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Winter 2013

 

Date Speaker Title Abstract
Jan 16 Josef Pradler
(JHU)
Rare Event Searches underground: New physics opportunities and old claims

A diversification of the physics output in many existing rare event searches is possible. In this talk I will present theoretical scenarios of the hidden sector with an emphasis of their test in direct detection and neutrino experiments. I will show how DM multiplets can be probed in searches for the neutrinoless double beta decay and how, in turn, new forces in the neutrino sector can be tested in DM experiments. In a second part of the talk, the DAMA claim for a positive detection of Dark Matter in the laboratory will be scrutinized and comments on recent arXiv activity will be offered.

Jan 23 Susanne Westhoff
(Pitt)
The Top-Quark Charge Asymmetry with a Jet Handle

Top-quark physics provides us with a portal to potential physics beyond the Standard Model. To date, the only evidence of an anomaly in top-quark physics is the large forward-backward asymmetry observed at the Tevatron. Shedding light on this anomaly by measuring a charge asymmetry at the LHC, however, is a difficult endeavor. I will discuss the prospects to observe a charge asymmetry in top-antitop production in association with an energetic jet. This "jet handle" can further help to discriminate between new-physics scenarios that attempt to explain the Tevatron anomaly.

Jan 30 Andrea Puhm Black holes, fuzzballs and firewalls

The information paradox and the infall problem have been long-standing puzzles in the understanding of black holes. The idea of free infall is in considerable tension with unitarity of the evaporation process and recent developements have made this tension sharp. In the first part of my talk I will address the information question and argue that unitarty requires every quantum of radiation leaving the black hole to carry information about the initial state. Unitary evaporation is thus inconsistent with an information-free horizon at every step of the evaporation process. This immediately raises the question of what the required horizon-scale structure is? I will show an explicit construction of near-extremal black hole microstates which put flesh and branes on the fuzzball proposal and may realize firewalls in string theory. Finally I will address the question of what happens to an observer falling into a fuzzball.

Feb 6 Matthew Gonderinger
(Wayne State)
Vacuum Stability, Standard Model Extensions, and the 125 GeV Higgs

Though the discovery of a 125 GeV candidate Higgs boson resolves the origin of electroweak symmetry breaking, questions remain regarding physics beyond the Standard Model, the energy scale associated with new physics, and the nature of dark matter. I will discuss several extensions of the Standard Model (scalar singlets, a type-2 seesaw mechanism scalar triplet, electroweak multiplets, and an extra U(1) gauge symmetry) that address these questions. In the Standard Model and these extensions, the question arises whether or not the very minimum of the scalar potential responsible for electroweak symmetry breaking is stable up to the fundamental Planck energy scale. My research into the vacuum stability of these models provides insight into the new physics, the energy scale, and the composition of dark matter.

Feb 20 Jennifer Kile
(Northwestern)

Dark Matter from Weak Polyplets

We investigate the possibility of new fermion multiplets charged under the Standard Model gauge group, with the aim of obtaining a possible dark matter candidate. These new fermions are charged under SU(2)xU(1); their quantum numbers are determined by requiring anomaly cancellation and insisting that all new particles become massive via Yukawa couplings with the SM Higgs boson. Constraints from colliders, electroweak precision measurements, and DM direct detection are considered. We find that this model can accommodate a viable DM candidate in the case of large Higgs mass; for a Higgs mass of 125 GeV, a subdominant DM contribution can be achieved.

Feb 27 Daniel Harlow Quantum Computation vs. Firewalls

Almheiri, Marolf, Polchinski, and Sully (AMPS) have recently argued that unitary of black hole evaporation is inconsistent with a smooth horizon as seen by an infalling observer. In this talk I briefly review their argument and then discuss recent work with Patrick Hayden, in which we argue that due to quantum computational restrictions the type of thought experiment used by AMPS to motivate their setup cannot be done in practice.

Mar 13 Dmitry Zhuridov
(Wayne)
Neutrino Masses and Leptogenesis from Extra Fermions

The observable nonzero neutrino masses and baryon asymmetry of the Universe cannot be explained within the minimal Standard Model of particle physics and cosmology. However many Standard Model extensions generate both the baryon asymmetry through Leptogenesis (LG) and the neutrino masses . The model independent upper bound on the CP asymmetry relevant for LG with hierarchical heavy neutrinos is called Davidson-Ibarra bound. I will revise it and show that in the case of one massless neutrino this bound essentially depends on the type of the light neutrino mass hierarchy. I will give the classification of LG scenarios according to the new fermion mass spectra, and discuss resonant scenarios, which help to avoid the problem of too high reheating temperature in the early Universe. In particular, I will introduce freed LG, which violates Davidson-Ibarra bound in a special class of models.

Mar 20 Phil Szepietowski Comments on a-maximization from gauged supergravity

In this talk I will discuss the holographic realization of a-maximization in five-dimensional gauged supergravity. After reviewing the relevant details of the holographic description of a-maximization, I will discuss its application to a particular consistent truncation of M-theory to five-dimensional gauged supergravity. This theory contains AdS_5 solutions which are dual to SCFTs arising as the IR limit of M5-branes wrapped on Riemann surfaces and I will illustrate how one can use holographic techniques to determine the U(1)_R symmetry.

Mar 27 Jim Halverson
(KITP)
Stringy Hidden Valleys

Gauge theories arising from the compactification of string / F / M-theory are strongly constrained due to consistency conditions on topological data; for example, rk(G) can be bounded and the representation theory is limited. I will discuss constraints on chiral matter spectra which are necessary for string consistency but go beyond those necessary for the cancellation of gauge anomalies. The differences between string constraints and QFT constraints can be understood in terms of transitions in the landscape. I will argue that they provide a useful, perhaps new, guiding principle for physics beyond the standard model. As a rich example, I will present a class of models where quasi-hidden sectors are added to fix otherwise inconsistent MSSM quivers. We have dubbed these models "Stringy Hidden Valleys," and happily they exhibit a number of generic features. These features include new electroweak multiplets, an anomalous U(1) symmetry which protects messenger masses and has strong consequences for superpotential couplings, a rich phenomenology of heavy and light Z' bosons, and axionic couplings required for anomaly cancellation. I will discuss possibilities for dark matter and supersymmetry breaking in light of these generic features.

Apr 3 Anson Hook
(IAS)
Learning how to Count

We introduce a search technique that is sensitive to a broad class of signals with large final state multiplicities. Events are clustered into large radius jets and jet sub- structure techniques are used to count the number of subjets within each jet. The search consists of a cut on the total number of subjets in the event as well as the summed jet mass and missing energy. Two different techniques for counting subjets are described and expected sensitivities are presented for eight benchmark signals. These signals exhibit diverse phenomenology, including 2-step cascade decays, direct three body decays, and multi-top final states. We find improved sensitivity to these signals as compared to previous high multiplicity searches as well as a reduced re- liance on missing energy requirements. One benefit of this approach is that it allows for natural data driven estimates of the QCD background.

Apr 10 Constantinos Papageorgakis
(Rutgers)
On the (2,0) theory and 5D SYM

We will review the connection between the six-dimensional (2,0) theory and maximally supersymmetric Yang-Mills in five dimensions (MSYM). We will discuss the implications of a conjectured relation between the two, at all energy scales, for MSYM. We will also deconstruct MSYM from a four-dimensional circular quiver gauge theory and consider the possibility of instanton-solitons contributing to perturbative amplitudes.

Apr 24 Benson Way
(UCSB)
Black Funnels

The Hartle-Hawking state of N=4 SYM at strong coupling and large N on a fixed black hole background has two proposed gravitational duals: a black funnel or a black droplet. We construct the black funnel solutions that are dual to the Hartle-Hawking state on a Schwarzschild black hole and on a class of three-dimensional asymptotically flat black hole backgrounds. We compute their holographic stress tensor and argue for the stability of these solutions.