Transition Pathways Connecting Stable and Metastable Phases
An-Chang Shi McMaster University
PIRSA:13120010
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Monte Carlo Field-Theoretic Simulations Applied to Block Copolymer Melts
Mark Matsen University of Waterloo
PIRSA:13120009 -
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The Planet Within: Caves from Earth to Mars and Beyond
Penelope Boston National Cave and Karst Research Institute
PIRSA:13120045 -
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The Galactic Real Estate Market: The Physics and Chemistry of Habitability
Penelope Boston National Cave and Karst Research Institute
PIRSA:13120044 -
Jets Without Jets
Daniele Bertolini Massachusetts Institute of Technology (MIT)
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Quantum Mechanics as Classical Physics
Charles Sebens University of Michigan–Ann Arbor
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Fully exploring exotic production of the 125 GeV Higgs
Felix Yu Fermi National Accelerator Laboratory (Fermilab)
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13/14 PSI - Condensed Matter - Lecture 15
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Anushya Chandran Perimeter Institute for Theoretical Physics
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Roger Melko University of Waterloo
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Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
PIRSA:13110045 -
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Transition Pathways Connecting Stable and Metastable Phases
An-Chang Shi McMaster University
PIRSA:13120010Phase transitions are ubiquitous in nature. Understanding the kinetic pathways of phase transitions has been a challenging problem in physics and physical chemistry. From a thermodynamics point of view, the kinetics of phase transitions is dictated by the characteristics of the free energy landscape. In particular, the emergence of a stable phase from a metastable phase follows specific paths, the minimum energy paths, on the free energy landscape. I will describe the characteristics of the minimum energy paths and introduce an efficient method, the string method, to construct them. I will use self-assembled phases of block copolymers as examples to demonstrate the power of the method. In particular, I will show how precisely determined transition pathways provide understanding and surprises when we try to connect the different ordered phases of block copolymers. -
Monte Carlo Field-Theoretic Simulations Applied to Block Copolymer Melts
Mark Matsen University of Waterloo
PIRSA:13120009Monte Carlo field-theoretic simulations (MC-FTS) are performed on melts of symmetric diblock copolymer for invariant polymerization indexes extending down to experimentally relevant values of N=104. The simulations are performed with a fluctuating composition field, W-(r), and a pressure field, W+(r), that follows the saddle-point approximation. Our study focuses on the disordered-state structure function, S(k), and the order-disorder transition (ODT). Although short-wavelength fluctuations cause an ultraviolet (UV) divergence in three dimensions, this is readily compensated for with the use of an effective Flory-Huggins interaction parameter, ce. The resulting S(k) matches the predictions of renormalized one-loop (ROL) calculations over the full range of ceN and N examined in our study, and agrees well with Fredrickson-Helfand (F-H) theory near the ODT. Consistent with the F-H theory, the ODT is discontinuous for finite N and the shift in (ceN)ODT follows the predicted N-1/3 scaling over our range of N. -
O Topology
Randall Kamien University of Pennsylvania
PIRSA:13120008Yes, quite. But also with some applications. -
The Planet Within: Caves from Earth to Mars and Beyond
Penelope Boston National Cave and Karst Research Institute
PIRSA:13120045We can set foot on faraway planets, in a sense, by exploring the world beneath our
feet. Underground caves provide unique insights into what we might find beneath
alien landscapes. We are studying caves on Earth to understand how they
form, the spectacular minerals they produce, and the unusual creatures – from
microbes to vertebrates – that thrive in them.
By understanding the caves of our own planet, we can use them as models for the
subsurfaces of other planets. This work provides insights into the lava tubes
on celestial bodies including Mars and our Moon, as well as possible dissolved
caves on Titan, which orbits Saturn. There are many possibilities surrounding
cave formation on practically every type of object in the Solar System.
Some of the most extreme cave environments on Earth are inhabited by an amazing array
of microorganisms. Some of these creatures eat their way through bedrock,
some live in hyperacid conditions, some produce unusual biominerals and rare
cave formations, and many produce compounds of potential pharmaceutical and
industrial significance. We study these unique organisms and the physical
and chemical biosignatures they leave behind. Such traces can be
used to provide a “Field Guide to Unknown Organisms” for developing life-detection
space missions. Additionally, the lava tubes clearly present on Mars
and the Moon can provide the basis for future human habitations on those
planets. -
Direct Detection of Classically Undetectable Dark Matter through Quantum Decoherence
Jess Riedel NTT Research
Although various pieces of indirect evidence about the nature of dark matter have been collected, its direct detection has eluded experimental searches despite extensive effort. If the mass of dark matter is below 1 MeV, it is essentially imperceptible to conventional detection methods because negligible energy is transferred to nuclei during collisions. Here I propose directly detecting dark matter through the quantum decoherence it causes rather than its classical effects such as recoil or ionization. I show that quantum spatial superpositions are sensitive to low-mass dark matter that is inaccessible to classical techniques. This provides new independent motivation for matter interferometry with large masses, especially on spaceborne platforms. The apparent dark matter wind we experience as the Sun travels through the Milky Way ensures interferometers and related devices are directional detectors, and so are able to provide unmistakable evidence that decoherence has galactic origins. -
The Galactic Real Estate Market: The Physics and Chemistry of Habitability
Penelope Boston National Cave and Karst Research Institute
PIRSA:13120044Exoplanets, planets circling distant stars, are proving to be an extraordinary source of new thinking about the potential for life beyond Earth. Until recently, we have assumed that our Solar System and its planets were probably representative of such systems elsewhere. But the amazing array of very odd exoplanets that are being uncovered have stimulated a renaissance of thought on the subject of potential homes for life in the universe. Combined with work on extreme lifeforms here on Earth and intensive study of Mars and several other planets and moons in our system, new paradigms for life search missions are emerging. Science fiction has long drawn from and extrapolated out from science, but the cross-fertilization has gone both ways. Some of the more outrageous planets incorporated into fiction in the past may not be so outrageous after all. I will discuss what we think we know about exoplanets so far, how they are detected, how we are beginning to characterize their environments, and ideas about what this means for our search for living neighbors in our galaxy, whether they be microbes or folks we can actually chat with some day. -
Jets Without Jets
Daniele Bertolini Massachusetts Institute of Technology (MIT)
Jets are key tools for physics at the LHC. Usually, jets are identified through a jet algorithm. In this talk, I will present an alternative way of thinking about jets, by showing how a broad class of inclusive jet-based observables can be replaced by event shapes. These event shapes do not require any jet clustering, but they still implement a jet-like pT cut on "jets" with an R-like radius. I will discuss various applications, including event selection at trigger-level, event-wide trimming, and alternative definitions for boosted objects identifiers. -
Quantum Mechanics as Classical Physics
Charles Sebens University of Michigan–Ann Arbor
On the face of it, quantum physics is nothing like classical physics. Despite its oddity, work in the foundations of quantum theory has provided some palatable ways of understanding this strange quantum realm. Most of our best theories take that story to include the existence of a very non-classical entity: the wave function. Here I offer an alternative which combines elements of Bohmian mechanics and the many-worlds interpretation to form a theory in which there is no wave function. According to this theory, all there is at the fundamental level are particles interacting via Newtonian forces. In this sense, the theory is classical. However, it is still undeniably strange as it posits the existence of many worlds. Unlike the many worlds of the many-worlds interpretation, these worlds are fundamental, not emergent, and are interacting, not causally isolated. The theory will be presented as a fusion of the many-worlds interpretation and Bohmian mechanics, but can also be seen as a foundationally clear version of quantum hydrodynamics. A key strength of this theory is that it provides a simple and compelling story about the connection between the amplitude-squared of the wave function and probability. The theory also gives a natural explanation of the way the wave function transforms under time reversal and Galilean boosts. -
Fully exploring exotic production of the 125 GeV Higgs
Felix Yu Fermi National Accelerator Laboratory (Fermilab)
I consider the effects of exotic production modes of the 125 GeV Higgs and their impact on Higgs searches and the Higgs discovery. I emphasize that new production modes have been largely overlooked in contemporary tests of the Standard Model nature of the Higgs boson but experimental tests of exotic production modes are viable now or will be soon. I present a couple explicit examples of exotic production arising from chargino-neutralino associated production in the MSSM. As a corollary of this work, I point out that current Higgs coupling fits do not adequately explore the complete space of new physics deviations possible in Higgs measurements. -
Acceleration, Then and Now
Cliff Burgess McMaster University
There is good evidence that the universe underwent an epoch of accelerated expansion sometime in its very early history, and that it is entering a similar phase now. This talk is in two parts. The first part describes what I believe to be the take-home message about inflationary models, coming both from the recent Planck results and from attempts to embed inflation within a UV completion (string theory). I will argue that both point to a particularly interesting class of inflationary models that also evade many of the tuning problems of inflation. These models also turn out to make the tantalizing prediction that the scalar-to-tensor ratio, r, could be just out of reach, being predicted to be proportional to (n_s - 1)^2, where n_s ~ 0.96 is the spectral tilt of the scalar spectrum. The second part provides an update on an approach to solving the "cosmological constant problem", which asks why the vacuum energy seems to gravitate so little. This is the main theoretical obstruction that makes it so difficult to understand the origins of the present epoch of acceleration. In the approach described - Supersymmetric Large Extra Dimensions - observations can be reconciled with a large vacuum energy because the vacuum energy curves the extra dimensions and not the ones measured in cosmology. It leads to a picture of very supersymmetric gravity sector coupled to a completely non-supersymmetric particle-physics sector (which predicts in particular no superpartners to be found at the LHC). The update presented here summarizes the underlying mechanism whereby supersymmetry in the extra dimensions acts to suppress the gravitational effects of quantum fluctuations. Because the large quantum contributions are under control it becomes possible to estimate the size of to be expected of the observed dark energy. For the simplest configuratin the result is of order C (m Mg/4 pi Mp)^4, where m is the heaviest particle on the branes (and so no smaller than the top quark mass), Mg is the extra-dimensional gravity scale (no smaller than 10 TeV due to astrophysical constraints, implying two extra dimensions that are of order a micron in size) and Mp is the 4D Planck mass. C is a constant unsuppressed by symmetry-breaking effects, and C = 6 x 10^6 gives the observed dark energy density, using the smallest values given above for m and Mg. If there is time I will sketch arguments as to why there must be other light degrees of freedom in the theory as well, whose implications might ultimately be used to test the picture. -
Cornering Gluinos at the LHC
Jared Evans Rutgers University
Gluinos are expected to be light for a natural electroweak scale, but the LHC has not seen them yet. Many possibilities have been proposed to hide natural gluinos in the LHC data, but are these methods really effective? In this talk, I will discuss the current status of kinematically accessible gluinos. By noting the most common features - MET, tops, and high multiplicity - which pervade natural gluino decays, I will argue that there are few places left to hide. I will briefly discuss the remaining weaknesses in LHC coverage and how to bolster them. -
13/14 PSI - Condensed Matter - Lecture 15
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Anushya Chandran Perimeter Institute for Theoretical Physics
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Roger Melko University of Waterloo
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Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
PIRSA:13110045 -