Mechanical Lamb-shift analogue for the Cooper-pair box

We estimate the correction to the Cooper-pair box energy level splitting due to the quantum motion of a coupled micromechanical gate electrode. While the correction due to zero-point motion is very small, it should be possible to observe thermal motion-induced corrections to the photon-assisted tunneling current.Comment: To appear in Phonons 2001 Proceedings (Physica B

More loosely bound hadron molecules at CDF?

In a recent paper we have proposed a method to estimate the prompt production cross section of X(3872) at the Tevatron assuming that this particle is a loosely bound molecule of a D and a D*bar meson. Under this hypothesis we find that it is impossible to explain the high prompt production cross section found by CDF at sigma(X(3872)) \sim 30-70 nb as our theoretical prediction is about 300 times smaller than the measured one. Following our work, Artoisenet and Braaten, have suggested that final state interactions in the DD*bar system might be so strong to push the result we obtained for the cross section up to the experimental value. Relying on their conclusions we show that the production of another very narrow loosely bound molecule, the X_s=D_s D_s*bar, could be similarly enhanced. X_s should then be detectable at CDF with a mass of 4080 MeV and a prompt production cross section of sigma(X_s) \sim 1-3 nb.Comment: Minor revisions made. To appear in Phys Lett

Quantum phase transitions in superconducting arrays under external magnetic fields

We study the zero-temperature phase transitions of two-dimensional superconducting arrays with both the self- and the junction capacitances in the presence of external magnetic fields. We consider two kinds of excitations from the Mott insulating phase: charge-dipole excitations and single-charge excitations, and apply the second-order perturbation theory to find their energies. The resulting phase boundaries are found to depend strongly on the magnetic frustration, which measures the commensurate-incommensurate effects. Comparison of the obtained values with those in recent experiment suggests the possibility that the superconductor-insulator transition observed in experiment may not be of the Berezinskii-Kosterlitz-Thouless type. The system is also transformed to a classical three-dimensional XY model with the magnetic field in the time-direction; this allows the analogy to bulk superconductors, revealing the nature of the phase transitions.Comment: 9 pages including 7 figures, to appear in Phys. Rev.

Old Inflation in String Theory

We propose a stringy version of the old inflation scenario which does not require any slow-roll inflaton potential and is based on a specific example of string compatification with warped metric. Our set-up admits the presence of anti-D3-branes in the deep infrared region of the metric and a false vacuum state with positive vacuum energy density. The latter is responsible for the accelerated period of inflation. The false vacuum exists only if the number of anti-D3-branes is smaller than a critical number and the graceful exit from inflation is attained if a number of anti-D3-branes travels from the ultraviolet towards the infrared region. The cosmological curvature perturbation is generated through the curvaton mechanism.Comment: 31 pages, 3 figures; typos corrected and reference adde

Fermionic decays of sfermions: a complete discussion at one-loop order

We present a definition of an on-shell renormalization scheme for the sfermion and chargino-neutralino sector of the Minimal Supersymmetric Standard Model (MSSM). Then, apply this renormalization framework to the interaction between charginos/neutralinos and sfermions. A kind of universal corrections is identified, which allow to define effective chargino/neutralino coupling matrices. In turn, these interactions generate (universal) non-decoupling terms that grow as the logarithm of the heavy mass. Therefore the full MSSM spectrum must be taken into account in the computation of radiative corrections to observables involving these interactions. As an application we analyze the full one-loop electroweak radiative corrections to the partial decay widths \Gamma(\tilde{f} -> f\neut) and \Gamma(\tilde{f} -> f'\cplus) for all sfermion flavours and generations. These are combined with the QCD corrections to compute the corrected branching ratios of sfermions. It turns out that the electroweak corrections can have an important impact on the partial decay widths, as well as the branching ratios, in wide regions of the parameter space. The precise value of the corrections is strongly dependent on the correlation between the different particle masses.Comment: LaTeX 53 pages, 22 figures, 3 tables. Typos correcte

A Complete Set of In-plane Spin-transfer Coefficients for Small Angle pp Elastic Scattering at 200 MeV

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Understanding the newly observed Y(4008) by Belle

Very recently a new enhancement around 4.05 GeV was observed by Belle experiment. In this short note, we discuss some possible assignments for this enhancement, i.e. $\psi(3S)$ and $D^*\bar{D}^*$ molecular state. In these two assignments, Y(4008) can decay into $J/\psi\pi^0\pi^0$ with comparable branching ratio with that of $Y(4008)\to J/\psi\pi^+\pi^-$. Thus one suggests high energy experimentalists to look for Y(4008) in $J/\psi\pi^0\pi^0$ channel. Furthermore one proposes further experiments to search missing channel $D\bar{D}$, $D\bar{D}^*+h.c.$ and especially $\chi_{cJ}\pi^+\pi^-\pi^0$ and $\eta_c\pi^+\pi^-\pi^0$, which will be helpful to distinguish $\psi(3S)$ and $D^*\bar{D}^*$ molecular state assignments for this new enhancement.Comment: 4 pages, 5 figures. Typos correcte

Penetration depth anisotropy in two-band superconductors

The anisotropy of the London penetration depth is evaluated for two-band superconductors with arbitrary inter- and intra-band scattering times. If one of the bands is clean and the other is dirty in the absence of inter-band scattering, the anisotropy is dominated by the Fermi surface of the clean band and is weakly temperature dependent. The inter-band scattering also suppress the temperature dependence of the anisotropy

Dephasing in sequential tunneling through a double-dot interferometer

We analyze dephasing in a model system where electrons tunnel sequentially through a symmetric interference setup consisting of two single-level quantum dots. Depending on the phase difference between the two tunneling paths, this may result in perfect destructive interference. However, if the dots are coupled to a bath, it may act as a which-way detector, leading to partial suppression of the phase-coherence and the reappearance of a finite tunneling current. In our approach, the tunneling is treated in leading order whereas coupling to the bath is kept to all orders (using P(E) theory). We discuss the influence of different bath spectra on the visibility of the interference pattern, including the distinction between "mere renormalization effects" and "true dephasing".Comment: 18 pages, 8 figures; For a tutorial introduction to dephasing see http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm

Noise and Measurement Efficiency of a Partially Coherent Mesoscopic Detector

We study the noise properties and efficiency of a mesoscopic resonant-level conductor which is used as a quantum detector, in the regime where transport through the level is only partially phase coherent. We contrast models in which detector incoherence arises from escape to a voltage probe, versus those in which it arises from a random time-dependent potential. Particular attention is paid to the back-action charge noise of the system. While the average detector current is similar in all models, we find that its noise properties and measurement efficiency are sensitive both to the degree of coherence and to the nature of the dephasing source. Detector incoherence prevents quantum limited detection, except in the non-generic case where the source of dephasing is not associated with extra unobserved information. This latter case can be realized in a version of the voltage probe model.Comment: 15 pages, 5 figures; revised dicussion of voltage probe model