N(uclear) P(article) A(strophysics) C(osmology) Forum

Coordinates: 4274 Chamberlin, 4 PM, Thursdays

Spring, 2008

March 6
Stuart Raby
(Ohio) Title: The Heterotic Road to the MSSM
Abstract: String theory has been around for over 30 years. The string vacuum determines the spectrum of states and gauge interactions of the low energy theory. Some talk about on the order of 10^{300} vacua for string theory, BUT to date there are only a handfull of candidate vacua which look anything like our observed low energy world. In this talk I will discuss a new strategy for finding the minimal supersymmetric standard model in the immense string landscape.

March 13
Bradford Benson
(UC Berkeley) Title: Finding Clusters of Galaxies Using the South Pole Telescope
Abstract: The South Pole Telescope (SPT) is a 10 meter diameter millimeter wavelength telescope located at the South Pole. It's primary science project is to conduct a 4000 square degree survey to find clusters of galaxies via the Sunyaev-Zel'dovich (SZ) effect, the inverse Compton scattering of the CMB off of hot intra-cluster gas. An SZ survey of this size should find several thousand galaxy clusters, which can in principle place interesting constraints on the dark energy density and equation of state, as well as produce a host of other secondary science results (e.g. - measurements of small scale primary and other secondary CMB anisotropies, gravitational lensing of the CMB, point source catalogs at millimeter wavelengths, ...). To achieve this required over an order of magnitude increase in mapping speed over previous generation millimeter wavelength receivers, and was accomplished with the development of a 960 element large format bolometer array. I will discuss the design and construction of the SPT receiver, SPT's current project status, which recently began its second year of observations, and future plans for the SPT.

March 27
Pat Slane
(Harvard) Title: Particle Acceleration in Supernova Remnant Shocks
Abstract: Based on the overall energy budget and recurrence rate, supernova remnants have long been considered as prime candidates for the production of cosmic rays up to the "knee" of the spectrum. Fast shocks are believed to generate energetic particles through diffusive shock acceleration, wherein self-generated waves act to scatter particles and introduce multiple interactions with the shock front. However, direct evidence of such high energy particles in SNRs has been observed only over the past decade or so, and evidence for the acceleration of hadrons remains controversial. Here I summarize recent results from X-ray studies of young SNRs that show distinct signatures of multi-TeV electrons, as well as dynamical evidence for hadron acceleration. Using results of hydrodynamical simulations, I will summarize the effects of efficient particle acceleration on the evolution of SNRs, and will investigate the signatures expected from gamma-ray observations of these remnants.

March 28
Joint seminar with Pheno
Xiangdong Ji
(University of Maryland) Title: Scale of Left-Right Symmetry from CP-violating Observables
Abstract: In this talk, I consider the minimal left-right symmetric model at TeV scale. The right-handed quark mixing is solved in terms of the usual CKM parameters and the single spontanous CP-violating phase angle. I will constrain the symmetry scale and the spontaneous CP phase from low-energy CP-violating observables, including the neutron electric dipole moment.

April 3
Carter Hall
(University of Maryland) Title: Searching for double beta decay with the Enriched Xenon Observatory
Abstract: An observation of neutrinoless double beta decay would have profound consequences for our understanding of the lepton sector of the standard model. Double beta decay is only allowed if the neutrino and anti-neutrino are identical, which is a basic prediction of many extensions of the standard model, including many grand unified theories. Secondly, double beta decay could shed light on the scale of the neutrino mass spectrum. The EXO collaboration is developing sensitive searches for the double beta decay of Xenon-136. Our first experiment, EXO-200, is rapidly being constructed, and will be by far the largest double beta decay experiment ever attempted. We are also pursuing R&D to realize a system to tag the daughter barium nucleus of the decay using the techniques of single-ion spectroscopy. This would eliminate all conventional backgrounds, resulting in an ideal experiment.

April 10
Marco Peloso
(University of Minnesota) Title: The role of SUSY flat directions in reheating
Abstract: Reheating after inflation describes all the particle physics processes occurring from the decay of the inflaton up to the establishment of thermal equilibrium. Due to the strong model dependence, it is one of the most unknown stages in the history of the universe. It has been argued that SUSY flat directions are naturally excited during inflation, and that they slow down the thermalization of the inflaton decay products by providing a large effective mass to the fields they are coupled to. We discuss a nonperturbative decay channel for the flat directions which has been generally overlooked in the literature. It typically leads to a quick decay of the flat directions, and, consequently, to a suppression of their delaying effect for thermalization.

April 11
Joint seminar with Pheno
Location:
5280 Chamberlin
Time: 2:30 Kalliopi Petraki
(UCLA) Title: Dark-matter sterile neutrinos from decays of a gauge-singlet Higgs
Abstract: Sterile neutrinos are usually introduced to explain the masses of active neutrinos. If one of these fermions has mass of several keV, it can also account for the cosmological dark matter. The same particle can explain the observed velocities of pulsars, speed up the formation of the first stars and stir up supernova explosions. I will describe a mechanism for sterile neutrino production that involves a minimal extension of the Higgs sector by a gauge-singlet scalar. The relic abundance of sterile neutrinos is produced from decays of the singlet Higgs and does not depend on their mixing angle. The resulting dark matter is colder than the warm dark matter produced in neutrino oscillations. I will discuss the small-scale structure formation properties of these neutrinos and show that they comply with current observations. The presence of the gauge singlet in the Higgs sector has important implications for the electroweak phase transition, baryogenesis, and the upcoming experiments at the LHC.

April 17
Maxim Perelstein (TBC)
(Cornell University)
Title: Colliders to the Cosmos: Dark Matter and Electroweak Phase Transition
Abstract: Experiments at the Large Hadron Collider (LHC) will begin in the second half of this year. This machine, along with the proposed International Linear Collider (ILC), will directly probe physics at the TeV energy scale. The discoveries and measurements made by these experiments can have interesting implications for cosmology. I will discuss two examples of this connection. First, if dark matter is composed of weakly interacting massive particles, these particles may be directly produced and studied at the LHC and the ILC. Second, precise measurements of the Higgs boson properties may allow us to understand the dynamics of the electroweak phase transition in the early universe, with important implications for baryogenesis. In both cases, I will stress the aspects of the connection that do not depend on the (presently unknown) details of the fundamental theory at the TeV scale.

April 24
Vincenzo Cirigliano
(Los Alamos) Title: Minimal Flavor Violation: from quarks to leptons
Abstract: In this talk I discuss the formulation of the "minimal flavor violation" hypothesis in the lepton sector. I then construct the relevant low-energy effective field theory and analyze the phenomenological signatures of this scenario.

April 25
Joint seminar with Pheno
Location:
5280 Chamberlin
Time: 2:30 Chris Lee
(LBL) Title: Disentangling the Strong Interactions in Two-Jet Event Shapes
Abstract: Event shapes characterize hadronic final states produced in e+ e- collisions. The two-jet kinematic endpoint of event shape distributions is particularly sensitive to the nonperturbative effects of hadronization. Soft-collinear effective theory provides the tools to factorize event shape distributions in the two-jet region into perturbatively-calculable and nonperturbative contributions. From the resulting factorization theorem we can deduce the extent to which these nonperturbative contributions are universal across different event shapes.

May 1
Bira van Kolck
(University of Arizona)

May 8
Tom Crawford
(University of Chicago)

May 7
Joint seminar with Pheno
Eung Jin Chun
(KIAS)

May 15
Krishna Kumar
(University of Massachusetts)

May 16th
Joint Seminar with Pheno Christian Bauer
(LBL)

Fall, 2007

 

Date	Speaker	Title + Abstract
October 04	Michael Ramsey-Musolf  (UW-Madison)	Title: Baryogenesis, Electric Dipole Moments, and the Higgs Boson Abstract: Explaining the predominance of visible matter over antimatter remains one of the outstanding puzzles at the interface of cosmology with particle and nuclear physics. Although the Standard Model cannot account for the matter-antimatter asymmetry, new physics at the electroweak scale may provide the solution. In this talk, I discuss the general requirements for successful electroweak scale baryogenesis; recent theoretical work in computations of the matter-antimatter asymmetry; and implications for experimental searches for permanent electric dipole moments of the electron and neutron and for the Higgs boson at future colliders.
October   16 Special Location: 5280 Chamberlin Special Time: 2:30pm	Philip Mannheim  (U. Conn.)	Title: Dark Matter and Dark Energy - Fact or Fiction? Abstract: We show that the origin of the dark matter and dark energy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the induced global one which is effective for cosmology being altogether weaker than the induced local one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then the cosmological constant problem is solved not by quenching the cosmological constant itself but rather by quenching the amount of gravity that it produces. With the conformal theory having recently been shown by Bender and Mannheim to be a consistent theory of gravity at the quantum level, it is thus offered as a four-dimensional alternative to ten-dimensional string theory.
October 18	Dan Hooper  (Fermilab)	Title: Dark matter annihilations in the WMAP sky Abstract: The WMAP experiment has revealed an excess of microwave emission from the region around the center of our Galaxy. It has been suggested that this signal, known as the "WMAP Haze", could be synchrotron emission from relativistic electrons and positrons generated in dark matter annihilations. In particular, the angular distribution of the WMAP Haze matches the prediction for dark matter annihilations with a cusped density profile. Comparing the intensity in different WMAP frequency bands, a wide range of possible WIMP annihilation modes are consistent with the spectrum of the haze for a WIMP with a mass in the 100 GeV to multi-TeV range. Most interestingly, in order to generate the observed intensity of the haze, the dark matter annihilation cross section is required to be approximately equal to the value needed for a thermal relic, sigma v ~ 3 x 10^-26 cm^3/s. No boost factors are required. If dark matter annihilations are in fact responsible for the WMAP Haze, then the upcoming GLAST experiment is expected to detect gamma rays from the dark matter annihilations in the Galactic Center.
October 25	Shin'ichiro Ando  (Caltech)	Title: GeV gamma-ray astrophysics: Probe of high-energy astrophysical objects and dark matter Abstract: In the next decade, GLAST will reveal the high-energy universe with GeV photons. Various physics is involved there, ranging from the particle acceleration in ordinary astrophysical objects to exotic mechanisms predicted by some particle physics models. I will discuss several aspects of and implications for this GeV gamma-ray astrophysics/cosmology, focusing on blazars, galaxy clusters, gamma-ray bursts, and dark matter annihilation.
November 29 Special Location: 5310 Chamberlin	Juan Collar  (University of Chicago)	Title: Something Old, Something New Abstract: We'll discuss two initiatives in astroparticle and neutrino physics at the University of Chicago, both sharing in common the revival and deep revision of old technologies to address new experimental challenges. COUPP employs ultra-stable heavy liquid bubble chambers to search for WIMP dark matter. First results leading to improved limits on spin-dependent WIMP couplings will be presented, together with the most recent progress. COGENT aims at the detection of very faint (~100 eV) signals in detectors massive enough to allow searches for rare processes, using our recently developed p-type point contact (ppc) Germanium detectors. The broad range of applications (coherent neutrino scattering, light WIMP searches, double-beta decay) available for these new semiconductor devices will be described, as well as the status of an upcoming reactor (anti)neutrino experiment.
December 6	Stefan Westerhoff  (University of Wisconsin-Madison)	Title: New Results from the Pierre Auger Observatory Abstract: The Pierre Auger Observatory in Malargue, Argentina, is the world's largest detector for the study of the origin of ultrahigh energy cosmic rays. The experiment stretches over 3000 km^2 and measures cosmic rays with energies above 10^18 eV using two complementary detector types: an array of 1600 particle detectors on the ground, and 4 fluorescence detectors overlooking the ground array from the periphery. The observatory is now nearing completion, but scientific data taking started at the beginning of 2004. Since then, the Observatory has detected about 80 events above 40 EeV. The analysis of the data shows first indications that the arrival direction distribution of the highest energy cosmic rays is not isotropic, but might be associated with the positions of nearby extragalactic objects. In this talk, I will review recent results from the first few years of data taking, with a special emphasis on the arrival direction of the highest energy cosmic rays and their possible correlation with known astrophysical sources.
December 13	Cheng-Pang Liu  (University of Wisconsin-Madison)	Title: Tests of Parity and Time-Reversal Violation in Nuclear and Atomic Systems Abstract: Nuclear and atomic systems, which provide a great variety of selection rules and many-body enhancement, are powerful testing grounds for fundamental symmetries. In this talk, I will overview the current status and future effort on the tests of parity (scattering asymmetry, anapole moment, etc.) and time-reversal symmetries (permanent electric dipole moment, etc.), and discuss the theoretical work to be done for elucidating the underlying particle physics, either within or beyond the Standard Model.

Last updated 04/11/08

Organizer: Björn Garbrecht (bjorn@physics.wisc.edu)