Accomplishments

My 30+ year research career has led to significant contributions in several areas, including:

  • The thermal history of electroweak symmetry-breaking and implications for the origin of the cosmic matter-antimatter asymmetry
  • Probes of extended Higgs sectors at the Large Hadron Collider and prospective future high-energy colliders
  • Tests of fundamental interactions using nucleons and nuclei
  • Internal structure of nucleons as viewed by low-energy probes

Read more about my work on extended Higgs sectors and the electroweak phase transition, electroweak baryogenesis, and fundamental symmetries and neutrinos.

BSM Higgs and the Electroweak Phase Transition

My research in this area has involved studying simplified models and their phenomenology, as well as addressing quantum field theory issues as needed to obtain robust early Universe computations.

In recent work, I laid out generic features of SM Higgs sector extensions that can yield a first order electroweak phase transition (EWPT) that applies to a vast array of specific models.

  • “The Electroweak Phase Transition: A Collider Target”, M. J. Ramsey-Musolf, JHEP 09 (2020) 179 [1912.07189].

This work shows that there is generically an upper bound on the mass of the new scalars and lower bound on the strength of their coupling to the SM Higgs boson if the spontaneous symmetry-breaking transition to the present “Higgs phase” in the early universe was a first order transition. 

Gauge singlets:

The simplest Higgs sector extensions that can provide for a first order EWPT and/or dark matter involve adding real or complex gauge singlet scalars to the Standard Model. Gauge singlets often appear in complete BSM theories, such as the next-to-minimal supersymmetric Standard Model. By focusing on simplified models, we identify generic features that pertain to cosmology and collider probes that can then be applied to more complete theories. Highlights of this work include:

  •  “CERN LHC Phenomenology of an Extended Standard Model with a Real Scalar Singlet”, V. Barger, P. Langacker, M. McCaskey, M. J. Ramsey-Musolf, and G. Shaughnessy, Phys. Rev. D77: 035005 (2008).
  • “Singlet Higgs Phenomenology and the Electroweak Phase Transition”, S. Profumo, M. J. Ramsey-Musolf, and G. Shaughnessy, JHEP 0708:010 (2007).
  • “Singlet-Catalyzed Electroweak Phase Transitions and Precision Higgs Boson Studies”, 
Stefano Profumo, M. J. Ramsey-Musolf, Carroll L. Wainwright, and Peter Winslow, Phys. Rev. D91 (2015) 3, 035018 
[arXiv:1407.5342/hep-ph]
  • “Complex Singlet Extension of the Standard Model”, V. Barger, P. Langacker, M. McCaskey, M. J. Ramsey-Musolf, and G. Shaugnessy Phys. Rev. D79:015018 (2009) [arXiv:0811.0393/hep-ph].
  • “Vacuum Stability, Perturbativity, and Scalar Single Dark Matter”, M. Gonderinger, Y. Li, H. Patel, and M.J. Ramsey-Musolf, JHEP1001:002 (2010)  [arXiv:0910.3167] (2009).

Real triplets:

The simplest Higgs sector extension involving new particles that have electroweak interactions involves the real triplet scalar multiplet containing three new particles. Real triplets emerge in grand unified models. The real triplet extension provides a rich arena in which to explore both theoretical issues and novel phase transition dynamics. Our significant work includes:

  • “Triplet Scalars and Dark Matter at the LHC”, P. Fileviez Perez, H. H. Patel, M. J. Ramsey-Musolf, and K. Wang, Phys. Rev. D79:055024 (2009) [arXiv:0811.3957/hep-ph].
  • “Stepping Into Electroweak Symmetry Breaking: Phase Transitions and Higgs Phenomenology”, 
Hiren H. Patel and M. J. Ramsey-Musolf, Phys. Rev. D88 (2013) 035013 [arXiv:1212.5652/hep-ph].
  • “Electroweak Phase Transition in the SSM-I: Dimensional Reduction”, L. Niemi, H. Patel, M. J. Ramsey-Musolf, T. Tenkanen, and D. Weir, Phys. Rev. D100 (2019) 035002 [1802.10500].
  •  “Thermodynamics of a Two-Step Electroweak Phase Transition”, L. Niemi, M. J. Ramsey-Musolf, T.V.I. Tenkanen, D. Weir, Phys. Rev. Lett. 126 (2021) 171802 [2005.11332].
  • “Addressing the Gravitational Wave-Collider Inverse Problem”, L.S. Friedrich, M. J. Ramsey-Musolf, Tuomas V.I. Tenkanen, V.Q. Tran, [2203.05889].

Theoretical developments: gauge invariance:

In performing computations of phase transition properties, it essential to maintain theoretical rigor. Among the most important requirements in quantum field theory is maintaining gauge invariance when carrying out perturbative computations. However, this requirement has not been satisfied in much of the theoretical literature. Our work has demonstrated how to implement gauge invariance computing the finite-temperature effective potential (relevant for thermodynamics), effective action for nucleation, and the rate for electroweak sphaleron transitions in the symmetry-broken phase. Key papers include:

  • “Baryon Washout, Electroweak Phase Transition, and Perturbation Theory”, H. H. Patel and M. J. Ramsey-Musolf, JHEP 1107:029 (2011) [arXiv:1101.4665/hep-ph].
  • “Nucleation at Finite Temperature: A Gauge-Invariant, Perturbative Framework”, J. Lofgren, M. J. Ramsey-Musolf, P. Schicho, T.V.I. Tenkanen [arXiv:2112.05472/hep-ph].
  • “Computing the Gauge-Invariant Bubble Nucleation Rate in Finite Temperature Effective Field Theory”, J. Hirvonen, J. Lofgren, M. J. Ramsey-Musolf, P. Schicho, T.V.I. Tenkanen, JHEP 07 (2022) 135 [arXiv:2112.08912/hep-ph].

CP-Violation and Electroweak Baryogenesis

As with my work on the EWPT, my research on the dynamics of CP-violation (CPV) in electroweak baryogenesis (EWBG) is multifaceted, including development of theoretical tools, exploration of novel EWBG scenarios, and applications to widely studied BSM theories. The key theoretical challenge is to perform robust quantum transport theory computations using the methods of non-equilibrium quantum field theory.

Transport theory:

My collaborators and I have worked in two contexts: the so-called “vev-insertion approximation” (VIA) that builds on earlier work by Toni Riotto and the “vev-resummed” (VR) approach that utilizes the full set of Kadanoff-Baym equations within the closed-time path formulation of non-equilibrium QFT. In both cases, we showed how a clear delineation of the physical scales and their ratios allows one to perform systematic expansions of the equations, thereby making solutions tractable and allowing for quantification of the theoretical uncertainties. I highlight two papers:

  • “Flavored Quantum Boltzmann Equations”, V. Cirigliano, C. Lee, M.J. Ramsey-Musolf, and S. Tulin, Phys. Rev. D81:103502 (2010) [arXiv:0912.3523/hep-ph].
  • “Resonant Relaxation in Electroweak Baryogenesis”, C. Lee, V. Cirigliano, and M.J. Ramsey-Musolf, Phys. Rev. D71: 075010 (2005) [hep-ph/0412354].

Scenarios and phenomenology:

My collaborators and I invented a new paradigm known as “Two-Step Electroweak Baryogenesis.” The idea is that in a scenario of multi-step electroweak symmetry breaking, the baryon asymmetry can be produced via EWBG during the transition to an earlier symmetry-breaking vacuum and subsequently transferred to the present Higgs phase during a final transition, which is described in this paper:

  • “Two-Step Electroweak Baryogenesis”, S, Inoue, G. Ovanesyan and M. J. Ramsey-Musolf, Phys. Rev. D93 (2016) 015013 [arXiv:1508.05404].

In addition to this work, we have applied the developments of QFT to the CPV transport dynamics in several other models, including the Minimal Supersymmetric Standard Model (MSSM), SM extensions with vector-like fermions, and flavor-changing transitions in the Two Higgs Doublet Model, a scenario known as “flavored EWBG” (see the first two papers below):

  •  “Lepton-Flavored Electroweak Baryogenesis”, Huai-ke Guo, Ying-Ying Li, Tao Liu, M. J. Ramsey-Musolf, and Jing Shu, Phys. Rev. D96 (2017) 115034 [arXiv:1609.09848].
  • “Electroweak Beautygenesis: from b—> s CP-violation to the Cosmic Baryon Asymmetry”, T. Liu, M. J. Ramsey-Musolf, and J. Shiu, Phys. Rev. Lett. 108:221301 (2012) [arXiv:1109:4145/hep-ph].
  •  “MSSM Baryogenesis and Electric Dipole Moments: An Update on the Phenomenology”, V. Cirigliano, Y. Li, S. Profumo, and M. J. Ramsey-Musolf, JHEP1001:053 (2010) [arXiv:0910.4589/hep-ph] (2009).
  • “Yukawa Interactions and Supersymmetric Electroweak Baryogenesis”, D. Chung, B. Garbrecht, M. J. Ramsey-Musolf, and S. Tulin, Phys. Rev. Lett. 102:061301 (2009) [arXiv:0808.1144/hep-ph].
  • “Baryogenesis, Electric Dipole Moments, and Dark Matter in the MSSM”, V. Cirigliano, S. Profumo, and M. J. Ramsey-Musolf JHEP 0607:002 (2006).

Fundamental Symmetries and Neutrinos

Tests of fundamental symmetries and studies of neutrino properties have become a core component of nuclear physics research.  These experiments provide powerful probes of BSM physics, as well as the internal structure of nucleons and nuclei. The Standard Model theory of the strong interaction, Quantum Chromodynamics, determines this internal structure, but many mysteries remain that require novel experimental probes. The interpretation of these exquisitely sensitive experiments in terms of BSM physics or QCD requires equally robust theoretical computations involving SM or BSM dynamics.

One may further classify the observable properties and processes into two categories: (1) those that are strictly zero or highly suppressed within the SM and (2) those for which the SM predicts non-zero effects at the level of experimental sensitivity. In the former case, a non-zero experimental result would provide unambiguous evidence for either BSM physics or — in the case of electric dipole moments — the CP-violating term in the QCD Lagrangian. In the latter instance, one may either (a) assume the fundamental SM interaction is correct and interpret results in terms of aspects of nucleon and nuclear structure or (b) assume the nucleon and nuclear structure are under sufficient theoretical control that a deviation from the SM prediction points to BSM physics.

Standard Model suppressed or forbidden processes

I have concentrated on searches for four observables over the course of my career: electric dipole moments (EDMs) of leptons, nucleons, neutral atoms, and molecules; the neutrinoless double beta-decay (NDBD) of atomic nuclei; neutrino magnetic moments; and charged lepton flavor-changing (or violating) processes.

A) Electric Dipole Moments

My EDM research has included computations of EDMs in the MSSM and Two-Higgs Doublet Model, leptoquark theories, CPV “dark photon” interactions, and models leading to viable EWBG, such as the two-step EWBG mentioned above. I have also worked for many years on the interpretation of diamagnetic atom EDMs, focusing on corrections to so-called “Schiff screening.”  Highlights from my EDM research include:

  • “Left-Right Symmetry and Electric Dipole Moments: A Global Analysis”, M.J. Ramsey-Musolf and J. C. Vasquez, Phys. Lett. B 815 (2021) 136136 [2012.02799].
  • “Electric Dipole Moments from Scalar Leptoquark Interactions”, K. Fuyuto, M. J. Ramsey-Musolf, and T. Shen, Phys. Lett. B 788 (2019) 52 [1804.01137].
  • “Electric Dipole Moments of the Atoms, Molecules, Nuclei and Particles”, T. Chupp, P. Fierlinger, M. J. Ramsey-Musolf, J. Singh, Rev. Mod. Phys. 91 (2019) 015001  [1710.02504].
  • “Electric Dipole Moments of Nucleons, Nuclei, and Atoms: The Standard Model and Beyond”, 
Jonathan Engel, M. J. Ramsey-Musolf, U. van Kolck Prog. Part. Nucl. Phys. 71 (2013) 21-74 
[arXiv:1303.2371/nucl-th].
  • “CP-Violating Phenomenology of Flavor Conserving Two Higgs Doublet Models”, 
Satoru Inoue, M. J. Ramsey-Musolf, and Yue Zhang, Phys. Rev.D89 (2014) 11, 115023 
[arXiv:1403.4257/hep-ph].
  • “Higgs-Higgsino-Gaugino Induced Two Loop Electric Dipole Moments”, Y. Li, S. Profumo, and M. J. Ramsey-Musolf, Phys. Rev. D78:075009 (2008) [arXiv:0806.2693/hep-ph] (2008).
  • “Atomic Electric Dipole Moments: The Schiff Theorem and Its Corrections”, C.-P. Liu, M.J. Ramsey-Musolf, W.C. Haxton, R.G.E. Timmermans, and A.E.L. Dieperink, Phys. Rev. C76:035503 (2007).
  • “Electric Dipole Moments and the Mass Scale of New T-Violating, P-Conserving Interactions”, M.J. Ramsey-Musolf , Phys. Rev. Lett. 83, 3997 (1999); E-ibid. 84, 5681 (2000).
  • “Electric Dipole Moments of Nuclei”, J.F. Donoghue, B.R. Holstein, and M.J. Musolf,  Phys. Lett. B196 (1987) 196.

B) Neutrinoless Double Beta Decay

The search for neutrinoless double beta decay (NDBD) provides the most powerful test of the conservation of total lepton number. At the level of quantum corrections, the SM breaks this conservation through the “B+L anomaly,” whereas it is conserved at the classical (Lagrangian) level. A plethora of theoretical proposals for explaining the non-vanishing but tiny neutrino masses involve such a Lagrangian-level lepton number violation (LNV). If realized in nature, this LNV would imply that neutrinos are their own anti-particles, or so-called “Majorana fermions.” If not, then neutrinos are “Dirac fermions.” If such LNV is present, the associated mass scale is unknown. The beautiful seesaw neutrino mass mechanism implies that the scale is very high — well beyond the reach of any envisioned experiments. The primary low-energy implications would be Majorana masses for the light neutrinos and strong prospects for the observation of NDBD. My research has focused on the possibility that LNV lives at the TeV scale, making particles and interactions that mediate this symmetry violation experimentally accessible.  On the one hand, a careful and systematic interpretation of NDBD experiments in terms of TeV scale and (below) LNV requires the use of chiral effective field theory, about which my collaborators and I wrote the seminal paper 20 years ago. On the other hand, unpacking an NDBD signal or non-observation in terms of the underlying dynamics requires drawing on results from other frontiers, including astrophysical probes of neutrino masses and high-energy collider searches for new particles. Highlights from this NDBD work include:

  • “Neutrinoless Double Beta-Decay and Effective Field Theory”, G. Prezeau, M.J. Ramsey-Musolf, and P. Vogel, Phys. Rev. D68: 034016 (2003).
  • “TeV lepton number violation: From neutrinoless double β-decay to the LHC”, T. Peng. M. J. Ramsey-Musolf, and P. Winslow, Phys. Rev. D93 (2016) 093002 [arXiv: 1508.04444].
  • “Left-Right Symmetry and Leading Contributions to Neutrinoless Double Beta Decay”, G. Li, M. J. Ramsey-Musolf, J. C. Vasquez, Phys. Rev. Lett. 126 (2021) 151801 [2009.01257].

C) Neutrino Magnetic Moments

Chiral symmetry implies that the magnetic moments of massless neutrinos must vanish. It is natural to ask, then, how large we expect neutrino magnetic moments to be based on the observed scale of the light neutrino masses. My collaborators and I used effective field theory methods to address this question. We found that the expected size of neutrino magnetic moments could be vastly different, depending on whether neutrinos are Majorana or Dirac particles. The Majorana neutrino magnetic moments could, in principle, be several orders of magnitude larger than those for Dirac neutrinos, potentially putting them within the reach of neutrino magnetic moment searches. For Dirac neutrinos, on the other hand, an experimental signature is unlikely anytime soon. Thus, the experimental discovery of a non-vanishing neutrino magnetic moment would provide strong indirect evidence for LNV. You may read further about our magnetic moments work here:

  • “How Magnetic is the Dirac Neutrino”, N. Bell, V. Cirigliano, M.J. Ramsey-Musolf, P. Vogel, M.B. Wise, Phys. Rev. Lett. 95, 151802 (2005).
  • “Model Independent Bounds on Magnetic Moments of Majorana Neutrinos”, N. Bell, M. Gorchtein, M. J. Ramsey-Musolf, P. Vogel, P. Wang, Phys. Lett. B642, 377 (2006).

Standard Model Processes and Precision Measurements

My research has focused primarily on two processes in this category: parity-violating electron scattering (PVES) and beta-decay of the neutron and nuclei. For PVES, the primary observable is a “left-right” asymmetry A_PV that measures the difference in the rate for scattering left- and right-handed electrons from fixed targets. Depending on the experimental kinematics, A_PV is sensitive to contributions from physics beyond the Standard Model (BSM) and/or novel aspects of nucleon and nuclear internal structure, such as the impact of strange sea quarks on nucleon electromagnetic properties. For beta-decay, there are several observables of interest, including the decay rate (or “half-life”) and correlations between the outgoing particles and the spin of the decaying neutron or nucleus. In all cases, the proper theoretical interpretation requires the most robust Standard Model predictions. In this context, my work has concentrated on computing the higher order “electroweak radiative corrections” (EWRC). A particular challenge has been treating the impact of non-perturbative strong interactions on these corrections. My collaborators and I have relied on a number of tools to address this challenge, quantify the associated theoretical uncertainty, and develop methods for reducing that uncertainty. In addition, evaluating BSM contributions can require computing their effects in higher-order EWRC. Our most significant work includes:

  • “Parity-Violating Moller Scattering at Next-to-Next-to-Leading Order: Closed Fermion Loops”, Y. Du, A. Freitas, H.H. Patel, M. J. Ramsey-Musolf, Phys. Rev. Lett. 126 (2021) 131801 [1912.08220].
  •  “Dispersive Evaluation of Inner Radiative Correction in Neutron and Nuclear Beta Decay”, C. Y. Seng, M. Gorchtein, M. J. Ramsey-Musolf, Phys Rev. D 100 (2019) 013001 [1812.03352].
  • “Reduced Hadronic Uncertainty in the Determination of Vud “, C.-Y. Seng, M. Gorchtein, H. H. Patel, M. J. Ramsey-Musolf, Phys. Rev. Lett. 121 (2018) 241804 [1807.10197]
  • “The Weak Mixing Angle at Low Energies”, J. Erler and M.J. Ramsey-Musolf, Phys. Rev. D72: 073003 (2005).
  • “Probing Supersymmetry with Parity-Violating Electron Scattering”,  A. Kurylov, M.J. Ramsey-Musolf, and S. Su, Phys. Rev. D68 035008 (2003).
  • “The Weak Charge of the Proton and New Physics”, J. Erler, A. Kurylov, and M.J. Ramsey-Musolf, Phys. Rev. D68 : 016006 (2003).
  • “Charged Current Universality in the MSSM”, A. Kurylov and M.J. Ramsey-Musolf, Phys. Rev. Lett. 88: 071804 (2002).
  • “The Nucleon Anapole Moment and Parity Violating ep Scattering”, M.J. Ramsey-Musolf, Shi-lin Zhu, S.J. Puglia, and B.R. Holstein, Phys. Rev. D62:030008 (2000).
  • “Electroweak Corrections to Parity-Violating Neutral Current Scattering”, M.J. Musolf and B.R. Holstein, Phys. Lett. B242 (1990) 461.
  • “Semi-leptonic Probes of the Hadronic Neutral Current,” M.J. Musolf, T.W. Donnelly, J. Dubach, S.J. Pollock, S. Kowalski, and E.J. Beise, Phys. Rep. 239 (1994) 1.