1,571,399 research outputs found
A Note on Solitons in Brane Worlds
We obtain the zero mode effective action for gravitating objects in the bulk
of dilatonic domain walls. Without additional fields included in the bulk
action, the zero mode effective action reproduces the action in one lower
dimensions obtained through the ordinary Kaluza-Klein (KK) compactification,
only when the transverse (to the domain wall) component of the bulk metric does
not have non-trivial term depending on the domain wall worldvolume coordinates.
With additional fields included in the bulk action, non-trivial dependence of
the transverse metric component on the domain wall worldvolume coordinates
appears to be essential in reproducing the lower-dimensional action obtained
via the ordinary KK compactification. We find, in particular, that the
effective action for the charged (p+1)-brane in the domain wall bulk reproduces
the action for the p-brane in one lower dimensions.Comment: 13 pages, LaTe
Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators
Optical detection back-action in cantilever resonant or static detection
presents a challenge when striving for state-of-the-art performance. The origin
and possible routes for minimizing optical back-action have received little
attention in literature. Here, we investigate the position and mode dependent
optical back-action on cantilever beam resonators. A high power heating laser
(100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on
the first three resonance modes is detected via a low-power readout laser (1
{\mu}W) positioned at the cantilever tip. We find that the measured effect of
back-action is not only dependent on position but also the shape of the
resonance mode. Relevant silicon nitride material parameters are extracted by
fitting the temperature-dependent frequency response of the first three modes
to finite element (FE) simulations. In a second round of simulations, using the
extracted parameters, we successfully fit the FEM results with the measured
mode and position dependent back-action. Finally, different routes for
minimizing the effect of this optical detection back-action are described,
allowing further improvements of cantilever-based sensing in general
Transition from one- to two-mode generation regime in spin-torque nano-oscillator mediated by thermal noise
Two-mode model of spin-torque nano-oscillator (STNO) under the action of
thermal noise is considered. Langevin equations for mode amplitudes were
derived starting from general nonlinear oscillator model. Stationary
probability distribution function describing mean mode generation powers was
obtained using Fokker-Planck equation. It was shown that thermal noise can lead
to two-mode generation in STNO. An increase of thermal noise power leads to
excitation of the second mode in a system and to a two-mode generation regime
through intermediate state when two modes coexist only in some range of the
applied currents.Comment: 7 pages, 3 figure
Towards an effective-action approach to fermion-loop corrections
We present a study of the effective action approach to incorporate
higher-order effects in e^+e^- -> n fermions. In its minimal version, the
effective action approach is found to exhibit problems with unitarity and
high-energy behaviour. We identify the origin of these problems by
investigating the zero-mode solutions of the Ward Identities. A numerical
analysis of the importance of the zero-mode solutions is presented for
four-fermion production processes.Comment: 43 pages, 1 figure. Accepted for publication in Nuclear Physics
dRGT theory of massive gravity from spontaneous symmetry breaking
In this note we propose a topological action for a Poincare times
diffeomorphism invariant gauge theory. We show that there is Higgs phase where
the gauge symmetry is spontaneous broken to a diagonal Lorentz subgroup and
gives the Einstein-Hilbert action plus the dRGT potential terms. In this
vacuum, there are five (three from Goldstone modes) propagating degrees of
freedom which form polarizations of a massive spin 2 particle, an extra healthy
heavy scalar (Higgs) mode and no Boulware-Deser ghost mode. We further show
that the action can be derived in a limit from a topological de Sitter
invariant gauge theory in 4 dimensions.Comment: 5 pages, references and comments are added, equations corrected,
published versio
Methodological Individualism, the We-mode, and Team Reasoning
Raimo Tuomela is one of the pioneers of social action theory and has done as much as anyone over the last thirty years to advance the study of social action and collective intentionality. Social Ontology: Collective Intentionality and Group Agents (2013) presents the latest version of his theory and applications to a range of important social phenomena. The book covers so much ground, and so many important topics in detailed discussions, that it would impossible in a short space to do it even partial justice. In this brief note, I will concentrate on a single, though important, theme in the book, namely, the claim that we must give up methodological individualism in the social sciences and embrace instead irreducibly group notions. I wish to defend methodological individualism as up to the theoretical tasks of the social sciences while acknowledging what is distinctive about the social world and collective intentional action.
Tuomela frames the question of the adequacy of methodological individualism in terms of a contrast between what he calls the I-mode and the we-mode. He argues that we-mode phenomena are not reducible to I-mode phenomena, and concludes that we must reject methodological individualism. I will argue that the irreducibility of the we-mode to the I-mode, given how the contrast is set up, does not entail the rejection of methodological individualism. In addition, I will argue that the three conditions that Tuomela places on genuine we-mode activities, the group reason, collectivity, and collective commitment conditions, if they are understood in a way that does not beg the question, can plausibly be satisfied by a reductive account. Finally, I will argue that the specific considerations advanced in the book do not give us reason to think that a reductive account cannot be adequate to the descriptive and explanatory requirements of a theory of the social worl
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