Search

Motivated by the first observation of coherent-elastic neutrino-nucleus scattering at the COHERENT experiment, we confront the neutrino dipole portal giving rise to the transition of the standard model neutrinos to sterile neutrinos with the recently released CENNS 10 data from the liquid argon as well as the CsI data of the COHERENT experiment. Performing statistical analysis of those data, we show how the transition magnetic moment can be constrained for the range of the sterile neutrino mass between 10 keV and 40 MeV., 16 pages, 4 figures

We propose a novel and minimal framework where a light scalar field can give rise to dark matter (DM) self-interactions, while enhancing the CP symmetry required for successful baryon asymmetry of the Universe via leptogenesis route. For demonstration purpose we choose to work in a scotogenic seesaw scenario where the lightest among the right handed neutrinos (RHN), introduced for generating light neutrino masses radiatively, play the role of DM while the heavier two can play non-trivial roles in generating DM relic as well as lepton asymmetry. While dark matter self-interactions mediated by an additional singlet scalar can alleviate the small scale issues of cold dark matter paradigm, the same scalar can give rise to new one-loop decay processes of heavy RHN into standard model leptons providing an enhanced contribution to CP asymmetry, even with sub-TeV scale RHN mass. The thermally under-abundant relic of DM due to large annihilation rates into its light mediator receives a late non-thermal contribution from a heavier RHN. With only five new particles involved in the scotogenic seesaw, each having non-trivial roles in generating DM relic and baryon asymmetry, the model can explain non-zero neutrino mass while being verifiable at different experiments related to DM direct detection, flavour physics and colliders. The mechanism we demonstrated here by using a scotogenic seesaw scenario is also applicable to other models., Comment: 9 Pages, 6 Captioned Figures, Version accepted for publication in Phys. Rev. D

We study the possibility of probing the scale of left-right symmetry breaking in the context of left-right symmetric models (LRSM). In LRSM, the right handed fermions transform as doublets under a newly introduced $SU(2)_R$ gauge symmetry. This, along with a discrete parity symmetry $\mathcal{P}$ ensuring identical gauge couplings of left and right sectors make the model left-right symmetric, providing a dynamical origin of parity violation in electroweak interactions via spontaneous symmetry breaking. The spontaneous breaking of $\mathcal{P}$ leads to the formation of domain walls in the early universe. These walls, if made unstable by introducing an explicit parity breaking term, generate gravitational waves (GW) with a spectrum characterized by the wall tension or the spontaneous $\mathcal{P}$ breaking scale, and the explicit $\mathcal{P}$ breaking term. Considering explicit $\mathcal{P}$ breaking terms to originate from Planck suppressed operators provides one-to-one correspondence between the scale of left-right symmetry and sensitivities of near future GW experiments. This is not only complementary to collider and low energy probes of TeV scale LRSM but also to GW generated from first order phase transition in LRSM with different spectral shape, peak frequencies as well as symmetry breaking scales., 8 pages, 4 figures, matches version accepted for publication in Phys. Rev. D

Motivated by the growing evidence for a large neutrino asymmetry in the early universe from the recent $^4{\rm He}$ measurements, we point out the class of leptogenesis scenarios with decay or scattering being the source of lepton asymmetry, simultaneously consistent with such a large neutrino asymmetry as well as the observed baryon asymmetry of the universe. Considering $1 \rightarrow 2, 1 \rightarrow 3$ as well as $2 \rightarrow 2$ processes to be responsible for generating the asymmetries, we show that only TeV scale leptogenesis preferably of $1 \rightarrow N \, (N \geq 3)$ type can generate the required lepton asymmetry around sphaleron temperature while also generating a large neutrino asymmetry $\sim \mathcal{O}(10^{-2})$ by the epoch of the big bang nucleosynthesis. This also offers the possibility of cogenesis if dark matter is in the form of a sterile neutrino resonantly produced in the early universe due to the presence of a large neutrino asymmetry. While such low scale leptogenesis has tantalising detection prospects at laboratory experiments, the indication of a large neutrino asymmetry provides a complementary indirect signature., 6 pages, 5 captioned figures

We analyze the classically scale-invariant $B-L$ model in the context of resonant leptogenesis with the recently proposed mass-gain mechanism. The $B-L$ symmetry breaking in this scenario is associated with a strong first order phase transition that gives rise to detectable gravitational waves (GWs) via bubble collisions. The same $B-L$ symmetry breaking also gives Majorana mass to right-handed neutrinos inside the bubbles, and their out of equilibrium decays can produce the observed baryon asymmetry of the Universe via leptogenesis. We show that the current LIGO-VIRGO limit on stochastic GW background already excludes part of the $B-L$ parameter space, complementary to the collider searches for heavy $Z^{\prime}$ resonances. Moreover, future GW experiments like Einstein Telescope and Cosmic Explorer can effectively probe the parameter space of leptogenesis over a wide range of the $B-L$ symmetry-breaking scales and gauge coupling values., 11 pages, 3 figures and 2 tables,version to appear in PRD

We propose a novel way of probing high scale Dirac leptogenesis, a viable alternative to canonical leptogenesis scenario where the total lepton number is conserved, keeping light standard model (SM) neutrinos purely Dirac. The simplest possible seesaw mechanism for generating light Dirac neutrinos involve heavy singlet Dirac fermions and a singlet scalar. In addition to unbroken global lepton number, a discrete $Z_2$ symmetry is imposed to forbid direct coupling between right and left chiral parts of light Dirac neutrino. Generating light Dirac neutrino mass requires the singlet scalar to acquire a vacuum expectation value (VEV) that also breaks the $Z_2$ symmetry, leading to formation of domain walls in the early universe. These walls, if made unstable by introducing a soft $Z_2$ breaking term, generate gravitational waves (GW) with a spectrum characterized by the wall tension or the singlet VEV, and the soft symmetry breaking scale. The scale of leptogenesis depends upon the $Z_2$-breaking singlet VEV which is also responsible for the tension of the domain wall, affecting the amplitude of GW produced from the collapsing walls. We find that most of the near future GW observatories will be able to probe Dirac leptogenesis scale all the way upto $10^{11}$ GeV., 7 pages, 4 captioned figures, matches version accepted for publication in Phys. Rev. D

We study the possibility of realising leptogenesis from three body decay, dark matter (DM) and neutrino mass in a minimal framework. We propose a first of its kind model to implement the idea of leptogenesis from three body decay where CP asymmetry arises from interference of multiple $1 \rightarrow 3$ diagrams using resummed propagators along with DM. The standard model is extended by three heavy singlet fermions, one scalar singlet and one scalar doublet with appropriate discrete charges. Two of these singlet fermions not only play non-trivial roles in generating light neutrino mass at radiative level in scotogenic fashion, but also act as mediators in three body decay of the third singlet fermion leading to desired CP asymmetry through interference of such diagrams. With just one additional field compared to the minimal scotogenic model, we show that successful leptogenesis can occur at a scale as low as approximately 1 TeV which is much lower than the leptogenesis scale found for minimal scotogenic model. Also, the realisation of this three body decay leptogenesis naturally leads to a two component scalar singlet-doublet dark matter scenario offering a rich phenomenology. Apart from having interesting interplay of different couplings involved in processes related to both leptogenesis and dark matter, the model can also be tested at different experiments due to the existence of its particle spectrum at TeV scale., Comment: Version 3: 51 pages, 20 captioned figures, accepted for publication in Phys. Rev. D

The Standard Model of Particle Physics cannot explain the observed baryon asymmetry of the Universe. This observation is a clear sign of new physics beyond the Standard Model. There have been many recent theoretical developments to address this question. Critically, many new physics models that generate the baryon asymmetry have a wide range of repercussions for many areas of theoretical and experimental particle physics. This white paper provides an overview of such recent theoretical developments with an emphasis on experimental testability., Comment: Contribution to Snowmass 2021. Solicited white paper from TF08. v2: includes additional contributions

We study a dark $SU(2)_D$ gauge extension of the standard model (SM) with the possibility of a strong first order phase transition (FOPT) taking place below the electroweak scale in the light of NANOGrav 12.5 yr data. As pointed out recently by the NANOGrav collaboration, gravitational waves (GW) from such a FOPT with appropriate strength and nucleation temperature can explain their 12.5 yr data. We impose a classical conformal invariance on the scalar potential of $SU(2)_D$ sector involving only a complex scalar doublet with negligible couplings with the SM Higgs. While a FOPT at sub-GeV temperatures can give rise to stochastic GW around nano-Hz frequencies being in agreement with NANOGrav findings, the $SU(2)_D$ vector bosons which acquire masses as a result of the FOPT in dark sector, can also serve as dark matter (DM) in the universe. The relic abundance of such vector DM can be generated in a non-thermal manner from the SM bath via scalar portal mixing. We also discuss future sensitivity of gravitational wave experiments to the model parameter space., Comment: 10 pages, 6 captioned figures. accepted for publication in JCAP. arXiv admin note: substantial text overlap with arXiv:2105.01007

Minimalistic Dirac radiative neutrino mass model based on modular symmetry is proposed. We predict maximum number of observables possible including neutrino mass splittings, neutrino mass scale, lepton mixing angles, and Dirac phases in the leptonic sector with minimum number of input parameters possible. Model is capable of accommodating multicomponent dark matter, thanks to the $\emph{R}-$parity and accidental scotogenic $\mathbb{Z}_2$ discrete symmetry. Furthermore, even-though neutrinos are Dirac in our model, matter-antimatter asymmetry of the Universe is achieved via neutrinogenesis mechanism. Phenomenology of the dark sector including various dark matter candidates is briefly discussed., Comment: 24 pages, 6 figures, 4 tables

We propose a new mechanism for generating matter-antimatter asymmetry via the interference of tree-level diagrams only, where the imaginary part of the Breit-Wigner propagator for an unstable mediator plays a crucial role. We first derive a general result that a nonzero $CP$-asymmetry can be generated via at least two sets of interfering tree-level diagrams involving either $2\rightarrow2$ or $1\rightarrow n$ (with $n\geq3$) processes. We illustrate this point in a simple TeV-scale extension of the Standard Model with an inert Higgs doublet and right-handed neutrinos, along with an electroweak-triplet scalar field, where small Majorana neutrino masses are generated via a combination of radiative type-I and tree-level type-II seesaw mechanisms. The imaginary part needed for the required $CP$-asymmetry comes from the trilinear coupling of the inert doublet with the triplet scalar, along with the width of the triplet scalar mediator. The real part of the neutral component of the inert doublet serves as a cold dark matter candidate. The evolutions of the dark matter relic density and the baryon asymmetry are intimately related in this scenario., 12 pages, 7 figures and 1 table, title changed, some figures updated and added, more comments, version to appear in PRD

We consider the possibility of probing left-right symmetric model (LRSM) via cosmic microwave background (CMB). We adopt the minimal LRSM with Higgs doublets, also known as the doublet left-right model (DLRM), where all fermions including the neutrinos acquire masses only via their couplings to the Higgs bidoublet. Due to the Dirac nature of light neutrinos, there exist additional relativistic degrees of freedom which can thermalise in the early universe by virtue of their gauge interactions corresponding to the right sector. We constrain the model from Planck 2018 bound on the effective relativistic degrees of freedom and also estimate the prospects for planned CMB Stage IV experiments to constrain the model further. We find that $W_R$ boson mass below 4.06 TeV can be ruled out from Planck 2018 bound at $2\sigma$ CL in the exact left-right symmetric limit which is equally competitive as the LHC bounds from dijet resonance searches. On the other hand Planck 2018 bound at $1\sigma$ CL can rule out a much larger parameter space out of reach of present direct search experiments, even in the presence of additional relativistic degrees of freedom around the TeV corner. We also study the consequence of these constraints on dark matter in DLRM by considering a right handed real fermion quintuplet to be the dominant dark matter component in the universe., Comment: 29 pages, 8 figures, matches version accepted for publication in Phys. Rev. D

We scrutinise the widely studied minimal scotogenic model of dark matter (DM) and radiative neutrino mass from the requirement of a strong first order electroweak phase transition (EWPT) and observable gravitational waves at future planned space based experiments. The scalar DM scenario is similar to inert scalar doublet extension of standard model where a strong first order EWPT favours a portion of the low mass regime of DM which is disfavoured by the latest direct detection bounds. In the fermion DM scenario, we get newer region of parameter space which favours strong first order EWPT as the restriction on mass ordering within inert scalar doublet gets relaxed. While such leptophilic fermion DM remains safe from stringent direct detection bounds, newly allowed low mass regime of charged scalar can leave tantalising signatures at colliders and can also induce charged lepton flavour violation within reach of future experiments. While we get such new region of parameter space satisfying DM relic, strong first order EWPT with detectable gravitational waves, light neutrino mass and other relevant constraints, we also improve upon previous analysis in similar model by incorporating appropriate resummation effects in effective finite temperature potential., 36 pages, 6 figures, matches version accepted for publication in JCAP

We propose a novel mechanism to realize leptogenesis through the Breit-Wigner resonance of a dark $U(1)_D$ gauge boson $Z_D$, which mediates lepton number violating annihilations of dark matter (DM) in the context of the scotogenic model with a $U(1)_D$. The processes occur out of equilibrium and the DM freezes out lately giving rise to the observed abundance. The CP violation required for leptogenesis can be achieved by the interference between tree-level t-channel scattering of DM and the subsequent 1-loop mediated by $Z_D$, which arises due to the unremovable imaginary part of either the $Z_D$ propagator coming from its self-energy correction or the 1-loop giving rise to the effective coupling of $Z_D\bar{\nu}\nu$., Comment: 15 pages and 5 figures, added 2 References

We consider a simple extension of the minimal left-right symmetric model (LRSM) in order to explain the PeV neutrino events seen at the IceCube experiment from a heavy decaying dark matter. The dark matter sector is composed of two fermions: one at PeV scale and the other at TeV scale such that the heavier one can decay into the lighter one and two neutrinos. The gauge annihilation cross sections of PeV dark matter are not large enough to generate its relic abundance within the observed limit. We include a pair of real scalar triplets $\Omega_{L,R}$ which can bring the thermally overproduced PeV dark matter abundance into the observed range through late time decay and consequent entropy release thereby providing a consistent way to obtain the correct relic abundance without violating the unitarity bound on dark matter mass. Another scalar field, a bitriplet under left-right gauge group is added to assist the heavier dark matter decay. The presence of an approximate global $U(1)_X$ symmetry can naturally explain the origin of tiny couplings required for long-lived nature of these decaying particles. We also show, how such an extended LRSM can be incorporated within a non-supersymmetric $SO(10)$ model where the gauge coupling unification at a very high scale naturally accommodate a PeV scale intermediate symmetry, required to explain the PeV events at IceCube., Comment: 33 pages, 9 figures, 4 tables; error in relic density calculation fixed and discussion expanded for better clarity; matches published version

The ANtarctic Impulsive Transient Antenna (ANITA) collaboration has observed two EeV-energy, upward going events originating from below the horizon. As no standard model (SM) particles, propagating through the earth at such energy and exit angles, can give rise to the required survival probability for the observed events, several beyond standard model (BSM) proposals have come up. We propose a scenario where a $Z_2$ odd sector is responsible for such anomalous events. The next to lightest $Z_2$ odd particle or the next to lightest stable particle (NLSP), created from ultra high energy neutrino interactions with nucleons, can pass through the earth and then decay into the lightest $Z_2$ odd particle or the lightest stable particle (LSP) and a tau lepton. The long-lived nature of the NLSP requires its coupling with the LSP to be very small, keeping the LSP out of thermal equilibrium in the early universe. The LSP can then be a non-thermal dark matter while the tau leptons produced from NLSP decay after passing through the earth can explain the ANITA events. We first show that a purely non-thermal dark matter scenario can not give rise to the required event rates while a hybrid scenario where dark matter can have both thermal as a well non-thermal contribution to its relic abundance, serves the purpose., 21 pages, 6 figures, accepted for publication in Physical Review D

We discuss the possibility of realising a two-component dark matter (DM) scenario where the two DM candidates differ from each other by virtue of their production mechanism in the early universe. One of the DM candidates is thermally generated in a way similar to the weakly interacting massive particle (WIMP) paradigm where the DM abundance is governed by its freeze-out while the other candidate is produced only from non-thermal contributions similar to freeze-in mechanism. We discuss this in a minimal extension of the standard model where light neutrino masses arise radiatively in a way similar to the scotogenic models with DM particles going inside the loop. The lepton asymmetry is generated at the same time from WIMP DM annihilations as well as partially from the mother particle for non-thermal DM. This can be achieved while satisfying the relevant experimental bounds, and keeping the scale of leptogenesis or the thermal DM mass as low as 3 TeV, well within present experimental reach. In contrast to the TeV scale thermal DM mass, the non-thermal DM can be as low as a few keV, giving rise to the possibility of a sub-dominant warm dark matter (WDM) component that can have interesting consequences on structure formation. The model also has tantalizing prospects of being detected at ongoing direct detection experiments as well as the ones looking for charged lepton flavour violating process like $\mu \rightarrow e \gamma$., Comment: 29 pages, 9 figures, matches version accepted for publication in Phys. Rev. D

Models of spontaneous baryogenesis have an interaction term $\partial_\mu\theta j^\mu_B$ in the Lagrangian, where $j^\mu_B$ is the baryonic current and $\theta$ can be a pseudo-Nambu-Goldstone boson. Since the time component of this term, $\dot{\theta} j^0_B$, equals $\dot{\theta} n_B$ for a spatially homogeneous current, it is usually argued that this term implies a splitting in the energy of baryons and antibaryons thereby providing an effective chemical potential for baryon number. In thermal equilibrium, one {then obtains} $n_B \sim \dot{\theta} T^2$. We however argue that a term of this form in the Lagrangian does not contribute to the single particle energies of baryons and antibaryons. We show this for both fermionic and scalar baryons. But, similar to some recent work, we find that despite the above result the baryon number density obtained from a Boltzmann equation analysis can be proportional to $\dot{\theta} T^2$. Our arguments are very different from that in the standard literature on spontaneous baryogenesis., Comment: 16 pages, matches with the published version

We propose a way to generate tiny couplings of freeze-in massive particle dark matter with the Standard Model particles dynamically by considering an extension of the electroweak gauge symmetry. The dark matter is considered to be a singlet under this extended gauge symmetry which we have assumed to be the one in a very widely studied scenario called left-right symmetric model. Several heavy particles, that can be thermally inaccessible in the early Universe due to their masses being greater than the reheat temperature after inflation, can play the role of portals between dark matter and Standard Model particles through one loop couplings. Due to the loop suppression, one can generate the required non-thermal dark matter couplings without any need of highly fine tuned Yukawa couplings beyond that of electron Yukawa with the Standard Model like Higgs boson. We show that generic values of Yukawa couplings as large as $\mathcal{O}(0.01)$ to $\mathcal{O}(1)$ can keep the dark matter out of thermal equilibrium in the early Universe and produce the correct relic abundance later through the freeze-in mechanism. Though the radiative couplings of dark matter are tiny as required by the freeze-in scenario, the associated rich particle sector of the model can be probed at ongoing and near future experiments. The allowed values of dark matter mass can remain in a wide range from keV to TeV order keeping the possibilities of warm and cold dark matter equally possible., Comment: 28 pages, 7 figures, 2 tables, loop expressions corrected, conclusion remains unaltered, two new appendices are added

We propose a novel scenario of generating lepton asymmetry via annihilation and coannihilation of dark sector particles including t-channel processes. In order to realistically implement this idea, we consider the scotogenic model having three right handed neutrinos and a new scalar doublet, all of which are odd under an in-built $Z_2$ symmetry. The lightest $Z_2$ odd particle, if electromagnetically neutral, can be a dark matter candidate while annihilation and coannihilation between different $Z_2$ odd particles into standard model leptons serve as the source of lepton asymmetry. The light neutrino masses arise at one loop level with $Z_2$ odd fields going inside the loop. We show that experimental data related to light neutrinos, dark matter relic abundance and baryon asymmetry can be simultaneously satisfied in the model for two different cases: one with fermion dark matter and the other with scalar dark matter. In both scenarios, t-channel annihilation as well as coannihilation of $Z_2$ odd particles play a non-trivial role in producing the non-zero CP asymmetry. Both the scenarios remain allowed from DM direct detection while keeping the scale of leptogenesis as low as TeV or less, lower than the one for vanilla leptogenesis scenario in scotogenic model along with the additional advantage of explaining the baryon-dark matter coincidence to some extent. Due to such low scale, the model is testable through rare decay experiments looking for charged lepton flavour violation., Comment: Version 2: Major revision, 32 pages, 8 figures, matches version accepted for publication in Eur. Phys. J. C

We present a detailed discussion on neutrinoless double beta decay $(0\nu \beta \beta)$ within left-right symmetric models based on the gauge symmetry of type $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ as well as $SU(3)_L \times SU(3)_R \times U(1)_{X}$ where fermion masses including that of neutrinos are generated through a universal seesaw mechanism. We find that one or more of the right-handed neutrinos could be as light as a few keV if left-right symmetry breaking occurs in the range of a few TeV to 100 TeV. With such light right-handed neutrinos, we perform a detailed study of new physics contributions to $0\nu \beta \beta$ and constrain the model parameters from the latest experimental bound on such a rare decay process. We find that the new physics contribution to $0\nu \beta \beta$ in such a scenario, particularly the heavy-light neutrino mixing diagrams, can individually saturate the existing experimental bounds, but their contributions to total $0\nu \beta \beta$ half-life cancels each other due to unitarity of the total $6\times 6$ mass matrix. The effective contribution to half-life therefore, arises from the purely left and purely right neutrino and gauge boson mediated diagrams. We find that the parameter space saturating the $0\nu \beta \beta$ bounds remain allowed from the latest experimental bounds on charged lepton flavour violating decays like $\mu \rightarrow e \gamma$. We finally include the bounds from cosmology and supernova to constrain the parameter space of the model., Comment: 42 pages, 9 figures, to appear in Int. J. Mod. Phys. A

We study the possibility of generating tiny Dirac masses of neutrinos in Left-Right Symmetric Model (LRSM) without requiring the existence of any additional symmetries. The charged fermions acquire masses through a universal seesaw mechanism due to the presence of additional vector like fermions. The neutrinos acquire a one-loop Dirac mass from the same additional vector like charged leptons without requiring any additional discrete symmetries. The model can also be extended by an additional $Z_2$ symmetry in order to have a scotogenic version of this scenario predicting a stable dark matter candidate. We show that the latest Planck upper bound on the effective number of relativistic degrees of freedom $N_{\text{eff}}=3.15 \pm 0.23$ tightly constrains the right sector gauge boson masses to be heavier than 3.548 TeV. This bound on gauge boson mass also affects the allowed values of right scalar doublet dark matter mass from the requirement of satisfying the Planck bound on dark matter relic abundance. We also discuss the possible implications of such a scenario in charged lepton flavour violation and generating observable electric dipole moment of leptons., 24 pages, 12 figures, Published version

We study the possibility of generating tiny Dirac neutrino masses at one loop level through the \textit{scotogenic} mechanism such that one of the particles going inside the loop can be a stable cold dark matter (DM) candidate. Majorana mass terms of singlet fermions as well as tree level Dirac neutrino masses are prevented by incorporating the presence of additional discrete symmetries in a minimal fashion, which also guarantee the stability of the dark matter candidate. Due to the absence of total lepton number violation, the observed baryon asymmetry of the Universe is generated through the mechanism of Dirac leptogenesis where an equal and opposite amount of leptonic asymmetry is generated in the left and right handed sectors which are prevented from equilibration due to tiny Dirac Yukawa couplings. Dark matter relic abundance is generated through its usual freeze-out at a temperature much below the scale of leptogenesis. We constrain the relevant parameter space from neutrino mass, baryon asymmetry, Planck bound on dark matter relic abundance, and latest LUX bound on spin independent DM-nucleon scattering cross section. We also discuss the charged lepton flavour violation $(\mu \rightarrow e \gamma)$ and electric dipole moment of electron in this model in the light of the latest experimental data and constrain the parameter space of the model., Comment: 16 pages, 8 figures, matches the version accepted by JCAP

We study the new physics contributions to neutrinoless double beta decay ($0\nu\beta \beta$) half-life and lepton flavour violation (LFV) amplitude within the framework of the minimal left-right symmetric model (MLRSM). Considering all possible new physics contributions to $0\nu\beta \beta$ and charged lepton flavour violation $\mu \rightarrow e \gamma, \mu \rightarrow 3e$ in MLRSM, we constrain the parameter space of the model from the requirement of satisfying existing experimental bounds. Assuming the breaking scale of the left-right symmetry to be $\mathcal{O}(1)$ TeV accessible at ongoing and near future collider experiments, we consider the most general type I+II seesaw mechanism for the origin of tiny neutrino masses. Choosing the relative contribution of the type II seesaw term allows us to calculate the right handed neutrino mass matrix as well as Dirac neutrino mass matrix as a function of the model parameters, required for the calculation of $0\nu\beta \beta$ and LFV amplitudes. We show that such a general type I+II seesaw structure results in more allowed parameter space compared to individual type I or type II seesaw cases considered in earlier works. In particular, we show that the doubly charged scalar masses $M_{\Delta}$ are allowed to be smaller than the heaviest right handed neutrino mass $M_N$ from the present experimental bounds in these scenarios which is in contrast to earlier results with individual type I or type II seesaw showing $M_{\Delta} > M_N$., Comment: 23 pages and 21 figures. minor revision, to appear in JHEP. arXiv admin note: text overlap with arXiv:1509.01800

We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14., Comment: 36 pages, 42 pdf figures, 2 tables. Few references added. Accepted in JHEP

We have shown a new scenario of successful leptogenesis with one $L$ violating coupling and a relative Majorana phase playing the role of $CP$ violation. This is in contrast to the usual consideration of Feynman diagram with at least two $L$ violating couplings. We have considered $R$-parity violating Minimal Supersymmetric Standard Model (MSSM) for leptogenesis at TeV scale. This scenario is also consistent with generating light neutrino mass if asymmetry is generated through semileptonic $\lambda^{\prime}$ coupling., Comment: 11 pages, 3 figures, Major changes in text and figures

We present a minimal left-right dark matter framework that can simultaneously explain the recently observed 3.55 keV X-ray line from several galaxy clusters and gauge coupling unification at high energy scale. Adopting a minimal dark matter strategy, we consider both left and right handed triplet fermionic dark matter candidates which are stable by virtue of a remnant $\mathcal{Z}_2\simeq (-1)^{B-L}$ symmetry arising after the spontaneous symmetry breaking of left-right gauge symmetry to that of the standard model. A scalar bitriplet field is incorporated whose first role is to allow radiative decay of right handed triplet dark matter into the left handed one and a photon with energy 3.55 keV. The other role this bitriplet field at TeV scale plays is to assist in achieving gauge coupling unification at a high energy scale within a non-supersymmetric $SO(10)$ model while keeping the scale of left-right gauge symmetry around the TeV corner. Apart from solving the neutrino mass problem and giving verifiable new contributions to neutrinoless double beta decay and charged lepton flavour violation, the model with TeV scale gauge bosons can also give rise to interesting collider signatures like diboson excess, dilepton plus two jets excess reported recently in the large hadron collider data., Comment: Version 2: 26 pages, 8 figures, to appear in Physical Review D

We study a specific version of $SU(2)_R \times SU(2)_L \times U(1)_{B-L}$ models extended by discrete symmetries where the new physics sector responsible for tiny neutrino masses at leading order remains decoupled from the new physics sector that can give rise to observable signatures of lepton number violation such as neutrinoless double beta decay. More specifically, the dominant contribution to light neutrino masses comes from a one-loop Dirac mass. At higher loop level, a tiny Majorana mass also appears which remains suppressed by many order of magnitudes in comparison to the Dirac mass. Such a model where the active neutrinos are predominantly of Dirac type, also predicts observable charged lepton flavour violation like $\mu \rightarrow 3e, \mu \rightarrow e \gamma$ and multi-component dark matter., Comment: 33 pages, 16 figures, to appear in JHEP

The recent results of 13 TeV ATLAS and CMS di-photon searches show an excess at di-photon invariant mass of 750 GeV. We look for possible explanation of this within minimal left right symmetric model (MLRSM). The possible candidate is a neutral Higgs of mass 750 GeV that can decay to di-photon via charged Higgs and right handed gauge boson loop. However, the cross-section is not consistent with the ATLAS and CMS results. We then discuss one possible variation of this model with universal seesaw for fermion masses that can explain this excess., 19 pages, 5 figures

We study neutrinoless double beta decay in left-right symmetric extension of the standard model with type I and type II seesaw origin of neutrino masses. Due to the enhanced gauge symmetry as well as extended scalar sector, there are several new physics sources of neutrinoless double beta decay in this model. Ignoring the left-right gauge boson mixing and heavy-light neutrino mixing, we first compute the contributions to neutrinoless double beta decay for type I and type II dominant seesaw separately and compare with the standard light neutrino contributions. We then repeat the exercise by considering the presence of both type I and type II seesaw, having non-negligible contributions to light neutrino masses and show the difference in results from individual seesaw cases. Assuming the new gauge bosons and scalars to be around a TeV, we constrain different parameters of the model including both heavy and light neutrino masses from the requirement of keeping the new physics contribution to neutrinoless double beta decay amplitude below the upper limit set by the GERDA experiment and also satisfying bounds from lepton flavor violation, cosmology and colliders., v2: 30 pages, 14 figures, Accepted for publication in JHEP

The Standard Model gauge group can be extended with minimal matter content by introducing anomaly free U(1) symmetry, such as $L_e-L_{\mu}$ or $L_e-L_{\tau}$. If the neutral gauge boson corresponding to this abelian symmetry is ultra-light, then it will give rise to flavor-dependent long-range leptonic force, which can have significant impact on neutrino oscillations. For an instance, the electrons inside the Sun can generate a flavor-dependent long-range potential at the Earth surface, which can suppress the $\nu_{\mu} \to \nu_e$ appearance probability in terrestrial experiments. The sign of this potential is opposite for anti-neutrinos, and affects the oscillations of (anti-)neutrinos in different fashion. This feature invokes fake CP-asymmetry like the SM matter effect and can severely affect the leptonic CP-violation searches in long-baseline experiments. In this paper, we study in detail the possible impacts of these long-range flavor-diagonal neutral current interactions due to $L_e-L_{\mu}$ symmetry, when (anti-)neutrinos travel from Fermilab to Homestake (1300 km) and CERN to Pyh\"asalmi (2290 km) in the context of future high-precision superbeam facilities, DUNE and LBNO respectively. If there is no signal of long-range force, DUNE (LBNO) can place stringent constraint on the effective gauge coupling $\alpha_{e\mu} < 1.9 \times 10^{-53}~(7.8 \times 10^{-54})$ at 90% C.L., which is almost 30 (70) times better than the existing bound from the Super-Kamiokande experiment. We also observe that if $\alpha_{e\mu} \geq 2 \times 10^{-52}$, the CP-violation discovery reach of these future facilities vanishes completely. The mass hierarchy measurement remains robust in DUNE (LBNO) if $\alpha_{e\mu} < 5 \times 10^{-52}~(10^{-52})$., Comment: 44 pages, 54 pdf figures, 7 tables. Published in JHEP

We attempt to simultaneously explain the recently observed 3.55 keV X-ray line in the analysis of XMM-Newton telescope data and the galactic center gamma ray excess observed by the Fermi gamma ray space telescope within an abelian gauge extension of standard model. We consider a two component dark matter scenario with tree level mass difference 3.55 keV such that the heavier one can decay into the lighter one and a photon with energy 3.55 keV. The lighter dark matter candidate is protected from decaying into the standard model particles by a remnant $Z_2$ symmetry into which the abelian gauge symmetry gets spontaneously broken. If the mass of the dark matter particle is chosen to be within $31-40$ GeV, then this model can also explain the galactic center gamma ray excess if the dark matter annihilation into $b\bar{b}$ pairs has a cross section of $\langle \sigma v \rangle \simeq (1.4-2.0) \times 10^{-26} \; \text{cm}^3/\text{s}$. We constrain the model from the requirement of producing correct dark matter relic density, 3.55 keV X-ray line flux and galactic center gamma ray excess. We also impose the bounds coming from dark matter direct detection experiments as well as collider limits on additional gauge boson mass and gauge coupling. We also briefly discuss how this model can give rise to sub-eV neutrino masses at tree level as well as one-loop level while keeping the dark matter mass at few tens of GeV. We also constrain the model parameters from the requirement of keeping the one-loop mass difference between two dark matter particles below a keV. We find that the constraints from light neutrino mass and keV mass splitting between two dark matter components show more preference for opposite $CP$ eigenvalues of the two fermion singlet dark matter candidates in the model, Comment: 27 pages, 6 figures, to appear in Phys. Rev. D

Soft leptogenesis is a mechanism which generates the matter-antimatter asymmetry of the Universe via the out-of-equilibrium decays of heavy sneutrinos in which soft supersymmetry breaking terms play two important roles: they provide the required $CP$ violation and give rise to the mass splitting between otherwise degenerate sneutrino mass eigenstates within a single generation. This mechanism is interesting because it can be successful at the lower temperature regime $T \lesssim 10^9$ GeV in which the conflict with the overproduction of gravitinos can possibly be avoided. In earlier works, the leading $CP$ violation is found to be nonzero only if finite temperature effects are included. By considering generic soft trilinear couplings, we find two interesting consequences: (1) the leading $CP$ violation can be nonzero even at zero temperature realizing nonthermal $CP$ violation, and (2) the $CP$ violation is sufficient even far away from the resonant regime allowing soft supersymmetry breaking parameters to assume natural values at around the TeV scale. We discuss phenomenological constraints on such scenarios and conclude that the contributions to charged lepton flavor violating processes are close to the sensitivities of present and future experiments., Comment: 16 pages, 5 figures. We have included a new figure showing the result of numerical analysis. Updated to match the published version in PRD

In this paper we introduce an idea of leptogenesis scenario in higher derivative gravity induced DBI Galileon framework {\it aka Galileogenesis} in presence of one-loop R-parity violating couplings in the background of a low energy effective supergravity setup. We have studied extensively the detailed feature of reheating constraints and the cosmophenomenological consequences of thermal gravitino dark matter in light of PLANCK and PDG data. Finally we have also established a direct cosmological connection among dark matter relic abundance, reheating temperature and tensor-to-scalar ratio in the context of DBI Galileon inflation., 8 pages, 2 figures, Revision accepted by Nuclear Physics B

We study the possibility of generating tiny neutrino mass through a combination of type I and type II seesaw mechanism within the framework of an abelian extension of standard model. The model also provides a naturally stable dark matter candidate in terms of the lightest neutral component of a scalar doublet. We compute the relic abundance of such a dark matter candidate and also point out how the strength of type II seesaw term can affect the relic abundance of dark matter. Such a model which connects neutrino mass and dark matter abundance has the potential of being verified or ruled out in the ongoing neutrino, dark matter as well as accelerator experiments., Comment: v2: 19 pages, 6 figures, to appear in Nucl. Phys. B

For standard interactions of neutrinos with matter bimagic baseline of length about 2540 Km is known to be suitable for getting good discovery limits of neutrino mass hierarchy, $\sin^2 \theta_{13}$ and CP violation in the $\nu_e \rightarrow \nu_{\mu}$ oscillation channel. We discuss how even in presence of non-standard interactions (NSIs) of neutrinos with matter this baseline is found to be suitable for getting these discovery limits. This is because even in presence of NSIs one could get the $\nu_e \rightarrow \nu_\mu $ oscillation probability to be almost independent of CP violating phase $\delta$ and $\theta_{13}$ for one hierarchy and highly dependent on these two for the other hierarchy over certain parts of neutrino energy range. For another certain part of the energy range the reverse of this happens with respect to the hierarchies. We present the discovery limits of NSIs also in the same neutrino energy range. However, as with the increase of neutrino energy the NSI effect in the above oscillation probability gets relatively more pronounced in comparison to the vacuum oscillation parameters, so we consider higher neutrino energy range also for getting better discovery limits of NSIs. Analysis presented here for 2540 Km could also be implemented for longer bimagic baseline $> 6000$ Km., Comment: 16 pages, 37 figures (eps files), revtex4-1

We present a minimal framework of $U(1)_{B-L}$ gauge extension of the Standard Model explaining dark matter abundance and matter-antimatter asymmetry simultaneously through an attractive mechanism of TeV scale WIMPy leptogenesis, testable at the current and next generation of colliders. This framework can also explain small neutrino masses via a radiative mechanism. One of the key predictions of this model is an enhanced rate for lepton flavor violating decay $\mu \rightarrow e \gamma$ within the sensitivity reach of next generation experiments., Comment: 6 pages, 6 figures

We propose an extension of the Standard Model (SM) for radiative neutrino mass by introducing a dark $U(1)_D$ gauge symmetry. The kinetic mixing between the SM gauges and the dark $U(1)_D$ gauge arises at 1-loop mediated by new inert scalar fields. We show that the tiny neutrino mass and dark matter candidates are naturally accommodated. Motivated by the recent measurement of $(g-2)_{\mu}$ indicating $4.2~ \sigma$ deviation from the SM prediction, we examine how the deviation $\Delta a_{\mu}$ can be explained in this model., Comment: 15 pages, 3 figues