Alberto Salvio, Florian Staub, Alessandro Strumia, Alfredo Urbano
Motivated by the 750 GeV diphoton excess found at LHC, we compute the maximal width into $γγ$ that a neutral scalar can acquire through a loop of charged fermions or scalars as function of the maximal scale at which the theory holds, taking into account vacuum (meta)stability bounds. We show how an extra gauge symmetry can qualitatively weaken such bounds, and explore collider probes and connections with Dark Matter.
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The recently observed diphoton anomaly at the LHC appears to suggest the presence of a rather broad resonance. In this note, it is pointed out that this does not hold if the two photons are produced along with an extra state. Specifically, the diphoton invariant mass arising from various $A \to Bγγ$ processes, with $A,B$ being scalars, fermions, or vectors, though peaked at a rather large value, would naturally be broad and could fit rather well the observed deviations. This interpretation has a number of advantages over the two-photon resonance hypothesis, for example with respect to the comp…
We investigate a possibility if a loop diagram via Higgsino can enhance the Higgs to diphoton decay width in supersymmetric models with an extension of Higgs sector. A model with an additional non-renormalizable term of Higgs fields is firstly analyzed where the higher order term can introduce the Higgs coupling to Higgsinos as well as charged Higgs bosons. We point out that a choice of the Higgs coupling to obtain a significant size of enhancement of diphoton decay width reduces the Higgs mass and/or a size of non-renormalizable term needs to be large and a cutoff scale is around the weak sca…
The recent reported 750 GeV diphoton excess at the 13 TeV LHC is explained in the framework of effective field theory assuming the diphoton resonance is a scalar (pseudoscalar) particle. It is found that the large production rate and the broad width of this resonance are hard to simultaneously explain if only visible final states are considered. Therefore an invisible decay channel to dark matter (DM) is strongly favored by the diphoton excess with a broad width, given a large coupling of the new scalar to DM. We set constraints on the parameter space in this scenario using the results from LH…
We consider the phenomenology of a resonance that couples to photons but not gluons, and estimate its production rate at the LHC from photon-photon fusion in elastic pp scattering using the effective photon and narrow width approximations. The rate is sensitive only to the mass, the spin, the total width of the resonance, and its branching fraction to photons. Production cross sections of 5-10 fb at 13 TeV can be easily accommodated for a 750 GeV resonance with partial photon width of 15 GeV. This provides the minimal explanation of the reported diphoton anomaly in the early LHC Run II data.
The ATLAS and CMS experiments at the LHC have reported an excess of diphoton events with invariant mass around 750 GeV, with local significance of about $3.6 σ$ and $2.6 σ$, respectively. We entertain the possibility that this excess is due to new physics, in which case the data suggest a new particle with 13 TeV LHC production cross section times diphoton branching ratio of about 5~fb. Interestingly, ATLAS reports a mild preference for a sizeable width for the signal of about 45 GeV; this result appears consistent with CMS, and is further supported by improving the compatibility of the 8 TeV …
One of the most exciting explanations advanced for the recent diphoton excess found by ATLAS and CMS is in terms of sgoldstino decays: a signal of low-energy supersymmetry-breaking scenarios. The sgoldstino, a scalar, couples directly to gluons and photons, with strength related to gaugino masses, that can be of the right magnitude to explain the excess. However, fitting the suggested resonance width, Gamma ~ 45 GeV, is not so easy. In this paper we explore efficient possibilities to enhance the sgoldstino width, via the decay into two Higgses, two Higgsinos and through mixing between the sgol…
Motivated by recent results from Higgs searches at the Large Hadron Collider, we consider possibilities to enhance the diphoton decay width of the Higgs boson over the Standard Model expectation, without modifying either its production rate or the partial widths in the WW and ZZ channels. Studying effects of new charged scalars, fermions and vector bosons, we find that significant variations in the diphoton width may be possible if the new particles have light masses of the order of a few hundred GeV and sizeable couplings to the Higgs boson. Such couplings could arise naturally if there is la…
It is shown that the 750 GeV diphoton excess can be explained in extensions of Two-Higgs-Doublet Models that do not involve large multiplicities of new electromagnetically charged states. The key observation is that at moderate and large $\tanβ$ the total decay width of the 750 GeV Higgs is strongly reduced as compared to the Standard Model. This allows for much more economical choices of new states that enhance the diphoton signal to fit the data. In particular, it is shown that one family of vector-like quarks and leptons with SM charges is enough to explain the 750 GeV diphoton excess. More…
We study models with heavy exotics that account for the LHC $750$ GeV diphoton excess in light of current vector-like quark bounds. Utilizing only exotics that may appear in three-stack and four-stack D-brane models, we show that a narrow width diphoton excess can be accounted for while evading existing bounds if multiple exotics are added, with vector-like leptons of mass $M_L\lesssim 375$ GeV and vector-like quarks with masses up to $\simeq 3$ TeV. However, a large width $(Γ/M \sim 0.06)$, as suggested by the ATLAS data, cannot be easily accommodated in this framework. Renormalization group …
Recently, the CMS and ATLAS collaborations have reported a diphoton peak at 750 GeV in the RunII of LHC at 13 TeV. We assume that the heavy fourth generation quark doublet $z,~y$ with $380 $GeV mass, and the width of $z,t$ is much less $b$ quark. Then we show that the contributions of the $(z \bar z+y \bar y)/\sqrt{2}$ bound state $η_{zy}(1S)$ to the diphoton measurements through $σ(pp\to η_{zy}(1s)\to γγ) $ are $ 5.6^{+5.6}_{-2.8} {\rm fb}$ at $\sqrt S=13$ TeV. They are constant with the 750 GeV diphoton excess measured by the CMS ant ATLAS collaborations.
ATLAS and CMS have each reported a modest diphoton excess consistent with the decay of a broad resonance at ~ 750 GeV. We show how this signal can arise in a weakly coupled theory comprised solely of narrow width particles. In particular, if the decaying particle is produced off-shell, then the associated diphoton resonance will have a broad, adjustable width. We present simplified models which explain the diphoton excess through the three-body decay of a scalar or fermion. Our minimal ultraviolet completion is a weakly coupled and renormalizable theory of a singlet scalar plus a heavy vector-…
We construct a model containing a viable dark matter candidate, in the framework of left-right symmetry, which can explain both width and cross-section of the observed 750 GeV diphoton excess at the LHC. We introduce a fermion quintuplet whose neutral component can be a possible dark matter candidate, whereas the charged components enhance the loop induced coupling of a 750 GeV singlet scalar with a pair of photons. We study the photo-production of the singlet scalar and its various decay modes, successfully addressing both the ATLAS and the CMS diphoton excess.
We consider the possibility that the recently observed excess in the diphoton invariant mass spectrum around 750 GeV is due to two narrow scalars. We demonstrate that there is no need to introduce invisible decay modes to enlarge the widths as long as the two scalars exhibit an appropriate mass splitting. Nevertheless we investigate the possible connection of these two scalars to the dark matter in a toy model with a Majorana fermionic dark matter candidate. We explore how large the widths of the two scalar widths could be taking into account various constraints from collider and dark matter e…
The ATLAS and CMS experiments at the LHC have found significant excess in the diphoton invariant mass distribution near 750 GeV. We interpret this excess in a predictive nonsupersymmetric SU(5) grand unified framework with a singlet scalar and light adjoint fermions. The 750 GeV resonance is identified as a gauge singlet scalar. Both its production and decays are induced by 24 dimensional adjoint fermions predicted within SU(5). The adjoint fermions are assumed to be odd under $Z_2$ symmetry which forbids their direct coupling to the standard model fermions. We show that the observed diphoton …
We explore the possibility of a beyond the standard model scalar ($ϕ$) as a possible explanation of the diphoton resonance at 750~GeV invariant mass reported by the ATLAS and CMS collaborations at the large hadron collider (LHC). We first present in a model-independent way the scalar-gluon-gluon and scalar-photon-photon effective couplings needed for obtaining the required diphoton cross-section at the LHC for different total widths. We investigate here two new-physics possibilities that can generate these effective couplings, namely, (i) the 2-Higgs-doublet model (2HDM) in the alignment limit…
In this paper we consider signal-background interference effects in Higgs-mediated diphoton production at the LHC. After reviewing earlier works that show how to use these effects to constrain the Higgs boson total decay width, we provide predictions beyond NLO accuracy for the interference and related observables, and study the impact of QCD radiative corrections on the Higgs width determination. In particular, we use the so-called soft-virtual approximation to estimate interference effects at NNLO in QCD. The inclusion of these effects reduce the NNLO prediction for the total Higgs cross-sec…
I perform a combined analysis of the ATLAS and CMS diphoton data, using both Run-I and Run-II results, including those released at the 2016 Moriond conference. I find combining the ATLAS and CMS results from Run-II increases the statistical significance of the reported 750 GeV anomaly, assuming a spin-0 mediator coupling to gluons or heavy quarks with a width much smaller than the detector resolution. This significance does not decrease when the 8 TeV data is included. A spin-2 mediator is disfavored compared to the spin-0 case. The cross section required to fit the ATLAS anomaly is in tension…
We propose that the sbino, the scalar partner of a Dirac bino can explain the 750 GeV diphoton excess observed by ATLAS and CMS . We analyze a model in which the sbino couples to pairs of Standard Model (SM) gauge bosons. We analyze an effective operator model, as well as a completion in which the sbino couples to pairs of gauge bosons through loops of heavy sfermions. We find that the sbino may be given an appreciable decay width through tree level coupling in the Higgs or Higgsino sector and additionally fit the 750 GeV excess by considering gluon fusion processes with decay to diphotons.
The existence of dark matter (DM) and the origin of the baryon asymmetry are persistent indications that the SM is incomplete. More recently, the ATLAS and CMS experiments have observed an excess of diphoton events with invariant mass of about 750 GeV. One interpretation of this excess is decays of a new spin-0 particle with a sizable diphoton partial width, e.g. induced by new heavy weakly charged particles. These are also key ingredients in models cogenerating asymmetric DM and baryons via sphaleron interactions and an initial particle asymmetry. We explore what consequences the new scalar m…
We examine the observed diphoton excess at 750 GeV in the framework of constrained Minimal Supersymmetric Standard Model (cMSSM). The consistency of cMSSM with the discovery of a 125 GeV Higgs boson and PLANCK/WMAP data for dark matter relic density (RD) demands large mixing in the scalar top (stop) sector and consequently, the existence of a light stop quasi-degenerate with the lightest neutralino. Small decay width due to kinematic and loop suppression of such a stop allows for the existence of stop-antistop bound states (stoponia). Identifying the particular part of cMSSM parameter space co…
We study models in which the 750 GeV diphoton excess is due to a scalar decaying to two pseudo-Nambu-Goldstone bosons that subsequently decay into two pairs of highly boosted photons, misidentified as individual photons. Performing a model independent analysis we find that, with axion mass around $200$ MeV, this class of theories can naturally explain the observed signal with a large width, without violating monojet constraints. At the same time the requirement of a prompt axion decay can be satisfied only with a relatively large axion-photon coupling, leading to many new charged particles at …
The ATLAS and CMS Collaborations of the Large Hadron Collider (LHC) have reported an excess of events in diphoton channel with invariant mass of about 750 GeV. With low energy supersymmetry breaking, we systematically consider the sgoldstino scalar $S$ as the new resonance, which is a linear combination of the CP-even scalar $s$ and CP-odd pseudoscalar $a$. Because we show that $s$ and $a$ can be degenerated or have large mass splitting, we consider two cases for all the following three scenarios: (1) Single resonance. $s$ is the 750 GeV resonance decays to a pair of 1 GeV pseudoscalar $a$. Wi…
In this paper we explain the 750 GeV diphoton resonance observed at the run-2 LHC as a scalar singlet $S$, that plays a key rule in generating tiny but nonzero Majorana neutrino masses. The model contains four electroweak singlets: two leptoquarks, a singly charged scalar and a neutral scalar $S$. Majorana neutrino masses might be generated at the two-loop level as $S$ get nonzero vacuum expectation value. $S$ can be produced at the LHC through the gluon fusion and decays into diphoton at the one-loop level with charged scalars running in the loop. The model fits perfectly with a wide width of…
In this paper we explain the diphoton excess in the invariant mass M $\approx$ 750 GeV , claimed by the ATLAS and CMS collaborations at the run-2 LHC, as the signal of a scalar singlet in a string inspired exceptional supersymmetric standard model (ESSM). The scalar singlet might play a rule in the spontaneous breaking of the $U(1)^\prime$ gauge symmetry of the ESSM and couples to diphoton and/or gluon pair with the help of exotic quarks and Higgs-like supermultiplets, which are contained in the fundamental representation of the $E_6$ group. The model might give rise to a large enough producti…
We investigate the 750 GeV diphoton excess in terms of supersymmetric models which preserve grand unification in the ultraviolet. We show that minimal extensions of the MSSM by a singlet and a vector-like 5-plet or 10-plet of SU(5) can explain the observed signal while remaining perturbative up to the GUT scale. Different from previous analyses we rely on light sfermions in the loops which - compared to the analog non-supersymmetric models - enhance the diphoton cross section by up to a factor of seven. While the resonance decay width is narrow, mass splitting of the scalar and pseudoscalar co…
ATLAS and CMS recently released the first results of searches for diphoton resonances in 13 TeV data, revealing a modest excess at an invariant mass of approximately 750 GeV. We find that it is generically possible that a singlet scalar resonance is the origin of the excess while avoiding all other constraints. We highlight some of the implications of this model and how compatible it is with certain features of the experimental results. In particular, we find that the very large total width of the excess is difficult to explain with loop-level decays alone, pointing to other interesting bounds…
In this paper, we interpret the 750 GeV diphoton excess in the Zee-Babu extension of the two-Higgs-doublet model by introducing a top partner ($T$)/bottom partner ($B$). In the alignment limit, the 750 GeV resonance is identified as the heavy CP-even Higgs boson ($H$), which can be sizably produced via the QCD process $pp \to T\bar{T}$ or $pp \to B\bar{B}$ followed by the decay $T\to Ht$ or $B \to Hb$. The diphoton decay rate of $H$ is greatly enhanced by the charged singlet scalars predicted in the Zee-Babu extension and the total width of $H$ can be as large as 7 GeV. Under the current LHC c…
We investigate the robustness of the resonance like feature centred at around a 750 GeV invariant mass in the 13 TeV diphoton data, recently released by the ATLAS collaboration. We focus on the choice of empirical function used to model the continuum diphoton background in order to quantify the uncertainties in the analysis due to this choice. We extend the function chosen by the ATLAS collaboration to one with two components. By performing a profile likelihood analysis we find that the local significance of a resonance drops from $3.9σ$ using the ATLAS background function, and a freely-varyin…
The ATLAS and CMS collaborations recently reported a mild excess in the diphoton final state pointing to a resonance with a mass of around 750 GeV and a potentially large width. We consider the possibility of a scalar resonance being produced via gluon fusion and decaying to electroweak gauge bosons, jets and pairs of invisible particles, stable at collider scales. We compute limits from monojet searches on such a resonance and test their compatibility with the requirement for a large width. We also study whether the stable particle can be a a dark matter candidate and investigate the correspo…
Inspired by the 750 GeV diphoton state recently reported by ATLAS and CMS, we propose a U(1)_{B-L} extension of the MSSM which predicts the existence of four spin zero resonance states that are degenerate in mass in the supersymmetric limit. Vector-like fields, a gauge singlet field, as well as the MSSM Higgsinos are prevented from acquiring arbitrary large masses by a U(1) R-symmetry. Indeed, these masses can be considerably lighter than the Z' gauge boson mass. Depending on kinematics the resonance states could decay into right handed neutrinos and sneutrinos, and/or MSSM Higgs fields and Hi…
We investigate a possibility for explaining the recently announced 750\,GeV diphoton excess by the ATLAS and the CMS experiments at the CERN LHC in a model with multiple doubly charged particles, which was originally suggested for explaining tiny neutrino masses through a three-loop effect in a natural way. The enhanced radiatively generated effective coupling of a new singlet scalar $S$ with diphoton with multiple charged particles in the loop enlarges the production rate of $S$ in $pp\to S+X$ via photon fusion process and also the decay width $Γ(S\to γγ)$ even without assuming a tree level p…
As an interpretation of the 750 GeV diphoton excesses recently reported by both ATLAS and CMS collaborations, we consider a simple extension of the Standard Model with a Dirac fermion dark matter where a singlet complex scalar field mediates between dark matter and SM particles via effective couplings to SM gauge bosons and/or Higgs-portal. In this model, we can accommodate the diphoton events through the direct and/or cascade decays of pseudo-scalar and real scalar partners of the complex scalar field. We show that mono-jet searches and gamma-ray observations are complementary in constraining…
The CMS and ATLAS reports on a possible excess of diphoton events at $750$ GeV are the cause of great excitement and hope. We show that a pseudoscalar axion coupled to the topological density of hypercharge, suggested in the past by Brustein and Oaknin as a candidate for inducing baryogenesis, can explain the signal in the diphoton channel. The hypercharge axion (HCA) can also decay to $Zγ$ and $ZZ$. The expected number of events in these channels is too small to have been detected, but such decays should be observed in the future. The HCA can be produced via vector boson fusion (VBF) or via a…
We propose a new $SU(6)\otimes U(1)_{X}$ GUT model free from anomalies, with a 750 GeV scalar candidate which can decay into two photons, compatible with the recent diphoton signal reported by ATLAS and CMS collaborations. This model gives masses to all fermions and may explain the 750GeV signal through one loop decays to $γγ$ with charged vector and charged Higgs bosons, as well as up- and electron-like exotic particles that arise naturally from the condition of cancellation of anomalies of the $SU(6)\otimes U(1)_{X}$ group. We obtain, for different width approximations, allowed mass regions …
We consider minimal effective interactions of the 750 GeV mass resonance observed recently by ATLAS and CMS. Assuming a new scalar and gauge invariant effective interactions leads to non-trivial two particle scattering amplitudes with asymptotic gauge boson states. The longitudinally polarized $W\pm$ and $Z$ bosons interacting via dimension-five effective operators provide stringent constraints on the validity of the effective model. The large width found by ATLAS implying a bound of approximately 500 GeV already below the resonance, turns this scenario unlikely. For production mainly in gluon…
We show that contrary to naive expectations the recently observed diphoton excess can be explained by a vector resonance, which decays to a photon and a light scalar $s$, followed by a decay of the scalar into two photons: $Z' \rightarrow γs \rightarrow 3 γ$. As the two photons from the scalar decay are highly boosted, the experimental signature is an apparent diphoton final state. In fact all the necessary ingredients are naturally present in $Z'$ models: Additional fermions with electroweak quantum numbers are required in order to render the theory anomaly free and naturally induce the requi…
We propose an NMSSM scenario that can explain the excess in the diphoton spectrum at 750 GeV recently observed by ATLAS and CMS. We show that in a certain limit with a very light pseudoscalar one can reproduce the experimental results without invoking exotic matter. The 750 GeV excess is produced by two resonant heavy Higgs bosons with masses ~750 GeV, that subsequently decay to two light pseudoscalars. Each of these decays to collimated photon pairs that appear as a single photon in the electromagnetic calorimeter. A mass gap between heavy Higgses mimics a large width of the 750 GeV peak. The…
In the context of a nonuniversal and anomaly free $U(1)_{X}$ extension of the standard model, we examine the decay of a $750$GeV scalar singlet state, $ξ_χ$, as a possible explanation of the observed diphoton excess announced by the ATLAS and CMS collaborations at CERN-LHC collider. One-loop decay to photons is allowed through three heavy singlet quarks and one charged Higgs boson into the loop. We obtain, for different width approximations and for masses of the exotic singlet quarks in the region $[900,\,3000]$ GeV, a production cross section $σ(pp\toξ_χ\toγγ)$ compatible with ATLAS and CMS c…
In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and $h\to μτ$ in an extension of the two-Higgs-doublet model (2HDM) with additional vector-like fermions and a CP-odd scalar singlet ($P$) which is identified as the 750 GeV resonance. This 750 GeV resonance has a mixing with the CP-odd scalar ($A$) in 2HDM, which leads to a coupling between $P$ and the SM particles as well as a coupling between $A$ and the vector-like fermions. Such a mixing and couplings are strongly constrained by $τ\toμγ$, muon g-2 and the 750 GeV diphoton data. We scan over the paramete…
We propose that the 750 GeV resonance, presumably observed in the early LHC Run 2 data, could be a heavy composite axion that results from condensation of a hypothetical quark in a high-colour representation of conventional QCD. The model, motivated by a recently proposed solution to the strong CP problem, is very economical and is essentially defined by the properties of the additional quark - its colour charge, hypercharge and mass. The axion mass and its coupling to two photons (via axial anomaly) can be computed in terms of these parameters. The axion is predominantly produced via photon f…
We interpret the di-photon excess recently reported by the ATLAS and CMS collaborations as a new resonance arising from the sgoldstino scalar, which is the superpartner of the Goldstone mode of spontaneous supersymmetry breaking, the goldstino. The sgoldstino is produced at the LHC via gluon fusion and decays to photons, with interaction strengths proportional to the corresponding gaugino masses over the supersymmetry breaking scale. Fitting the excess, while evading bounds from searches in the di-jet, $Zγ$, $ZZ$ and $WW$ final states, selects the supersymmetry breaking scale to be a few TeV, …
The study of the forward scattering amplitude $V(k,λ) V(k'λ')\to V(k,λ) V(k',λ')$ of real massless gauge bosons $V$, e.g. photons or gluons, leads to a sum-rule that can be used to investigate beyond the Standard Model signals at LHC in the $γγ$ channel. The sum-rule only relies on general properties such as analyticity, unitarity and crossing. We use the now buried 750 GeV diphoton resonance as a case of study to exemplify the constraints that the forward sum-rule requires to any new physics candidate. In the case of a large $γγ$ or $gg$ partial width, of the order of 10 GeV in our 750 GeV an…
Recently, an excess of events in diphoton channel with invariant mass of about 750 GeV has been reported by the ATLAS and CMS Collaborations. Considering it as a tantalizing hint for new physics beyond the Standard Model (SM), we propose a simple extension of the SM with an additional doublet Higgs $H^{'}$ and a singlet $s$. We consider the neutral component $H^{\prime }_0$ of $H'$ as the 750 GeV resonance, and assume that $s$ is lighter than 2.6 GeV. In particular, $H^{\prime }_0$ can be produced at tree level via $q{\bar q}$ production, and decay into a pair of $s$ at tree level. And then $s…
A recent signal of 750 GeV diphotons at the LHC can be explained within the framework of supersymmetric unification by the introduction of vector quarks and leptons with Yukawa couplings to a singlet S that describes the 750 GeV resonance. We study the most general set of theories that allow successful gauge coupling unification, and find that these Yukawa couplings are severely constrained by renormalization group behavior: they are independent of ultraviolet physics and flow to values at the TeV scale that we calculate precisely. As a consequence the vector quarks and leptons must be light; …
The new scalar resonance contribution to the 750 GeV diphoton excess observed at the LHC 13 TeV necessarily interferes with the continuum background in the $gg\to γγ$. The interference has two considerable effects: (1) enhancing or suppressing diphoton signal rate due to the imaginary-part interference and (2) distorting resonance shape due to the real-part interference. From the best-fit study of two benchmark models (two Higgs doublets with $\sim$50 GeV widths and a singlet scalar with 5 GeV width, both extended with vector-like fermions), we find that the resonance contribution to the 750 G…
Perturbative supersymmetric gauge coupling unification is possible in six theories where complete SU(5) TeV-scale multiplets of vector matter account for the size of the reported $750~{\rm GeV}$ diphoton resonance, interpreted as a singlet multiplet $S = (s+ia)/\sqrt{2}$. One of these has a full generation of vector matter and a unified gauge coupling $α_G \sim 1$. The diphoton signal rate is enhanced by loops of vector squarks and sleptons, especially when the trilinear $A$ couplings are large. If the $SH_u H_d$ coupling is absent, both $s$ and $a$ can contribute to the resonance, which may t…
Motivated by the diphoton excess at 750 GeV reported by the ATLAS and CMS experiments, we present an F-theory inspired flipped $SO(10)$ model embedded in an $E_6$ GUT. The low energy spectrum includes the three MSSM chiral families, vectorlike color triplets, several pairs of charged $SU(2)_L$ singlet fields $(E^c, \bar E^c)$, as well as MSSM singlets, one or more of which can contribute to the resonance. Total decay width in the multi-GeV range can arise from couplings involving the singlet and MSSM fields
We argue that the QCD axion can arise from many aligned axions with decay constants much smaller than the conventional axion window. If the typical decay constant is of {\cal O}{(100)} GeV to 1 TeV, one or more of the axions or saxions may account for the recently found diphoton excess at \sim 750 GeV. Our scenario predicts many axions and saxions coupled to gluons with decay constants of order the weak scale, and therefore many collider signatures by heavy axions and saxions will show up at different energy scales. In particular, if the inferred broad decay width is due to multiple axions or …
A 750 GeV resonance has been observed at the Run 2 LHC in the diphoton channel. In this paper, we explain this resonance as a CP-even scalar, S, that triggers the spontaneous breaking of local $U(1)_B$ or $U(1)_{B+L}$ gauge symmetries. S couples to gluon and photon pairs at the one-loop level, where particles running in the loop are originally introduced to cancel anomalies. The gluon fusion is the dominate production channel of S at the LHC. The model automatically contains a scalar dark matter candidate, stabilized by the new gauge symmetry. Our study shows that both the observed production …
A very plausible explanation for the recently observed diphoton excess at the 13 TeV LHC is a (pseudo)scalar with mass around 750 GeV, which couples to a gluon pair and to a photon pair through loops involving vector-like quarks (VLQs). To accommodate the observed rate, the required Yukawa couplings tend to be large. A large Yukawa coupling would rapidly run up with the scale and quickly reach the perturbativity bound, indicating that new physics, possibly with a strong dynamics origin, is near by. The case becomes stronger especially if the ATLAS observation of a large width persists. In this…
The hint for a possible resonance in the diphoton channel with mass of 750~GeV disappeared in the data presented at ICHEP'16 by ATLAS and CMS. However, the diphoton final state remains as one of the golden channels for new physics discoveries at the TeV scale in the LHC experiments. This motivates us to analyze model-independently the implications of an O(TeV) bump in the $γγ$ final state. By means of forward sum-rules for $γγ$ scattering, we show that a spin-0 resonance with mass of the order of the TeV and a sizable $γγ$ partial width -of the order of a few GeV- must be accompanied by higher…
We interpret the potential observation of the 750 GeV di-photon resonance at the LHC in models, in which an $SU(2)$ isospin-singlet scalar boson mixes with the Standard Model (SM) Higgs boson through an angle $α$. Allowing the singlet scalar boson to have renormalizable couplings to vector-like leptons and quarks and introducing sizable decay width of the 750 GeV di-photon resonance into non-SM particles such as dark matters, we can explain the large production cross section $σ(H_2) \times B(H_2 \to γγ)$ as well as the apparent large total width of the boson without conflicts from the results …
In this paper, we study the recent 750 GeV diphoton excess in the Hill Model with vector-like fermions, in which the singlet-like Higgs boson is chosen as 750 GeV resonance and is mainly produced by the gluon fusion through vector-like top and bottom quarks. Meanwhile its diphoton decay rate is greatly enhanced by the vector-like lepton. Under the current experimental and theoretical constraints, we present the viable parameter space that fits the 750 GeV diphoton signal strength at 13 TeV LHC. We find that the heavier vector-like fermion masses are, the smaller mixing angle $θ$ is required. T…
The 750-760 GeV diphoton resonance may be identified as one or two scalars and/or one or two pseudoscalars contained in the two singlet superfields S_{1,2} arising from the three 27-dimensional representations of E_6 . The three 27s also contain three copies of colour-triplet charge \mp 1/3 vector-like fermions D,\bar{D} and two copies of charged inert Higgsinos \tilde{H}^{+},\tilde{H}^{-} to which the singlets S_{1,2} may couple. We propose a variant of the E_6SSM where the third singlet S_3 breaks a gauged U(1)_N above the TeV scale, predicting Z'_N, D,\bar{D}, \tilde{H}^{+},\tilde{H}^{-} at…
A colored heavy particle with sufficiently small width may form non-relativistic bound states when they are produced at the large hadron collider\,(LHC), and they can annihilate into a diphoton final state. The invariant mass of the diphoton would be around twice of the colored particle mass. In this paper, we study if such bound state can be responsible for the 750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit signal cross section is obtained for the SU(2)$_L$ singlet colored fermion $X$ with $Y_X=4/3$. Having such an exotic hypercharge, the particle is expected to…
We investigate a simple setup in which an excess in the di-photon invariant mass distribution around $750$ GeV, as seen by the ATLAS and CMS collaborations, is originated through a pair of collimated photon pairs. In this framework a scalar state $s$ decays into two light pseudo-Goldstone bosons $a$, each of which subsequently decays into a pair of collimated photons which are misidentified as a single photon. In a minimal context of spontaneous symmetry breaking, we show that coupling a complex scalar field $Φ=(s+ia)/\sqrt{2}$ to a fermionic dark matter candidate $χ$, also responsible for gen…
We show that low-mass-scale string compactifications, with a generic D-brane configuration that realizes the standard model by open strings, can explain the relatively broad peak in the diphoton invariant mass spectrum at 750 GeV recently reported by the ATLAS and CMS collaborations. Under reasonable assumptions, we demonstrate that the excess could originate from a closed string (possibly axionic) excitation φthat has a coupling with gauge kinetic terms. We estimate the φproduction rate from photon-photon fusion in elastic pp scattering, using the effective photon and narrow width approximati…
Interpreting the excesses around 750 GeV in the diphoton spectra to be the signal of a new heavy scalar decaying to photons, we point out the possibility of looking for correlated signals with virtual photons. In particular, we emphasize that the effective operator that generates the diphoton decay will also generate decays to two leptons and a photon, as well as to four leptons, independently of the new resonance couplings to $Zγ$ and $ZZ$. Depending on the relative sizes of these effective couplings, we show that the virtual diphoton component can make up a sizable, and sometimes dominant, c…
We propose that the SU(2) x SU(2) x U(1) (aka G221) models could provide us a 750 GeV scalar resonance that may account for the diphoton excess observed at the LHC while satisfying present collider constraints. The neutral component of the $SU(2)_R$ scalar multiplet can be identified as the 750 GeV scalar. In the lepto-phobic and fermio-phobic G221 models the new charged gauge boson W' could be light, and we find that the diphoton decay width could be dominated by the loop contribution from the $W'$. To initiate gluon fusion production, it is necessary to extend the G221 symmetry to the Pati-S…
We consider the possibility that the diphoton excess at 750 GeV is caused by a new scalar resonance produced in photon fusion. This scenario is parametrised by only one relevant effective couplings and is thus minimal. We show that this setup can reproduce both the production rate and width of the resonance, and is not in conflict with the 8 TeV limits on the diphoton cross section. The scenario also predicts event rates for $WW$, $ZZ$, $Zγ$ final states. We suggest to perform precision measurements by studying light-by-light scattering with intact protons detected in forward detectors. We con…
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