Heather E. Logan
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Research Interests
Heather E. Logan has a total of 69 co-authors. Here are the top co-authors by number of shared publications:
- Katy Hartling
Ottawa-Carleton Institute for Physics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada
12 shared publications - Baradhwaj Coleppa
Indian Institute of Technology Gandhinagar
10 shared publications - Terry Pilkington
Ottawa-Carleton Institute for Physics Carleton University 1125 Colonel By Drive K1S 5B6 Ottawa Ontario Canada
9 shared publications - Kunal Kumar
Ottawa-Carleton Institute for Physics Carleton University 1125 Colonel By Drive K1S 5B6 Ottawa Ontario Canada
7 shared publications - Adam Martin
University of Notre Dame
6 shared publications - Carlos Henrique de Lima
TRIUMF
6 shared publications
Latest Publications
- Open Access
- 6 October 2026
- Published by American Physical Society (APS) in Physical Review D
- Vol. 114 (7)
Analytic approximations for fermionic preheating
Nonthermal fermions can be produced nonperturbatively in the early Universe during coherent oscillations of a scalar field. We explore fermion production in λ ϕ 4 inflation through this mechanism and analyze the momentum spectrum of the fermions produced, which depends on a coupling parameter q . For q ≳ 0.01 , the main contribution to the total number density comes from an approximately half-filled Fermi sphere as a result of nonadiabaticity. For q ≲ 0.01 , we find that the major contributions instead come from resonance peaks at higher momentum values. We find a simple relation to predict the momentum values corresponding to resonance peaks for any q . We observe power-law behavior for the total number density of fermions as a function of q and find numerical approximations for the integrals describing the total number density. We find that it is proportional to q 1 / 2 for q ≲ 0.01 and proportional to q 3 / 4 for q ≳ 10 . If fermions produced by this mechanism make up the entirety of dark matter, we estimate lower bounds on their mass.
- 6 October 2026
- Published by American Physical Society (APS) in Physical Review D
- Vol. 114 (7)
Open AccessAnalytic approximations for fermionic preheating
Nonthermal fermions can be produced nonperturbatively in the early Universe during coherent oscillations of a scalar field. We explore fermion production in λ ϕ 4 inflation through this mechanism and analyze the momentum spectrum of the fermions produced, which depends on a coupling parameter q . For q ≳ 0.01 , the main contribution to the total number density comes from an approximately half-filled Fermi sphere as a result of nonadiabaticity. For q ≲ 0.01 , we find that the major contributions instead come from resonance peaks at higher momentum values. We find a simple relation to predict the momentum values corresponding to resonance peaks for any q . We observe power-law behavior for the total number density of fermions as a function of q and find numerical approximations for the integrals describing the total number density. We find that it is proportional to q 1 / 2 for q ≲ 0.01 and proportional to q 3 / 4 for q ≳ 10 . If fermions produced by this mechanism make up the entirety of dark matter, we estimate lower bounds on their mass.
- Open Access
- 12 November 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 110 (9)
Can be conserved in the two-Higgs-doublet model?We study the conditions under which the C P violation in the quark mixing matrix can leak into the scalar potential of the real two-Higgs-doublet model (2HDM) via divergent radiative corrections, thereby spoiling the renormalizability of the model. We show that any contributing diagram must involve 12 Yukawa-coupling insertions and a factor of the U ( 1 ) PQ -breaking scalar potential parameter λ 5 , thereby requiring at least six loops; this also implies that the 2HDM with only softly broken U ( 1 ) PQ is safe from divergent leaks of C P violation to all orders. We demonstrate that additional symmetries of the six-loop diagrams in the type I and II 2HDMs guarantee that all of the divergent C P -violating contributions cancel at this order. We also show that these symmetries are violated at seven loops and enumerate the classes of diagrams that can contribute to C P -violating divergences, providing evidence that the real 2HDM is theoretically inconsistent starting at the seven-loop level. Published by the American Physical Society 2024
- 12 November 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 110 (9)
Open AccessCan be conserved in the two-Higgs-doublet model?We study the conditions under which the C P violation in the quark mixing matrix can leak into the scalar potential of the real two-Higgs-doublet model (2HDM) via divergent radiative corrections, thereby spoiling the renormalizability of the model. We show that any contributing diagram must involve 12 Yukawa-coupling insertions and a factor of the U ( 1 ) PQ -breaking scalar potential parameter λ 5 , thereby requiring at least six loops; this also implies that the 2HDM with only softly broken U ( 1 ) PQ is safe from divergent leaks of C P violation to all orders. We demonstrate that additional symmetries of the six-loop diagrams in the type I and II 2HDMs guarantee that all of the divergent C P -violating contributions cancel at this order. We also show that these symmetries are violated at seven loops and enumerate the classes of diagrams that can contribute to C P -violating divergences, providing evidence that the real 2HDM is theoretically inconsistent starting at the seven-loop level. Published by the American Physical Society 2024
- Open Access
- 12 November 2024
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 133 (20) , 201801
Is the Real Two-Higgs-Doublet Model Consistent?
We provide strong evidence that the widely studied real two-Higgs-doublet model is inconsistent under renormalization due to quark-induced divergent C P violation ( C P V ). We identify the necessary ingredients for the C P V to enter the renormalization-group equations based on symmetry proprieties of the divergent diagrams. We demonstrate that while these ingredients are present starting at six loops, the divergent C P V is zero at that order due to approximate symmetries. We show that these symmetries are broken at seven loops and determine the parameter dependence of the resulting divergent C P V . Published by the American Physical Society 2024
- 12 November 2024
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 133 (20) , 201801
Open AccessIs the Real Two-Higgs-Doublet Model Consistent?
We provide strong evidence that the widely studied real two-Higgs-doublet model is inconsistent under renormalization due to quark-induced divergent C P violation ( C P V ). We identify the necessary ingredients for the C P V to enter the renormalization-group equations based on symmetry proprieties of the divergent diagrams. We demonstrate that while these ingredients are present starting at six loops, the divergent C P V is zero at that order due to approximate symmetries. We show that these symmetries are broken at seven loops and determine the parameter dependence of the resulting divergent C P V . Published by the American Physical Society 2024
- Open Access
Is the real two-Higgs-doublet model consistent?
We provide strong evidence that the widely-studied real two-Higgs-doublet model is inconsistent under renormalization due to quark-induced divergent CP violation (CPV). We identify the necessary ingredients for the CPV to enter the renormalization-group equations based on symmetry proprieties of the divergent diagrams. We demonstrate that while these ingredients are present starting at six loops, the divergent CPV is zero at that order due to approximate symmetries. We show that these symmetries are broken at seven loops and determine the parameter dependence of the resulting divergent CPV.
Open AccessIs the real two-Higgs-doublet model consistent?
We provide strong evidence that the widely-studied real two-Higgs-doublet model is inconsistent under renormalization due to quark-induced divergent CP violation (CPV). We identify the necessary ingredients for the CPV to enter the renormalization-group equations based on symmetry proprieties of the divergent diagrams. We demonstrate that while these ingredients are present starting at six loops, the divergent CPV is zero at that order due to approximate symmetries. We show that these symmetries are broken at seven loops and determine the parameter dependence of the resulting divergent CPV.
- Open Access
Can CP be conserved in the two-Higgs-doublet model?
We study the conditions under which the CP violation in the quark mixing matrix can leak into the scalar potential of the real two-Higgs-doublet model (2HDM) via divergent radiative corrections, thereby spoiling the renormalizability of the model. We show that any contributing diagram must involve 12 Yukawa-coupling insertions and a factor of the $U(1)_{PQ}$-breaking scalar potential parameter $λ_5$, thereby requiring at least six loops; this also implies that the 2HDM with only softly-broken $U(1)_{PQ}$ is safe from divergent leaks of CP violation to all orders. We demonstrate that additional symmetries of the six-loop diagrams in the type I and II 2HDMs guarantee that all of the divergent CP-violating contributions cancel at this order. We also show that these symmetries are violated at seven loops and enumerate the classes of diagrams that can contribute to CP-violating divergences, providing evidence that the real 2HDM is theoretically inconsistent starting at the seven-loop level.Open AccessCan CP be conserved in the two-Higgs-doublet model?
We study the conditions under which the CP violation in the quark mixing matrix can leak into the scalar potential of the real two-Higgs-doublet model (2HDM) via divergent radiative corrections, thereby spoiling the renormalizability of the model. We show that any contributing diagram must involve 12 Yukawa-coupling insertions and a factor of the $U(1)_{PQ}$-breaking scalar potential parameter $λ_5$, thereby requiring at least six loops; this also implies that the 2HDM with only softly-broken $U(1)_{PQ}$ is safe from divergent leaks of CP violation to all orders. We demonstrate that additional symmetries of the six-loop diagrams in the type I and II 2HDMs guarantee that all of the divergent CP-violating contributions cancel at this order. We also show that these symmetries are violated at seven loops and enumerate the classes of diagrams that can contribute to CP-violating divergences, providing evidence that the real 2HDM is theoretically inconsistent starting at the seven-loop level. - Open Access
- 20 December 2022
- Published by American Physical Society (APS) in Physical Review D
- Vol. 106 (11) , 115020
Unavoidable Higgs coupling deviations in the -symmetric Georgi-Machacek modelThe -symmetric version of the Georgi-Machacek model does not possess a decoupling limit in which all the new particles can be made arbitrarily heavy, opening the possibility that the model can be entirely excluded if experiments reveal no deviations from the Standard Model. We explore this model, focusing on the part of parameter space in which the vacuum expectation value of the triplets, , is small. In the small- limit, the second custodial-singlet scalar field necessarily becomes very light and can contribute to the total width of the 125 GeV Higgs boson via . We show that this process, together with LHC measurements of the rate, entirely excludes masses and thereby severely constrains the parameter space, setting an experimental lower bound on the vacuum expectation value of the triplets. This lower bound makes it impossible to avoid deviations from the Standard Model in the couplings of to fermion and vector boson pairs. We study the remaining parameter space after imposing constraints from direct searches for the additional Higgs bosons, and show that it is on the edge of being fully excluded at 95% confidence level by LHC measurements of the 125 GeV Higgs boson’s couplings. Measurements of these couplings at the future high-luminosity run of the LHC will have sufficient precision to entirely exclude the model at if no deviations from the Standard Model are observed.- 20 December 2022
- Published by American Physical Society (APS) in Physical Review D
- Vol. 106 (11) , 115020
Open AccessUnavoidable Higgs coupling deviations in the -symmetric Georgi-Machacek modelThe -symmetric version of the Georgi-Machacek model does not possess a decoupling limit in which all the new particles can be made arbitrarily heavy, opening the possibility that the model can be entirely excluded if experiments reveal no deviations from the Standard Model. We explore this model, focusing on the part of parameter space in which the vacuum expectation value of the triplets, , is small. In the small- limit, the second custodial-singlet scalar field necessarily becomes very light and can contribute to the total width of the 125 GeV Higgs boson via . We show that this process, together with LHC measurements of the rate, entirely excludes masses and thereby severely constrains the parameter space, setting an experimental lower bound on the vacuum expectation value of the triplets. This lower bound makes it impossible to avoid deviations from the Standard Model in the couplings of to fermion and vector boson pairs. We study the remaining parameter space after imposing constraints from direct searches for the additional Higgs bosons, and show that it is on the edge of being fully excluded at 95% confidence level by LHC measurements of the 125 GeV Higgs boson’s couplings. Measurements of these couplings at the future high-luminosity run of the LHC will have sufficient precision to entirely exclude the model at if no deviations from the Standard Model are observed. - Open Access
TASI 2013 lectures on Higgs physics within and beyond the Standard Model
These lectures start with a detailed pedagogical introduction to electroweak symmetry breaking in the Standard Model, including gauge boson and fermion mass generation and the resulting predictions for Higgs boson interactions. I then survey Higgs boson decays and production mechanisms at hadron and $e^+e^-$ colliders. I finish with two case studies of Higgs physics beyond the Standard Model: two-Higgs-doublet models, which I use to illustrate the concept of minimal flavor violation, and models with isospin-triplet scalar(s), which I use to illustrate the concept of custodial symmetry.Open AccessTASI 2013 lectures on Higgs physics within and beyond the Standard Model
These lectures start with a detailed pedagogical introduction to electroweak symmetry breaking in the Standard Model, including gauge boson and fermion mass generation and the resulting predictions for Higgs boson interactions. I then survey Higgs boson decays and production mechanisms at hadron and $e^+e^-$ colliders. I finish with two case studies of Higgs physics beyond the Standard Model: two-Higgs-doublet models, which I use to illustrate the concept of minimal flavor violation, and models with isospin-triplet scalar(s), which I use to illustrate the concept of custodial symmetry. - Open Access
- 21 July 2021
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2021 (7) , 1-36
CP violation from charged Higgs bosons in the three Higgs doublet model
We demonstrate a new type of cancellation of contributions to the electron and neutron electric dipole moments (EDMs) that occurs in three Higgs doublet models (3HDMs) when CP violation appears in the charged Higgs sector. The cancellation becomes exact when the two physical charged Higgs bosons in the model are degenerate in mass. Depending on the model parameters, degeneracies at the 10% level are however sufficient to evade current bounds on the electron and neutron EDMs. We demonstrate that viable parameter space remains with both charged Higgs bosons lighter than 500 GeV and large CP-violating phases while also satisfying theoretical constraints from perturbativity and experimental ones from $$ \overline{B} $$ → Xsγ and direct searches.- 21 July 2021
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2021 (7) , 1-36
Open AccessCP violation from charged Higgs bosons in the three Higgs doublet model
We demonstrate a new type of cancellation of contributions to the electron and neutron electric dipole moments (EDMs) that occurs in three Higgs doublet models (3HDMs) when CP violation appears in the charged Higgs sector. The cancellation becomes exact when the two physical charged Higgs bosons in the model are degenerate in mass. Depending on the model parameters, degeneracies at the 10% level are however sufficient to evade current bounds on the electron and neutron EDMs. We demonstrate that viable parameter space remains with both charged Higgs bosons lighter than 500 GeV and large CP-violating phases while also satisfying theoretical constraints from perturbativity and experimental ones from $$ \overline{B} $$ → Xsγ and direct searches. - Open Access
CP violation from charged Higgs bosons in the three Higgs doublet model
We demonstrate a new type of cancellation of contributions to the electron and neutron electric dipole moments (EDMs) that occurs in three Higgs doublet models (3HDMs) when CP violation appears in the charged Higgs sector. The cancellation becomes exact when the two physical charged Higgs bosons in the model are degenerate in mass. Depending on the model parameters, degeneracies at the 10\% level are however sufficient to evade current bounds on the electron and neutron EDMs. We demonstrate that viable parameter space remains with both charged Higgs bosons lighter than 500 GeV and large CP-violating phases while also satisfying theoretical constraints from perturbativity and experimental ones from $\bar{B} \to X_s \gamma$ and direct searches.Open AccessCP violation from charged Higgs bosons in the three Higgs doublet model
We demonstrate a new type of cancellation of contributions to the electron and neutron electric dipole moments (EDMs) that occurs in three Higgs doublet models (3HDMs) when CP violation appears in the charged Higgs sector. The cancellation becomes exact when the two physical charged Higgs bosons in the model are degenerate in mass. Depending on the model parameters, degeneracies at the 10\% level are however sufficient to evade current bounds on the electron and neutron EDMs. We demonstrate that viable parameter space remains with both charged Higgs bosons lighter than 500 GeV and large CP-violating phases while also satisfying theoretical constraints from perturbativity and experimental ones from $\bar{B} \to X_s \gamma$ and direct searches. - Open Access
- 28 June 2021
- Published by American Physical Society (APS) in Physical Review D
- Vol. 103 (11) , 115034
Probing dark sector violation with electric dipole moments and collidersWe study the experimental constraints on violation originating in a dark sector that communicates with the Standard Model through a Higgs portal coupling , where the is from a new gauge symmetry which is assumed to couple to lepton number. We compute explicitly the leading two-loop contribution of this effective operator to the electron electric dipole moment (EDM) and show that the resulting constraints are comparable to those from direct searches at electron-positron colliders when the effective operator is generated at tree level. We also examine an explicit UV completion for this effective operator that was first introduced to achieve electroweak baryogenesis and show that collider constraints from factories already exclude viable baryogenesis for masses below 10 GeV, and that future electron-positron Higgs factories will exclude viable baryogenesis for masses up to the center-of-mass energy if anticipated luminosities are achieved. For higher masses, the full viable baryogenesis parameter space lies within 6 orders of magnitude of the current upper bound on the electron EDM.- 28 June 2021
- Published by American Physical Society (APS) in Physical Review D
- Vol. 103 (11) , 115034
Open AccessProbing dark sector violation with electric dipole moments and collidersWe study the experimental constraints on violation originating in a dark sector that communicates with the Standard Model through a Higgs portal coupling , where the is from a new gauge symmetry which is assumed to couple to lepton number. We compute explicitly the leading two-loop contribution of this effective operator to the electron electric dipole moment (EDM) and show that the resulting constraints are comparable to those from direct searches at electron-positron colliders when the effective operator is generated at tree level. We also examine an explicit UV completion for this effective operator that was first introduced to achieve electroweak baryogenesis and show that collider constraints from factories already exclude viable baryogenesis for masses below 10 GeV, and that future electron-positron Higgs factories will exclude viable baryogenesis for masses up to the center-of-mass energy if anticipated luminosities are achieved. For higher masses, the full viable baryogenesis parameter space lies within 6 orders of magnitude of the current upper bound on the electron EDM.