284 research outputs found
GLSM's for gerbes (and other toric stacks)
In this paper we will discuss gauged linear sigma model descriptions of toric
stacks. Toric stacks have a simple description in terms of (symplectic, GIT)
quotients of homogeneous coordinates, in exactly the same
form as toric varieties. We describe the physics of the gauged linear sigma
models that formally coincide with the mathematical description of toric
stacks, and check that physical predictions of those gauged linear sigma models
exactly match the corresponding stacks. We also check in examples that when a
given toric stack has multiple presentations in a form accessible as a gauged
linear sigma model, that the IR physics of those different presentations
matches, so that the IR physics is presentation-independent, making it
reasonable to associate CFT's to stacks, not just presentations of stacks. We
discuss mirror symmetry for stacks, using Morrison-Plesser-Hori-Vafa techniques
to compute mirrors explicitly, and also find a natural generalization of
Batyrev's mirror conjecture. In the process of studying mirror symmetry, we
find some new abstract CFT's, involving fields valued in roots of unity.Comment: 43 pages, LaTeX, 3 figures; v2: typos fixe
Decomposition and the Gross-Taylor string theory
It was recently argued by Nguyen-Tanizaki-Unsal that two-dimensional pure
Yang-Mills theory is equivalent to (decomposes into) a disjoint union of
(invertible) quantum field theories, known as universes. In this paper we
compare this decomposition to the Gross-Taylor expansion of two-dimensional
pure SU(N) Yang-Mills theory in the large N limit as the string field theory of
a sigma model. Specifically, we study the Gross-Taylor expansion of individual
Nguyen-Tanizaki-Unsal universes. These differ from the Gross-Taylor expansion
of the full Yang-Mills theory in two ways: a restriction to single instanton
degrees, and some additional contributions not present in the expansion of the
full Yang-Mills theory. We propose to interpret the restriction to single
instanton degree as implying a constraint, namely that the Gross-Taylor string
has a global (higher-form) symmetry with Noether current related to the
worldsheet instanton number. We compare two-dimensional pure Maxwell theory as
a prototype obeying such a constraint, and also discuss in that case an
analogue of the Witten effect arising under two-dimensional theta angle
rotation. We also propose a geometric interpretation of the additional terms,
in the special case of Yang-Mills theories on two-spheres. In addition, also
for the case of theories on two-spheres, we propose a reinterpretation of the
terms in the Gross-Taylor expansion of the Nguyen-Tanizaki-Unsal universes,
replacing sigma models on branched covers by counting disjoint unions of stacky
copies of the target Riemann surface, that makes the Nguyen-Tanizaki-Unsal
decomposition into invertible field theories more nearly manifest. As the
Gross-Taylor string is a sigma model coupled to worldsheet gravity, we also
briefly outline the tangentially-related topic of decomposition in
two-dimensional theories coupled to gravity.Comment: 95 pages, LaTe
Cluster decomposition, T-duality, and gerby CFT's
In this paper we study CFT's associated to gerbes. These theories suffer from
a lack of cluster decomposition, but this problem can be resolved: the CFT's
are the same as CFT's for disconnected targets. Such theories also lack cluster
decomposition, but in that form, the lack is manifestly not very problematic.
In particular, we shall see that this matching of CFT's, this duality between
noneffective gaugings and sigma models on disconnected targets, is a worldsheet
duality related to T-duality. We perform a wide variety of tests of this claim,
ranging from checking partition functions at arbitrary genus to D-branes to
mirror symmetry. We also discuss a number of applications of these results,
including predictions for quantum cohomology and Gromov-Witten theory and
additional physical understanding of the geometric Langlands program.Comment: 61 pages, LaTeX; v2,3: typos fixed; v4: writing improved in several
sections; v5: typos fixe
Non-birational twisted derived equivalences in abelian GLSMs
In this paper we discuss some examples of abelian gauged linear sigma models
realizing twisted derived equivalences between non-birational spaces, and
realizing geometries in novel fashions. Examples of gauged linear sigma models
with non-birational Kahler phases are a relatively new phenomenon. Most of our
examples involve gauged linear sigma models for complete intersections of
quadric hypersurfaces, though we also discuss some more general cases and their
interpretation. We also propose a more general understanding of the
relationship between Kahler phases of gauged linear sigma models, namely that
they are related by (and realize) Kuznetsov's `homological projective duality.'
Along the way, we shall see how `noncommutative spaces' (in Kontsevich's sense)
are realized physically in gauged linear sigma models, providing examples of
new types of conformal field theories. Throughout, the physical realization of
stacks plays a key role in interpreting physical structures appearing in GLSMs,
and we find that stacks are implicitly much more common in GLSMs than
previously realized.Comment: 54 pages, LaTeX; v2: typo fixe
Quantization of Fayet-Iliopoulos Parameters in Supergravity
In this short note we discuss quantization of the Fayet-Iliopoulos parameter
in supergravity theories. We argue that in supergravity, the Fayet-Iliopoulos
parameter determines a lift of the group action to a line bundle, and such
lifts are quantized. Just as D-terms in rigid N=1 supersymmetry are interpreted
in terms of moment maps and symplectic reductions, we argue that in
supergravity the quantization of the Fayet-Iliopoulos parameter has a natural
understanding in terms of linearizations in geometric invariant theory (GIT)
quotients, the algebro-geometric version of symplectic quotients.Comment: 21 pages, utarticle class; v2: typos and tex issue fixe
Effects of musical training and event probabilities on encoding of complex tone patterns
Background: The human auditory cortex automatically encodes acoustic input from the environment and differentiates regular sound patterns from deviant ones in order to identify important, irregular events. The Mismatch Negativity (MMN) response is a neuronal marker for the detection of sounds that are unexpected, based on the encoded regularities. It is also elicited by violations of more complex regularities and musical expertise has been shown to have an effect on the processing of complex regularities. Using magnetoencephalography (MEG), we investigated the MMN response to salient or less salient deviants by varying the standard probability (70%, 50% and 35%) of a pattern oddball paradigm. To study the effects of musical expertise in the encoding of the patterns, we compared the responses of a group of non-musicians to those of musicians. Results: We observed significant MMN in all conditions, including the least salient condition (35% standards), in response to violations of the predominant tone pattern for both groups. The amplitude of MMN from the right hemisphere was influenced by the standard probability. This effect was modulated by long-term musical training: standard probability changes influenced MMN amplitude in the group of non-musicians only. Conclusion: This study indicates that pattern violations are detected automatically, even if they are of very low salience, both in non-musicians and musicians, with salience having a stronger impact on processing in the right hemisphere of non-musicians. Long-term musical training influences this encoding, in that non-musicians benefit to a greater extent from a good signal-to-noise ratio (i.e. high probability of the standard pattern), while musicians are less dependent on the salience of an acoustic environment.<br
Playing and Listening to Tailor-Made Notched Music: Cortical Plasticity Induced by Unimodal and Multimodal Training in Tinnitus Patients
Background. The generation and maintenance of tinnitus are assumed to be based on maladaptive functional cortical reorganization. Listening to modified music, which contains no energy in the range of the individual tinnitus frequency, can inhibit the corresponding neuronal activity in the auditory cortex. Music making has been shown to be a powerful stimulator for brain plasticity, inducing changes in multiple sensory systems. Using magnetoencephalographic (MEG) and behavioral measurements we evaluated the cortical plasticity effects of two months of (a) active listening to (unisensory) versus (b) learning to play (multisensory) tailor-made notched music in nonmusician tinnitus patients. Taking into account the fact that uni- and multisensory trainings induce different patterns of cortical plasticity we hypothesized that these two protocols will have different affects. Results. Only the active listening (unisensory) group showed significant reduction of tinnitus related activity of the middle temporal cortex and an increase in the activity of a tinnitus-coping related posterior parietal area. Conclusions. These findings indicate that active listening to tailor-made notched music induces greater neuroplastic changes in the maladaptively reorganized cortical network of tinnitus patients while additional integration of other sensory modalities during training reduces these neuroplastic effects
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