# Presentation: 190387

## Theoretical Physics:Directions

- Andreas Kronfeld
- FRA Visiting Committee
- April 20–21 2007

## Theoretical Physics Group

- Scientists I–III
- William Bardeen
- Marcela Carena
- Bogdan Dobrescu
- Estia Eichten
- R. Keith Ellis
- Walter Giele
- Christopher Hill
- Boris Kayser
- Andreas Kronfeld
- Joseph Lykken
- Paul Mackenzie
- Stephen Parke
- Chris Quigg

- Associate Scientists
- Thomas Becher (9/2004)
- Peter Skands (2/2007)
- Patrick Fox (10/2007)
- Research Associates
- Richard Hill (‘05)
- Jay Hubisz (‘05)
- Kyoungchul Kong (‘06)
- Jack Laiho (‘04)
- Enrico Lunghi (‘05)
- Rakhi Mahbubani (‘06)
- José Santiago (‘04)
- Ruth Van de Water (‘05)
- (Skands)

## Theoretical Physics Group

- Associated colleagues:
- Carl Albright (ex-NIU)
- André de Gouvea (NU)
- Elizabeth Freeland (SAIC)
- Wai-Yee Keung (UIC)
- Stephen Martin (NIU)
- Stephen Mrenna (CD)
- Jim Simone (CD)
- Tim Tait (ANL)
- ...
- Visitors:
- Frank Petriello (1–5/06)
- JoAnne Hewett (3–4/07)
- Matthias Neubert (7-9/07)
- Mariano Quirós (10-11/07)

- Alumni:
- Mu-Chun Chen -> UC Irvine
- Olga Mena -> Roma I
- Upcoming departures:
- Laiho -> Washington U.
- Santiago -> ETH Zürich
- Incoming postdocs:
- Yang Bai <- Yale
- Jon Bailey <- Wash. U.
- Jan Winter <- Dresden
- Latin American Students:
- Boris Panes (Chile)
- Juan Racker (Argentina)

## Community Service

- American Physical Society
- DPF: Lykken (Past Chair), Kayser (Chair-Elect), Kronfeld (ExecCom), Carena (NomCom, Outreach)
- APS: Bardeen (candidate for APS presidency), Carena (CISA)
- Agency advisory committees
- HEPAP: Lykken
- P5: Carena, Kayser
- Other subpanels: Kayser, Lykken, ...
- Institutional advisory committees
- Aspen Center for Physics: Carena, Lykken
- KITP Board: Lykken
- Fermilab PAC: Kayser
- Fermilab-CERN Hadron Collider Physics Summer School
- Dobrescu

## Community Service (2)

- ILC Policy
- Kronfeld (WWS-OC, Fermilab ILC Task Force, ...)
- Neutrino Physics Policy
- Kayser (all possible panels), Parke, Mena
- Lattice QCD Policy
- USQCD: Mackenzie (ExecCom), Kronfeld (SPC Chair)
- DOE SciDAC, US NSF, KEK (Japan): Mackenzie
- Education
- IMSA Board: Quigg
- Editorial
- Annual Review of Nuclear and Particle Science: Kayser
- International conference advising and convening duties
- All & too numerous to mention

## Laboratory Service

- Academic Lectures (to educate on-site grad students)
- Organization: Carena, Becher, Kronfeld, Quigg, ...
- Lectures: Quigg, Kayser, Parke, Ellis, Giele, _Lunghi_, Becher, Kronfeld; Langacker, Plunkett, Dodelson, Cabrera, Green, Berryhill, Herndon
- Fermilab Seminars
- Colloquium: Dobrescu (w/ many others)
- Joint Experimental-Theoretical Physics: Becher, Giele
- Theoretical Physics: Kronfeld, Skands
- Scientific Committees at Fermilab
- FCSA: Eichten
- Scientist III committee: Bardeen
- Wilson Fellows: Quigg -> Kronfeld
- URA (now FRA?) thesis award: Dobrescu
- Awards: Quigg
- Joint Appointments with nearby universities
- Lab policy: Hill
- Search with University of Chicago: Bardeen, Ellis, Kronfeld

## Conferences and Workshops (@ Fermilab)

- Monte Carlo Tools for Beyond-the-Standard Model Physics
- Skands
- USQCD Collaboration Meeting
- Kronfeld
- Joint Fermilab-CERN Hadron Collider Physics Summer School
- Dobrescu
- The LHC Early Phase for the ILC Workshop
- Carena
- LoopFest VI: Radiative Corrections for the LHC and ILC
- Ellis, Giele
- Neutrino Physics Summer School (2007)
- Kayser

## Cosmological Connections

- Scientific collaboration with colleagues in the Theoretical Astrophysics Group has always been healthy:
- Classic papers: Hill & Schramm; Frieman, Hill, Stebbins, Waga
- Neutrino cosmology: Barenboim, Mena, Quigg
- Modified gravity: Mena, Santiago, and Weller (2005)
- WIMPs at colliders: Carena, Hooper, Skands (2006)
- Pizza nights
- Grudge matches
- Soccer
- (American) football
- Softball
- Basketball (Bardeen was unavailable)
- Computational Cosmology Task Force
- Includes lattice theorist and lattice computing experts

## Lattice QCD

- Major theoretical and computational effort
- Three senior scientists: Kronfeld, Mackenzie, Simone (CD); computing support from Holmgren, Singh, ...
- Typically two postdocs: Van de Water and Laiho -> Bailey.
- Fermilab Lattice Collaboration at Fermilab, UIUC, DePaul, SAIC
- Collaboration of Collaborations with MILC Collaboration
- Cooperation with HPQCD Collaboration
- USQCD hardware Project
- PC clusters, funded by DOE-HEP and DOE-NP
- $9.2 M over FYs ‘06–’09.
- Earlier DOE-funded QCDOC (FYs ‘04, ‘05; HEP, NP, SciDAC, ASCR).
- Lab infrastructure from Fermilab, JLab, BNL.
- Fermilab physics projects within USQCD:
- B and D Meson Decays: 10% -> 13% of USQCD resources
- Quarkonium Physics: 3.2% -> 4.5%
- BK with mixed action (_Laiho_, _Van de Water_): 2.9% -> 6.0%

## Lattice Status

- Benjamín Grinstein at CKM 2006 (December in Nagoya):
- “I’ll believe a 3% lattice [QCD] theory error when the lattice has produced one successful **pre**diction and several 3% **post**dictions.”
- Nine 1–3% postdictions in March 2003 from HPQCD, MILC, and Fermilab Lattice Collaborations.  PRL.
- Predictions of D meson semileptonic decays in August 2004; mass of Bc meson in November 2004; and D meson leptonic decay in June 2005.  (All PRL.)  Verified by FOCUS, Belle, CLEO; CDF; CLEO, BaBar....
- Hardest part: sea quarks
- Successful post- and predictions with fastest approach to sea quarks; other (theoretically cleaner) methods making strides.

## Lattice Flavor Physics

- pre-
- Tevatron

## Lattice Flavor Physics

- D0
- 10%

## Lattice Flavor Physics

- _Okamoto_
- Average 

- CDF
- 1%

## Fermilab Lattice Flavor Physics

- Unitarity triangle
- Vcb units
- B decays, K & B mixing
- After success with D mesons, we simply change the quark mass.
- B  D(*)l yields Vcb
- _Laiho_, Kronfeld
- B  l yields Vub
- _Van de Water_, Mackenzie
- SM B mixing yields Vtd
- Simone, UIUC, DePaul
- SM K mixing constrains apex
- _Laiho_, _Van de Water_

## Aubin, Laiho, Van de Water

- Neutral kaon mixing
- Measure K
- Calculate BK
- Staggered sea ready to go
- Chiral valence simpler (theoretically)
- “Mixed” action needs one new (unphysical) parameter
- ChPT [hep-lat/0609009]
- Numerical: straightforward
- Will yield one of best calculations of BK: target 5% uncertainty

*m*2

*f*

*m**q*

## Lunghi & Soni

- Type III 2-Higgs Doublet Model in B Physics
- One doublet for top quark; another for the rest.
- New parameters:
- Last two induce FC and CP violation in 23 & 13 processes
- Sensitive to
- Asymmetry in *B* -> ***K**S*, *a****K*
- Neutral kaon mixing, *K*
- Rare decay *B* -> *X*s
- |Vub/Vcb|
- Asymmetries  in *K*

## Lunghi & Soni (2)

- Constraints from B Physics
- Look at
- UT fit B -> Xs, B -> 
- *K* and *a****K* depend strongly on **
- Fix ** to accommodate *a****K* we have no freedom left to adjust *K*.
- Same region improves fit to *K* asymmetries.

## Becher and Melnikov

- Two-loop QED corrections to Bhabha scattering.
- Used to measure luminosity at lepton colliders.
- At present and past e+e - machines luminosity uncertainty is theory dominated.
- Simple relation between massive and massless gauge theory amplitudes at large momentum transfers.
- Massless loop amplitudes are much easier to evaluate.
- Obtain the result for massive Bhabha scattering using known results for the massless case and for the massive form factor.
- First independent check of
- two-loop photonic corrections calculated by Penin ‘05.
- electron loop contributions by Bonciani et al. ‘04.
- New result for muon loop contribution.
- Same method is applicable to QCD, for example to heavy quark production at large energies.
- Paper to appear; see Becher’s talk at Loopfest VI.

## Becher and Melnikov (2)

- Size of the two-loop corrections in units of the tree-level cross section (*s* = 1 GeV2).
- Plot assumes that MC generates soft radiation (have set all soft logarithms ln(*E*) to zero).
- Corrections need to be implemented into MC program.

## Giele, Kosower, Skands

- VINCIA Parton Showers
- Antenna functions
- Exact expansions
- C++ code
- Standalone version
- PYTHIA plug-in version
- Matching at LO, NLO (and framework for NnLO).
- Numerical implementation
- General purpose
- Overhead at startup
- Fast event generation
- Flexible

## Giele, Kosower, Skands (2)

- Example: H  gg  ggg
- Unmatched shower varied from “soft” to “hard” : soft shower has “radiation hole”. Filled in by matching.

## Mena, Nunokawa, Parke

- NOA and T2K: the Race for the Neutrino Mass Hierarchy [hep-ph/0609011]
- Examine by combining experiments at different *L* but same *E*/*L*, such as NOA and T2K.

## Mena, Nunokawa, Parke (2)

- Left:
- Right:
- Cf. talk by N. Saoulidou.

## Chen, de Gouvea, Dobrescu

- TeV Scale Seesaw [Phys. Rev. D75 (2007) 055009]
- Conventional wisdom: small neutrino masses  GUT-scale physics
- Small neutrino mass can also arise from TeV-scale physics
- SM + non-anomalous U(1)’ + 3 R
- All particles charged under U(1)’
- U(1)’ forbids usual dim-4, dim-5 operators
- Neutrino mass generated by operators of much higher dimension
- Anomaly cancellations relate U(1)’ charges of different particles  predict flavor mixing
- Through coupling to Z’: can probe neutrino sector at colliders

## Chen, de Gouvea, Dobrescu (2)

- Anomaly cancellation condition generally hard to solve: finding rational solutions to cubic equation  Fermat’s last theorem
- “Leptocratic” model with 3 R:
- Solutions exist for flavor-blind U(1)’ charges for quarks & generation dependent charges for leptons
- Only 2 parameters (a,b) in lepton sector; they describe charge diff
- Bi-large mixing can arise for some (a,b)
- Three active neutrinos can either be Dirac or Majorana
- Three light sterile neutrinos:
- Two heavier ones: 1 keV ~ 1 MeV
- One ultra-light one: 10-9 eV
- Active-sterile mixing  10-3  may have interesting cosmological and astrophysical implications (pulsar kicks, ... etc)
- MZ’ < 1 TeV : can be produced at LHC
- Most models predict 1 for the ratio of BF’s; in leptocratic model can differ from 1 (depend on a, which also govern neutrino mixing)

## Carena, Hubisz, Perelstein, Verdier

- T-odd quark pair production in Little Higgs models with T-parity
- New parity odd vector-like color triplet states
- pair produced
- decay to 2j + MET
- MET is lightest T-parity odd particle (massive neutral gauge boson)
- Implemented in MadGraph, preserving spin correlations
- Calculated production cross sections, studied distributions
- Used full DØ background analysis
- Realistic study of Tevatron discovery potential
- Placed limit of ~350GeV on new states
- Reach is ~400GeV with 8fb-1
- Take into account dark matter constraints

## Carena, Hubisz, Perelstein, Verdier (3)

## Carena, Pontón, Santiago, Wagner

- New Signatures from Warped Extra Dimensions
- Original model (Randall-Sundrum)
- Solves hierarchy problem
- Suggests theory of flavor
- Towers of copies of SM particles
- Out of LHC reach
- New ideas
- Compatible with current data
- Accessible at Tevatron and LHC
- Symmetries: custodial and LR
- Custodial protects mW/mZ
- Both together protect Zbb coupling

## Carena, Pontón, Santiago, Wagner (2)

- Model agrees with recent measurements of mt, mW
- Masses:
- Exotically charged quarks, Q5/3 -> W+W+b–1/3

## Dobrescu, Kong, Mahbubani

- Dobrescu, _Kong_, _Mahbubani_

- Leptons and photons at the LHC: Cascades through spinless adjoints [hep-ph/0703231]
- Phenomenology of Burdman, Dobrescu, and Ponton’s 6 UED chiral square model

## Dobrescu, Kong, Mahbubani (2)

## Hill & Hill

- Topological Interactions of Higgs Bosons
- 	[hep-ph/07010444]
- Consideration of composite Higgs models leads to questions
- What is the most general 4-d Lagrangian for Goldstone bosons?
- What is the most general low-energy description of (bound states of) strongly-coupled fermions?
- Constraints of topology and
- 	symmetry constrain former:
- 	index *p* (cf. *N**c* in WZW for
- 	pions).
- Topological action for bosons 
- 				chiral fermion interpretation.

## Hill & Hill (2)

- Physical implications
- “Little Higgs” and “composite Higgs” are points of view
- Interaction induced by anomalies always there
- Identity of (putative) Higgs bosons tied up in these interactions.
- Unless *p* = 0, T parity merges with spatial inversion to form “the” parity.  Analogous to pion parity in QCD.

## Conclusions

- Service
- Theorists at Fermilab are actively engaged in many activities sustaining and planning the future of particle physics.
- Research
- The senior theorists at Fermilab are acknowledged experts in many subfields of particle physics.
- Education
- Fermilab’s Theoretical Physics Department is a training ground for many of the best young theorists in the world, focusing on those with a keen interest in experimental and observational results, aka physics!