Right Sneutrino Dark Matter and a Monochromatic Photon Line

The inclusion of right-chiral sneutrino superfields is a rather straightforward addition to a supersymmetric scenario. A neutral scalar with a substantial right sneutrino component is often a favoured dark matter candidate in such cases. In this context, we focus on the tentative signal in the form of a monochromatic photon, which may arise from dark matter annihilation and has drawn some attention in recent times. We study the prospect of such a right sneutrino dark matter candidate in the contexts of both MSSM and NMSSM extended with right sneutrino superfields, with special reference to the Fermi-LAT data.


I. INTRODUCTION
Various observations ranging from galactic rotation curves to the observed anisotropy in the cosmic microwave background radiation, have strengthened our belief in a substantial cold Dark Matter (DM) component of the universe. It is therefore hardly surprising that, side by side with direct searches, all indirect evidences of dark matter are also of great interest.
Analyses of the publicly available Fermi-LAT [1] data found a tentative hint through an observation of a γ-ray line at ∼ 130 GeV coming from the vicinity of the galactic center [2][3][4][5]. In ref. [3] it was shown that a possible explanation for such a γ-ray line could be via DM pair annihilations into two photons, with a DM mass of 129.8 ± 2.4 +7 −13 GeV and annihilation cross-section σv γγ = 1.27 ± 0.32 +0. 18 −0.28 × 10 −27 cm 3 s −1 [4][5][6][7][8][9][10][11]. Moreover, there is a faint indication (1.4σ) of two lines which can be extracted from the Fermi data, one at ∼ 130 GeV and a weaker one at ∼ 114 GeV [5,12]. Such a pair of lines can be naturally explained by a DM particle of mass ∼ 130 GeV annihilating into γγ and γZ with a relative annihilation cross-section σv γZ / σv γγ = 0.66 +0. 71 −0.48 [13]. Though there is no well-accepted astrophysical process that can explain the γ-ray line, doubts have been raised [14,15] to its line feature by making it compatible with a diffuse background. Preliminary analysis of the Fermi-LAT Collaboration also confirms a line feature around ∼ 133 GeV but with a lower statistical significance [16] and concluded that more data would be required to establish the origin of such a feature.
Following reference [3], various models have been proposed to explain the monochromatic feature of the γ-ray, see e.g. . Most models are further constrained from the continuum flux of photons arising from annihilations of the DM into W and Z bosons and the Standard Model (SM) fermions [23,[41][42][43][44]. Supersymmetric (SUSY) theories with a viable cold DM candidate have been well studied in this context. However it is found that within the minimalistic versions where the lightest neutralino is the DM candidate, it is very difficult to accommodate the γ-ray line signal. We can summarize the shortcomings as follows: • In the minimal version, viz. the Minimal Supersymmetric Standard Model (MSSM), it is difficult to obtain the large annihilation cross-section of neutralino pairs into photons σv γγ [49], while satisfying constraints imposed by the thermal relic density and large continuum flux [22] data.
• In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), which addresses the µ-problem in MSSM, one can accommodate the large annihilation cross-section of the neutralino pairs into photons by exploiting the very singlet like CP-odd Higgs boson resonance [40,50,51]. However, the parameter space is tightly constrained by the direct searches for the DM, most importantly by the data from XENON100 and LUX [52,53]. It is however observed that in a specific region of the parameter space, where µ ef f < 0, constraints from direct detection can be relaxed by an order, in compliance with the bound from XENON100 [45].
In addition, a 130 -135 GeV photon signal can be produced both in the the MSSM and the NMSSM through internal bremsstrahlung [47,54], although a a significant boost factor is required [47] in the latter scenario.
In this work we study the feasibility of a new DM candidate, viz. a right-chiral sneutrino, ν R (with some degree of mixing with a left-chiral one), as the candidate for producing the photon line. The simplest way to accommodate non-zero (Dirac) neutrino masses in SUSY models is by introducing a right-handed singlet neutrino. This would entail addition of right-chiral neutrino superfields in the MSSM * . In addition we ensure that the thermal relic density is in agreement with WMAP data [55] and also satisfies constraints from DM-nucleus scattering [52,53]. Thanks to their singlet nature, the right-handed sneutrinos (ν R ), acting as cold DM candidates [56][57][58] in the MSSM, can account for all tentative evidences of DM we have so far. A sizeable volume of work has also taken place on the LHCs signals of (right) sneutrino DM [59], and also on the related scenarios carrying implications on different aspects of phenomenology [60,61]. However, as we will discuss, a 130-135 GeVν R DM, that can produce σv γγ ∼ 1.2 × 10 −27 , falls short in accounting for all the continuum constraints.
To get around this difficulty, we consider a similar scenario in the Next-to-Minimal Supersymmetric Standard Model (ν R NMSSM) with a scale invariant superpotential, assuming aν R type DM. Notably,ν R can naturally acquire a Majorana mass term of O(1) TeV. In addition to contributing neutrino masses and mixings [62,63],ν R DM in the NMSSM may have rich phenomenology as discussed in ref: [64][65][66][67]. As will be discussed in detail, in this * In the standard seesaw extensions of MSSM, Majorana mass scale for the right handed neutrino superfields is very close the gauge coupling unification scale (M G ∼ 10 16 GeV) which makes right handed sneutrinos very massive (close to M G ), thus not suitable for electro-weak scale dark matter candidate. case, one can even evade the continuum constraints when considering resonant annihilation mediated via a singlet-like Higgs boson. Additionally, the constraints from XENON100 and LUX on the spin-independent direct detection cross-section can also be satisfied. This paper is organized as follows: in Section II we discuss resonant annihilation of DM; following which, in Section III, we explore the possibility of explaining the observed γ signal withν R DM in the MSSM and the NMSSM. Finally, we summarize in Section IV.

II. BREIT-WIGNER RESONANCE: EFFECT OF THRESHOLD
The pair annihilation ofν R into two photons can proceed via a dominantly singlet/doublet like CP-odd (CP-even) Higgs A (H) in the s-channel. Before getting into specific models, we first discuss the annihilation of a spin-0 dark matter particle (ν R in our context) with mass m, mediated via a spin-0 particle of mass M near the resonance. DM annihilations near resonances and thresholds have been previously studied [68][69][70]. Our discussion closely follows [69,70].
The cross-section of an s-channel scattering process, near the resonance, is given by, where β i = 1 − 4m 2 M 2 ; B i and B f are the branching fractions of the intermediate particle into the initial and final channels respectively and Γ is the total decay width of the same; E 1 and E 2 are the energies of the two annihilating particles; s = (p 1 + p 2 ) 2 where p 1 and p 2 represent the four-momenta of the two annihilating particles. In the thermal averaging of σv, in the context of DM, the Møller velocity (v) is used [68]. However, in the rest frame of one of the annihilating particles, and also in the center of momentum (CM) frame, the Møller velocity is reduced to the relative velocity of these particles. Following Ref. [69], to quantify the resonance, an auxiliary parameter δ is introduced, such that, Since, in the present context, the annihilating particles in resonance are non-relativistic, |δ| ≪ 1 is assumed. Note that for δ < 0, a physical pole (s = M 2 ) is encountered when v ≃ 2 |δ| (in the CM frame, where v denotes the magnitude of the relative velocity of the annihilating particles); while, for δ > 0, a physical pole is never encountered. In the former situation B i , B f are well-defined, consequently Eq. (1) holds good in this region.
However, in the latter (δ > 0), the intermediate particle can no longer decay into two dark matter particles; consequently B i and β i are unphysical (imaginary numbers). However, B i /β i remains well-defined. In this case, Eq. 1 can also be expressed as, where, C denotes the coupling between dark matter particles and the mediating particle which in our context areν R and the CP-even or CP-odd Higgs respectively. In the CM frame, with non-relativistic dark matter particles (v ≪ 1), we have s ≡ 4m 2 (1 + v 2 /4). Eq.
Since DM annihilation into γγ, in our case, is a loop-suppressed process, the required σ(ν RνR → γγ)v ≃ 10 −27 cm 3 s −1 apparently leads to a larger σ ann v , where σ ann denotes the total annihilation cross-section of the DM into the SM particles. As all the tree-level processes are mediated by the same intermediate state (at resonance), it leads to a much lower thermal relic abundance. We therefore now discuss about how we achieve the required cross-sectio σv for the γ signal, as well as the correct relic abundance.
• In the context of the γ signal, σv annihilation cross-section needs to be evaluated at late times, i.e. typically when v rel ∼ 0.001. Thus, in Eq. 4, with |δ| ∼ O(10 −2 ), v can be ignored in the denominator. As we shall discuss in the next section, by suitably choosing the coupling C (as in Eq. 3) along with δ, γ, it is possible to achieve the required cross-section in theν R NMSSM.
• During freeze-out, away from a pole, the typical velocity of cold DM is about 0.3. Here, by freeze-out, we mean when (n − n eq ) ≃ n eq ; n and n eq represent the DM density at a given time/temperature and the equilibrium value of the same respectively. Let the corresponding freeze-out temperature be denoted by T f . † Since after freeze-out (in the absence of a pole) annihilations do not affect the relic abundance of DM significantly, the abundance at T f usually provides a good estimate of relic abundance. Since DM is non-relativistic at freeze-out, the thermal abundance at T f is exponentially suppressed by a factor x f = m T f . The situation is different for the two regions in the vicinity of the pole, namely, δ > 0 and δ < 0.
When δ > 0 (a scenario consistent with narrow width resonance), in the region v 2 > 4 max (δ, γ), the cross-section σ is dominated by γ/v 2 . Thus, σv , at a temperature T ∼ mv 2 0 , v 2 0 ≫ max (δ, γ), is determined by γ/v 2 0 . At such large v 0 , s > M 2 , and thus annihilations dominantly occur further away from the pole, and may have cross-sections similar to the other annihilation channels (if allowed) not mediated via the resonance. However, as T , and therefore v 0 , decreases, the annihilation channels mediated via the resonance tend to have larger σv , and thus, do not decouple. Consequently DM can continue to annihilate through these channels until v 2 0 < 4 max (δ, γ). After that, the corresponding σ does not change any more, and, assuming that these are the only annihilation channels, the relic density would be determined by δ and γ only. [69]. † We have used micrOMEGAs to obtain the freeze-out temperature, and also the relic abundance. Note that, micrOMAGAs uses n(T f ) = 2.5 n eq (T f ) to estimate the freeze-out temperature T f [71].
For δ < 0, the pole is physical. Therefore, unlike the previous case, at s = M 2 or v 2 ≃ 4|δ|, σ is very large. At high temperatures, T ∼ m|δ|, σv is large, and then decreases with T . Thus, in this case, the annihilation channels mediated via the resonance decouple early. Consequently, the relic density of the DM, at late times, remain similar to a scenario where DM has a similar annihilation cross-section even without the resonance [69]. For smaller values of |δ| and γ a large boost factor (defined ) can be obtained in this case too [70].
• The time of freeze-out, while a little away from the pole, also has a moderate dependence on the coupling C (see Eq. 3). When δ > 0, for large v 0 , such that contribution to the thermally averaged annihilation cross-section at early times for δ < 0. This, in turn, results in late freeze-out and a lower relic abundance [69]. As we will elaborate in the next section, for our benchmark points, we could obtain large relic in the former scenario, i.e. with δ > 0. On the other hand, since DM annihilations into two photons happens at late time, even with δ > 0 it is possible to obtain the required σv γγ .

III. PHOTON SIGNAL WITHν R DARK MATTER
In the following, we discuss the different avenues of indirect detections for a relatively lightν R dark matter focusing on the γ ray line observed at E γ ∼ 130 − 135 GeV. As mentioned earlier, we extend the MSSM and the NMSSM with three generations of right handed neutrino superfields (ν c R ). Assuming that theν c R is the lightest SUSY particle (LSP) in the supersymmetric particle spectrum, we enforce that the following phenomenological constraints always hold.
• Constraints from B-physics which has little impact for the tan β considered here.
• Upper bounds on annihilation cross sections into W + W − , ZZ, bb and ττ channels from the Fermi LAT collaboration [72,73], as well as bounds from PAMELA on the anti-proton flux [74].
For exact calculation of the sneutrino mass and mixing matrices as well as two-loop renormalization group equations (RGEs) for all SUSY parameters, we have used the publicly available code called SARAH [75]. These RGEs are then implemented in the software package SPheno [76] for numerical evaluation of all physical parameters and phenomenological constraints. For computation of relic density, all indirect detection cross-sections and fluxes, we implement SARAH generated CalcHEP [77] model files into micrOMEGAs [71]. We however calculate the cross-section for the photon line σv γγ signal with our own mathematica code based on Ref. [69,70]. We ignore the contribution of σv γγ in the relic density computation.
In both the models that we have considered, we scan the parameter space while keeping the soft SUSY breaking terms in the following preferred ranges.
• Squark masses of 2-3 TeV are assumed to alleviate LHC constraints from direct SUSY searches. The latter choice also helps to enhance the lightest Higgs boson mass irrespective of the choice of tan β. Similarly, gluino masses (M G ) is fixed around ∼ 2 TeV.
The slepton masses are assumed to be around 300 GeV to have consistent spectra with muon anomalous magnetic moment.
• We use m 2 ν R as free parameter. Similarly, the couplings y ν and T ν for ν l − ν R and ν l −ν R are assumed flavor diagonal. In the present context, we refrain from exact calculation of neutrino masses and mixing angles.
• We have used the top quark pole mass m top = 173.1 GeV.
A.ν R and the MSSM In this section, we discuss the status ofν c R dark matter in the (R-parity conserving) MSSM with three generations of right-handed (s)neutrinos. The neutrino masses arise from the Yukawa interaction only (purely Dirac-type) and can be obtained from the following superpotential: where W M SSM denotes the MSSM superpotential;Ĥ u ,L andν c R represents the up-type Higgs, lepton doublet and right-handed neutrino superfields respectively. For simplicity, we consider all mass and coupling parameters to be real and suppress flavor indices for neutrino families. Assuming soft-supersymmetry breaking, as in the MSSM, the soft-breaking scalar potential becomes, where V M SSM denotes the soft-supersymmetry breaking terms in the MSSM and soft trilinear coupling is given by T ν ≡ T να y να , where α denotes the generation index. Neutrino masses can be expressed as, where v ≃ 246 GeV is the vacuum expectation value (VEV) of the standard-model -like Higgs boson, and tan β = H 0 u / H 0 d . Clearly, neutrino masses (m ν ∼ 0.1 eV) put constraints on the size of the neutrino Yukawa couplings y ν ∼ O(10 −12 ). Ignoring flavor mixing in theν sector ‡ the (2×2) mass matrix forν α for any flavor α, can be written as, with where ml α is the soft breaking term forl α . The lightest sneutrino mass eigenstatesν 1 R , as obtained after diagonalization ofν α , can be a valid candidate for DM. Moreover, such ã ν 1 R can also produce viable photon signal σv γγ,γZ ∼ 10 −27 cm 3 s −1 , through the resonant annihilations via heavier CP-even (H 2 ) or CP-odd Higgs boson (A). Note that the resonant annihilation through CP-odd Higgs boson A can only take place if T να is complex, as otherwise the coupling among Aν 1

Rν
1 * R vanishes. The CP-odd Higgs resonance avoids stringent constraints on σv W + W − ,ZZ coming from continuum fluxes of gamma rays § . We found that it requires large values of Im(T να ) to obtain the desired cross-section for the di-photon final state. However, a dominantly CP-odd Higgs resonance falls short in accounting for the desired thermal relic abundance; and, more importantly, the viable parameter space has been ruled out by constraints from the continuum spectrum of γ rays. In particular, we found that annihilation cross-sections to the following final states are somewhat above the upper limits set by the Fermi-LAT for a NFW halo profile [37,44], viz.
where W M SSM denotes the MSSM superpotential without the µ term. TheŜ denotes the singlet superfield that already appears in the NMSSM. When the scalar component ofŜ § Note that a complex value for T ν leads to a mixing among the CP-even and CP-odd Higgses in the mass eigen-basis.
gets a VEV of the order of electro-weak scale, µ term of correct size would be generated.
Similarly, the right handed neutrinos also acquire an effective Majorana mass around the electro-weak values as long as the dimensionless coupling y r is order one [62]. At the tree level the (3 × 3) light neutrino mass matrix, that arises via the seesaw mechanism, has a very well-known structure given by, Unlike MSSM, here y ν ∼ O(10 −6 ) can reproduce the neutrino mass and mixing data [63].
As before, flavor mixings in the slepton sector can be induced radiatively by the off-diagonal entries in the neutrino Yukawa coupling, which are suppressed due to the smallness of Yukawa couplings. However, for simplicity we assume neutrino Yukawa couplings to be diagonal which alleviates the slepton flavor mixings completely. The soft-supersymmetrybreaking scalar potential is given by, where V M SSM denotes the soft-supersymmetry breaking terms in the MSSM and T ν ≡ T να y να where α denotes the generation indices. We do not assign VEV toν c R , thus R-parity is unbroken at the minimum of the scalar potential. In particular, the neutral scalar fields can develop, in general, the following vacuum expectation values at the minimum of the scalar potential.
We further assume that y r and T r are flavor-diagonal for simplicity and consider the lightest ν c R as the lightest R-parity odd particle; and forefore the DM candidate. We begin by decomposing the sneutrino fields in terms of real and imaginary components.
where, φ L , φ R are the CP -even and σ L , σ R are the CP -odd scalar fields. The presence of The mass matrix for CP-even eigenstates (φ L , φ R ) or for CP-odd eigenstates (σ L , σ R ) is given by, where, The mass matrices can be diagonalized by unitary matrices Z I and Z R , where m D ν I and m D ν R denote the diagonalized mass matrices respectively, and the corresponding mass eigenstates are denoted by σ i and φ i (i ∈ {1, 2}); g 1 and g 2 are the SU(2) L gauge couplings; m 2 l is the soft-supersymmetry breaking mass term for slepton doublet. The other parameters are described in Eqs. (10) and (12). Generically, φ i and σ i are non-degenerate, thanks to the ∆L = 2 term present in the superpotential.
In general, lightest of the states σ i or φ i could be the lightest SUSY particle in different regions of the parameter space. Depending on the choice of the parameters, σ i or φ i can have dominant gauge and/or Yukawa interactions. Their mass difference, defined by ∆m = |m φ i − m σ i | cannot be arbitrary, especially when σ i and φ i have dominant left-handed component, i.e., σ i and φ i are ofν L -type. In this case, the one-loop contributions to the neutrino mass matrix can be quite large which essentially limits ∆m ≃ 100 keV [63,78]. Moreover, due to its doublet nature under SU(2) L , stringent constraints would also appear from the sneutrino-nucleus scattering (via t-channel Z boson exchange processes) [79].
On the other hand, aforementioned constraints can be evaded naturally, if we assume that φ 1 and σ 1 are dominantly right-handed. In fact these states are completely unconstrained, and their splitting can be traced back to ∆L = 2 terms present in the mass matrix. However, nearly degenerate or degenerate σ 1 and φ 1 may be achieved, provided all ∆L = 2 in  combination vanishes. The condition for degeneracy, thus, can be expressed as, Though, it seems a bit fine-tuned, we find that, potentially testable photon signals can be achieved. Based on the above facts, we consider the following possibilities for a 130-135 GeṼ ν R type dark matter, as presented in Table I.
In the first scenario, we illustrate how CP eigenstates φ 1 or σ 1 can annihilate through singlet-like CP-even Higgs (H 2 ) resonance to γγ (see Fig. 1). The singlet nature of H 2 helps to accommodate constraints from the continuum γ. In addition, the narrow width of a singlet-like H 2 also reduces the contribution of the resonance mediated channels to the relic density.
The couplings C r,o in Eq. 3, between the singlet-like CP-even Higgs and φ 1 /σ 1 takes the following form, The term proportional to T r comes from the soft-supersymmetry breaking sector, while the other terms come from the F-term contributions to the scalar potential. Eq. 10. Since the contribution from the charginos (χ ± ) running in the loop dominates, light higgsino-like χ ± are desired to enhance the signal. In Fig. 2, we present σv γγ with representative values of the input parameters around the Higgs threshold. Interestingly, we can easily obtain the σv γγ with the pole mass below or above the threshold, i.e. (2m σ 1 /φ 1 ).
However, the correct thermal relic density can be obtained only when the pole is below the  Table I. threshold, as shown in the left panel of Fig. 3. To understand it better, we also depict the parameter x f (i.e. m/T f , as already discussed in Sec. II), which characterises the freeze-out, against M H in the Fig. 4. As can be seen from Fig. 4, x f is larger for M H above the threshold (260 GeV), implying late freeze-out compared to the scenario when M H is below the threshold. Therefore, in this region a lower relic density is obtained.
As noted in Eq. 17 and Eq. 14, both the couplings C r,o , as well as the mass of σ 1 , depend on T r and y r , while the other free parameters involved in these equations also affect, among others, the Higgs sector. Therefore, in Fig. 5, we present the allowed parameter space in the (T r , y r ) plane; assuming the following input parameters (at the SUSY scale): Our choice for these parameters are consistent with the LHC data on the SM-like CP-even Higgs while providing us with another singlet-like CP-even Higgs with a mass of 260 GeV. All other parameters are set to alleviate LHC constraints as mentioned in Sec. III. We also set soft breaking parameter of the right handed sneutrino so to have σ 1 as LSP with mass 130.5 GeV. With the given parameters, we obtain m H SM = 125.7 GeV while for the singlet like Higgs we get m H 2 = 260.1 GeV. Assuming, for simplicity, that the third generation right handed sneutrino as the LSP, we only varied T 33 r and y 33 r to deliniate the WMAP satisfied region in the vicinity of H 2 resonance. In this region, due to the singlet nature of H 2 and the smallness of the coupling among σ 1 − H 2 − σ 1 , the annihilation channels mediated by the lightest CP-even Higgs boson contributes singnificantly in satisfying the relic density.
These points are also allowed by the recent bounds from LUX [53]. Interestingly, the whole parameter space can provide with adequate cross-section for σv γγ .
For the benchmark point presented in column (B) of Table I, we assume σ 1 to be the DM. ¶ The representative values, as shown in column (B) of Table I satisfy the desired σv γγ and other mentioned constraints including WMAP. In the calculation of σv γγ , we ¶ Note that by simply reversing the signs of y r and T r , one can have CP-even φ 1 as the LSP while the mass spectra remains unchanged. Consequently, one can explain the observed γ signal with CP-even φ 1 DM.   have been shown in red and green respectively. In the right panel the CP-odd Higgs mass is varied to demonstrate the relic abundance below and above the threshold (270 GeV).
given by, where, Z A denotes the mixing matrices of the CP-odd Higgs and all other symbols are as defined before.
As in the previous case, σv γγ can easily be enhanced by increasing C (thus y r and/or λ), but that could lead to small relic abundance. A light higgsino-like χ ± is desired to enhance the same. Again, we consider m As < 2m φ 1 −σ 1 , i.e., part of the parameter space where the pole of the propagator is below the threshold, to obtain the right thermal relic abundance. In To demonstrate our results, we present in the left panel of Fig. 6, the thermally averaged cross-section, when the pole falls above the threshold (270 GeV), is a little larger than the same when the pole falls below the threshold. Also, as the right panel of Fig. 6 shows, in the former case, freeze-out happens a little later. Consequently, the thermal relic abundance decreases in the former case. Note that, due to the much smaller width of A s compared to that of H 2 in the previous case, the effect of the resonance on the relic density is quite small.
A benchmark point in column (A) of Table I has been presented to summarize the results.
The relic density can be obtained mainly via the annihilation channels mediated via the off-shell CP-even Higgs bosons. In the calculation of σv γγ , we have Br(A s → γγ) ≃ 5 × 10 −4 , Γ As = 0.003 GeV and δ = 0.002. All phenomenological constraints, from both direct and indirect detection data, can easily be satisfied for the benchmark point (A) shown in Table I, thanks to the singlet nature of A s .

Constraints from direct detection
An interesting issue for the models, which give the desired σv γγ , is to address constraints coming from the spin-independent direct detection, particularly in the light of XENON-100 and LUX data. In the NMSSM, the parameter space for a 130-135 GeV neutralino DM, achieving the desired σv γγ , is constrained by the present bound σ(p) SI < ∼ 1.2 × 10 −8 pb and σ SI < ∼ 1.5 × 10 −9 pb for M DM ∼ 130 − 135 GeV from XENON-100 [52] and LUX [53] respectively. An important issue concerns the quark coefficient in the nucleon which may lead to large theoretical uncertainty in the calculation. In this work, we always keep the default values that are used in micrOMEGAs-3.
Being a real scalar, φ 1 (σ 1 ) interacts with nucleons via Higgs exchange processes. As is quite small. Also, since both φ 1 and σ 1 are dominantly right-chiral, Z boson exchange does not lead to large σ(p) SI even when these are degenerate. The only term, which gives rise to dominant contribution to σ(p) SI originates from the F-term contribution (λ y r 2ν c Rν c R H u .H d + h.c). While both λ and y r appears in σv γγ , note that it is possible to achieve large σv γγ with small y r by increasing the soft-term T r appropriately. In summary, the scenarios proposed here are not significantly constrained by the XENON-100, these are moderately constrained by the LUX data.

IV. SUMMARY AND CONCLUSIONS
We have explored the possibility that the annihilation of 130-135 GeV right-chiral sneutrino DM into two photons can produce the observed line-like feature in the Fermi-LAT data.
In this context, we examine the candidature of right-sneutrino dark matter -a scenario that can have somewhat unusual phenomenological implications. It is, however, seen that the augmentation of the MSSM just with right-chiral neutrino superfields is inadequate. The difficulty arises from severe constraints on various annihilation channels of the dark matter, most notably into ZH and bb, derived from the continuum flux of photons. However, in the extension of the next-to-minimal model (NMSSM), annihilating right-chiral sneutrino DM, can produce the observed line feature. Due to the extra singlet field present in this model, a singlet-like CP-odd or CP-even Higgs boson resonance produces adequate annihilation cross-section to fit the observation. We find that in case of a CP-odd Higgs resonance, one needs the lightest CP-even and the lightest CP-odd right-chiral sneutrino states to be (almost) degenerate. In the latter case however, this is not a requirement. We present a few benchmark points to substantiate our claims and highlight the spectrum which is consistent with the data. While our benchmark points also satisfy the present direct detection bounds, improved bounds in near future may be able to explore the viability of our scenario. In addition, we show that when the pole in the resonance is a little below twice the mass of the DM, the thermal production of right-chiral sneutrino dark matter can be sufficient to also account for the DM abundance, as required by the CMBR data, especially in the case of degeneracy in the sneutrino sector.

V. ACKNOWLEDGEMENT
AC and DD would like to thank Florian Staub for useful discussions about the code SARAH.
The work of AC, BM and SKR was partially supported by funding available from the Department of Atomic Energy, Government of India, for the Regional Centre for Accelerator-based Particle Physics (RECAPP), Harish-Chandra Research Institute (HRI). DD acknowledges support received from the DFG, project no. PO-1337/3-1 at the Universität Würzburg. DD thanks RECAPP, Allahabad, for hospitality during the initial part of the proejct.