Transcript Document 7403058

Status of Linear Collider
Physics Studies in India
Sreerup Raychaudhuri
Indian Institute of Technology @ Kanpur
LC Physics Study Meeting
KEK, March 6, 2005
The ILCWG
► Indian
Linear Collider Working Group
• Formed in 2001
• Four meetings: 2001, 2002, 2003, 2004
• Hosted 6th ACFA Conference (2003)
► Contributions in three main areas
• Physics possibilities
• Machine design/development
• Data analysis (when there is data…)

1.
2.
3.
4.
5.
6.
Seven participating Institutions
Tata Institute, Mumbai
Indian Institute of Science, Bangalore
Physical Research Laboratory, Ahmedabad
Harish-Chandra Research Institute, Allahabad
Centre for Advanced Technology, Indore
University of Delhi
7. Indian Institute of Technology, Kanpur
+
A. Gurtu
R.M. Godbole
S.D.Rindani
B. Mukhopdhyaya
S. Krishna Rajagopal
D. Choudhuri
S. Raychaudhuri
Some other individuals in other institutions and some
postdocs in foreign countries
 Modus Operandi is flexible
Individual researchers are encouraged to work in LC physics and
to collaborate, but no targets are set
► Experimental
Research:
• Still to take off properly
• Some accelerator studies in CAT
• HEP experimentalists in India are
heavily comitted to
D0, CMS, ALICE, BELLE, INO
• Larger financial commitment required
► Good News (?)
• This has now come to the notice of policymakers who control the funding…
Indian involvement in accelerator-based
HEP experiments goes back very far…
1958
Cyclotron developed by M.N.Saha et al in Kolkata
1960s & 1970s
Attention shifted to cosmic ray studies, culminating in the
Kolar Gold Field (KGF) experiment to detect proton decay
1980s Experimental participation in UA2
Collider Monte Carlo simulations pioneered by D.P.Roy,
R.M.Godbole
1990s Participation in LEP-1 and LEP-2, D0, CMS…
Growth of a school of collider phenomenologists
2000s Time to participate in a major way in the international
efforts…
Why does the (Indian) HEP
community find the idea of
+
a high energy linear e e
collider so exciting?
Physics advantages of a linear collider:
• e+e- offers a clean environment compared to
a hadron collider
• Energy of each event is sharply defined
• Laboratory frame is centre-of-mass frame
• Possibility of beam polarization
• Possibility of very high luminosities
• Can be run in four different modes:
–
–
–
–
e+ee-ee

usual mode
requires beam division
requires laser back-scattering
requires laser back-scattering
Major areas of research in electroweak physics:
• Standard Model: precision measurements
• New gauge bosons:
– W , Z
– Exotic charges, exotic couplings
• Non-standard Higgs bosons
– MSSM & Two-Higgs doublets
– Little Higgs models
• Exotic fermions
– Exotic quantum numbers
– Exotic couplings
• Supersymmetry
– Breaking schemes: mSUGRA, GMSB, AMSB, gaugino-MSB
– R-parity violation
• Extra Dimensions
– Large extra dimensions (ADD)
– Warped spacetime (Randall-Sundrum)
●
●
Split SUSY
UED
Standard Model at a linear collider:
• We expect a linear collider to have a very high luminosity,
typically 10 - 1000 fb-1
• This should lead to copious production of W and Z bosons,
through
– e+e-  W+W– e+e-  Z Z
• We can then study the decay products of W and Z, e.g.
`gold-plated’ Z  l+l- to determine the mass and width of
the W and the Z
• A linear collider can also act as a top quark factory
– e+e-  t t high luminosity leads to copious production
– Precision measurement of top quark mass and width possible
• Can also study the SM Higgs boson (discussed later)
• No special Indian contributions to this area
• P.Mathews, V. Ravindran, K. Sridhar (hep-ph/0405292):
NLO QCD corrections to two-jet production in ADD/RS gravity
New gauge bosons:
• Mixing of Z with exotic states is already strongly
constrained by LEP-2; must consider new particle
production and decays
• We can pair produce W/, Z/ just like WW or ZZ or γγ
• We then typically focus on leptonic decays as trigger:
– W/  l+ ν
and Z/  l+ l-
• Reconstruction of parent gauge bosons from final
states is possible’
– W/+ W/-  l+ ν q q/ with quadratic ambiguity
– Z/ Z/  l+ l- l+ l- with no ambiguity (`gold-plated’ signal)
• Presence of exotic states will show up in
– ET distribution of leptons (both W/, Z/ )
– Resonances in l+ l- invariant mass (Z/)
• In E6-type models, V and A couplings of Z/ are
different from Z ; this will show up in AFB
• No special Indian contributions to this area
Gauge bosons with exotic charges and couplings:
• W++ exists in some GUT models; usually heavy, but can be
made light using discrete symmetries
– Decay chain W++  W+ l+  l+ l+ ν
• Possibility of exotic triple gauge vertices (TGV): assume SM
is low-energy limit of some renormalizable theory:
– WWγ, WWZ
– Zγγ, ZZγ, ZZZ
– 3γ is forbidden by C-invariance
• parametrize TGV in terms of form factors which are
coefficients of dimension-5 and dimension-6 operators
– 3 are CP-conserving, 2 are CP-violating
• Obtain bounds on these form factors by looking at
– Total cross-sections (will pick up contributions from extra terms)
– Kinematic distributions (will be different because of exotic operators)
– CP-violating asymmetries
• Indian contribution: calculation of Zγγ, ZZγ, ZZZ vertices at
one-loop in SM and MSSM
– D.Choudhury, S.Dutta, S.D.Rindani (hep-ph/0001205 )
Higgs bosons I:
• Standard Model H0 is still to be discovered
– Possible that it may be discovered at Tevatron Run-2 or at LHC
• Intermediate mass H0 (115 – 150 GeV) may still escape
detection (according to famous CMS study)
– This is the most interesting mass regime since MSSM (and minor
extensions, e.g. MSSM + Higgs singlet) predicts light Higgs in just
this region
• Linear collider at 500 GeV is ideal for this mass region
– Higgs-strahlung process: e+ e-  Z*  Z H0  l+ l- b b
– Clean environment for detection of b-jets compared to hadron
collider
• Lots of exotic Higgs models:
– Two-Higgs doublet models, e.g. MSSM
– Singlet Higgses, coloured Higgses, composite Higgses
– Little Higgs models (latest fashion…)
Higgs bosons II:
• Indian contribution: study of heavy Higgs bosons (MH > 2MZ )
- D.Choudhury, T.Tait, C.Wagner (hep-ph/0202162)
-They consider
- e+e-  Z*  Z H0 (Higgs-strahlung)
- e+e-  ν ν H0
(W-boson fusion)
- e+e-  e+ e- H0
(Z-boson fusion)
- Higgs principal decay modes H0  WW, ZZ
-Multi-lepton and multi-b-jet final states
-Involved combinatorics
- They consider both SM and MSSM Higgs bosons
- Conclude that with 1000 fb-1
• full parameter space of SM is observable
(consistent with Higgs mass from precision electroweak measurements)
• MSSM parameter space is observable up to kinematic limit
Higgs bosons III:
• Indian contribution: doubly-charged Higgses H++ at a γγ collider
– S.Chakravarty, D.Choudhury, R.M.Godbole, B.Mukhopadhyaya
ph/9804297)
– D.K.Ghosh, R.M.Godbole, B.Mukhopadhyaya (hep-ph/ 9605407)
• Higgs triplets have structure (H++, H+, H0 )
• Exist in non-Standard models, e.g. L-R symmetric model
• Decay mode: H++  H+ H+
– They consider γγ  H++ H --  H+ H+ H - H – Final states depend on the mass:
• If H+ is heavier than top quark, will decay into t b
• If H+ is lighter than top quark, will decay into 2 jets (c s) or τ ντ
– All possible final states considered
– Conclude that large regions of parameter space are accessible
• Accessibility increases with centre-of-mass energy
• Accessibility increases with luminosity (no surprise!)
(hep-
Higgs bosons IV:
• Indian contribution: use of tau polarisation in Higgs
studies
– Original idea due to Bullock, Martin and Hagiwara
• Consider one-prong decays of a tau lepton (mostly into a
charged pion): accompanying neutral energy (mostly due
to one or two neutral pions) will differ between L and R
• This can distinguish between tau’s arising through Lhanded or R-handed couplings and hence can be used as a
powerful discriminator between models
– CP properties: R.M.Godbole, R.K.Singh, S.Kraml
(hep-ph/0501027)
– SUSY Higgs: R.M.Godbole, M.Guchait, D.P.Roy
(hep-ph/0411306)
Indian contribution: Top Quark pairs and exotic couplings:
– S.D. Rindani & collaborators
– (hep-ph/9809203, 0011321, 0211136, 0211134, 0204233, 0304046,
0309260, 0408083)
– Several investigations of tt production in e+e- and 
– Mostly consider intermediate scalar or vector state
• Exotic t-t-scalar or t-t-vector couplings or leptoquarks
• Form factors, both conserving CP and violating CP
• Study lepton asymmetry in semi-leptonic top quark decays
– P.Poulose, S.D. Rindani, L.M.Sehgal (hep-ph/0111134)
– They consider e+e-  W+W- in BESS models
• Essentially parametrize Z-W-W coupling in strong limit in terms of form
factors
• Measurement of lepton asymmetry will yield information on these form
factors
– R.M. Godbole & collaborators
– Several investigations of `total’ cross sections at e+e• Essentially add up beamstrahlung contributions
• Use updated parametrizations for photon structure function
Supersymmetry:
• SUSY has a very rich sparticle spectrum (awaiting
discovery!)
– Gauginos
• 2 charginos χ+, χ• 4 neutralinos χ0i (I = 1,4)
• 8 gluinos ği ( i = 1,8 )
– Sleptons
• Charged sleptons ěLi ěRi ( i = flavour index)
• Sneutrinos (only left-chiral, one for each flavour)
– Squarks
• Squarks and gluinos are strongly interacting
– QCD production at hadron colliders more promising
• Hence focus is on chargino, neutralino and slepton
production at linear colliders
Signals for sparticles at a linear collider:
• Some hundreds of production and decay channels
– Heavily dependent on mass spectrum of sparticles
– Mostly encoded in Monte Carlo event generators:
• ISASUSY
• SPYTHIA
• HERWIG
– No longer worthwhile to simply calculate cross-sections!
– More detailed study needed: detector simulations?
• Linear collider likely to become operational only after
LHC has run for a few years
– Early discoveries may be made at LHC
• Physics possibilities at a linear collider:
– Try to pin-down parameters of the model in question using crosssections etc.
– Try to isolate exotic signals normally lost in background at a
hadron collider
– Particularly focus on regions of parameter space where hadron
collider signals are not clearly-defined
SUSY parameter space:
• MSSM has 124 unknown parameters
– Hardly any predictive power; we require to reduce parameter
space with theoretical assumptions
• Most new parameters arise from SUSY-breaking scheme:
– Gaugino masses M1, M2, M3
• (corresponding to U(1), SU(2), SU(3) sectors)
– Squark and slepton mass parameters
– Higgsino mixing parameter: 
– Tri-linear (scalar) couplings
– Ratio of Higgs vev-s: tan 
• Constraints on parameter space will come only if
mechanism of SUSY-breaking (i.e. generation of these
parameters) is considered
– Usual idea: SUSY is broken spontaneously in a `hidden’ sector
with very heavy (unobservable) fields; communicated to `visible’
sector (observable fields) by some intermediate fields
Principal SUSY-breaking schemes I:
• mSUGRA: minimal supergravity
– SUSY-breaking is carried from hidden sector to observable
sector by graviton-gravitino fields
• We assume gauge unification at the GUT scale
• Electroweak symmetry is broken spontaneously by radiative corrections
to Higgs sector, driving (one) Higgs mass parameter negative
– Model has 5 free parameters:
• m0, m1/2, A, sign(), tan 
– All sparticle masses are predicted in terms of these 5:
• Usually the lightest neutralino χ01 is the LSP
(escapes detection leading to missing E and p)
• Usually we expect squarks and gluinos to be very heavy (~ 800 GeV)
• Usually we expect sleptons and snutrinos to be light (~100 GeV)
– LEP-2 constraints force us to take tan  > 2 (approx)
– Tevatron constrains the m0 - m1/2 plane for different tan 
Principal SUSY-breaking schemes II:
• GMSB: Gauge-mediated SUSY-breaking
– SUSY-breaking is carried from hidden sector to observable sector
by some heavy gauge fields
– We assume gauge unification at the GUT scale
– Electroweak symmetry may or may not be broken radiatively (both
scenarios viable)
• Model has 5 free parameters
– Mmess, Nmess, Λ, sign( ), tan 
– mess stands for messenger gauge fields
– Λ is the scale of SUSY-breaking
• Gravitino is the LSP and neutralino χ01 is the nextto-lightest sparticle (NLSP)
– Nearly massless gravitino escapes detection
– Missing E and p signatures
– Typically χ01  γ Ğ
– Hard photons and missing energy are usually part of
final state (useful to trigger on)
Principal SUSY-breaking schemes III:
• AMSB: anomaly-mediated SUSY-breaking
– Inspired by brane-world scenarios
– Invented to solve SUSY flavour problem
– Place hidden and visible sector on different `branes’ I.e. fourdimensional subspaces of higher dimensional space, separated by
distance in extra dimensions
– SUSY-breaking is through conformal anomaly on hidden brane
– Carried to visible brane across extra dimensions by gravitongravitino fields
• Model has 4 free parameters
– M3/2, sign(), tan 
– Slepton mass-squared is negative  sleptons become tachyonic!
– Add on a slepton mass parameter m0 to make it positive
• Different spectrum from GMSB:
– Neutralino LSP χ01 is nearly degenerate with chargino χ+1
– Chargino decay: χ+1  χ01 π+ (pion is very soft  may not be
detected)
– Chargino may just leave a track like a heavy lepton
Production processes at an e+e- collider:
• Gauginos:
– Charginos: e+e-  χ+i χ-j- (i,j = 1,2)
• s-channel: photon, Z
• t-channel: sneutrino
– Neutralinos: e+e-  χ0i χ-j0
• s-channel: Z
• t-channel: selectron
• Sleptons:
– Charged sleptons: e+e-  ěLi ěLi , ěRi ěRi , ěLi ěRi
• s-channel: photon, Z
• t-channel: neutralino
– Sneutrino pairs:
• s-channel: Z
• t-channel: chargino
Principal decay modes of sparticles:
• All sparticles must ultimately decay to LSP, which escapes the
detector.
– Origin of sparticle cascade decays
– We detect the SM particles in the cascade
• Chargino  Neutralino + W*  Neutralino + f f/
– We detect the fermions and missing E, p
– W can be reconstraucted only if it decays hadronically
• Neutralino (heavy)  Neutralino (LSP) + Z*  Neutralino + f f
– We detect the fermions and missing E, p
– Can reconstruct the Z from both leptonic and hadronic decays
– If Z decays to neutrinos, heavy neutralino is also invisible
• Slepton  Neutralino + Lepton of same charge, same flavour
 Chargino + Lepton of different charge, same flavour
– We detect the charged leptons and/or cascade decay products of
chargino
• This is a somewhat over-simplified picture: in practice we need to
compute branching ratios to all gauginos, all final state fermions
– Signals can be quite messy
Indian contributions 1: parameter determination
• Determination of parameters of chargino sector
– Y.Choi, M.Guchait, J.Kalinowski, P.MZerwas (hepph/0001175)
– Y.Choi, A.Djouadi, M.Guchait, J.Kalinowski, H.S.Song,
P.M.Zerwas (hep-ph/0002033)
They consider e+e-  χ+i χ-j- (i,j = 1,2)
Measure 3 cross-sections
Measure several spin-correlations
Use these data to pin down parameters of chargino sector, viz.
• M1, M2, μ, tan 
– Discuss relative merits of different combinations of these
– Consider radiatively-corrected cross-sections
–
–
–
–
• Determination of mixing angles of stau sector:
– M.Guchait, J.Kalinowski, P.Roy (hep-ph/0103161)
– SuperK results indicate mixing between muon neutrino & tau neutrino:
seems to indicate mixing between corresponding superfields, I.e.
between muon and tau sneutrinos and smuon and stau through RG
evolution
– Treat mixing angles as free parameters and measure from cross-sections
for smuon pair production and stau pair production
Indian contributions 2: `invisible’ sparticles
• Single photon signals for `virtual LSP’ scenarios
– A.Datta, A.K.Datta, SR (hep-ph/9605432)
– Consider scenario when next-to-LSP is the sneutrino
–
–
–
–
Decays to neutrino + neutralino (both invisible)
Consider radiative neutralino and sneutrino pair-production
Signal is photon + missing E, p
Should be observable over SM background ( νν with ISR γ)
– Extend to scenario when next heavier sparticle is second neutralino
– Invisible decays to neutrino + sneutrino, LSP + Z* (neutrinos)
• Consider AMSB-inspired scenario when next-to-LSP is the
chargino:
–
–
–
–
A.Datta, S.Maity (hep-ph/0104086)
Chargino decays to neutralino + soft pions (unobservable)
Consider radiative (ISR) chargino production
Again signal is photon + missing E, p
• Consider same AMSB scenario at a γγ collider
– D.Choudhury, B.Mukhopadhyaya, S.Rakshit (hep-ph/0205103)
– Final state is either photon + missing E, p or photon + π+π-
Indian contributions 3: GMSB signals
• Single photon signals in e+e- collisions:
– A.Datta, A.K.Datta, A.Kundu, B.Mukhopadhyaya, S.Roy
(hep-ph/9707239)
–
–
–
–
–
They consider neutralino pair production e+e-  χ01 χ-10
One neutralino decays χ01  γ Ğ
Other neutralino decays χ01  Z Ğ  ν ν Ğ
Final state is photon + missing E, p
Use polarized beams
– A.Ghoshal, A.Kundu, B.Mukhopadhyaya (hep-ph/9709431)
– Consider left-right asymmetry in above signal
– Use to probe photon-photino-gravitino & Z-Zino-gravitino couplings
• Tri-electron signals for GMSB at e colliders:
– A.Ghoshal, A.Kundu, B.Mukhopadhyaya (hep-ph/9709431)
– They consider e  χ01 ĕR  e ĕR ĕR
– Each selectron goes to electron + gravitino
– Very small backgounds from SM and MSSM;
– `smoking gun’ for GMSB
Indian contributions 4: AMSB signals
• AMSB signals in selectron pair-production:
– D.K.Ghosh, P.Roy, S.Roy (hep-ph/0004127)
– They consider e+e-  ĕL ĕL
– One ĕL  electron + neutralino (LSP), one  neutrino + chargino
– Chargino decays to pion + neutralino LSP
– Two possibilities:
• Chargino leaves a heavy track in the detector
• Chargino decays to pion with a displaced vertex
– Trigger on hard electron, missing E, p and look for heavy tracks or
displaced vertices (claim `smoking gun’ for AMSB)
• AMSB signals in pair-production of sparticles:
– D.K.Ghosh, A.Kundu, P.Roy, S.Roy (hep-ph/0104217)
– More comprehensive study: They consider e+e-  pairs of
Selectrons (L-L, L-R, R-R), Sneutrinos, Neutralinos (12, 22), Charginos
– Final decay signal will still involve heavy tracks/displaced vertices
• AMSB signals in e colliders:
– D.Choudhury, D.K.Ghosh, S.Roy (hep-ph/0208240)
– They consider e  sneutrino + chargino (rest is similar)
R-parity violation:
• R-parity is a discrete quantum number
– R = (-1) L + 2S + 3B = +1 for SM particles
= -1 for sparticles
– If R is not conserved, we will have rapid proton decay
– R-parity conservation implies that sparticles always appear in pairs
at any vertex
– R-parity conservation is responsible for stability of LSP
– R-parity is assumed conserved in all of previous discussion
• Can R-parity be violated? Answer is YES
– Ensure violation of either L or of B, but not both
– Ensures proton stability is protected
• Three kinds of R-parity-violating operators:
–
–
–
–
λ LLĒ : 9 such λ’s
λ´ LQĎ : 27 such λ’s
λ ŪĎĎ : 9 such λ’s
Essentially 45 Yukawa-type couplings
• For phenomenological purposes we assume that only one
coupling is dominant (different choices analyzed separately)
Indian contributions 5: R-parity violation
• Signals for LSP decay at e+e- collider
– D.K.Ghosh, R.M.Godbole, SR (hep-ph/990233)
– In R-violating scenario LSP neutralino decays
• LLE: dilepton + neutrino
• LQD: dijet + neutrino, dijet + charged lepton
• UDD: three jets
– Produce neutralino and chargino pairs: consider all
possible cascade decays (84 channels !)
• LLE has very clear multi-lepton signals
• LQD has interesting like-sign dilepton signals (Majorana LSP)
• UDD must be detected in multijet scenarios
– Possibility of neutralino/chargino mass reconstruction
• Signals for LSP decay at e collider:
– D.K.Ghosh, SR (hep-ph/ 9711473) Very similar study
• Bilinear R-parity violation:
– B.Mukhopadhyaya, S.Roy (hep-ph/9612447)
• Sneutrino resonances with associated photons:
– Choudhury, Rai, SR (2005)
Large Extra Dimensions:
• Original idea due to Kaluza (1921), Klein (1926):
– unification of electromagnetism with gravity in 5 dim
• Embedded in superstring theory:
– 10 dimensions, 6 compact
• Revived to solve hierarchy problem (1998):
– N.Arkani-Hamed, S.Dimpoulos, G.Dvali
–
–
–
–
–
There are d extra dimensions (d = 1- 6)
Extra dim are all compact (radii upto 250 microns)
Gravity free to propagate in 4+d dimensions
Assume gravity is strong at TeV scale: cutoff for SM
Newtonian gravity appears weak because graviton wave function
spreads out into 4+d dimensions
• Observable consequences:
– There exists a whole tower of closely-spaced massive graviton states
– Collective interaction of these builds up to near-electroweak strength
– Detection of gravitational effects at colliders is possible!
ADD phenomenology at linear colliders:
• Each ADD graviton escapes detection
– Missing E, p signals
• Most important process for real gravitons is
– e+e-  *  G (Peskin et al)
– Single-photon + missing energy signals
– Need to distinguish from all sorts of other new physics possibilities
• Indian contribution:
– Part of ILCWG programme:
–
–
–
–
confirmatory process: e+e-  e+e- G
S.Dutta, P.Konar, B.Mukhopadhyaya, SR (2003)
2  3 process; 28 Feynman diagrams
Calculation is long and messy Predict significant deviations from
Standard Model
• Total cross-section
• Kinematic distributions
– Results of Peskin et al process and this one are correlated
Warped gravity models:
• L.Randall and R. Sundrum (1999)
• Created to solve hierarchy problem without large dimensions
–
–
–
–
Model has one extra dimension: orbifolded S1/Z2 (small)
There are two branes at each end: visible & invisible
Negative cosmological constant in bulk and visible brane
Fine-tuning of cosmological constants
• Leads to a unique `warped’ solution of Einstein equations
• Gravity is strong (~ electroweak) on invisible brane, but graviton wave
function dies out exponentially (`warp factor) across bulk and reaches
visible brane very weak - natural solution to hierarchy problem
• Observable consequences:
–
–
–
–
Again there is a tower of massive graviton states
Graviton masses are ~ electroweak scale
Each graviton couples with electroweak strength
Each graviton behaves like a WIMP
• Require a bulk scalar field to hold branes at correct distance apart
– Leads to light scalar `radion’ field on visible brane
– Higgs-like couplings with SM fields
RS graviton phenomenology at linear colliders:
• RS gravitons must be heavier than 210 GeV (LEP-2)
• RS graviton width grows very rapidly with graviton mass
– Only first three can form narrow resonances
– For large part of parameter space only first resonance is viable
• RS gravitons decay to all particle pairs
– Maximum BR is to jets
– Width to WW and ZZ is also sizable
• Consider graviton resonances in SM processes, such as Bhabha
scattering and e+e-  +• Indian Contribution: RS graviton exchange in e-e colliders
– D.K.Ghosh and SR (hep-ph/0007354)
– Only t-channel graviton exchanges occur (no resonances)
– Deviations from SM in total cross-section and angular distributions
– Constraints on parameter space
• Indian Contribution: Single photon signals for RS gravitons
– Part of ILCWG programme:
– S.K.Rai and SR (2003)
– Process is e+e-   : resonance is highlighted by spread in energy
Radion phenomenology at linear colliders:
• Radion phenomenology is rather similar to Higgs
phenomenology for tree-level processes
• Indian contribution:
• At one-loop, effect of kinetic terms in radion-fermion
couplings becomes important; can use to distinguish
radions from Higgses (P.Das, S.K.Rai, SR: 2004)
• radion exchange effects in  colliders
– S.R.Choudhury, A. Cornell, G.C.Joshi
– They mainly consider one-loop processes in SM (box diagrams)
which have tree-level contributions in RS model
–    with graviton exchange
• (hep-ph/0007043)
–    with radion exchange
• (hep-ph/0012043)
–   ZZ with graviton & radion exchange
• (hep-ph/0202272)
Outlook
• Many exciting physics possibilities at a linear
collider
• Major Indian participation: mostly beyond-SM
physics
• Maximum contributions in SUSY and extra
dimensions
• Encouraging: Lot of participation from younger
people
• Crying need to make studies more realistic
– Detector simulation, ISR, FSR, beamstrahlung, etc.
Lot of scope for collaboration
between different countries,
groups, institutions, individuals