@article{21933, abstract = {We consider the liquid drop model with a positive background density in the thermodynamic limit. We prove a two-term asymptotics for the ground state energy per unit volume in the dilute limit. Our proof justifies the expectation that optimal configurations consist of droplets of unit size that arrange themselves according to minimizers for the Jellium problem for point particles. In particular, we provide the first rigorous derivation of what is known as the gnocchi phase in astrophysics.}, author = {Frank, Rupert L. and Lewin, Mathieu and Seiringer, Robert}, issn = {1097-0312}, journal = {Communications on Pure and Applied Mathematics}, publisher = {Wiley}, title = {{Liquid drop model for nuclear matter in the low density limit}}, doi = {10.1002/cpa.70039}, year = {2026}, } @article{22292, abstract = {We show that a suitable choice of boundary conditions for the Laplacian allows for the appearance of an arbitrary number of condensates, described by arbitrary harmonic functions, in the thermodynamic limit of an ideal Bose gas.}, author = {De Wilde, Michiel and Seiringer, Robert}, issn = {1089-7658}, journal = {Journal of Mathematical Physics}, number = {6}, publisher = {AIP Publishing}, title = {{Arbitrary harmonic functions as Bose–Einstein condensates}}, doi = {10.1063/5.0325354}, volume = {67}, year = {2026}, } @article{21472, abstract = {We study the ground state energy of a gas of spin 1/2 fermions with repulsive short-range interactions. We derive an upper bound that agrees, at low density e, with the Huang–Yang conjecture. The latter captures the first three terms in an asymptotic low-density expansion, and in particular the Huang–Yang correction term of order e^7/3. Our trial state is constructed using an adaptation of the bosonic Bogoliubov theory to the Fermi system, where the correlation structure of fermionic particles is incorporated by quasi-bosonic Bogoliubov transformations. In the latter, it is important to consider a modified zero-energy scattering equation that takes into account the presence of the Fermi sea, in the spirit of the Bethe–Goldstone equation.}, author = {Giacomelli, Emanuela L. and Hainzl, Christian and Nam, Phan Thành and Seiringer, Robert}, issn = {1097-0312}, journal = {Communications on Pure and Applied Mathematics}, number = {8}, pages = {1919--1972}, publisher = {Wiley}, title = {{The Huang–Yang formula for the low-density Fermi gas: Upper bound}}, doi = {10.1002/cpa.70040}, volume = {79}, year = {2026}, } @article{22639, abstract = {We present an abstract Dyson expansion for perturbations that are merely relatively form-bounded, and apply it to the polaron problem. For a large class of polaron-type models, including the Fröhlich and Nelson models, we prove that the vacuum expectation value of the heat semi-group is a completely monotone function of the square of the total momentum. Consequently, the ground-state energy is a concave function of the square of the momentum, a result recently proved for the Fröhlich model in [14] using a probabilistic approach via Wiener integrals.}, author = {Desio, Davide and Seiringer, Robert}, issn = {1573-0530}, journal = {Letters in Mathematical Physics}, number = {4}, publisher = {Springer Nature}, title = {{Dyson expansion for form-bounded perturbations and applications to the polaron problem}}, doi = {10.1007/s11005-026-02107-2}, volume = {116}, year = {2026}, } @article{21270, abstract = {The one-dimensional Fröhlich model describing the motion of a single electron interacting with optical phonons is a paradigmatic model of quantum many-body physics. We predict the existence of an arbitrarily large number of bound excited states in the strong-coupling limit and calculate their excitation energies. Numerical simulations of a discretized model demonstrate the complete amelioration of the projector Monte Carlo sign problem by walker annihilation in an infinite Hilbert space. They reveal the threshold for the occurrence of the first bound excited states at a value of 𝛼≈1.73 for the dimensionless coupling constant. This puts the threshold into the regime of intermediate interaction strength. We find a significant spectral weight and increased phonon number of the bound excited state at threshold.}, author = {Taylor, J. and Čufar, M. and Mitrouskas, David Johannes and Seiringer, Robert and Pahl, E. and Brand, J.}, issn = {2469-9969}, journal = {Physical Review B}, number = {18}, publisher = {American Physical Society}, title = {{Bound excited states of Fröhlich polarons in one dimension}}, doi = {10.1103/s9p9-jflq}, volume = {112}, year = {2025}, } @article{19403, abstract = {We study the BCS critical temperature on half-spaces in dimensions d =1, 2, 3 with Dirichlet or Neumann boundary conditions. We prove that the critical temperature on a half-space is strictly higher than on Rd, at least at weak coupling in d = 1, 2 and weak coupling and small chemical potential in d = 3. Furthermore, we show that the relative shift in critical temperature vanishes in the weak coupling limit.}, author = {Roos, Barbara and Seiringer, Robert}, issn = {1432-0673}, journal = {Archive for Rational Mechanics and Analysis}, publisher = {Springer Nature}, title = {{BCS critical temperature on half-spaces}}, doi = {10.1007/s00205-025-02088-x}, volume = {249}, year = {2025}, } @article{19628, abstract = {We consider the critical temperature for superconductivity, defined via the linear BCS equation. We prove that at weak coupling the critical temperature for a sample confined to a quadrant in two dimensions is strictly larger than the one for a half-space, which in turn is strictly larger than the one for R^2. Furthermore, we prove that the relative difference of the critical temperatures vanishes in the weak coupling limit.}, author = {Roos, Barbara and Seiringer, Robert}, issn = {2050-5094}, journal = {Forum of Mathematics, Sigma}, publisher = {Cambridge University Press}, title = {{Enhanced superconductivity at a corner for the linear BCS equation}}, doi = {10.1017/fms.2024.145}, volume = {13}, year = {2025}, } @article{20251, abstract = {The Lane–Emden inequality controls (math. formular) in terms of the L^1 and L^p norms of p. We provide a remainder estimate for this inequality in terms of a suitable distance of p to the manifold of optimizers.}, author = {Carlen, Eric and Lewin, Mathieu and Lieb, Elliott H. and Seiringer, Robert}, issn = {1432-0835}, journal = {Calculus of Variations and Partial Differential Equations}, number = {7}, publisher = {Springer Nature}, title = {{Stability estimate for the Lane–Emden inequality}}, doi = {10.1007/s00526-025-03062-x}, volume = {64}, year = {2025}, } @article{17478, abstract = {We study the Fröhlich polaron model in R3, and prove a lower bound on its ground state energy as a function of the total momentum. The bound is asymptotically sharp at large coupling. In combination with a corresponding upper bound proved earlier (Mitrouskas et al. in Forum Math. Sigma 11:1–52, 2023), it shows that the energy is approximately parabolic below the continuum threshold, and that the polaron’s effective mass (defined as the semi-latus rectum of the parabola) is given by the celebrated Landau–Pekar formula. In particular, it diverges as α4 for large coupling constant α.}, author = {Brooks, Morris and Seiringer, Robert}, issn = {1618-1913}, journal = {Publications Mathematiques de l'Institut des Hautes Etudes Scientifiques}, pages = {271--309}, publisher = {Springer Nature}, title = {{The Fröhlich polaron at strong coupling: Part II — Energy-momentum relation and effective mass}}, doi = {10.1007/s10240-024-00150-0}, volume = {140}, year = {2024}, } @article{18958, abstract = {This workshop brought together experts on the analysis of quantum many-body problems and quantum statistical mechanics, with the goal of discussing the state-of-the-art of the field, recent developments as well as challenges for the future. The main topics of discussion concerned the equilibrium and dynamical behavior of (bosonic or fermionic) quantum gases, quantum spin systems, as well as quantum field theory models like the Nelson or Fröhlich model.}, author = {Hainzl, Christian and Schlein, Benjamin and Seiringer, Robert and Warzel, Simone}, issn = {1660-8941}, journal = {Oberwolfach Reports}, number = {3}, pages = {2247--2302}, publisher = {EMS Press}, title = {{Many-body quantum systems}}, doi = {10.4171/owr/2023/39}, volume = {20}, year = {2024}, } @article{18107, abstract = {We consider a dilute fully spin-polarized Fermi gas at positive temperature in dimensions d∈{1,2,3} . We show that the pressure of the interacting gas is bounded from below by that of the free gas plus, to leading order, an explicit term of order adρ2+2/d, where a is the p-wave scattering length of the repulsive interaction and ρ is the particle density. The results are valid for a wide range of repulsive interactions, including that of a hard core, and uniform in temperatures at most of the order of the Fermi temperature. A central ingredient in the proof is a rigorous implementation of the fermionic cluster expansion of Gaudin, Gillespie and Ripka (Nucl. Phys. A, 176.2 (1971), pp. 237–260).}, author = {Lauritsen, Asbjørn Bækgaard and Seiringer, Robert}, issn = {2050-5094}, journal = {Forum of Mathematics, Sigma}, publisher = {Cambridge University Press}, title = {{Pressure of a dilute spin-polarized Fermi gas: Lower bound}}, doi = {10.1017/fms.2024.56}, volume = {12}, year = {2024}, } @article{14931, abstract = {We prove an upper bound on the ground state energy of the dilute spin-polarized Fermi gas capturing the leading correction to the kinetic energy resulting from repulsive interactions. One of the main ingredients in the proof is a rigorous implementation of the fermionic cluster expansion of Gaudin et al. (1971) [15].}, author = {Lauritsen, Asbjørn Bækgaard and Seiringer, Robert}, issn = {1096-0783}, journal = {Journal of Functional Analysis}, number = {7}, publisher = {Elsevier}, title = {{Ground state energy of the dilute spin-polarized Fermi gas: Upper bound via cluster expansion}}, doi = {10.1016/j.jfa.2024.110320}, volume = {286}, year = {2024}, } @article{12183, abstract = {We consider a gas of n bosonic particles confined in a box [−ℓ/2,ℓ/2]3 with Neumann boundary conditions. We prove Bose–Einstein condensation in the Gross–Pitaevskii regime, with an optimal bound on the condensate depletion. Moreover, our lower bound for the ground state energy in a small box [−ℓ/2,ℓ/2]3 implies (via Neumann bracketing) a lower bound for the ground state energy of N bosons in a large box [−L/2,L/2]3 with density ρ=N/L3 in the thermodynamic limit.}, author = {Boccato, Chiara and Seiringer, Robert}, issn = {1424-0637}, journal = {Annales Henri Poincare}, pages = {1505--1560}, publisher = {Springer Nature}, title = {{The Bose Gas in a box with Neumann boundary conditions}}, doi = {10.1007/s00023-022-01252-3}, volume = {24}, year = {2023}, } @article{13178, abstract = {We consider the large polaron described by the Fröhlich Hamiltonian and study its energy-momentum relation defined as the lowest possible energy as a function of the total momentum. Using a suitable family of trial states, we derive an optimal parabolic upper bound for the energy-momentum relation in the limit of strong coupling. The upper bound consists of a momentum independent term that agrees with the predicted two-term expansion for the ground state energy of the strongly coupled polaron at rest and a term that is quadratic in the momentum with coefficient given by the inverse of twice the classical effective mass introduced by Landau and Pekar.}, author = {Mitrouskas, David Johannes and Mysliwy, Krzysztof and Seiringer, Robert}, issn = {2050-5094}, journal = {Forum of Mathematics}, pages = {1--52}, publisher = {Cambridge University Press}, title = {{Optimal parabolic upper bound for the energy-momentum relation of a strongly coupled polaron}}, doi = {10.1017/fms.2023.45}, volume = {11}, year = {2023}, } @article{13207, abstract = {We consider the linear BCS equation, determining the BCS critical temperature, in the presence of a boundary, where Dirichlet boundary conditions are imposed. In the one-dimensional case with point interactions, we prove that the critical temperature is strictly larger than the bulk value, at least at weak coupling. In particular, the Cooper-pair wave function localizes near the boundary, an effect that cannot be modeled by effective Neumann boundary conditions on the order parameter as often imposed in Ginzburg–Landau theory. We also show that the relative shift in critical temperature vanishes if the coupling constant either goes to zero or to infinity.}, author = {Hainzl, Christian and Roos, Barbara and Seiringer, Robert}, issn = {1664-0403}, journal = {Journal of Spectral Theory}, number = {4}, pages = {1507–1540}, publisher = {EMS Press}, title = {{Boundary superconductivity in the BCS model}}, doi = {10.4171/JST/439}, volume = {12}, year = {2023}, } @article{13225, abstract = {Recently the leading order of the correlation energy of a Fermi gas in a coupled mean-field and semiclassical scaling regime has been derived, under the assumption of an interaction potential with a small norm and with compact support in Fourier space. We generalize this result to large interaction potentials, requiring only |⋅|V^∈ℓ1(Z3). Our proof is based on approximate, collective bosonization in three dimensions. Significant improvements compared to recent work include stronger bounds on non-bosonizable terms and more efficient control on the bosonization of the kinetic energy.}, author = {Benedikter, Niels P and Porta, Marcello and Schlein, Benjamin and Seiringer, Robert}, issn = {1432-0673}, journal = {Archive for Rational Mechanics and Analysis}, number = {4}, publisher = {Springer Nature}, title = {{Correlation energy of a weakly interacting Fermi gas with large interaction potential}}, doi = {10.1007/s00205-023-01893-6}, volume = {247}, year = {2023}, } @article{14254, abstract = {In [10] Nam proved a Lieb–Thirring Inequality for the kinetic energy of a fermionic quantum system, with almost optimal (semi-classical) constant and a gradient correction term. We present a stronger version of this inequality, with a much simplified proof. As a corollary we obtain a simple proof of the original Lieb–Thirring inequality.}, author = {Seiringer, Robert and Solovej, Jan Philip}, issn = {1096-0783}, journal = {Journal of Functional Analysis}, number = {10}, publisher = {Elsevier}, title = {{A simple approach to Lieb-Thirring type inequalities}}, doi = {10.1016/j.jfa.2023.110129}, volume = {285}, year = {2023}, } @article{14441, abstract = {We study the Fröhlich polaron model in R3, and establish the subleading term in the strong coupling asymptotics of its ground state energy, corresponding to the quantum corrections to the classical energy determined by the Pekar approximation.}, author = {Brooks, Morris and Seiringer, Robert}, issn = {1432-0916}, journal = {Communications in Mathematical Physics}, pages = {287--337}, publisher = {Springer Nature}, title = {{The Fröhlich Polaron at strong coupling: Part I - The quantum correction to the classical energy}}, doi = {10.1007/s00220-023-04841-3}, volume = {404}, year = {2023}, } @article{14662, abstract = {We consider a class of polaron models, including the Fröhlich model, at zero total momentum, and show that at sufficiently weak coupling there are no excited eigenvalues below the essential spectrum.}, author = {Seiringer, Robert}, issn = {1664-0403}, journal = {Journal of Spectral Theory}, number = {3}, pages = {1045--1055}, publisher = {EMS Press}, title = {{Absence of excited eigenvalues for Fröhlich type polaron models at weak coupling}}, doi = {10.4171/JST/469}, volume = {13}, year = {2023}, } @article{14854, abstract = {We study the spectrum of the Fröhlich Hamiltonian for the polaron at fixed total momentum. We prove the existence of excited eigenvalues between the ground state energy and the essential spectrum at strong coupling. In fact, our main result shows that the number of excited energy bands diverges in the strong coupling limit. To prove this we derive upper bounds for the min-max values of the corresponding fiber Hamiltonians and compare them with the bottom of the essential spectrum, a lower bound on which was recently obtained by Brooks and Seiringer (Comm. Math. Phys. 404:1 (2023), 287–337). The upper bounds are given in terms of the ground state energy band shifted by momentum-independent excitation energies determined by an effective Hamiltonian of Bogoliubov type.}, author = {Mitrouskas, David Johannes and Seiringer, Robert}, issn = {2578-5885}, journal = {Pure and Applied Analysis}, keywords = {General Medicine}, number = {4}, pages = {973--1008}, publisher = {Mathematical Sciences Publishers}, title = {{Ubiquity of bound states for the strongly coupled polaron}}, doi = {10.2140/paa.2023.5.973}, volume = {5}, year = {2023}, }