HERWIG/src/hwhigb.f

   1
   2 CDECK  ID>, HWHIGB.
   3
   4 *CMZ :-        -23/08/94  13.22.29  by  Mike Seymour
   5
   6 *-- Author :    Ulrich Baur & Nigel Glover, adapted by Ian Knowles
   7
   8 C-----------------------------------------------------------------------
   9
  10       FUNCTION HWHIGB(NOMASS,S,T,EH2,EQ2)
  11
  12 C-----------------------------------------------------------------------
  13
  14 C     One loop scalar integrals, used in HWHIGJ.
  15
  16 C     If NOMASS=.TRUE. use a small mass approx. for particle in loop.
  17
  18 C-----------------------------------------------------------------------
  19
  20       INCLUDE 'HERWIG61.INC'
  21
  22       DOUBLE COMPLEX HWHIGB,HWHIGC,HWHIGD,HWUCI2,HWULI2,EPSI,PII,Z1,Z2
  23
  24       DOUBLE PRECISION S,T,EQ2,EH2,RAT,COSH,DLS,DLT,DLM,RZ12,DL1,DL2,
  25
  26      & ST,ROOT,XP,XM
  27
  28       LOGICAL NOMASS
  29
  30       EXTERNAL HWULI2,HWUCI2
  31
  32       COMMON/SMALL/EPSI
  33
  34 C-----------------------------------------------------------------------
  35
  36 C     B_0(2p1.p2=S;mq,mq)
  37
  38 C-----------------------------------------------------------------------
  39
  40       PII=CMPLX(ZERO,PIFAC)
  41
  42       IF (NOMASS) THEN
  43
  44          RAT=DABS(S/EQ2)
  45
  46          HWHIGB=-DLOG(RAT)+TWO
  47
  48          IF (S.GT.ZERO) HWHIGB=HWHIGB+PII
  49
  50       ELSE
  51
  52          RAT=S/(FOUR*EQ2)
  53
  54          IF (S.LT.ZERO) THEN
  55
  56             HWHIGB=TWO-TWO*DSQRT(ONE-ONE/RAT)
  57
  58      &                    *DLOG(DSQRT(-RAT)+DSQRT(ONE-RAT))
  59
  60          ELSEIF (S.GT.ZERO.AND.RAT.LT.ONE) THEN
  61
  62             HWHIGB=TWO-TWO*DSQRT(ONE/RAT-ONE)*DASIN(DSQRT(RAT))
  63
  64          ELSEIF (RAT.GT.ONE) THEN
  65
  66             HWHIGB=TWO-DSQRT(ONE-ONE/RAT)
  67
  68      &                *(TWO*DLOG(DSQRT(RAT)+DSQRT(RAT-ONE))-PII)
  69
  70          ENDIF
  71
  72       ENDIF
  73
  74       RETURN
  75
  76 C-----------------------------------------------------------------------
  77
  78       ENTRY HWHIGC(NOMASS,S,T,EH2,EQ2)
  79
  80 C-----------------------------------------------------------------------
  81
  82 C     C_0(p{1,2}^2=0,2p1.p2=S;mq,mq,mq)
  83
  84 C-----------------------------------------------------------------------
  85
  86       PII=CMPLX(ZERO,PIFAC)
  87
  88       IF (NOMASS) THEN
  89
  90          RAT=DABS(S/EQ2)
  91
  92          HWHIGC=HALF*DLOG(RAT)**2
  93
  94          IF (S.GT.ZERO) HWHIGC=HWHIGC-HALF*PIFAC**2-PII*DLOG(RAT)
  95
  96          HWHIGC=HWHIGC/S
  97
  98       ELSE
  99
 100          RAT=S/(FOUR*EQ2)
 101
 102          IF (S.LT.ZERO) THEN
 103
 104             HWHIGC=TWO*DLOG(DSQRT(-RAT)+DSQRT(ONE-RAT))**2/S
 105
 106          ELSEIF (S.GT.ZERO.AND.RAT.LT.ONE) THEN
 107
 108             HWHIGC=-TWO*(DASIN(DSQRT(RAT)))**2/S
 109
 110          ELSEIF (RAT.GT.ONE) THEN
 111
 112             COSH=DLOG(DSQRT(RAT)+DSQRT(RAT-ONE))
 113
 114             HWHIGC=TWO*(COSH**2-PIFAC**2/FOUR-PII*COSH)/S
 115
 116          ENDIF
 117
 118       ENDIF
 119
 120       RETURN
 121
 122 C-----------------------------------------------------------------------
 123
 124       ENTRY HWHIGD(NOMASS,S,T,EH2,EQ2)
 125
 126 C-----------------------------------------------------------------------
 127
 128 C     D_0(p{1,2,3}^2=0,p4^2=EH2,2p1.p2=S,2p2.p3=T;mq,mq,mq,mq)
 129
 130 C-----------------------------------------------------------------------
 131
 132       PII=CMPLX(ZERO,PIFAC)
 133
 134       IF (NOMASS) THEN
 135
 136          DLS=DLOG(DABS(S/EQ2))
 137
 138          DLT=DLOG(DABS(T/EQ2))
 139
 140          DLM=DLOG(DABS(EH2/EQ2))
 141
 142          IF (S.GE.ZERO.AND.T.LE.ZERO) THEN
 143
 144             DL1=DLOG((EH2-T)/S)
 145
 146             Z1=T/(T-EH2)
 147
 148             Z2=(S-EH2)/S
 149
 150             HWHIGD=DLS**2+DLT**2-DLM**2+DL1**2
 151
 152      &            +TWO*(DLOG(S/(EH2-T))*DLOG(-T/S)+HWULI2(Z1)-HWULI2(Z2)
 153
 154      &                 +PII*DLOG(EH2/(EH2-T)))
 155
 156          ELSEIF (S.LT.ZERO.AND.T.LT.ZERO) THEN
 157
 158             Z1=(S-EH2)/S
 159
 160             Z2=(T-EH2)/T
 161
 162             RZ12=ONE/(Z1*Z2)
 163
 164             DL1=DLOG((T-EH2)/(S-EH2))
 165
 166             DL2=DLOG(RZ12)
 167
 168             HWHIGD=DLS**2+DLT**2-DLM**2+TWO*PIFAC**2/THREE
 169
 170      &            +TWO*DLOG(S/(T-EH2))*DLOG(ONE/DBLE(Z2))
 171
 172      &            +TWO*DLOG(T/(S-EH2))*DLOG(ONE/DBLE(Z1))
 173
 174      &            -DL1**2-DL2**2-TWO*(HWULI2(Z1)+HWULI2(Z2))
 175
 176      &            +TWO*PII*DLOG(RZ12**2*EH2/EQ2)
 177
 178          ENDIF
 179
 180          HWHIGD=HWHIGD/(S*T)
 181
 182       ELSE
 183
 184          ST=S*T
 185
 186          ROOT=DSQRT(ST**2-FOUR*ST*EQ2*(S+T-EH2))
 187
 188          XP=HALF*(ST+ROOT)/ST
 189
 190          XM=1-XP
 191
 192          HWHIGD=TWO/ROOT*(-HWUCI2(EQ2,S,XP)-HWUCI2(EQ2,T,XP)
 193
 194      &         +HWUCI2(EQ2,EH2,XP)+DLOG(-XM/XP)
 195
 196      &         *(LOG(EQ2+EPSI)-LOG(EQ2+EPSI-S*XP*XM)
 197
 198      &          +LOG(EQ2+EPSI-EH2*XP*XM)-LOG(EQ2+EPSI-T*XP*XM)))
 199
 200       ENDIF
 201
 202       RETURN
 203
 204       END