

How I Learned to Like w<-1 Dark Energy
March 17, 2006 | LASR Conference Room | 12:00 PM
Nemanja Kaloper, University of California, Davis

We will discuss mechanisms which can simulate dark energy with w<-1, but do not use any ghosts, phantoms or other occult beasts.

Modeling Galaxy Clustering with the Halo Occupation Distribution
March 31, 2006 | LASR Conference Room | 12:00 PM
Jeremy Tinker, University of Chicago

Measurements of the galaxy two-point correlation function create strong constraints on the statistical occupation of galaxies within dark matter halos, referred to as the Halo Occupation Distribution (HOD). Using the HOD, one can make predictions for other clustering statistics for a given cosmology. Recent results have demonstrated a tension between galaxy clustering results and the so-called "concordance cosmology". These results include cluster mass-to-light ratios, galaxy pairwise velocity dispersions, and redshift-space anisotropies. All of these discrepancies are ameliorated if one assumes a cosmology in agreement with the new WMAP year 3 results. This methodology for constraining the HOD relies on the simplifying assumption that halo occupation is a function of halo mass only, independent of the halo's environment. This assumption has been called into question with recent theoretical results. I will present new measurements of void statistics from the SDSS public DR4 database and compare these data to HOD predictions using the standard assumptions. Voids provide a sensitive test for the environmental dependence of halo occupation, a test the HOD passes with flying colors.

Major mergers and the assembly of massive elliptical galaxies
April 7, 2006 | LASR Conference Room | 12:00 PM
Michael Boylan-Kolchin, UC, Berkeley

Several independent lines of evidence indicate that gas-poor mergers play an important role in assembling massive elliptical galaxies. Since low-redshift ellipticals are observed to obey well-defined scaling relations, dissipationless mergers can place interesting constraints on galaxy formation theories. I will present the results of numerical simulations of these mergers, including their locations relative to the observed fundamental plane, Faber-Jackson, and stellar mass-size relations, as well as possible implications for the black hole M-sigma relation in massive galaxies. I will also discuss dissipationless merging in the context of the formation of giant ellipticals and brightest cluster galaxies.

The Cosmological Information Content of the Halo-Model Dark-Matter Power
April 14, 2006 | LASR Conference Room | 12:00 PM
Mark Neyrinck, University of Hawaii

I will discuss explorations, using the halo model, of the information content as a function of scale of the nonlinear dark-matter power spectrum. The halo model gives similar results as Rimes and Hamilton recently found from N-body simulations. Both methods predict a paucity of cosmological information on translinear (k ~ 0.1-1 h/Mpc) scales, which may be partially explained in the halo model by Poisson fluctuations (particularly large for the largest haloes) in halo number density in a given volume. I will also discuss whether information is preserved in time in the halo model, and how halo model parameters might be constrained by requiring that information cannot be created.

Tests of Newton's Inverse Square Law to Short Distances
April 21, 2006 | LASR Conference Room | 12:00 PM
Dan Kapner, KICP

I will describe a series of experiments that test the Inverse-Square Law (ISL) down to 65 micron separations. A variety of physics beyond the standard model motivates such a search; the exchange of new bosons, extra dimensions, or even the energy scale of dark energy might lead to a violation of the ISL. Our torsion balance tests set new limits for these scenarios. New results will be presented.

Galaxy Mergers: Simulations, Observations, and Active Galactic Nuclei
April 28, 2006 | LASR Conference Room | 12:00 PM
Joel Primack, University of California, Santa Cruz

In this informal talk, I will summarize the large suites of high-resolution hydrodynamic simulations of galaxy encounters that my current and former PhD students have been running and analyzing, and comparisons with observational data especially from the ongoing DEEP2 survey. In particular, I will discuss what the data from DEEP tell us about the morphologies of the galaxies that host AGNs, and the interesting implications for theoretical models. The people involved include my former PhD students T.J. Cox and Patrik Jonsson (who stayed on at UCSC as a postdoc), my current students Greg Novak, Matt Covington, and Christy Pierce, and my former postdoc Jennifer Lotz.

Neutrino Physics Beyond SNO
May 5, 2006 | LASR Conference Room | 12:00 PM
Mark Chen, Queen's University

The Sudbury Neutrino Observatory (SNO) will stop taking data at the end of 2006. The heavy water in SNO will be removed in 2007. What should be done next? By filling SNO with a liquid scintillator (called SNO+) a new, multipurpose detector with diverse physics goals could be a successor. Located in the deepest underground lab, SNO+ would have unique capabilities including detection of pep and CNO solar neutrino. By measuring the flux of pep solar neutrinos, with precision, one can test the neutrino-matter interaction which is sensitive to new physics. SNO+ could also detect geo-neutrinos -- the neutrinos from radioactivity in the Earth -- and is favourably located for such a measurement since it is surrounded by Canadian Shield continental crust, a simple geological configuration. Fundamental questions in geoscience could be addressed by a SNO+ geo-neutrino measurement. Lastly, double beta decay isotopes might be deployed in the liquid scintillator resulting in a competitive next-generation search. The prospects are being studied and SNO+ R&D will be presented.

Mapping the Polarized Sky with WMAP: Methods and Cosmological Implications
May 19, 2006 | LASR Conference Room | 12:00 PM
Olivier Dore, CITA

The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite designed to produce high resolution full sky maps of the temperature and polarization of the cosmic microwave background (CMB). The accurate characterization of the fluctuations in the CMB contains exquisite information about the global structure, composition, and evolution of the universe. Relying on the first three years of observations, WMAP has now measured these fluctuations with unprecedented accuracy. I will illustrate how a greater signal-to-noise in the temperature measurement but also a new large scale polarization signal detection have significantly sharpened our cosmological interpretation. A simple six-parameters cosmological model (flat LCDM); consisting of baryons, dark matter, a cosmological constant, initial perturbation spectrum amplitude and slope, and optical depth; is an excellent fit to the WMAP data, as well as a host of other astronomical experiments. The new WMAP data also hint at a small deviation from scale invariance in the primordial fluctuation power spectrum, a key prediction of inflation. If confirmed this would strengthen our confidence in the inflationary scenario and allow detailed model testing. Besides, the combination of WMAP data and other astronomical data places even stronger constraints on the density of dark matter and dark energy, the properties of neutrinos, the properties of dark energy and the geometry of the Universe.

The Star Formation and Metallicity History of Disk Galaxies: 0
May 26, 2006 | LASR Conference Room | 12:00 PM
Lisa Kewley, University of Hawaii

Observing the star formation rate and chemical abundances since the earliest times in the universe is crucial to understanding galaxy formation and evolution. I present results from (1) our investigation into the H-alpha, infrared, and [OII] star formation rate (SFR) indicators and (2) our recent investigation into the metallicity history of galaxies between redshifts 0
High Resolution Imaging of Cerenkov Light from Air Showers
June 2, 2006 | LASR Conference Room | 12:00 PM
Elizabeth Hays, The University of Chicago and Argonne National Laboratory

Above TeV energies, the cosmic-ray flux becomes prohibitively small for direct observations by balloon-borne detectors. However, large ground-based arrays cannot be used to identity the type of nucleus initiating an air shower on an event-by-event basis and so, the inferences of cosmic-ray composition depend heavily on simulations and have large uncertainties. The Cerenkov emission accompanying an air shower includes light from the primary nucleus passing through the upper atmosphere before the first interaction. This "direct" Cerenkov component is a very fast and compact signal that provides a measurement of the charge of the primary particle using an air Cerenkov telescope with sufficiently high angular and timing resolution. In addition to a precision measurement of composition at TeV energies, the ability to identify the type of particle generating an air shower has potential applications to ground-based gamma-ray observations, where cosmic-rays are a dominant background. The Track Imaging Cerenkov Experiment, TrICE, is a prototype instrument to test the use of a high resolution camera in a Cerenkov telescope and to look for the "direct" Cerenkov component of cosmic-ray-induced air showers. TrICE has been constructed at Argonne National Lab and is currently being commissioned. I will discuss the "direct" Cerenkov measurement and show some of the first data taken with TrICE this Spring.

Digging for new (Astro-)Physics in the old CMB
June 9, 2006 | LASR Conference Room | 12:00 PM
Niayesh Afshordi, Harvard University

The residents of KICP need little reminder that there is much more to CMB than the last scattering surface. The secondary anisotropies, even though a foreground to the high redshift universe, illuminate the nature of different astrophysical processes, and may even open a window to new physics on large scales. I start by summarizing different attempts to detect the Integrated Sachs-Wolfe (ISW) effect, and the constraints that they put on theories of dark energy, or modified gravity, including a theory which may only be distinguished from LCDM through its ISW signature. Turning focus onto small scales, I outline an optimized method to extract the SZ signature of the intracluster medium (ICM) from a low resolution CMB map (such as WMAP), in combination with an X-ray cluster catalog. I then report an 11sigma, model-independent detection of the SZ signal in the WMAP 3yr, and the resulting ICM pressure profile around the virial radius.

The Photometric Properties of the Most Massive, High-Redshift Galaxies
September 29, 2006 | LASR Conference Room | 12:00 PM
Brant Robertson, KICP

The presence of massive galaxies at high-redshifts (z>7) places constraints on hierarchical scenarios for the cosmological formation of structure. By combining high-resolution hydrodynamical simulations of the hierarchical formation of a redshift z~6 quasar, stellar population synthesis models, prescriptions for interstellar and intergalactic absorption, and the photometric response of modern telescopes, we calculate the observable properties of quasar progenitors at high-redshifts. The rapidly star-forming progenitors of z~6 quasars should be detectable using pre-existing photometric selection techniques like those used to identify distant galaxies in the Hubble Ultra Deep Field, but their low number densities will likely require future surveys of large portions of the sky.

Dark Matter in the Neutrino Sector: Sterile Neutrinos
October 6, 2006 | LASR Conference Room | 12:00 PM
Kevork Abazajian, UMD College Park

Hidden in the neutrino sector may be one or more fermions with no standard model interactions that nonetheless couple to neutrinos via their mass generation mechanism, namely sterile neutrinos. Such a particle may be the dark matter, produced in the early universe through matter-suppressed neutrino mixing or matter-enhanced resonant mixing. I will overview the kinetics of relativistic mixed neutrinos in dense environments, and will specify with sterile neutrino dark matter production in the early universe. I will discuss how this candidate alters cosmological structure formation and the resulting constraints from observed cosmological matter clustering. In addition, I discuss how this candidate may be detected by X-ray telescopes, as well as current constraints from X-ray observations.

Can We See Gravitational Waves from the End of Inflation?
October 13, 2006 | LASR Conference Room | 12:00 PM
Eugene Lim, Yale University

We show that, generically, the process of pre/reheating at the end of inflation is potentially a strong source of gravitational waves. We demonstrate numerically that, for a wide class of simple inflationary models, the gravitational wave energy density produced by such processes can be up to 5 orders of magnitude larger than the most optimistic predictions of the usual primordial gravitational wave spectra. This spectrum is scale-dependent, with its peak frequency inversely proportional to the square root of the scale of inflation. We show that for low scale inflation, this power spectrum is potentially detectable by the next generation GW detectors such as LIGO II.

The XENON10 Dark Matter Search and the Promise of Noble Liquids for a Very Large Scale Dark Matter Experiment
October 27, 2006 | LASR Conference Room | 12:00 PM
Tom Shutt, Case Western Reserve University

Current searches for WIMP dark matter, led by the CDMSII experiment, are entering an exciting regime of probing the range of models predicted by supersymmetry. However a full test of the WIMP hypothesis will require a scale up from current experiments at the kg scale to experiments at the ton scale or beyond. Liquid noble gasses are a particularly attractive option, and their properties for dark matter detection are only now beginning to be understood. I will review the status and promise of liquid noble gas-based detectors, report on the status of the XENON10, which has begun underground operations, and discuss the prospects for a truly large-scale dark matter search, particularly within the context of DUSEL (Deep Underground Science and Engineering Laboratory).

Motion of Satellites and Structure of Outer Parts of Galaxies
November 3, 2006 | LASR Conference Room | 12:00 PM
Anatoly Klypin, New Mexico State University

I will discuss results on the distribution of mass in galaxies as measured by the motion of satellites using SDSS. Updated database of SDSS and improved statistical methods allow us to measure the three key properties of the satellites around galaxies: the rms velocity, the shape of line-of-sight distribution, and the angular distribution of the satellites. Using these results, I will put strict constraints the LCDM model and on MOND. The LCDM fits the data remarkably well. This extends the success of the standard model from magaparsecs down to 50kpc. MOND has a unique prediction on those scales, which I will describe in my talk.

Shooting the Moon: Getting Serious About Gravity
November 10, 2006 | LASR Conference Room | 12:00 PM
Tom Murphy, University of California, San Diego

The fundamental incompatibility of quantum mechanics with general relativity together with our well-quantified ignorance of large-scale gravity (dark energy, dark matter) strongly suggests that we intensify our tests of gravity. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is a new project that will bring about order-of-magnitude improvements in testing several fundamental aspects of gravity. Using a 3.5 meter telescope to bounce laser pulses off of the retroreflector arrays left on the moon by the Apollo astronauts, APOLLO is capable of one-millimeter range-precision. By determining the exact shape of the lunar orbit, it will be possible to test the equivalence principle, the time-rate-of-change of the gravitational constant, gravitomagnetism, and geodetic precession to at least ten times better precision than currently tested. In addition, APOLLO will be sensitive to departures from the inverse-square law of gravity and can potentially probe the effects of extra dimensions to which only gravity has access. APOLLO's record-breaking successes thus far will be reported.

New Views of the High-Redshift Universe
November 17, 2006 | LASR Conference Room | 12:00 PM
Peng Oh, University of California, Santa Barbara

Our knowledge of the high-redshift grows apace. I discuss some theoretical interpretation of recent observations of the z~6 universe in quasar absorption lines and high-redshift Lyman-alpha emitters, and implications for the reionization. I then focus on prospects for detection of the high-redshift IGM in 21cm emission, and in particular novel techniques for mining the forthcoming data.

Imprints of Tachyonic Preheating on the CMB
December 1, 2006 cancelled | LASR Conference Room | 12:00 PM
James M. Cline, McGill University


We have recently proven that the fluctuations of a tachyonic field, which arise at the end of hybrid or brane-antibrane inflation, can act as a source of density perturbations at second order in cosmological perturbation theory. This typically results in a very blue (n=4) contamination of the power spectrum at small scales, as well as nongaussianities. The effect gives rise to powerful new constraints on the parameter space of hybrid-like inflation models, as well as the possibility of new features in the power spectrum.