Christopher T. Hill

{{Short description|American theoretical physicist}}

{{Infobox scientist

| name = Christopher T. Hill

| image = Image: ChristopherTHillphysics.jpg

| caption =

| birth_date = {{birth date and age|1951|6|19}}

| birth_place = Neenah, Wisconsin

| death_date =

| death_place =

| nationality = American

| residence =

| known_for = Infrared fixed point of the top quark; Topcolor; Top quark condensate; Dimensional deconstruction; Chiral symmetry breaking in Heavy-Light Mesons; Theory of UHE Cosmic Rays; Soft Nambu-Goldstone Boson model of Dark Matter.

| alma_mater = Massachusetts Institute of Technology (BS, MS)
California Institute of Technology (PhD)

| thesis_title = Higgs scalars and the nonleptonic weak interactions

| thesis_url = https://thesis.library.caltech.edu/4505/

| thesis_year = 1977

| doctoral_advisor = Murray Gell-Mann

| work_institution = Fermilab

| prizes =

| footnotes =

}}

Christopher T. Hill (born June 19, 1951) is an American theoretical physicist, formerly of the Fermi National Accelerator Laboratory, who did undergraduate work in physics at M.I.T. (B.S., M.S., 1972), and graduate work at Caltech (Ph.D., 1977, Murray Gell-Mann"Murray Gell-Mann," Physics Today, (2020); https://physicstoday.scitation.org/doi/10.1063/PT.3.4480 (2020)). Hill's Ph.D. thesis, "Higgs Scalars and the Nonleptonic Weak Interactions" (1977) contains one of the first detailed discussions of the two-Higgs-doublet model

and its impact upon weak interactions.[https://thesis.library.caltech.edu/4505/ "Higgs Scalars and the Nonleptonic Weak Interactions" (1977)] His work mainly focuses on new physics that can be probed in laboratory experiments or cosmology.

Hill is an originator, with William A. Bardeen and Manfred Lindner, of the idea that the Higgs boson is composed

of top and anti-top quarks. This emerges from the concept of the

top quark infrared fixed point,{{cite journal| title=Quark and lepton masses from renormalization-group fixed points|journal=Physical Review D|date=1 August 1981|volume=24|issue=3|pages=691–703|doi=10.1103/PhysRevD.24.691|bibcode=1981PhRvD..24..691H|last1=Hill|first1=Christopher T.}} with

which Hill predicted (1981) that the top quark would be very heavy, contrary

to most popular ideas at the time. The fixed point prediction

lies within 20% of the observed top quark mass (1995). This implies

that the top quarks may be strongly coupled at very short

distances and could form a composite Higgs boson, which led to top quark condensates,{{cite journal | year = 1990 | title = Minimal dynamical symmetry breaking of the standard model | journal = Phys. Rev. D | volume = 41 | issue = 5| pages = 1647–1660 | bibcode = 1990PhRvD..41.1647B | doi = 10.1103/PhysRevD.41.1647 | pmid = 10012522 | last1 = Bardeen | first1 = William A. | last2 = Hill | first2 = Christopher T. | last3 = Lindner | first3 = Manfred }} topcolor,{{cite journal | year = 1995 | title = Topcolor Assisted Technicolor | journal = Phys. Lett. B | volume = 345 | issue = 4| pages = 483–489 | doi=10.1016/0370-2693(94)01660-5| arxiv = hep-ph/9411426 | bibcode = 1995PhLB..345..483H | last1 = Hill | first1 = Christopher T. | s2cid = 15093335 }}{{cite journal | doi=10.1016/0370-2693(91)91061-Y | volume=266 | issue=3–4 | title=Topcolor: top quark condensation in a gauge extension of the standard model | year=1991 | journal=Physics Letters B | pages=419–424 | bibcode=1991PhLB..266..419H | last1=Hill | first1=Christopher T. | s2cid=121635635 }} and dimensional deconstruction, a renormalizable lattice description of extra dimensions of space.{{cite journal | year = 2001 | title = Gauge invariant effective Lagrangian for Kaluza-Klein modes | url = http://inspirehep.net/record/541000 | journal = Phys. Rev. D | volume = 64 | issue = 10| page = 105005 | doi=10.1103/physrevd.64.105005| arxiv = hep-th/0104035 | bibcode = 2001PhRvD..64j5005H | last1 = Hill | first1 = Christopher T. | last2 = Pokorski | first2 = Stefan | last3 = Wang | first3 = Jing | s2cid = 7377062 }}

The original minimal top condensation model predicted the Higgs boson mass to be

about twice the observed value of 125 GeV, but extensions of the

theory achieve concordance with both the Higgs boson and top quark masses.

Several new heavy Higgs bosons, such as a b-quark scalar bound state,

may be accessible to the LHC.{{cite journal|title=Is the Higgs boson associated with Coleman-Weinberg dynamical symmetry breaking?|journal=Physical Review D|date=4 April 2014|volume=89|issue=7|pages=073003|doi=10.1103/PhysRevD.89.073003|bibcode=2014PhRvD..89g3003H|arxiv=1401.4185|last1=Hill|first1=Christopher T.|s2cid=119192830}}

{{cite journal|title= Where are the Next Higgs Bosons?|journal=Physical Review|date= 2019|volume=D100|issue=1|pages=015051|doi=10.1103/PhysRevD.100.015051|arxiv=1904.04257|last1=Hill|first1=Christopher T.|last2=Machado|first2=Pedro|last3=Thomsen|first3=Anders|first4=Jessica|last4=Turner|s2cid=104291827|bibcode=2019PhRvD.100a5051H}}

{{cite journal|title= Scalar Democracy|journal=Physical Review|date= 2019|volume=D100|issue=1|pages=015015|doi=10.1103/PhysRevD.100.015015|arxiv=1902.07214|last1=Hill|first1=Christopher T.|last2=Machado|first2=Pedro|last3=Thomsen|first3=Anders|first4=Jessica|last4=Turner|s2cid=119193325|bibcode=2019PhRvD.100a5015H}}

Hill coauthored (with Elizabeth H. Simmons) a comprehensive review of strong dynamical theories and electroweak symmetry breaking

that has shaped many of the experimental searches for new physics at the Tevatron and LHC.{{cite journal | year = 2003 | title = Strong dynamics and electroweak symmetry breaking. | url = http://inspirehep.net/record/0203079 | journal = Phys. Rep. | volume = 381 | issue = 4–6 | page = 235 | doi = 10.1016/S0370-1573(03)00140-6 | arxiv = hep-ph/0203079 | last1 = Hill | first1 = Christopher T. | last2 = Simmons | first2 = Elizabeth H. | s2cid = 118933166 | bibcode = 2003PhR...381..235H | access-date = 2019-05-03 | archive-date = 2019-05-03 | archive-url = https://web.archive.org/web/20190503124159/http://inspirehep.net/record/0203079 | url-status = dead }}

Heavy-light mesons contain a heavy quark and a light anti-quark, and provide a window on the chiral symmetry dynamics of a single light quark.

Hill and Bardeen showed that the (spin){{super|parity}} $(0^-,1^-)$ ground states are split from the $(0^+,1^+)$ parity partners by a universal mass gap of about $~\; \backslash Delta\; M\; \backslash approx\; 350\; \backslash text\{\; MeV,\}~$ due to the light quark chiral symmetry breaking.{{cite journal| title=Chiral dynamics and heavy quark symmetry in a solvable toy field theoretic model|journal=Physical Review D|date=1994|volume=49|issue=1|pages=409–425|doi=10.1103/PhysRevD.49.409|pmid=10016779|bibcode=1994PhRvD..49..409B |last1 = Bardeen | first1 = William A. |last2 =Hill |first2=Christopher T.|s2cid=1763576|arxiv=hep-ph/9304265}} This correctly predicted an abnormally long-lived resonance,

the $D\_\{s0^+\}^*(2317)$ (and the now confirmed $D\_\{s1^+\}^*(2460)$), ten years before its discovery, and numerous decay modes which have

been confirmed by experiment.{{cite journal| title=Chiral multiplets of heavy-light mesons|journal=Physical Review D|date=2003|volume=68|issue=5|pages=054024|doi=10.1103/PhysRevD.68.054024|bibcode=2003PhRvD..68e4024B |last1 = Bardeen | first1 = William A. |last2 =Eichten | first2=Estia |last3 =Hill |first3=Christopher T.|s2cid=10472717|arxiv=hep-ph/0305049}}

Similar phenomena should be seen in the $B\_s$ mesons and

$ccs,\; bcs,\; bbs$ (heavy-heavy-strange baryons).

Hill is a contributor to the theory of topological interactions and, with collaborators,

was first to obtain the full Wess-Zumino-Witten term for the standard model which describes the physics of the

chiral anomaly in Lagrangians, including pseudoscalars, spin-1 vector mesons, and the $W^\backslash pm$ and $Z^0$. The WZW term requires a non-trivial counter-term to map the "consistent" anomaly into the "covariant" anomaly, as

dictated by the conserved currents of the standard model. With the full WZW-term,

new anomalous interactions were revealed such as the $\backslash gamma\backslash omega\; Z^0$ vertex. This leads to $\backslash nu\; +\; X\; \backslash rightarrow\; \backslash nu+\; \backslash gamma\; +\; X$

where $X$ is a heavy nucleus, and may contribute

to excess photons seen in low energy neutrino experiments.{{cite journal | year = 2007 |volume = 30 | title = Standard Model Gauging of the Wess-Zumino-Witten Term: Anomalies, Global Currents and pseudo-Chern-Simons Interactions| journal = Phys. Rev. D| pages = 085017| doi = 10.1103/PhysRevD.77.085017 | last1 = Harvey | first1 = Jeffrey A.

| last2 = Hill| first2 = Christopher T. | last3 = Hill| first3 = Richard

|issue = 8 |arxiv = 0712.1230}} The result reproduces B+L violation by the anomaly in the standard model, and predicts numerous other anomalous processes.

Hill has given a derivation of the coefficients of consistent and covariant chiral anomalies (even D), and Chern-Simons terms (odd D), without resorting to fermion loops,

from the Dirac monopole construction and its generalization ("Dirac Branes") to higher dimensions.C. T. Hill,

"Dirac Branes and Anomalies/Chern-Simons terms in any D,"

arXiv:0907.1101 [hep-th]. For fermion loops see: "Lecture notes for massless spinor and massive spinor triangle diagrams," arXiv:hep-th/0601155 [hep-th].

Hill is an originator of cosmological models of dark energy and dark matter based upon ultra-low mass pseudo-Nambu-Goldstone bosons associated with

symmetries of neutrino masses. He proposed that the cosmological constant is

connected to the neutrino mass, as $\backslash Lambda\backslash sim\; m\_\backslash nu^4${{cite journal | year = 1995 | title = Cosmology with ultralight pseudo Nambu-Goldstone bosons | journal = Phys. Rev. Lett. | volume = 75 | issue = 11| pages = 2077–2080 | arxiv = astro-ph/9505060 | bibcode = 1995PhRvL..75.2077F | doi = 10.1103/PhysRevLett.75.2077 | pmid = 10059208 | last1 = Frieman | first1 = Joshua A. | last2 = Hill | first2 = Christopher T. | last3 = Stebbins | first3 = Albert | last4 = Waga | first4 = Ioav | s2cid = 11755173 }}{{cite book| year = 1989 | chapter= Cosmological Structure Formation from Soft Topological Defects | chapter-url = http://inspirehep.net/record/264619/files/v19-n1-p25.pdf | title= Comments on Nucl. Part. Phys. | volume = 19 | issue = 1| pages = 25–39| last1= Hill | first1= Christopher T. | last2= Schramm | first2= David N. | last3= Fry | first3= James N. }} and developed modern theories of the origin of ultra-high-energy nucleons and neutrinos from grand unification relics.{{cite journal|last1=Hill|first1=Christopher T.|last2=Schramm|first2=David N.|title=Ultrahigh-energy cosmic-ray spectrum|journal=Physical Review D|date=1 February 1985|volume=31|issue=3|pages=564–580|doi=10.1103/PhysRevD.31.564|pmid=9955721|bibcode=1985PhRvD..31..564H}}{{cite journal | year = 1987 | title = Ultrahigh-Energy Cosmic Rays from Superconducting Cosmic Strings | journal = Phys. Rev. D | volume = 36 | issue = 4| pages = 1007–1016 | doi=10.1103/physrevd.36.1007| pmid = 9958264 | bibcode = 1987PhRvD..36.1007H| last1 = Hill | first1 = Christopher T. | last2 = Schramm | first2 = David N. | last3 = Walker | first3 = Terry P. }}{{cite journal | year = 1992 | title = "Grand unified theories," topological defects and ultrahigh-energy cosmic rays | journal = Phys. Rev. Lett. | volume = 69 | issue = 4| pages = 567–570 | bibcode = 1992PhRvL..69..567B | doi = 10.1103/PhysRevLett.69.567 | pmid = 10046974 | last1 = Bhattacharjee | first1 = Pijushpani | last2 = Hill | first2 = Christopher T. | last3 = Schramm | first3 = David N. | s2cid = 20633612 | hdl = 2060/19920009031 | hdl-access = free }}{{cite journal| doi=10.1016/0550-3213(83)90386-3 | volume=224 | issue=3 | title=Monopolonium | year=1983 | journal=Nuclear Physics B | pages=469–490 | bibcode=1983NuPhB.224..469H | last1=Hill | first1=Christopher T. | osti=1155484 }} He has shown that a cosmic axion field will induce an effective oscillating electric dipole moment for any magnet.{{cite journal| doi=10.1103/PhysRevD.91.111702 | volume=224 | issue=3 | title= Axion Induced Oscillating Electric Dipole Moments| year=2015 | journal=Physical Review D | pages=111702| bibcode= 2015PhRvD..91k1702H| last1=Hill | first1=Christopher T. | osti=1212736| arxiv=1504.01295 | s2cid=96444192 }}{{cite journal| doi=10.1103/PhysRevD.93.025007 | volume=224 | issue=3 | title= Axion Induced Oscillating Electric Dipole Moment of the Electron| year=2016 | journal=Physical Review D | pages=025007| bibcode= 2016PhRvD..93b5007H| last1=Hill | first1=Christopher T.| osti=1223242 | arxiv=1508.04083 | s2cid=119221466 }}

In an unpublished talk at the Vancouver Workshop on Quantum Cosmology (May, 1990),

Hill discussed possible roles for Nambu-Goldstone bosons in cosmology and suggested that a pseudo-Nambu-Goldstone boson might provide a "natural inflaton," the

particle responsible for cosmic inflation. He noted that this required a spontaneously broken global symmetry, such as U(1), near the Planck scale, and explicit symmetry breaking near the Grand Unification Scale. The idea seemed ad hoc, however subsequent

work on Weyl invariant theories offered a better rationale for a natural inflation scenario

connected to Planck scale physics. Hill collaborated with Graham Ross and Pedro G. Ferreira and focused on spontaneously broken scale symmetry (or Weyl symmetry), where the scale of gravity (Planck mass) and the inflationary phase of the ultra-early universe are generated together as part of a unified phenomenon dubbed "inertial symmetry breaking." The Weyl symmetry breaking occurs because the Noether current is the derivative of a scalar operator, called the "kernal." During

a period of pre-Planckian expansion any conserved current must red-shift

to zero, hence the kernal approaches a constant value

which determines the Planck mass and the Einstein-Hilbert action of General Relativity is emergent. The theory is in good agreement with cosmological observation.{{cite journal|last1=Ferreira|first1=Pedro G.|last2=Hill|first2=Christopher T.|last3=Ross|first3=Graham G.|s2cid=119269154|title=Weyl current, scale-invariant inflation, and Planck scale generation|journal=Physical Review D|date=8 February 2017|volume=95|issue=4|pages=043507|doi=10.1103/PhysRevD.95.043507|bibcode=2017PhRvD..95d3507F|arxiv=1610.09243}}{{cite journal|last1=Ferreira|first1=Pedro G.|last2=Hill|first2=Christopher T.|last3=Ross|first3=Graham G.|s2cid=119267087|title=Inertial Spontaneous Symmetry Breaking and Quantum Scale Invariance|journal=Physical Review D|volume=98|issue=11|pages=116012|arxiv=1801.07676|year=2018|doi=10.1103/PhysRevD.98.116012|bibcode=2018PhRvD..98k6012F}}{{cite journal|last1=Hill|first1=Christopher T.|last2=Ross|first2=Graham G.|s2cid=222067042|title=Gravitational Contact Terms and the Physical Equivalence of Weyl Transformations in Effective Field Theory|journal=Physical Review D|volume=102|issue=|pages=125014|arxiv=2009.14782|year=2020|doi=10.1103/PhysRevD.102.125014|bibcode=}}

Hill has returned to the issue of composite scalars in relativistic field

theory, developing a novel analytic approach to bound states of chiral fermions

by generalizing the Nambu—Jona-Lasinio model to non-pointlike interactions.{{cite journal|last1=Hill|first1=Christopher T.|title=Bilocal Field Theory for Composite Scalar Bosons|journal=Entropy|date=2024|volume=26|issue=2|pages=146|doi=10.3390/e26020146 |doi-access=free |arxiv=2310.14750|bibcode=2024Entrp..26..146H }}{{citation |last1=Hill|first1=Christopher T.|title="Nambu and Compositeness"|date=2024 |arxiv=2401.08716}} He feels the most important challenge to the CERN LHC program is to determine if the Brout-Englert-Higgs boson is

a pointlike fundamental particle or a composite bound state near the TeV energy scale. The former case

may evidence some yet-to-be developed version of Supersymmetry; the latter case would imply new dynamics.