2,609 research outputs found
Mixed Heavy-Light Matching in the Universal One-Loop Effective Action
Recently, a general result for evaluating the path integral at one loop was
obtained in the form of the Universal One-Loop Effective Action. It may be used
to derive effective field theory operators of dimensions up to six, by
evaluating the traces of matrices in this expression, with the mass-dependence
encapsulated in the universal coefficients. Here we show that it can account
for loops of mixed heavy-light particles in the matching procedure. Our
prescription for computing these mixed contributions to the Wilson coefficients
is conceptually simple. Moreover it has the advantage of maintaining the
universal structure of the effective action, which we illustrate using the
example of integrating out a heavy electroweak triplet scalar coupling to a
light Higgs doublet. Finally we also identify new structures that were
previously neglected in the universal results.Comment: 22 pages, 3 figures; v2: expanded discussion in Section 3, typos
correcte
Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit
We resolve phonon number states in the spectrum of a superconducting qubit
coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp
frequency dependence in the qubit-phonon interaction engineered by coupling the
qubit to surface acoustic waves in two locations separated by acoustic
wavelengths. In analogy to double-slit diffraction, the resulting
self-interference generates high-contrast frequency structure in the
qubit-phonon interaction. We observe this frequency structure both in the
coupling rate to multiple cavity modes and in the qubit spontaneous emission
rate into unconfined modes. We use this sharp frequency structure to resolve
single phonons by tuning the qubit to a frequency of destructive interference
where all acoustic interactions are dispersive. By exciting several detuned yet
strongly-coupled phononic modes and measuring the resulting qubit spectrum, we
observe that, for two modes, the device enters the strong dispersive regime
where single phonons are spectrally resolved.Comment: 9 pages, 8 figures; revised arguments in paragraphs 3 and 8, added
Hamiltonian description, and corrected typo
Encounters of the dust trails of comet 45P/Honda-Mrkos-Pajdusakova with Venus in 2006
The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceAims. We aim to investigate the dynamical fate of meteoroids ejected during past perihelion passages of comet 45P/Honda-Mrkos-Pajdusakova that intersect the orbit of Venus. Of particular interest is the possibility, borne of previous work, that a significant flux of these particles will reach the planet during early June and late August 2006, when the Venus Express spacecraft will be operating in orbit around Venus. Methods. We have simulated the generation of meteoroid trails ejected by the comet at some past perihelion passages, and numericaly integrated them forward in time until they approach Venus in 2006. Results. On the inbound leg of the comet's path towards perihelion, we find a trail composed of dust particles ejected between 1943 and 1980 that encounters Venus on 9 June 2006 at a distance of 0.009 AU. On the outbound leg, we observe a dense trail of particles ejected between 1985 and 2001 that measures 3.4 × 10−4 AU (5 × 104 km) in half-width, and passes under the planet at a distance of 1.72 × 10−3 AU (2.6 × 105 km) on 30 August. Based on these results, we conclude that, on both occasions, the incident flux at Venus will likely be too low to allow for the detection of a shower by optical means. We discuss the circumstances under which Venus Express may encounter a significant flux of small particles detectable through impact ionization or disturbances in the interplanetary magnetic field
The dust trail complex of comet 79P/du Toit-Hartley and meteor outbursts at Mars
The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceAims. Meteoroid trails ejected during past perihelion passages of the Mars-orbit-intersecting comet 79P/du Toit-Hartley have the potential of generating meteor outbursts in the Martian atmosphere. Depending on timing and intensity, the effects of these outbursts may be detectable by instrumentation operating in the vicinity of Mars. We aim to generate predictions for meteor activity in the martian atmosphere related to that comet; to search for evidence, in planetary mission data, that such activity took place; and to make predictions for potentially detectable future activity. Methods. We have modelled the stream by integrating numerically the states of particle ensembles, each ensemble representing a trail of meteoroids ejected from the comet during 39 perihelion passages from 1803, and propagated them forward in time, concentrating on those particles that physically approach Mars in the recent past and near future. Results. We find several instances where meteor outbursts of low to moderate intensity may have taken place at Mars since 1997. A search through Mars Global Surveyor (MGS) radio science data during two periods in 2003 and 2005 when data coverage was available showed that a plasma layer did indeed form in the martian ionosphere for a period of a few hours in April 2003 as a direct consequence of the predicted outburst. The apparent failure to identify such an event in 2005 could be due to those meteoroids ablating lower in the atmosphere or that the cometary dust follows a different particle size distribution than what was assumed. Our study highlights the need for further theoretical modelling of the response of the martian ionosphere to a time-variable meteoroid flux, observations of the comet itself and, most importantly, regular monitoring of the martian ionosphere during future outbursts predicted by our model
Linear collider test facility: ATF2 final focus active stabilisation pertinence
International audienceBeam motion at the Interaction Point (IP) of ATF2 has to be less than 10nm relative to the instrumentation used for measurements. Due to ground motion (GM), the beam can pass off-axis through the quadrupoles of the beam line and hence be deflected. It was shown in previous studies that good spatial coherence of the GM over a few meters makes the relative motion of the Final Doublets (FD) small enough for the tolerance not to be exceeded. However, since the coherence drops rapidly with distance, other quadrupoles further upstream can be expected to induce significant effects. In this paper, an evaluation taking into account all ATF2 quadrupoles is presented, using a GM generator with parameters tuned to dedicated measurements done recently along the ATF2 beam line and propagating to the IP with the optical transfer matrices. It was shown that although large IP beam motion can indeed be induced by some specific upstream quadrupoles, the combined effect of all is small because of compensations. The tolerance can thus be achieved without specially stabilising these quadrupoles
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