Radion/Higgs phenomenology and the diphoton excess at the LHC

Conclusions

Radion/Higgs phenomenology and the diphoton excess at the LHC

Anibal D. Medina^†

†IPhT CEA/Saclay and Universite Paris-Saclay

Planck Conference

Conclusions

Warped Extra Dimensions

Very versatile model that has prompted many interesting ideas given its simplicity.

Randall and Sundrum

Solves thehierarchy problemusing the space-timegeometryby means of localizing the Higgs field near the IR brane.

When Standard Model fields in the bulk→generate fermion masses by localization in the extra dimension (explainsfermion mass hierarchies).

AdS/CFTcorrespondence relates the 5D setup to a 4D conformal theory.

Conclusions

Presence ofIR brane→spontaneous breakingof the conformal symmetry→ existence of aNambu-Goldstone bosonknown asradionin the 5D

language/dilatonin the 4D dual.

One way tostabilizethe extra dimension is to couple the radion to an additional scalar field→gravity-scalarsystem provides stabilizing potential and generates a massfor the radion.Goldberger and Wise, Csaki et al.

These interactionsimplydeformationsfrom pureAdS5space↔explicit breaking of the conformal symmetry.

Assumption that theonly light statesbesides SM particles are the radion/dilaton and the Higgs.

Study the Higgs-radion mixing with theHiggsa fundamental5D scalarin thebulk of the extra dimensionand construct ageneral effective Lagrangian.

See how the radion may provide anexplanationfor thediphoton excessat the LHC.

Conclusions

4D effective action

Deformations fromAdS5space/explicit breaking of the conformal symmetry→

generatesradion/dilaton massandmass mixingwith the Higgs.

Mostgeneral effective phenomenological Lagrangianfor light scalar degrees of freedom,

L_eff = 1

2∂µh(x)∂^µh(x)−1

2m²_hh(x)²+1 2 1+c2

v_ew² Λ²_r

!

∂µr(x)∂^µr(x)

− 1

2m²_rr(x)²−c1

vew

Λr

∂µh(x)∂^µr(x)−c3

vew

Λr

m²_rh(x)r(x), wherec₁,c₂andc₃areO(1)numerical coefficients.

Conclusions

Mass mixing matrix and mass eigenstates

Diagonalize kinetic termby the shifth=h⁰+c1(vew/Λr)r⁰/Zandr=r⁰/Z, where

Z²=1+ (c2+c₁²)v_ew² Λ²r

.

Mass matrixin the basis(r⁰,h⁰),





m²_r Z² + ¹

Z² v_ew²

Λ²_r (c²₁m²_h+2c₁c₃m_r²) _Z^1v_Λ^ew

r (c₁m²_h+c₃m²_r)

1 Z

v_ew

Λ_r (c₁m_h²+c₃m²_r) m²_h



.

Mass eigenbasisis obtained by the orthogonal transformation, r⁰

h⁰

=

Ur,− Ur,+

Uh,− U_h,+

φ−

φ+

.

Gauge basisrelated tomass basisvia (note ,c_ih²+c²_ir6=1 fori=h,r)

r = crrφ++crhφ−= 1

Z(Ur,+φ++Ur,−φ−), h = c_hrφ++c_hhφ−= (U_h,++c1

Z vew

Λr

Ur,+)φ++ (Uh,−+c1

Z vew

Λr

Ur,−)φ−.

Conclusions

Higgs and radion couplings

Higgsis a lightscalar doubletcharged underSU(2)L×U(1)Y.

Couplingeffectsdue tomixing or loop effectsinvolving resonances of the conformal sector,suppresseddue toheavyresonances mass,mres∼gρf→we restrictto SM Higgs couplings values.

For radion/dilaton we use 5D language as aneasy toolto calculate couplings, results aregeneralwith the replacementΛr∼f.

Particularly interesting is theradion coupling to Higgs kinetic term(in the bulk), S_matter =

Z

d⁴xdy√

g(DµH^†D^µH)

= Z

d⁴xdy e^{−4(A(y)+F(x,y))}(1+2F(x,y))e^{2(A(y)+F(x,y))}DµH^†D^µH

≈ Z

d⁴xdy(1−4F²(x,y) +O(F(x,y)³))e^−2A(y)DµH^†D^µH, where the index on the r.h.s is contracted using theMinkowskimetric.

Conclusions

Higgs and radion couplings

Radion-diHiggscoupling:(2m_h²−(c1/2)m²_r)/Λr.

Phenomenologically relevant couplingsof the gauge statesh(x)andr(x)to SM particles

h(x) r(x)

f¯f −mf

v mf

Λr

WW 2m2

vW −2

Λr 1 kL

ZZ m2

Z

v −1

Λr 1 kL

γγ 1

v

F1(τW,h) +4 3F1/2(τt,h)

αEM

2π −1

Λr 1

kL+ h

bQED−F1(τW,r)−4 3F1/2(τt,r)

iαEM 2π

gg 1

v α3

4πF1/2(τt,h) −1

Λr 1

kL+ h

bQCD−1 2F1/2(τt,r)

iα3 2π

Conclusions

The Diphoton Excess

RecentlyATLAS and CMSreported a mild excess in thediphoton channel around mγγ≈750 GeVfor collisions at√

s=13 TeV.

Broad or narrowresonance still uncertain (ATLAS prefers large while CMS prefers narrow).

Eventsdo notseem to come along with other particles.

Resonance wasnot seenin previous run at the LHC for√

s=8 TeV.

Conclusions

The Diphoton Excess

We use thecross sectionspreferred by the diphoton excesses derived inButtazzo et al.: µ^ATLAS_{13 TeV}=σ(pp→S)13 TeV× B(S→γγ) =10⁺⁴₋₃fb,

µ^CMS_{13 TeV}=σ(pp→S)13 TeV× B(S→γγ) =3.7^+1.5_−1.3fb.

Most importantconstraintsfrom 8 TeV searches Final State Observed Bound

t¯t <300 fb

WW <38 fb

ZZ <17 fb

Zγ <4.0 fb

γγ <1.4 fb

hh <36 fb

jj <2.5 pb

Table:Constraints on the radion from 8 TeV resonance searches.

Conclusions

The Diphoton Excess

Scanwith flat priors in the range−2≤c1,c3≤2, 5≤kL≤35 and 1 TeV

≤Λr≤5 TeV

Demand thatφ+identified with the750 GeV resonancesatisfies resonances searches constraints whileφ−state is identified with the125 GeV SM-like Higgs and is consistent with the measured Higgs signal strengths at the 2-σlevel.

chrgives a measure of how muchHiggs-likecouplings the heavier eigenstate possesses.

chrin the limitv/Λr 1 points towardsalignmentc1≈ −c₃,

c_hr= (c₁+c₃) m²_r m_r²−m²_h

vew

Λr

+O

(vew/Λr)³ ,

For large values ofc1, radion coupling to two Higgs isenhanced→constraints fromDiHiggssearches.

Non-Unitarityimplies that thoughchr≈0 thatdoes notmean thatcrh≈0 and thuslighter statemay haveradion-likecouplings.

Conclusions

Conclusions

The Diphoton Excess

Branching ratiosfor a 750 GeV radion to various SM final states vskL.

Conclusions

Ratio of radion productioncross sections at√

s=13 TeV and√

s=8 TeV σ(pp→r)13 TeV

σ(pp→r)_{8 TeV} ≈4.7

Simultaneouslyhave 6 fb diphoton signal at 13 TeV while avoiding ditop searches, B(r→t¯t)

B(r→γγ)< 300

6 ×σ(pp→r)13 TeV

σ(pp→r)_{8 TeV} ≈235.

Not satisfied forkL≈30 but forkL.20−15.Decreasingthe size of the extra dimensionincreasesthe coupling toggandγγ.

Conclusions

The Diphoton Excess

Region consistent with diphoton excess imposing all constraints ingreen, while theblueandredregions are excluded by the 8 TeVdiphotonandditopsearches respectively. All in thealignmentlimit.

Conclusions

The Diphoton Excess

Alignment limit→DiHiggsmay dominate the constraints forc1&0.35. . Composite scaleΛr &2 TeV forc₁=0 andΛr&3.5 TeV forc₁=0.5 . Smallerwarping factor→"Little Randall-Sundrum".

Possibility of exploring this scenario withditopfinal states anddiHiggsin the alignment limit at LHC run 2 .

Width is small,Γ.1 GeV

Conclusions

Conclusions

Constructed themost general effective Lagrangianthat describes the mixing in the radion-Higgs system.

Crucial propertythat radion coupling to pair ofmassive gauge bosons is suppressedcompared to usual brane Higgs models→explain thediphoton excessat the LHC while avoidingstringentconstraint from diboson searches.

We are able tomatchthe observed excess whileavoidingthe 8 TeV searches for

Λr&(2−3.5)TeV andkL.20−15.

Dominant decay modes tot¯tandgg, with theformerproviding the most stringent bounds and best prospects forprobingin amodel-independentway in the immediate future. In thealignmentcase it is possible that thediHiggssignal may dominate the branching ratio and may be the best way to probe the model.