SMU Physics Department Speaker Series - Jing Xiaoxian and Yingnan Xu

all right well welcome everybody I'm going to go ahead and make the introductory remarks here and buy everybody a few extra minutes to get connected um so let me Begin by welcoming everybody back to the SMU physics department speaker series for fall 2020 um this is our penultimate event in the series for this semester so this is the last week of classes although there are no classes today and tomorrow exams begin next week we're definitely getting to the end of the semester and it's it's nice to conclude our November series and its theme of New Frontiers in physics with the presentations today and today's a really special event because it it contains two shorter presentations from two of our PhD candidates who were supported this semester through the department and the college to conduct research toward their PHD um these departmental research support opportunities are are never guaranteed and sort of considered on a case-by casee basis um and they're especially intended for students who need to make substantive progress toward the completion of their degree and where it is likely that external funding to support their work can be obtained so this allows us as a department to try to bridge them forward toward their PHD um as a result of this we as a department have a broader stake in their success and today we will hear about the progress that they have made this semester so each of our speakers will speak for about 20 minutes with introductions from their research advisers preceding their talks so in just a moment I'm going to hand things over to Professor paval mulski to introduce our first Speaker Jing sha Shan but before we get started the quick reminders as usual so to our audience joining us live and interactively on Zoom to ask a question you have to write speak in the chat window that'll set up a little speaker Q uh we can interrupt the talk during the presentations by each of the students today uh we'll just catch them at the next slide boundary and and let them know there's a question and then unmute you or you can save your question for the Q&A at the end which will come after the two presentations all right so it's sort of up to you we are live streaming this simultaneously also on YouTube but that's non- interactive but nonetheless Welcome to our participants on the YouTube stream today all right so let me go ahead and welcome Professor pav nadeli to introduce our first Speaker Jing shaan and while he's introducing you Jing you can go ahead and start sharing your slides okay very good uh thank you so much Steve um so it's my pleasure to introduce Jin who uh he has been working on with us um on various interesting iCal calculations including the studies of the hrin structure now uh the for those who uh didn't didn't attend the seminars U dedicated to the structure of the proton uh let me point out that uh many experiments in particle physics required to know very well what the protons are made of and um the protons are small but very fascinating objects you can see a picture of one behind me it's it's it's an artist visualization how the protons looks like you have to keep in mind that this object is very small and also has very uh unique uh Quantum properties which need to be understood now uh uh has been with our group since 2016 and his main work is um uh based on Research done together with C soal CAC T collaboration so we CAC is a big um group of researchers that study Quantum chromodynamics and its applications at various um domains uh now Jin works with a subgroup with with in CC called CT and uh we focus on the studying the structure of the proton but also providing uh parameterizations for the protons that are used by many experimentalists uh last year uh Jin spent uh spent I think eight to nine months at Jefferson lab which is a major National Laboratory in the United States where he worked with another subgroup within CC called CC jlab and so that group focuses on understanding uh low low energy effects in qcd and so uh basically uh their approach to the studies of of the hrant is somewhat different compared to what we do with in C and it is very interesting to compare what we learned from the different uh um studies of the experimental data which are Pur both by by CT and CJ since what we find is that the fixed Target experiments like the ones that are done at Jefferson lab or at the future electron collider will play uh will continue to play very essential role in constraining partn distributions for example when we look look at the hick physics production you find that very important constraints uh on PDFs or pent distributions in the regional elant for his production come from uh the fixed Target experiments and what Jin has been doing in the past year he was applying methods from um uh data dat data science to understand how constraints on pent distributions arise from a variety of experiments including fixed Target experiments and so that's what he will is going to present to us in the next 20 minutes so J I think you can start okay thank you for your introduction um today my talk is going to be part on distributions nuclear deeplay in elastic scaring and Electro week Precision measurements at LHC my talk will be consist of three parts first I will introduce uh what the PDF function is and I think most part has been uh discussed by Professor pav also I will talk about the PDF feting how does it work and eventually I'm going to talk about the sensitivity method which provide us a deeper understanding of the PDFs and the experiments for the PDFs first PDF functions so PDF usually they take form of a set of functions with a with variable x and q for the quarks and GLS they are needed for predicting a variety of processes and the LHC including the hi Bon production and searches for the new phix beyond the standard model say is reir the probability of finding a pum carrying proton momentum fraction at the scale Q on the right hand side we can see it is a typical PDF function how it looks like it comes with a central value and also the air band the air band it is also called the PDF uncertainty it comes from the experimental measurement errors and also from the theoretical approximations the PDF value itself is not observable that can be directly measured so we related this uh variable to the measurable quantity which is called the crosssection so crosssection it is related to the PDF through the cross through a convolution between the PDF function and the Matrix elements of the various PDF of various physics processes such a Jan process um we know that there is no first principal prediction for the PDFs so what we do is we come up with very um different kinds of functions to fit the PDF uh I've been working with the two groups as um introduced by the professor Pavo they are the CAC T and CAC jlab group u in both groups so PDF parameterization take the same form take a similar form U it is a a polinomial function with some anticipated Behavior at low and high which are represented by these parts they also have lots of difference between these two groups for example the CT fit it contains more data and the treatment is of at next next line order but it contains no nuclear treatment for the CJ fit it is at next linear order and it is specialized in the nuclear correction the two groups they also fit different set of experiments as shown in this table what we need to do in a PDF Feit is that we need to determine the PDF value at the initial scale q0 which is approximate at one GV so PDF value at higher energy level can be culate through the PDF value at low energy level through the dlap evolution function we need to determine the PDF value for various quarks and anti quark and the gr therefore it's contains a lots of par parameterization parameters for example in the CJ5 it contains 24 parameters and in ct18 it can 29 parameters next I'm going to introduce what are the experiments included in the ct8 PDF Fit U as SE as shown in this plot we have the in inclusive jet wz production TT bar and Z production also hairs dis and fixed Target dis and dran uh in general these experiments can be categorized into these three types of physics processes the D dis experiments which is a lepton Hardon scaling with exchange of a virtual Photon and then later Decay into a pair of leptons the dran process it happens where a quk from one Hardon and an antiquark from another hard say annihilate into a virtual photon or that bosom and later Decay into a pair of oppositely charged leptons the jet production is similar to um the pr previous protess but it produce the Chrome of Hardon or other particles uh so measurable variable in this experiments is the crosssection PDF act as a bridge connecting scaring amplitude and the crosssection as shown in this slide so cross-section of the D experiment it is a convolution between the PDF function and the um scattering amplitude of the Hardon process for the dran process it's we need to conclude both of the PDF of two protons and the har scaring Matrix Elements which is calcul by the theory and J production is all similar we also just talked about the H production the hi production essentially it is similar it is also interaction between two hard hardons C4 the hi production cross-section it is a conclusion of the two PDF functions of the uh protons and the hard cor section uh the hard Matrix element here so next I'm going to discuss on the flow of the PDF analysis how do we assemble all the pieces we have talked about and come up with the F eventually uh we have if we have the experimental data the are the cross-sections of various experiments we also have the theory calculation of these experiments and the theory calculations that depend on the PDF F the fxq and the F the PDF functions that depend on the PDF parameters a therefore with this two we can calculate the kai Square total K Square which is going to be a function of the PDF parameters then we minimalize the toal Kai square and we can obtain the final best fit PDF parameters which is called the aot with the a notot we can obtain the central PDF sets for various flavors and the total Kai Square for Central PDF sets if we allow the total Kai Square along each icon direction to increase by 10 units we will obtain a uh set of PDF air PDF sets which is exact the same number of two times the number of PDF parameters this flowchart it is quite complicated here's the reason um in each step there are lots of source of of complexity for example the data selection which experiments to be included in the PDF feed the treatment of these errors how do we treat the correlated and uncorrelated error also different PDF groups they have the different PDF parameterizations and the theory of assumption for these PDFs such as the flavor as symmetry or symmetry the hard qu the heavy Quark treatments do we use the fix flavor or other skin also the behavior at low and high EGS and on the theory side on the order of peration and the theory calculation method are also some complexity of this part and for the minimalization um process different groups uh use different methods for example the CT group use a gradient descend method for CJ group they use a met quad method and with all of these complexities can we understand and compare the experimental constraints in the CJ and CT PDF feelds also can one tell which modern experiments are the most constraining ones in the latest PDF feed to answer this question we apply the hashing sensitivity method so H sensitivity method on one of the inuse one of the case is L2 sensitivity so L2 sensitivity it is the linear approximation for Delta Kai square of 13 experiment E when some PDF value increases by the 68% of confidence level of the hashen PDF uncertainty and this it is very fast to calculate with good accuracy here are some results uh if we wish to understand the atlas uh weak mixing angle and it's Cor with PDF flavor combinations um we can check this plots so we mix angle it is the key parameter in the electro weak sector of the standard model um from this plot we can see the correlation between the weak mixing angle it is closely correlated to U and D quarks so if we wish to Hon understand the U quark and D Quark also the weak mix angle we wish to understand which experiments they constrain the dnu and what kind of treatment affect the D DN you flavor PDF functions here we applied this method on the CJ group in the CJ group we try two kinds of fits as discussed previously one with a dual correction which is fixed the other one is without detal correction on the left hand side it is W without and on the right it is with fix the Dual correction we can see that if we remove the d correction the tension between the two group of experiments essentially the gamma jet and the DI Dum they can be very large up to 30 units and when we introduce a fixed dual Corrections the tension is reduc reduced to a scale of five therefore we conclude that the nuclear correction reduce the tension between the different groups of experiments which can lead to the reduction of the air band we apply the same tactic or same treatment to the CT group but we found that the scale is almost same or we notice that although the scale is quite similar but the impact of certain group such as the dis Dum is greatly changed uh dis duton it is the group four and we can see at highx the behavior Chang a lot so for d correction it's can affect the pool of certain experiments um eventually we are going to talk about another type of treatment of the deuteron correction uh we we allow the deuteron correction to be fitted which is a free DET correction and we notice that in the CJ U if we allow the duton correction parameter to change the tension is going to be reduced and which may lead to the reduction of the PDF airband next I'm going to talk about the this method applied in the EIC yellow paper EIC yellow paper on so here this plot shows the stivity the stivity of H C uh cross-section calculation on each data point of the e experiment datas so sensitivity is represented by the color of each data point the result we see is that the constraint of the GL and other PDF at EIC will reduce the PDF uncertainty on the H production at RC experiment also if we wish to understand which data points they have the major impact on the hi production we can just tell by the color if the color is very red that means these data points have a direct impact on the hi production so uh to summarize my talk uh we know that PDF stivity it is a statistical indicator that visualize the constraint from experiments on the PDF in CC Global PDF feeds I apply this scientific method to understand the origin of U over D pools with CT and CJ PF Fe the pools are affected by the nuclear Corrections in the fixed Target dis the treatment of this nuclear effect in the PDFs help us in understanding the uncertainties of the proton PDFs in high Luminosity LHC experiments so okay thank you for your attention that is all my talk okay yeah thank you very much Jing uh let's try to give you a little Applause here I see Roberto clapping that's very nice excellent excellent um well so since you have your slides up why don't we why don't we alter the bargain I said at the beginning and why don't we open the floor up now for questions for you that way you don't have to worry about bringing your slides up again later so if anybody has a question just go ahead and type speak in the chat window um I have a couple but I'll wait and see if anybody writes anything there all right well while we're waiting for people to think of questions do you mind if I ask one Jin sure please um so on Slide Five you mentioned the importance of nuclear Corrections you know may need to be in included in that ctec tea uh doesn't include those but CC jlab does include those uh and then you pointed out later how at least in one PDF said it it seems to resolve some of the tension between between different uh PDFs how does one incorporate the nuclear Corrections into this polom formula approach or is that done separately Al to answer that question we know that uh there's the nuclear correction it is effector collection of some the off share pons and firing motions and everything like that we use uh aox a function to we use a polinomial which contains around two U parameters to calculate the PDF function of the dutron so the D it is not just the sum of the proton and neutron it is the sum and then plus the polinomial as the coefficient Does this answer your question I I I think so so I mean so it enters in then as modifications to the coefficient here with no other changes to the formula or does it alter the formula in some other way no it does not alter the formula here but it alter the formula for the deuteron PDF okay so specifically it Alters the formula for that specific PDF then okay yes okay all right does anybody else have questions if not I have I have one more for you if that's okay could you go back to that nice slide you showed that you mentioned was was something that had been done for the EIC yellow report um so just for the benefit of the audience could you just briefly explain what is the yellow report intended to do and then uh then I'll actually get to my actual question so could you just briefly explain what is the yellow report the E report uh it is a proposal on the how the future EIC experiments how it's going to the experiments how it's going to affect the PDF PR uh the PDF airband for different PDF groups and uh flavors yeah so yeah to sort of project the impact of the EIC and some of that impact is potentially shown here so the red points you said are especially impactful on so the hi production calculations is that right yes that's correct right so and these are all points that the EIC in principle should be able to cover with one process or another as you've Illustrated in the legend uh yes so it contains the neutral current and charg current of the electron proton and the electron Neutron there are different data points here do you do you know roughly how much data has to be integrated for each of those to get the desired impact like an inverse fto barns do you happen to know roughly the size of data that's needed at the EIC I do know that the neutral current is around 100 inverse fent and the Char current is approx 10 and the duon it is approximate 10 and the proton is 100 okay that's fantastic yeah so it's not all just you know half a year or one year of data taking it maybe a little bit less or a little bit more in some cases then yes okay oh sorry Roberto you had a question I think you can go ahead and unmute so go ahead and ask your question oh you're still muted Roberto uh let me see here is that good yeah that's fine there we go good in the theoretical calculation of the cross-section uh to what order I guess it depends on the processes that you're considering but uh I guess how how do you H how sensitive are these uh results that you get for the fits on the order of perturbation theory that you use for the cross-section and how in this procedure that you follow you make sure you don't double count uh um contributions coming from the Parton distribution functions with uh higher order processes in your cross-section oh that is very interesting question so to my experience um what I have done with the CJ uh what we did is to Cate next leading order and uh in my experience we performed the next leading order calculation with two method one is with the K Factor method which is fixed I mean a ratio of the next order and linear order for each being is fixed and the other method is the Apple GD uh calculation and with this two calculation for the next linear order we find that the PDF Central value does not change much the Ed band does not change much but at certain regions it will have a noticeable impact and to answer um how do we avoid the double count of the PDF uh and the The Matrix of the scanning amplitude oh I'm not sure about I don't have the answer to this question right [Music] now that's all right yeah it's just I'm just curious I mean there'll be time for you to think about it before we get to the end Q&A anyway so maybe you'll have an answer later on thesis defense what's that we will save it for the thesis defense oh nice teaser I like that saved by your advisor Jen that's good that's a good question but Jing let me ask you like for example suppose uh well you see the PDFs and the hard cross sections they depend on the uh parameters called me right so so what is what is the purpose of this parameter and so it doesn't have any relation to preventing the double Counting Oh you mean so energy scale here yeah so in other words you you see both the PDF and the hard crosssection depend on the parameter me so what is that and uh does it have any role in uh preventing the double counting so first of what the MU stand for the en scale here um and the PDF value as we discussed it is a function of the MU it is the the Q here um it tells which energy level the proton is at so at low how does does it help to avoid the multic counting let me see well maybe it's too much to discussing but but you can think about it so so I I think part of the answer to Roberto is that well we we introduced the special skill and somehow it plays the role uh in preventing the double counting and so uh uh and then okay so one of your tasks is to figure out what it is and how how exactly it works perfect yeah nothing like having homework [Laughter] right all right well thank you very much uh we can always come back if people think of other questions at the end after we've had a chance to hear from Nan and and ask him questions we can have kind of a a general question period at the end in case somebody wants to go back and ask Jing something um so let's let's thank Jing one more time so thank you very much Jing and I'm going to hand things over to Roberto now to introduce our next speaker nnan Shu okay nnan uh graduated from oring college uh with a bachelor's in math and physics after graduation he went back to China and tried his hand at teaching uh physics in High School uh but he had he had been bitten by the physics uh mosquito I guess and he wanted to come back and do a do a graduate degree and he came to SMU and uh he's been one of the best students in my Quantum class so I was very happy when he asked me to uh work with me on on a project he's going to be talking about a simple extension of the standard model um and he'll tell you more about that so I'll let him do the talking that's it okay uh thank you uh so so today uh I'm going to talk about the dark Photon Theory and uh here's the uh references I used for my research so the motivation here is that uh we know that uh currently the most successful theoretical framework in partic physics is the stand model but it not complete for example it doesn't expl phenomenon such as gravity dark matter and dark energy matter antimatter is symmetry as Central and it also has uh thetical problems like the naturalist problem and hierarchy problem so there are a lot of efforts has been made to extend the standard model into a grand UniFi Ser uh where the standard model is regarded as a low energy effective Theory and the stand model gauge group can be thought as a result from spontaneous a spontaneous symmetry breaking of a larger symmetry group uh most of the extensions lead to an extra Ur langage associated with the field which we will call it a dark Photon to the stand model and uh this is just the simplest addition and it is not the whole picture uh the completion of it requires a Dark Sector dark in the sense that fields in the in this sector do not carry stand model charges uh but we be will say that we can G some insights on the Dark Matter recover couplings of fir on set Centra uh the dark Photon that field may be massive or massless and we shall discuss its phenomenology separately massive dark photon is a particular interest for it couples directly to the stand model current and itself can be a candidate for dark matter so let's look at the theoretical structure so the the most General kinetic part of two un gauge groups uh the the the L ring we can write down is this so fmu here is just the normal field strength tensor and you can see there is a kinetic mixing term of these two uh un gauges uh A and B so the absent here uh should be very small because we don't want to we don't it effect our current physics so uh it should come from Loop suppressions uh and we suppose that the field a of B mu couples to the stand model current J mu and a of a mu couples to the dark current J Prime mu so the interaction LR we can write down is this um because because of this uh kinetic mixing term we cannot identify the iCal state so we may rotate the kinetic mixing term Away by orthogonal Transformations like this uh where we will identify this a prime mu as the dark Photon and this a mu as the normal the ordinary standard model Photon okay so then we have the L rounding like this and this data is just a rotational parameter and it is arbitary so we can choose s Theta equal Epsilon so that the dark Photon only cose to the dark current and ordinary Photon couples to both the stand model current and dark current so that's the L in Define the massless dark Photon you can say that a prime mu only coupl to J Prime mu and this a mu the standard model Photon couples to J Prime mu and J mu so the fean diagram correspond to this like groundin is this so uh gamma is the standard model uh Photon it couples to stand mod firmance f uh and uh fance in the dark tector Kai and Gamma Prime here is the dark Photon and it only cose two firmance in the Dark Sector uh you should note that uh the coupling between the duck seor and ordinary Photon it's called a m charge this this e Prime Epsilon over the square root of over Yus Epsilon squ so so that's for the massless dark Photon for the massive dark Photon it the uh we can either it can acquire Mass either from spontaneous spontaneous symmetry breaking uh which will correspond to the dark hi mechanism or by the stobber lrin so that's the stobber lren uh so that's this m square is the mass for the standard mod Photon and this m Prime this m Prime is the mass for the dark Photon in this case we do not have the freedom of choosing Theta arbitrarily uh we obtain Theta by diagonalizing the mass Matrix we obtain s s of theta and cosine Theta separately uh but we still want the standard model Photon remain massless uh oh this Delta here is uh M over M Prime so we want the ordinary Photon remain massless so we set m equal zero and with this Choice the ordinary Photon couples only two ordinary matter and the massive photon is uh couples to both the standard model phot uh standard modal current and the uh excuse me uh so you can say that the dark Photon couples to both the standard model current and the dark current but uh the standard model Photon only couples to the standard model Uh current so that's the fman diagram Cor respond to this L rounding so that's the uh stand mod of photon cose to stand mod of fance and uh that's the dark Photon uh it can cose to both the standard model fance and dark fance uh so since we know that uh mless so so now we will discuss their phenomenology uh so you can see that uh as mentioned before the massless dark Photon only compos to uh Dark Sector so it can it interact with ordinary matter only through operators of Dimension greater than four so that and a dimensional five operator that we can write down so here e d is just a coupling and this uh Lambda 5 is a cut of energy uh this side here uh is just a drug field and the sigma menu here is uh proportional to the Antique commutator of uh gamma matrices uh this DM and D here are uh magnetic dipole moment and electric dipole moment separately uh and this will correspond to a triangle triangular F diagram like this uh where Q uh where Q is uh dark dark firmance and uh this little Q is stand mod FAL uh this s here is a massenger field uh and we believe that uh stand model current interact with dark current through uh such a field uh so this s is bosonic and uh so the first L ring here uh is obtained from the second L Rin so from this one uh this L roundin is of dimensional six with a gauge group has You2 taken at The Unbroken symmetry of the L rounding and the standard Mo standard mode of fum group into double side air and single I so in general we can have as many dark firmance as there are in the standard model dark fance interact with the standard model uh standard model via scalar Master field to the super partner of fance as we mentioned before so you can say that because there's a sigma munu here uh so this kind of interaction actually involves a cality flipping process so I actually evaluated these two diagrams and here's the loop function uh so this XF here is just a mass of the doc fan Square over the mass of the M fi Square uh and here uh Ms is proportional to the is obtained from the vacuum expectation value of the of those scalar fields and Lambda here is just the cut of energy here so matching this model to the L ring before uh this two L ring uh we can identify the cut of energy as this uh this V of H here is just the vacuum expectation value of the Heats uh so this process uh actually help us explain the flavor hierarchy problem if for each stand mode of firan there exist a massive fan partner in the Dark Sector uh singet under stand model gaug groups and set of scalar Master field as then the recover coupling is generated at Van Loop via spontaneously spontaneous symmetry breaking and due to cality the ukaa coupling is proportional to the dark Veria masses uh the obor the hierarchy just reflects the structure of the dark fmia Spectrum uh I personally don't really like this uh explanation because I think it merely translate the problem the uh you hierarchy problem of the stam model to the Dark Sector okay so here's the uh phenomenology for the massive dark Photon uh and its relation to Dark Matter so very light massive dark Photon can be dark matter candidate if produced nonthermally in the early Universe when the H constant value drop below the mass of the duck Photon it field start to oscillate and behave like cod du matter but uh we have two problems in this scenario the first the initial value must be fine-tuned to reproduce the critical density uh and the Decay and the second is that decay into photons and stand mod of fance must not affect the cosmic wave background uh the later requires the absolent value uh this Epsilon is what we see in the first L rounding the very first L rounding the Epsilon equals less than 10^ the minus 9 and the mass of the dark Photon less than one m e uh so when the mass of the dark photon is heavier uh such like uh it's greater than two times the mass of some dark fmos then we have the anation channel uh to dark fance uh anate into standard model firmance and uh VAR in a scenario of flight dark matter and uh I evaluated the crosssection uh so that's the cross section uh so here Alpha is the fine structure constant and Alpha is the fine struct fine structure constant in the DU sector uh and this is not uh hard to evaluate because the whole process is just like the uh electron muon scattering so the F diagram is like this um so the thermally averaged cross-section in the non- relativistic limit is this uh so here we defined the yeld variable y equal Epsilon squ Alpha d uh times the mass of the dark firia over the mass of the uh dark Photon to the force so this y variable is very useful because later we will say that it helps us to uh put constraints from cosmology uh and this is this by because this by is related to the uh radic density uh so this Omega Kai is a dimension dimensionless parameter is the density of the dark firmance over the critical density and H Square here is just the dimensionless uh Hubble diameter so here's the graph of the Y variable uh as a fun ploted as a function of the mass of the uh dark firmance so you can say uh there are experiments like the light matter Direct Direct detection uh like this one this uh uh cre set to and there are also beam dump experiments like this uh bdx so that's uh so that's blue dash line and um here we also have the experimental limits for the massive do Photon of mass less than one m e so you can say that we have Atomic and nuclear experiments uh which aim to detect modifications of the Kum force due to dark photons uh those are basically around this area so you can see uh Atomic Spectra and the rberg experiments and there are also uh experimental limits from uh C ology so you can see that Kobe and furas and that's S I think that's the neutrino experiment from the sound okay so uh to draw a conclusion so the dark Photon theory is a low energy effective Theory and its completion requires ending a duck sector uh the answer to the eava coupling problem is unsatisfactory as it merely translates the hierarchy problem to the dock sector massive duck photons can be a dark matter cadate yet it introduces a new naturist problem uh in this review we are more interested in dark firmance as dark matter Cates there are also models where dark Photon couples to the inflation and its final abundance is dependent on its mass and H parameters in this model dark Photon can still be viable cidate for dark matter and uh you can see there are lot of constraints from cider physics and cosmology but the most stringent constraints uh come from cosmological observations okay yeah no thank you very much let's uh try to give you a little Applause here too as well so Roberto is reliable for that very good all right um let's open it up to questions from the audience any questions anyone want to ask don't forget to type speak in the chat window we'll get you unmuted oh yeah Richard has one so let's get down to Richard and okay Richard you should be able to unmute uh could you say something about the spin uh polarization of the mless dark Photon uh the what the mless dark photon does it have the spin polarization structure oh actually uh I [Music] uh I didn't read things about the spin and polarization of the dark Photon but uh I think think I'll uh find something later so so there is no no effect of the Spinners in this calculation uh which calculation this model uh there there's no uh the these photons are not polarized like they are in these models that be refer to at the end there that are coupled to inflation those models they these polarization effects but not in these uh these models mostly the these dark photons are not good candidates for Dark Matter any of that sort of stuff thank you right pav Europe up so so9 so um maybe we can go to the uh summary slide showing various measurements that look for the dark photom uh this one yeah so what's next again if you were just to give your opinion you like you said for something about the uh the dark the flavor uh of spectrum of the Dark Sector but you you could also perhaps say something about f f future interesting measurements what what do you think is most interesting in promising and uh if you were to contribute what would you what would you calculate or what would you try to predict um so so actually uh later I'm actually going to focus on uh this models uh I mentioned here where uh those this this dark photons can couple to the inflation and uh be a viable candidate for dark matter so basically I'm going to focus on this kind of models but uh here I think uh I just presented a like a very general introduction for the dark photo but but where will this model be for example on this on this plot so uh so like you have the coupling and you also have the mass so where could this models lie Yeah so basically I think it uh still requires that uh the mass is less than one mway but uh so those color region are uh so the existence of uh the massive dark Photon are excluded by the color region so I guess we have to focus on those uh blank crance and you don't have a preference where you are in that wide space um which is okay I'm just curious It's well I mean related to your question Pavo I I was trying to understand what that green line labeled dark matter means is that the line that's consistent with the Relic density of dark matter or is that something else and does that answer paavo's question then I guess well maybe again I can rephrase so so so here you show results of the experiments but of course you also talk about cosmological implications and so what I'm trying to G guess is that uh do you just look at the very very early universe or are there measurements that can probe that specific range of Epsilon and Ma Prime uh or yeah so so again so what what is the essential interplay between the particle physics experiments and cosmology oh oh so you can say that uh so in this case you have the yield variable right this is uh actually inversely proportional to The Relic density so I I think that's the connection between the abundance of the phot and cosmology oh yeah yes but but the question is do you just focus on cosmology or do you try to make predictions for the experiments as well um so here I think uh so I I think I um yeah I think I'll uh make predictions yes okay I I want to hear your answer to Steve's question uh the green line for Dark Matter yeah I think that uh comes from the uh yeah I think that's comes from the the zeric density yes so then is is everything above that allowed by our current knowledge of The Relic density yeah I I think it's uh below that everything below that is allowed by our knowledge of The Relic density yeah okay so yeah that I mean on that plot that you have your mouse on right now then not a whole lot has really been ruled out so sorry finish you oh and I was just going to say and then in the bottom plot it covers a slightly yeah it covers a different decade range right so there's still lot just a magnification of that part ah okay sorry but can I ask that do you assume that there is just one type of dark matter or it's dark matter in general uh so uh here I just consider the possibility of dark Photon as a dark matter but I think there are uh actually a lot of forms of dark matter like aels and particles in the Dark Sector so uh there are other possibilities yes but uh uh I think I here just focus on the possibility of dark matter as a dark Photon as a dark matter candidate okay I mean on that subject so you mentioned earlier in response to the questions about making predictions for experiments but you know dark matter with a mass of 108 me is going to affect experiments in a different way than dark matter with a mass of say 10 the -2 me um where maybe direct detection is more sensitive so there you know there's there's Axion experiments um there's CMD experiments there's tons of different experiments with all kinds of different ways of looking for effects on here um is it really practical to think you're going to make predictions for every single one of those um or in other words is it better to concentrate on something and you you kept coming back to cosmology which which may be an interesting Avenue if it's not so constrained yet yeah actually uh I think uh uh yeah I think uh so so yeah the most uh stringent limit are from cosmology and uh I think I'll focus more um the cosmological part and just out of curiosity um so and this is only your fifth semester at right so you've just began your research effectively half a year ago yes you're very early in the process whereas Jing is a more senior student so he's much further along closer to the PHD than you are so this has been kind of a rampup period for you and I'm curious you did mention some places um I'm just taking a look at my notes here um where did I note the slide um maybe can we flip back to um where you were talking about the yukawa hierarchy the yukawa coupling was that something that you uncovered in your work or did that come out of the references that you cited at the beginning oh yeah that's actually comes from the uh the the completion of the duck sector so uh it actually from the uh references okay all right so so then all right so what things in here so far if anything and don't feel bad if the answer is nothing yet because you're still early on what things in here represent unique work that you've been able to do so far even if it's something as basic as one of these calculations one of these cross-sections that would be I so most of the calculations here are so so yeah I evaluated most of the equations here yeah I guess where I'm going with this is they're not original okay that yeah that was my next question Roberto is is there some kernel of something original in here that you see expanding out into the future I was trying to look toward the future here with a question um you know you've been asked about where you're kind of going with this next I mean what is the next thing you want to do like what do you want to do in the spring for instance I'm putting you on the spot I recognize that but it won't be the last time somebody does it to you I mean is there a question left over at this stage that you would really like to answer that you want to focus on next and just to make sure we're not having technical problem are you able to speak H it's been real quiet uh yeah yeah okay there we go okay good I just wasn't sure if it was thinking silence or technical silence I mean you've mentioned cosmology right so one natural place to to to think about these kinds of theories is is um for the next generation of CMB experiment what constraints might those experiments place on these models if they don't see deviations and polarization from what's expected right what would be the signatures of a dark Photon appearing say in CMB data in the next generation of experiments is that something that you've thought about yet um he hasn't thought about that because these occur in models that he has not studied yet okay so there's there's more investigation that's the direction I want to point him in next uh to look at those models and and see uh there are there are polarization effects as as Richard mentioned and these uh these dark photons uh appear in coherent modes which certainly must have some uh measurable effects on on the uh CMB okay so that would be but that's not something anybody's really calculated yet then I think there are some papers out there that that are looking at that okay all right no very good all right are there any other questions pav you had another one sorry I just saw you just to to follow up on this idea of Poss applications well clearly the dark Photon models they are very very um um thoroughly being investigated and well right now we have an ongoing snow Mass study as well as the electron n collider study uh and both of them actually bring up the dark Photon models and possibility to look for new new new new U signatures of these kind of models either at the LHC or at the electron 9 collider and so now at the LHC you will be looking in the forward Direction and so there is a so called forward physics facility that has been proposed it is located in in the tunnel close to the atlas detector but it is very far from the from the um well Atlas detector itself and you you could try to look for evidence uh from like for example of course you will have neutrinos produced in the forward Direction let's say for from CH charm de case in inside the the atlas but you could also try to look for evidence for for the dark Photon signatures in that direction now at the EIC we have this unique opportunity to have polarization and that's precisely the opportunity to uh to well to address Richer's question because you could try to look for models that uh you know essentially they have couplings that depend on the on the well the the spin of the firan and uh again I think there is plenty of opportunities to try to write a potentially easy but and quick study but we will address some of the issues and it will be well contributing to the AIC physics program that is being developed right now so I think clearly there are there are there are opportunities to think about it and so again maybe we could discuss it sometime well whenever we meet or we can do it remotely and so yeah no that I mean having a little you know uh convocation on this amongst interested parties is certainly encouraged but this is uh this is certainly a nice level of Investigation at least pointing out the the features of these models and where there may still be opportunities left because you as you showed in those plots in on there's a lot of space potentially left to explore and it presumably doesn't end at the bottom of 10 to theg 17 uh on the milly charge the Epsilon parameter right I presume it can go lower there's nothing that prevents it from going lower yeah yeah there are actually a lot of proposed experiments and uh yeah yeah but thinking I think thinking about this broadly with uh with Roberto and other people in the department about where your work could have maximal impact if focused and directed now towards something that would be a very interesting question to explore in the next you know weeks basically so all right um any other questions for Annan or for Jing going once going twice okay great I don't see any more questions so let me just thank the advisers Pavo and Roberto and the the speakers Jing and on for these very nice talks we really appreciate you doing this uh this was very short and very Punchy today but very informative and