Weekly on Friday 11:30 am - 12:30 pm, at PRB M2005

COMING UP!

Fall 2015

11:30 am, Friday, Nov 20th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Peter Denton (Vanderbilt)

Title:Cosmic Ray Anisotropy with Partial Sky Exposure

Abstract: UHECRs are the highest energy particles in the universe, yet very little is known about them. Their composition, sources, acceleration, and propagation details are all wholly unknown. The first step to addressing this problem is determining the sources, which requires measuring an anisotropy. Above $E\sim55$ EeV, anisotropies are expected to appear due to the GZK horizon, yet no definitive signal has been seen. Here I overview the current experimental status and present a discussion of anisotropy reconstruction techniques, along with their strengths and weaknesses. I use spherical harmonics as a general tool to detect large scale anisotropies in a low statistics environment. I compare the benefits of a full sky experiment such as JEM-EUSO to ground based partial sky experiments such as the Pierre Auger Observatory and Telescope Array. I show that while Auger can reconstruct a quadrupole without a partial sky penalty, partial sky exposure generally leads to a loss of precision beyond that just from lower statistics compared to a full sky experiment.

11:30 am, Friday, Nov 6th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Tathagata Ghosh (TAMU)

Title: Limits on cascade annihilation models and decaying dark matter lifetime from dwarf galaxies using Fermi-LAT

Abstract: Dwarf spheroidal galaxies are promising targets for the indirect detection of dark matter through gamma-ray emission due to their proximity, lack of astrophysical backgrounds and high dark matter density. They are often used to place restrictive bounds on the dark matter annihilation cross section. Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation models, we review the compatibility of the dark matter interpretation of the Fermi-LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies using six years of Fermi-LAT data. In addition, we present the analysis of data from 20 Dwarf Spheroidal galaxies and derivation from a stacked analysis, robust 95% confidence level upper limits on the dark matter lifetime for several decay channels and dark matter masses between 10 GeV and 10 TeV.

11:30 am, Friday, Oct 30th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Gregory Dooley (MIT)

Title: The effect of Self-Interacting Dark Matter on tidal stripping in satellite galaxies and the galactic halo

Abstract: Observations of low surface brightness galaxies, low mass spiral galaxies, and Miky Way dwarf
spheroidals indicate that the central density of galaxies is lower than predicted in pure CDM simulations.
Self-interacting dark matter offers one possible explanation to the formation of low density cores in galactic
halos. Particles are allowed to elastically scatter, and in the higher density central regions of galaxies, an
increased scattering rate tends to drive out mass, transforming cusps into cores. Motivated by the lower
binding energy of cores vs. cusps, we investigate the effect that SIDM has on the tidal stripping of mass
in satellite galaxies around a Milky Way analog. Using n-body, dark matter only simulations of four different
models of SIDM, two of constant cross section and two with a velocity-dependent cross section, we
demonstrate that while the stripping of total bound dark matter mass is not significantly affected by permitted
SIDM models, the the stellar mass loss rate is appreciably increased. This implies a depression in the
satellite luminosity function in halos that pass within 50 kpc of their host. I will also present results that
differentiate the models which need further investigation.

11:30 am, Friday, Oct 23rd at PRB M2005 (Price Place)

11:30 am, Friday, Oct 9th at PRB M2005 (Price Place)

Special Seminar 1
Speaker: Basudeb Dasgupta ( Tata Institute of Fundamental Research )

Title: Neutrino Flavor Conversion at Very High Density
Abstract:
We show that the flavor content of a dense gas of neutrinos is
unstable to small oscillations in time. The tendency is to equilibrate
the fluxes and and spectra of all flavors. We argue that this can
happen at very high neutrino and matter densities, i.e., deeper
in a supernova than previously realized, and may have profound
consequences for core-collapse supernovae.

Special Seminar 2
Speaker: Rebecca Leane ( University of Melbourne )

Title: Dark Matter at the LHC
Abstract:
In this talk I consider several issues faced by WIMP dark matter searches.
Firstly, I discuss the popular use of effective field theories (EFTs) to quantify
LHC bounds on dark matter, and show that some EFT operators considered
do not respect the weak gauge symmetries of the standard model. These
operators break down at the electroweak scale, rather than the energy scale
of new physics, and are invalid at LHC energies. I consider the circumstances
in which such operators can arise, use the mono-W process to illustrate
potential issues in their interpretation and application, and discuss the
phenomenology of a UV complete model that avoids such difficulties. In addition,
as the WIMP parameter space is becoming increasingly constrained, I discuss
the phenomenology of a simple leptophilic dark matter model, where the absence
of tree-level dark matter couplings to quarks can relax the strong limits placed

11:30 am, Friday, Oct 2nd at PRB M2005 (Price Place)

11:30 am, Friday, Sept 25th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Prof. Jure Zupan (University of Cincinnati)

Title: Some thoughts on Higgs portal to dark matter
Abstract: In the talk I will cover two aspects of Higgs portal dark
matter: the effect of non-standard Higgs Yukawa couplings, and
the searches for the mediators that need to be present in the
case of fermionic dark matter.

Papers of interests this week:

11:30 am, Friday, Sept 18th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Joshua Yao-Yu Lin (National Taiwan University)

Title:  Impact of Gravitational Slingshot of Dark Matter on Galactic Halo Profiles
Abstract:
We study the impact of gravitational slingshot effect from massive astrophysical
objects (e.g. stars, black holes) on the distribution of cold dark matter in Milky Way
sized galaxies and dwarf galaxies. Multiple gravitational encounters of a lower mass
dark matter particle with massive astrophysical bodies would lead to an average
energy gain for the dark matter, similar to second order Fermi acceleration.
We calculate the average energy gain and model the integrated effect on the dark matter profile.
We find that such slingshot effect due to the intermediate mass black holes in
dwarf galaxies were significant in certain cases, which changes the dark matter distribution
at the galactic center and several alleviate small scale problems of cold dark matter.

Papers of interests this week:

11:30 am, Friday, Sept 11th at PRB M2005 (Price Place)

Special Seminar
Time: 11:30- 12:00
Speaker: Debtosh Chowdhury (INFN)

Title:  Dark Matter Annihilation to Fermions and a Photon
Abstract:
We know from recent analyses that the inclusion of electroweak corrections can alter significantly
the energy spectra of Standard Model particles originated from dark matter annihilations. We are
interested in the process where radiation of photon has a significant contribution, in particular,
where Majorana dark matter particle annihilate into a pair of light fermion. This process is helicity suppressed.
The inclusion of photon radiation removes the p-wave suppression. We study this effect in detail using
effective operators responsible for this process. We put bound on the effective operators considered from
indirect dark matter searches and compare them with the bounds obtained from the direct and collider searches.

Papers of interests this week:

Summer 2015

11:30 am, Friday, July 10th at PRB M2005 (Price Place)

Special talk by Carsten Rott (Sungkyunkwan University, Korea)

Search for Dark Matter in the Sun

Abstract:
 Dark Matter could be detected indirectly through the observation of neutrinos produced in self-annihilations or decays. Searches for such neutrino signals have resulted in the most stringent constraints on the lifetime of superheavy dark matter and world bests limits on spin-dependent scattering with matter. In recent years these searches have made significant progress in sensitivity through new search methodologies, new detection channels, and through the availability of rich datasets, foremost from the IceCube Neutrino Telescope. In this talk I will focus on the detection prospects for dark matter captured in the Sun by current and next-generation neutrino detectors.

11:30 am, Friday, May 29th at PRB M2015 (the Seminar Room)

Special talk (1) by Yoshiyuki Inoue (ISAS/JAXA)

Probing the nature of AGN coronae through future X-ray and sub-mm observations

Abstract:
 While the cosmic X-ray background is likely to originate from individual AGNs, the origin of the cosmic MeV gamma-ray background is not fully understood. We proposed that AGNs having non-thermal electrons in coronae may explain the MeV background. Such non-thermal electrons are expected to exist if a corona is heated by magnetic reconnections. However, the sensitivity of current MeV gamma-ray instrument is not sufficiently good to detect the expected power-law tail in the MeV band from individual AGNs. Furthermore, the heating mechanism of coronae in AGNs is still unknown, although magnetic reconnection heating is one possibility.  In this talk, I would like to introduce how we can probe the origin of the MeV background and the nature of AGN coronae such as magnetic field and non-thermal content through future observations by ASTRO-H and ALMA.

Special talk (2) by Irene Tamborra (GRAPPA)

High energy neutrinos from extra-galactic astrophysical sources

Abstract:
 The IceCube neutrino telescope recently discovered a flux of astrophysical neutrinos with energies up to few PeV.  In light of the new born high-energy neutrino astronomy era, I will discuss the expected high-energy neutrino emission from extra-galactic astrophysical sources as well as our chances to unveil the physics of the cosmic accelerators by employing neutrinos and their photon counterparts.

11:30 am, Friday, May 22th at PRB M2005 (Price Place)

Special talk (1) by Scott Adams (OSU)

Not with a Bang, but a Whimper: Evidence for Low-energy Supernovae

Abstract:
 I will present new HST and Spitzer late-time imaging of SN 2008S and NGC 300-OT,the prototypes of a class of stellar transients whose true nature is debated. Bothobjects have faded below the luminosity of their progenitors and are now undetectedin both the near and mid-IR, providing strong evidence that these events wereterminal. This, combined with the mass constraints on the progenitors, indicates thatthis class of transients likely arise from electron-capture supernovae.

Special talk (2) by Kimberly Boddy (University of Hawaii)

Indirect Detection of Dark Matter Using MeV-Range Gamma-Ray Telescopes

Abstract:
 The astrophysics community is considering plans for a variety of gamma-ray telescopes in the energy range 1--100 MeV, which can fill in the so-called "MeV gap" in current sensitivity. We investigate the utility of such detectors for the study of low-mass dark matter annihilation or decay. For annihilating (decaying) dark matter with a mass below about 140 MeV (280 MeV) and couplings to first generation quarks, the final states will be dominated by photons or neutral pions, producing striking signals in gamma-ray telescopes. We determine the sensitivity of future detectors to the kinematically allowed final states. In particular, we find that planned detectors can improve on current sensitivity to this class of models by up to a few orders of magnitude.

11:30 am, Friday, May 15th at PRB M2005 (Price Place)

Special talk by Ilias Cholis (Fermilab)

The Fermi Galactic Center excess

Abstract:
 The possible gamma-ray excess in the inner Galaxy and the Galactic center suggested by Fermi-LAT observations has triggered great interest in the astro-particle physics community. Among its various interpretations have been WIMP dark matter annihilations, gamma-ray emission from a population of millisecond pulsars, or emission from cosmic rays injected in a sequence of burst-like events or continuously at the GC. Given that the galactic diffuse emission is the dominant (by an order of magnitude or more) at any direction greater than 2 degrees from the GC understanding the background systematics has been a vital missing piece in the discussion. I will present the first comprehensive study of model systematics coming from the Galactic diffuse emission in the inner part of our Galaxy and their impact on the inferred properties of the excess emission at Galactic latitudes between 2 and 20 degrees and energies 300 MeV to 500 GeV. I will show both theoretical and empirical model systematics, which are deduced from a large range of Galactic diffuse emission models and a principal component analysis of residuals in numerous test regions along the Galactic plane. The hypothesis of an extended spherical excess emission with a uniform energy spectrum is compatible with the Fermi-LAT data in the region of interest at 95% CL.  Assuming that this excess is the extended counterpart of the one seen in the inner few degrees of the Galaxy, a lower limit of 10 degrees (95% CL) can be derived on its extension away from the GC.  In light of the large correlated uncertainties that affect the subtraction of the Galactic diffuse emission in the relevant regions, the energy spectrum of the excess is equally compatible with both a simple broken power-law of break energy 2.1 $\pm$ 0.2 and with spectra predicted by the self-annihilation of dark matter, implying in the case of $\bar{b}b$ final states a dark matter mass of 49$^{+6.4}_{-5.4}$ GeV. I will also briefly discuss interpretations of this excess, based on annihilating DM, leptonic CR outburst and a population of millisecond pulsars.

Spring 2015

11:30 am, Friday, May 8th at PRB M2005 (Price Place)

11:30 am, Friday, May 1st at PRB M2005 (Price Place)
Special talk by Walter Winter (DESY Zeuthen, Germany)

Interpretation of IceCube results in the multi-messenger context

The discovery of high-energetic cosmic neutrinos is one of the recent
major breakthroughs in science. We discuss the concept of the neutrino
production, and interpret recent results taking into account the
information from other messengers (gamma-rays, cosmic rays). For
example, one question is if these neutrinos come from the most powerful
accelerators in the universe, i.e., the ones which can accelerate cosmic
rays to the highest observed energies. We also discuss future
perspectives for neutrino astronomy.

11:30 am, Friday, April 24th at PRB M2005 (Price Place)
Special talk(~30 mins) by Laura Lopez (CfA, Harvard)

Observational Tests of Cosmic-ray Diffusion in the Magellanic Clouds

Cosmic rays (CRs) play an important role in the interstellar medium: they ionize
dense molecular gas, they are responsible for the light elements in the periodic
table, and they account for 20% of the ISM energy budget. However, the means
by which CRs are first accelerated and then transported through external
galaxies are not well understood. I will present results from a recent study of the
Magellanic Clouds to constrain CR transport using Fermi gamma-ray
observations. I will show how we have characterized the spatial distribution of
gamma rays in the LMC and SMC and used the findings, in conjunction with
available multiwavelength data, to constrain CR transport based on how the
emission depends on physical parameters, such as gas density, massive star
formation, magnetic field structure, and turbulence properties.

AstroParticle lunch paper list:

12:30 pm, Friday, April 10th at PRB M2005 (Price Place)

Special talk!

Sam Stafford (OSU)
Analysis Interferometry of the Antarctic Impulse Transient Antenna (ANITA)

Ultra-high energy (UHE) neutrinos may facilitate observation of sources in the
remotest parts of the universe.  A flux of UHE (E > 10^18eV) neutrinos is expected
from interaction of UHE cosmic rays with the cosmic microwave background.
The Antarctic Impulse Transient Antenna (ANITA) campaign is a NASA Long-duration
balloon mission searching for coherent radio emission induced by ultra-high energy
neutrinos interacting in the Antarctic ice, as well as by UHE cosmic ray particle
cascades in the air.  The third ANITA flight began in December 2014 and lasted
for 22 days.  I give a general description of the ANITA-III payload and flight, and
present analysis methods to be used in identifying and localizing radio pulse events.