Sunday, March 29, 2015

 

 



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía
 

rss_1.0 Recursos de colección

Caltech Authors (103,057 recursos)
Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 2,809

1. A Comparison Between Dislocation Theory and Experimental Measurements of Delayed Yield in Steel - Vreeland, T., Jr.; Wood, D. S.
A dislocation model of a yield nucleus for materials, such as annealed low-carbon steel, which exhibit a distinct yield point, is presented. On the basis of the model an analytical expression is derived which relates the time delay for yielding under constant applied stress to the magnitude of the stress and the temperature. This expression involves the ratio of the binding energy of a dislocation with a Cottrell “atmosphere" to the total energy of a dislocation. The expression also involves the frequency of thermal fluctuations associated with the release of a dislocation from an "atmosphere". The numerical values of these two constants are chosen to fit the analytical expression...

2. Quasinormal Modes Beyond Kerr - Zimmerman, Aaron; Yang, Huan; Mark, Zachary; Chen, Yanbei; Lehner, Luis
The quasinormal modes (QNMs) of a black hole spacetime are the free, decaying oscillations of the spacetime, and are well understood in the case of Kerr black holes. We discuss a method for computing the QNMs of spacetimes which are slightly deformed from Kerr. We mention two example applications: the parametric, turbulent instability of scalar fields on a background which includes a gravitational QNM, and the shifts to the QNM frequencies of Kerr when the black hole is weakly charged. This method may be of use in studies of black holes which are deformed by external fields or are solutions to alternative theories of gravity.

3. A 3d-3d appetizer - Pei, Du; Ye, Ke
We test the 3d-3d correspondence for theories that are labelled by Lens spaces. We find a full agreement between the index of the 3d N=2 "Lens space theory" T[L(p,1)] and the partition function of complex Chern-Simons theory on L(p,1). In particular, for p=1, we show how the familiar S^3 partition function of Chern-Simons theory arises from the index of a free theory. For large p, we find that the index of T[L(p,1)] becomes a constant independent of p. In addition, we studyT[L(p,1)] on the squashed three-sphere S^3_b. This enables us to see clearly, at the level of partition function, to what extent G_ℂ complex Chern-Simons theory can be...

4. IR fixed points in SU(3) gauge Theories - Ishikawa, K.-I.; Iwasaki, Y.; Nakayama, Yu; Yoshie, Y.
We propose a novel RG method to specify the location of the IR fixed point in lattice gauge theories and apply it to the SU(3) gauge theories with N_f fundamental fermions. It is based on the scaling behavior of the propagator through the RG analysis with a finite IR cut-off, which we cannot remove in the conformal field theories in sharp contrast with the confining theories. The method also enables us to estimate the anomalous mass dimension in the continuum limit at the IR fixed point. We perform the program for N_f=16, 12, 8 and N_f=7 and indeed identify the location of the IR fixed points in...

5. Long-lived Light Mediator to Dark Matter and Primordial Small Scale Spectrum - Zhang, Yue
We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population of the smallest DM halos gets enhanced. Possible...

6. Complementarity of LHC and EDMs for Exploring Higgs CP Violation - Chen, Chien-Yi; Dawson, S.; Zhang, Yue
We analyze the constraints on a CP-violating, flavor conserving, two Higgs doublet model from the measurements of Higgs properties and from the search for heavy Higgs bosons at LHC, and show that the stronger limits typically come from the heavy Higgs search channels. The limits on CP violation arising from the Higgs sector measurements are complementary to those from EDM measurements. Combining all current constraints from low energy to colliders, we set generic upper bounds on the CP violating angle which parametrizes the CP odd component in the 126 GeV Higgs boson.

7. Kinematic classifications of local interacting galaxies: implications for the merger/disk classifications at high-z - Hung, Chao-Ling; Rich, Jeffrey A.; Yuan, Tiantian; Larson, Kirsten L.; Casey, Caitlin M.; Smith, Howard A.; Sanders, D. B.; Kewley, Lisa J.; Hayward, Christopher C.
The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. The kinematic properties of galaxies as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of galaxy morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially...

8. NuSTAR and multifrequency study of the two high-redshift blazars S5 0836+710 and PKS 2149-306 - Tagliaferri, G.; Ghisellini, G.; Perri, M.; Hayashida, M.; Baloković, M.; Covino, S.; Giommi, P.; Madejski, G. M.; Puccetti, S.; Sbarrato, T.; Boggs, S. E.; Chiang, J.; Christensen, F. E.; Craig, W. W.; Hailey, C. J.; Harrison, F. A.; Stern, D.; Zhang, W. W.
The most powerful blazars are the flat spectrum radio quasars whose emission is dominated by a Compton component peaking between a few hundred keV and a few hundred MeV. We selected two bright blazars, PKS 2149-306 at redshift z=2.345 and S5 0836+710 at z=2.172, in order to observe them in the hard X-ray band with the NuSTAR satellite. In this band the Compton component is rapidly rising almost up to the peak of the emission. Simultaneous soft-X-rays and UV-optical observations were performed with the Swift satellite, while near-infrared (NIR) data were obtained with the REM telescope. To study their variability, we repeated these observations for both sources on...

9. Luminous and Dark Matter Profiles from Galaxies to Clusters: Bridging the Gap with Group-scale Lenses - Newman, Andrew B.; Ellis, Richard S.; Treu, Tommaso
Observations of strong gravitational lensing, stellar kinematics, and mass tracers on larger scales enable accurate measures of the distribution of dark matter and baryons in massive early-type galaxies (ETGs). While such techniques have previously been applied to galaxy-scale and cluster-scale lenses, the paucity of intermediate-mass systems with high-quality data has precluded a uniform analysis of mass-dependent trends. With the aim of bridging this gap, we present new observations and analyses of 10 group-scale lenses at hzi = 0.36 characterized by Einstein radii θ_(Ein) = 2. 005 − 5.001 and a mean halo mass of M_(200) = 10^(14.0)M_⊙. For these groups, we find a mean halo concentration c_(200)...

10. Pulsed excitation dynamics of an optomechanical crystal resonator near its quantum ground-state of motion - Meenehan, Sean M.; Cohen, Justin D.; MacCabe, Gregory S.; Marsili, Francesco; Shaw, Matthew D.; Painter, Oskar
Using pulsed optical excitation and read-out along with single phonon counting techniques, we measure the transient back-action, heating, and damping dynamics of a nanoscale silicon optomechanical crystal cavity mounted in a dilution refrigerator at a base temperature of 11mK. In addition to observing a slow (~740ns) turn-on time for the optical-absorption-induced hot phonon bath, we measure for the 5.6 GHz 'breathing' acoustic mode of the cavity an initial phonon occupancy as low as 0.021 ± 0.007 (mode temperature = 70mK) and an intrinsic mechanical decay rate of 328 ± 14 Hz (mechanical Q-factor = 1.7x10^7). These measurements demonstrate the feasibility of using short pulsed measurements for a variety of...

11. Quantum many-body models with cold atoms coupled to photonic crystals - Douglas, James S.; Habibian, H.; Hung, C. -L.; Gorshkov, A. V.; Kimble, H. Jeff; Chang, D. E.
Using cold atoms to simulate strongly interacting quantum systems represents an exciting frontier of physics. However, achieving tunable, coherent long-range interactions between atoms is an outstanding challenge, which currently leaves a large class of models inaccessible to quantum simulation. Here, we propose a solution exploiting the powerful new platform of cold atoms trapped near nano-photonic systems. We show that the dielectric contrast of an atom trapped near a photonic crystal can seed a localized cavity mode around the atomic position. In a dynamic form of "all-atomic" cavity QED, the length of these cavity modes can be tuned, and atoms separated...

12. Superradiance for atoms trapped along a photonic crystal waveguide - Goban, A.; Hung, C.-L.; Hood, J. D.; Yu, S.-P.; Muniz, J. A.; Painter, O.; Kimble, H. J.
We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D_1 transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as Γ_(SR)∝N¯⋅Γ_(1D) for average atom number 0.19≲N¯≲2.6 atoms, where Γ1D/Γ_0=1.1±0.1 is the peak single-atom radiative decay rate into the PCW guided mode and Γ_0 is the Einstein-A coefficient for free space. These advances provide new tools for investigations of photon-mediated...

13. Optomechanical creation of magnetic fields for photons on a lattice - Schmidt, M.; Keßler, S.; Peano, V.; Painter, O.; Marquardt, F.
We propose using the optomechanical interaction to create artificial magnetic fields for photons on a lattice. The ingredients required are an optomechanical crystal, i.e. a piece of dielectric with the right pattern of holes, and two laser beams with the right pattern of phases. One of the two proposed schemes is based on optomechanical modulation of the links between optical modes, while the other is an lattice extension of optomechanical wavelength-conversion setups. We illustrate the resulting optical spectrum, photon transport in the presence of an artificial Lorentz force, edge states, and the photonic Aharonov-Bohm effect. Moreover, we also briefly describe the gauge fields acting on the synthetic dimension related...

14. The VIMOS Ultra-Deep Survey: ∼10 000 galaxies with spectroscopic redshifts to study galaxy assembly at early epochs 2 < z ≃ 6^⋆ - Le Fèvre, O.; Capak, P.; Scoville, N.
We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ∼10 000 very faint galaxies to study the major phase of galaxy assembly 2 < z ≃ 6. The survey covers 1 deg^2 in 3 separate fields: COSMOS, ECDFS and VVDS-02h, with targets selection based on an inclusive combination of photometric redshifts and color properties. Spectra covering 3650 < λ < 9350Å are obtained with VIMOS on the ESO-VLT with integration times of 14h. Here we present the survey strategy, the target selection, the data processing, as well as the redshift measurement process, emphasizing the specific methods adapted...

15. Local renormalization group functions from quantum renormalization group and holographic bulk locality - Nakayama, Yu
The bulk locality in the constructive holographic renormalization group requires miraculous cancellations among various local renormalization group functions. The cancellation is not only from the properties of the spectrum but from more detailed aspects of operator product expansions in relation to conformal anomaly. It is remarkable that one-loop computation of the universal local renormalization group functions in the weakly coupled limit of the N=4 super Yang-Mills theory fulfils the necessary condition for the cancellation in the strongly coupled limit in its SL(2,Z) duality invariant form. From the consistency between the quantum renormalization group and the holographic renormalization group, we determine...

16. Higher-Dimensional Supertranslations and Weinberg's Soft Graviton Theorem - Kapec, Daniel; Lysov, Vyacheslav; Pasterski, Sabrina; Strominger, Andrew
Asymptotic symmetries of theories with gravity in d=2m+2 spacetime dimensions are reconsidered for m>1 in light of recent results concerning d=4 BMS symmetries. Weinberg's soft graviton theorem in 2m+2 dimensions is re-expressed as a Ward identity for the gravitational S-matrix. The corresponding asymptotic symmetries are identified with 2m+2-dimensional supertranslations. An alternate derivation of these asymptotic symmetries as diffeomorphisms which preserve finite-energy boundary conditions at null infinity and act non-trivially on physical data is given. Our results differ from those of previous analyses whose stronger boundary conditions precluded supertranslations for d>4. We find for all even d that supertranslation symmetry is spontaneously broken in the conventional vacuum and identify soft gravitons...

17. Generating Einstein gravity, cosmological constant and Higgs mass from restricted Weyl invariance - Edery, Ariel; Nakayama, Yu
Recently, it has been pointed out that dimensionless actions in four dimensional curved spacetime possess a symmetry which goes beyond scale invariance but is smaller than full Weyl invariance. This symmetry was dubbed {it restricted Weyl invariance}. We show that starting with a restricted Weyl invariant action that includes a Higgs sector with no explicit mass, one can generate the Einstein-Hilbert action with cosmological constant and a Higgs mass. The model also contains an extra massless scalar field which couples to the Higgs field (and gravity). If the coupling of this extra scalar field to the Higgs field is negligibly...

18. Bel-Robinson as stress-tensor gradients and their extensions to massive spin (0,1,2) - Deser, S.; Franklin, J.
We show that the Bel-Robinson (BR) tensor is - generically, as well as in its original GR setting - an autonomously conserved part of the, manifestly conserved, double gradient of a system's stress-tensor. This suggests its natural extension from GR to matter models, first to (known) massless scalars and vectors, then to massive ones, including tensors. These massive versions are to be expected, given that they arise upon KK reduction of massless D+1 ones. We exhibit the resulting spin (0, 1, 2) "massive" BR.

19. Positive Amplitudes In The Amplituhedron - Arkani-Hamed, Nima; Hodges, Andrew; Trnka, Jaroslav
The all-loop integrand for scattering amplitudes in planar N = 4 SYM is determined by an "amplitude form" with logarithmic singularities on the boundary of the amplituhedron. In this note we provide strong evidence for a new striking property of the superamplitude, which we conjecture to be true to all loop orders: the amplitude form is positive when evaluated inside the amplituhedron. The statement is sensibly formulated thanks to the natural "bosonization" of the superamplitude associated with the amplituhedron geometry. However this positivity is not manifest in any of the current approaches to scattering amplitudes, and in particular not in the cellulations of the amplituhedron related to on-shell diagrams...

20. Perturbative search for dead end CFTs - Nakayama, Yu
To explore the possibility of self-organized criticality, we look for CFTs without any relevant scalar deformations (a.k.a dead end CFTs) within powercounting renormalizable quantum field theories with weakly coupled Lagrangian description. In d=3 dimensions, the only candidates are the pure (Abelian) gauge theories, which may be further deformed by Chern-Simons terms. In d=4 dimensions, we show that there are infinitely many non-trivial candidates based on chiral gauge theories. From the three-loop beta functions, we compute the gap of scaling dimensions above the marginal value, and it may be as small as O(10^(−5)) and robust under the perturbative expansions. These classes...

Página de resultados:
 

Busque un recurso