Heat Transport in Mesoscopic Systems

Phonon heat transport in mesoscopic systems is investigated using methods analogous to the Landauer description of electrical conductance. A "universal heat conductance" expression that depends on the properties of the conducting pathway only through the mode cutoff frequencies is derived. Corrections due to reflections at the junction between the thermal body and the conducting bridge are found to be small except at very low temperatures where only the lowest few bridge modes are excited. Various non-equilibrium phonon distributions are studied: a narrow band distribution leads to clear steps in the cooling curve, analogous to the quantized resistance values in narrow wires, but a thermal distribution is too broad to show such features.Comment: To be published in Superlattices and Microstructures, special issue in honor of Rolf Landauer, March 198

Closing the window on single leptoquark solutions to the B-physics anomalies

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. R_D(◦)^exp \u3e R_D(◦)^SM or/and R_K(◦)^exp \u3c R_K(◦)^SM. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ_1^±ℓ_2^± modes, such as B(B → K μΤ). Improving the experimental upper bound on B(B → K μΤ) by two orders of magnitude could compromise the viability of the minimal U1 model as well

Closing the window on single leptoquark solutions to the B-physics anomalies

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. R_D(◦)^exp \u3e R_D(◦)^SM or/and R_K(◦)^exp \u3c R_K(◦)^SM. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ_1^±ℓ_2^± modes, such as B(B → K μΤ). Improving the experimental upper bound on B(B → K μΤ) by two orders of magnitude could compromise the viability of the minimal U1 model as well

Closing the window on single leptoquark solutions to the B-physics anomalies

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. R_D(◦)^exp \u3e R_D(◦)^SM or/and R_K(◦)^exp \u3c R_K(◦)^SM. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ_1^±ℓ_2^± modes, such as B(B → K μΤ). Improving the experimental upper bound on B(B → K μΤ) by two orders of magnitude could compromise the viability of the minimal U1 model as well

Closing the window on single leptoquark solutions to the B-physics anomalies

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. R_D(◦)^exp \u3e R_D(◦)^SM or/and R_K(◦)^exp \u3c R_K(◦)^SM. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ_1^±ℓ_2^± modes, such as B(B → K μΤ). Improving the experimental upper bound on B(B → K μΤ) by two orders of magnitude could compromise the viability of the minimal U1 model as well

Closing the window on single leptoquark solutions to the B-physics anomalies

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. R_D(◦)^exp \u3e R_D(◦)^SM or/and R_K(◦)^exp \u3c R_K(◦)^SM. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ_1^±ℓ_2^± modes, such as B(B → K μΤ). Improving the experimental upper bound on B(B → K μΤ) by two orders of magnitude could compromise the viability of the minimal U1 model as well

The Effect of Surface Roughness on the Universal Thermal Conductance

We explain the reduction of the thermal conductance below the predicted universal value observed by Schwab et al. in terms of the scattering of thermal phonons off surface roughness using a scalar model for the elastic waves. Our analysis shows that the thermal conductance depends on two roughness parameters: the roughness amplitude $\delta$ and the correlation length $a$. At sufficiently low temperatures the conductance decrease from the universal value quadratically with temperature at a rate proportional to $\delta ^{2}a$. Values of $\delta$ equal to 0.22 and $a$ equal to about 0.75 of the width of the conduction pathway give a good fit to the data.Comment: 10 pages, 5 figures. Ref. added, typo correcte

Absence of Embedded Mass Shells: Cerenkov Radiation and Quantum Friction

We show that, in a model where a non-relativistic particle is coupled to a quantized relativistic scalar Bose field, the embedded mass shell of the particle dissolves in the continuum when the interaction is turned on, provided the coupling constant is sufficiently small. More precisely, under the assumption that the fiber eigenvectors corresponding to the putative mass shell are differentiable as functions of the total momentum of the system, we show that a mass shell could exist only at a strictly positive distance from the unperturbed embedded mass shell near the boundary of the energy-momentum spectrum.Comment: Revised version: a remark added at the end of Section